From: John De Armond
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: MAF (auto) sensor
[I made this post to sci.electronics but it got involved enough that
I thought the list might be interested. JGD]
firstname.lastname@example.org (James Bach) writes:
>In article <1993Aug30.email@example.com>,
>firstname.lastname@example.org (Mark Shaw) writes:
>> I noticed you made reference a couple of times to a WOT enrichment to 12:1
>> air-fuel ratio. I was under the impression that 12:1 was the generally
>> accepted value for a smooth idle until the emissions control era (12:1
>> can produce 5-6% CO). The optimum ratio in my references (Heywood, Bosch,
>> Fayette) tend to indicate that maximum power is achieved at 13.5:1 air-fuel
>> ratio (which is more like 2-3% CO).
>All the references I've seen say that "Best Power" is at about 12.0:1,
>+/- a bit; I can't recall exactly, but I think "Best Economy" was at
>about 16:1, but I might be wrong (I'd have to look it up). I know MY
>car is cal'd at 12:1 for WOT.
"Best power" mixture depends on the engine and the control algorithm.
Among the factors involved are the combustion chamber turbulence,
chamber squish area, knock sensitivity, cam overlap and a few other things.
The excess fuel serves to cool the combustion chamber and mute the
peak combustion temperature - both functions contribute to more power.
I've tuned racing EFI WOT mixtures as rich as 10.75:1 for peak power
but typical street WOT enrichment is around 12:1. Since most cars
with engines larger than Geo Metros do not need WOT to achieve the EPA
smog cycle speed profiles, the mixture is unregulated and can be set
for whatever the engine needs, subject to CAFE restrictions.
"Best economy" is kinda undefined for most engines, since the cat requires
exactly stoichiometry (14.7:1 for gas) to work. The Honda VTEC engine
(lean burn) can go as lean as 22:1 but that's a special case.
>> Now, you have me curious as to why it might be better to run 12:1 for more
>> power? Like maybe I should offset my baseline mixture so that the WOT
>> switch will create an much richer mixture when it bumps the upper limit.
>> Does all the other tuning (EGR, automatic ignition advance, multi-point
>> fuel delivery, etc) allow the use of a richer mixture?
>I don't know; I wouldn't mess around with what your manufacturer
>(sounds like non-GM) set-up.
Hmm, do I detect James playing just a bit of I've-got-a-secret?
>> Seems like that would be hell on the catalytic converter for a prolonged
>> WOT condition (i.e. going up hill). Does the control strategy back off
>> the mixture, if the condition is prolonged?
>Yes, it can be hard on a converter. I can't specifically state what
>our algorithms do other than to say that "long grades" are conditions
>GM calibrators test seriously (so I would trust the converters won't
Yep, Seems to be I've-got-a-secret. Fortunately there is a remedy to
that problem - the facts.
First off, let me state that the myth built up in the popular press and
to an extent, here, that these ECUs do all kinds of clever algorithms
is patently false. These ECUs are little more than ROM-based
database engines, fetching data from a large number of lookup tables.
A lot of what OEMs do is of little interest to us. The EPA's method
for measuring emissions and CAFE makes them do some pretty amazing
things to squeak every last bit of clean efficiency out of the engines.
Hell, just the code to determine when to turn on the radiator fan
takes up pages! We won't notice +- 0.1 MPG but GM's comptroller
WILL if they miss the CAFE targets. Developing what goes in these
lookup tables is grunt work but not mysterious. The neat thing about
this stuff is that it works so well.
Let's look at the basic fuel delivery algorithm used by many Delco ECUs
used in GM vehicles. For speed-density (where fuel requirements are
infered from manifold pressure and RPM instead of using a MAF), the
BPW = BPC*MAPP*T*A/F*VE*F33C*BLM*DFCO*DE*CLT*F77
Where: (everything labeled "term" is from a lookup table)
BPW = Base pulse width in milliseconds
BPC = Base pulse constant term (table lookup, basic engine air and FI
calibration plus EGR calibration)
MAPP= Manifold absolute pressure term
T = Inverse air temperature term
A/F= Inverse air/fuel ratio term
VE= volumetric efficiency term
F33C= Battery voltage compensation (for the effect on FI open/close delay
and fuel pump delivery)
BLM= Block Learn Term (what the ECU has learned from the O2 sensor)
DFCO= Decel Fuel Cutoff Term (when to turn fuel off on decel)
DE= Decel enleanment term (when to lean instead of cutoff)
CLT= Closed loop correction term (result of O2 sensor Proportional/
integral closed loop)
F77= Turbo boost multiplier (if used)
Everything is expressed and calculated in terms of 8 bit unsigned bytes.
None of these terms other than the CLT (as a result of the integral action)
are time dependent. That is, none are changed as a result of the passage
of time. There are some transient terms but they affect such things as
cold start enrichment, throttle tip-in enrichment and so on. None affect
full power mixture strength.
There are a couple of protective fuel cutoffs designed to protect the
ENGINE from prolonged high speed operation. The first one is the High
Engine Speed Cutoff. This is triggered when the engine has been operating
greater than or equal to the high protective RPM setpoint for longer
than programmed number of seconds. The second is the High Engine Load
Shutoff that protects the engine from prolonged load. It is triggered
when the MAP pressure is above the protective setpoint for a programmed
number of seconds. Either protective trip causes the fuel injector pulse
to be set to zero, shutting off fuel until the trip condition is cleared.
Note that this is to protect the ENGINE and not the cat. The cat is not
damaged by rich WOT mixtures simply because there is essentially no
oxygen in the exhaust. With no oxygen, there is no catalyzed reaction and
with no reaction, there is no heat. Distinguish this condition from
misfires where there IS an ample supply of oxygen in the exhaust because
of the failure to fire one or more cylinders. Indeed, a cat-equipped
engine running on a dyno for an extended period of WOT time will not
heat the cat significantly hotter than the exhaust. On the other hand,
I have literally melted the cat off an old Pinto rental car by coasting
down a long mountain in 3rd gear, engine at the redline, throttle to the
floor and ignition off. :-) Was quite a show when that cat finally
*** Shameless commercial plug follows.
Anyone interested in EFI design and implementation should subscribe to
my magazine "Performance Engineering" (see .sig for free sample info).
The next issue starts a multi-part series on EFI design and
implementation that culminates in a Dallas Semiconductor DS-5000-based
(8052 superset) PC-programmable EFI you can build (and maybe even a
kit). As with everything I do, full source code is available. We've
already started a companion series on digital PC- programmable
distributorless ignition. It also concludes a series on building a
very inexpensive PC-driven electronic fuel injector flowbench for
characterizing fuel injectors. The current issue is available for $6.00
US/$US7.00 Canadian. (Foreigners contact me for pricing.)
Oh, in case anyone ever wondered, I never had and hopefully never will
have any businss relation, non-disclosure, etc with GM, Delco, their
contractors, etc. This information is available, though it takes a bit
of digging. In answer to the inevitable question "Where do I get this
information", my answer is "Subscribe to PE" :-)
Date: Mon Aug 8 14:50:35 1994
From: John De Armond
Subject: preignition, detonation, ping, or knock!
>of new exhaust, new air filter housing, and a new ECU "Chip" which
>"modifies the following under full throttle high boost conditions:
>Ignition maps, fuel maps, cam timing switch points, boost and speed
>limiting, and an increase in the rev. limit by 200 r.p.m." Well,
>after about 5 hours of driving this, when he was in one of these
>full throttle high boost conditions (at high speed) he heard what
>he thought was the muffler ratling around.
>If you take a look at the cylinders, two of them look like somebody
>took a blow torch to them, melting out holes about the size of a
>dime. Very little other damage was found around the tops of the
>cylinders. However the parts of the cylinder which separate the
>rings (is ring lands the correct term?) were busted up into maybe
>5 or 10 pieces.
>Any idea what caused this?
Yes. See paragraph one above. This is the deadly result of combining a
bozo chip maker who thinks he can out-guess the factory with a complete
imbecile driver who thinks that installing a "hotrod chip" is as
inconsequencial as installing neon wiper blades and who apparently pays
attention to everything but his car. The result was devastating,
audible-to-the-driver-in-the-next-lane detonation and preignition that
literally hammered his pistons apart while melting holes in them. This
is not a quick process. This bozo had to have literally stuck his foot
in it and left it there, oblivious to the detonation. And he probably
did it after filling up with a tank of Rot-Gut Regular.
Believe it or not, the factory guys tune these engines to less than
the maximum possible precisely because of such bozos whose only
qualification for owning a high performance car is the ability to
borrow the money for it.
Yes, I'm being harsh on this guy. He didn't "accidentally" cause this
kind of damage. He had to work at it. The kind of detonation that does
this sort of damage is LOUD and very obvious. This kind of damage is
NOT done at any less than wide-open throttle and after a relatively long
period of time. Of course this does conform to John's Philosophy of
Life which says that people ought to have to pay for the priviledge of
being stupid. Sounds like those new pistons will make a nice down
payment. Wonder if he'll leave this hotrod chip in after he gets
his wallet lightened for the repairs?
(This is probably why I don't have one of those cute, high priced car
botiques designed to separate yuppys from their money - I don't have
the patience to suffer these kinds of monied fools.)
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: Computer Chip Data - Its harder than you think
Forget about which CPU the car uses. You can get free
disassemblers for virtually every CPU. Disassembling
the (E)EPROM code is a waste of time. Sure you can do
it, but its not worth the time. Here's why:
Ok, you got your 16k x 8 EPROM out of your '87
to '90(?) GM car. You disassemble it. Tell me which
is code and which is data. You cant tell unless the
data all disassembles into illegal op-codes. Fat chance.
If you are real bright and have a few months you may
be able to determine where the data tables are after
finding the *real* assembly code.
Great, you've got kilobytes of hex numbers as look-up
tables. Look at John's earlier posting posting for
the fuel injector pulse. It pulls a dozen values from
a dozen different tables. And the equation to turn
on the radiator fan is just as complicated. This could
take about a year with a logic analyzer. If your
really serious create a mock-engine where you can hold
all the sensors at one state and let one sensor change.
Monitor all the equation changes and create a huge
matrix. You might be able to figure it out.
Or do what the aftermarket chip guys do. Infiltrate
the automaker and steal the EPROM listings.
I have replaced the GM EPROM from a '87 Sunbird Turbo
ECU with a EPROM emulator (something like dual-port RAM).
I then wrote some C code that allowed the user to change
the fuel vs. RPM table graphically. The new table was
written to the emulator and the engine ran using the new
table. The effects were recorded on the SuperFlow dyno.
The info was 'borrowed' from GM with something like an
academic license. We were running the ECU in Ga. Tech's
Formula SAE car. GM wont let us see their code for their
new ECU's. After having looked at the EPROM listings I
quickly came to the conclusion that no one figures out what
these things do - they steal the code.
From: Jim Conforti <emory!cpu.us.dynix.com!jec>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: Computer Chip Data - Its harder than you think
Tim (et. al.)
Here's how I disassembled Motronic ...
Using an 8051 disasm. pgm. (DIS8051 ver F.)
I got source code ...
Now which is data and which is code ?? hmm..
Well in the 8051, the way to move DATA out of CODE address space is the
movc a,@a+dptr instruction ...
The dptr is loaded by
mov dptr,#HHLL which assembles to hex 90 HH LL
Using a REAL kludgy code scanner I recorded ALL incidents of 90 and then
saved the next two bytes as addresses to the start of a MAP
Using the disassembler tag file, I tagged the region (approx.) from
0x4000 - 0x4fff as DB (MAPs) ...
With a little inside info, I found out that the EPROM is executed from
0x2000 up, the 0x0000-0x1fff region is ROM onboard the 80515
Adjusting the tag file and disasm'ing showed a bunch of "unresolved
address references in the region of "0x5000 - 0x6600" ...
After some thought, I had it figured out, ..
0x0000 - 0x1fff (Main internal code .. I need a friend at BOSCH!)
0x2000 - 0x3fff (Engine specific subroutines / interrupt service code)
0x4000 - 0x4fff (Data MAPs used by the EPROM subroutines)
0x5000 - 0x65ff (THIS IS THE GOOD STUFF!!!)
0x6600 - 0x7fff (More Engine specific subroutines working with 0x2000-3fff)
The MAIN MAPS in the region 0x5000 - 65ff are only refernced by ROM code
contained in the 80515 .. Now either a REAL cracking effort, or some
friends at BOSCH are needed to get the std 8k of ROM code and also the
code contained in the support chip (Yes, it seems Motronic has TWO ROMs
just to make life a little more difficult!)
Such is the current state of Motronic ... when I get back from vacation,
hopefully my SIEMENS 80535/515 databooks will be in and I can complete
my schematics of the Motronic circuitry ... then whith a little more work,
I'll have it all figured out ... (Yeah, right)
Oh, BTW, you might be surprized at how Motronic handles the spark timing
and dwell .. since it gets two signals, reference (1 pulse per 360deg) and
speed (N pulses per 360deg) .. It has a custom chip to run an angle counter
and comparator to fire coil ...
I'm going to simulate this using some std hardware: .. run the speed
signal thru a PLL (with div. by 3 in the feedback) setup to provide a
3x freq... count this in a counter, while comparing it to some latched
values (dwell and spark) in 8-bit identity comparators.. the comps output
to a flip-flop which thru an ignitor fires the coil ... a third comparator
will provide the reset signal to the counter ... all the CPU will need do
is look at inputs, go to a MAP or three and output two values to the
latched comparator registers .. the hardware does the timing for me :)
Oh well ... time to get ready for the vacation ...
(87 325is / 92 325i)
WORK: 1-800-288-8020 (x3406)
FAX: (801) 373-1889
From: emory!ll.mit.edu!psanders (Peter Sanders)
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: Computer Chip Data
>I have a computer chip from a 1990 Chevy 454. Reading out and changing
>the data is straightforward. But can anyone explain the meaning of
>these 1s and 0s in terms of engine operation? bruce roe
Well first you need to know what processor GM uses to control the
454. Next you need to dissassemble the machine code to assembly. After that
you can determine which part of the code is a "defined byte". Look up tables
are stored as defined bytes in the code. A simplified example would be:
Given a specific engine temp, RPM, incoming airflow, O2 reading etc
etc, the processor will look at a specific address and read the DB for the
amount of fuel required.
This is a very basic example as I'm not an expert on the subject.
More than just the code, you need an understanding of the hardware
in order to start modifing the DBs. You can't take the plug and chug
approach, you could do more damage than good.
I freind of mine wrote an HC11 disassembler. I used it to disassemble
the PROM from a VW Corrado G60. After looking at the code, I realized that I
needed a schematic for the ECU to determine what code was measuring what, and
when. I also looked at the code from some hi-po PROMs for the G60 and did some
comparisons between stock and the modified versions. The actual instuctions
were identical. The only difference was in the DBs.
I basically gave up on this project after realizing how much work and
time it was going to take to make modifications safely. I didn't want to blow
up my freinds new VW.
He ended up using the P-CHIP with the smaller supercharger pully and
a higher fuel pressure regulator. The kit claims 190hp, and after driving it,
I beleive it.
Just my experience with the subject.
[The GM processor is a bit different. I have the source code listings
and system description for one of GM's ECUs so I can speak with
a bit of authority. Each ECU is different so the addresses are
different for different ECUs. The "calpack" rom that everyone
changes contains only the "maps" or calibration data tables. For this
particular controller, one of the more complex since it controls everything
from the turbo wastegate to the lockup torque converter to the cooling fan, the
Calpack contains well over 100 tables. Everything is table-driven. Almost
nothing is done algorithmically. One way to figure out the Calpack is
to connect a logic analyzer to the prom and with the ECU on the bench
wtih carefully controlled inputs, observe what addresses are being addressed
by the processor. As one parameter is carefully varied, say, MAP,
an address will be observed to move. It is then pretty easy to map out the
range of the table. Most of the tables are two dimentional, though the
primary fuel map is typically 3 dimentional, relating MAP or MAF and engine
speed to fuel quantity. You likely won't be able to decipher the whole
Calpack this way but you should be able to figure out where the basic mixture
and advance maps (and boost as appropriate) are.
I'll report on how well this works in a few weeks. I'm about to assault
the ECU ROM from a mitsubishi 3000 GT/Dodge Stealth for a customer.
From: John De Armond
Subject: Re: Compression ratio, fuel octane , and aftermarket chips
Date: Fri, 01 Oct 1999 17:45:33 EDT
Robert Hiebert wrote:
> Hi All,
> I tend to agree in general with Will and Ralph, but, being a
> compulsive gear head and techno freak, I find it difficult to leave
> things alone. What I'm trying to do is separate the bullshit from
> reality, and probably somewhere close to the middle, find the truth.
> I've done a fair amount of research on the subject of aftermarket
> chips. Both Hypertech, and Superchip claim about the same thing. They
> put a vehicle on a chassis Dyno, and alter the fuel curves for maximum
> power in all ranges, and likewise for spark advance, using 92 octane
> fuel. They claim in some vehicles the mixture is enrichened, while in
> some it is leaned out. They also claim 10 to 20 rear wheel HP
> increase, and 1 or 2 MPG increase.
> In my opinion, this is quite fine tuning, and in order for a
> particular chip to be optimized, it must be used on a vehicle of the
> same engine and application as the test vehicle. When I queried both
> companys as to my application, ( 460 Ford 17,000 lb. motorhome ), I
> asked what they had used as a test bed. "Somthing similar to yours"
> was the best they could come up with. When I asked if they could
> provide me with the fuel and spark maps before and after chip
> installation, I was told that this information was gained at great
> expense and effort, and was therefore confidential. ( probably
> justifyable ) As they're developement is done on a dyno, I asked if
> before and after HP, torque and EGT graphs were available, I was told
> they were not. They also claim in their advertising, that any engine
> modifications,(headers etc. ), would require a custom chip. I have a
> "Banks Power Pack ", but when asked the same question on the phone,
> the answer was that the off the shelf chip would work just fine.
Let's take a look at this. Back in my Performance Engineering
Magazine days, we took a scientific look at the chips that were
available at the time. The summary of our look is, there is no rule
of thumb. One brand of chip we looked at was empty. That is, all
locations set to 0xFF. This put the ECU into limp-home mode. It
learned enough from closed loop feedback from the oxygen sensor to
run pretty good at low loads. Limp-home is fairly rich on top to
protect the engine and that could make more power if a better
exhaust and/or intake was fitted. Another chip slammed the timing
full advanced and let the knock sensor take care of finding the
right advance. Other chips did pretty much what they advertised.
Our look was 8 years ago so I'm not going to name names.
I have the source code listing for a GM ECU and CalPac. (the chip.)
There are over 100 tuning tables in the CalPac that address
literally everything from cranking to the first 20 seconds after
start to wide open throttle to part throttle coasting. The
manufacturers make many tradeoffs in programming the CalPacs.
Tradeoffs such as guaranteeing to meet emission standards over the
whole 100K mandated period, passing the emissions requirements at
all, warranty considerations, protecting the engine as much as
possible from idiot owners, etc. Many of these parameters can be
and are optimized for a specific market by the chip vendors. Some
vendors know that simple emissions checks don't look at the power
part of the operating envelope and so retune the map to make power
at some expense to emissions. While technically not legally kosher,
as a practical matter, it has little effect on emissions. To say
that map tuning is only "fine tuning" is quite misleading.
I can understand the chip maker's reluctance to disclose chip
contents. This information is generally NOT available from mfrs. I
once reverse engineered the ECU maps on a Mitsubishi GT3000 in the
process of hotrodding it for a customer. I spent literally weeks
with the ECU on the bench, dummying in sensor signals and watching
on a logic analyzer what locations were being accessed in the PROM.
That was for one model of one car. Imagine having to do that for
every model across a single brand's lineup.
Chips generally are NOT needed for minor modifications and for
fairly significant modifications to ECUs that use a mass air flow
meter. The ECU can learn new parameters on the fly. This applies
only to non OBD-II ECUs. OBD-II ECUs can learn too, but they'll
drop codes much quicker when things change per the federal mandate
> All of this tends to make me more than a bit suspicious.
> Let's analyze their claims. They claim to optimize fuel mixture.
> In my case, reading spark plugs after a hard run shows text book
> perfect tan colour.
With unleaded fuel, that means almost nothing. Unleaded fuel does
not leave deposits on the plugs to pick up the color. As a broad
measure, the shell at the base of the insulator can be read. A gray
ring means the mixture is close enough not to harm the engine. The
ONLY way to tune a modern engine is on a dyno using a data
acquisition system and and a wide range exhaust gas analyzer.
>To back this up, in open loop, below about 4"
> manifold vacuum, my exhaust gas oxygen meter indicates full rich.
Unless you have a wide range EGA (if you paid less than $1000 new
for it, it is not a WREGA.) These low cost "EGA" sold by Summit
Racing and the like that read a standard oxygen sensor are really
frauds. The standard oxygen sensor only has a range of lambda = 1
+_ perhaps a tenth. Lambda=1 is stoichiometric. The sensor is
essentially a toggle device, indicating either rich or lean. The
transfer function looks like a "Z" with the leg being almost
vertical. The ECU toggles the mix back and forth across lambda=1
because a) it is the easiest control modality and b) oxygen storage
cats work better that way.
Honda uses an oxygen sensor that is wide range on the lean side of
stoich on their lean-burn engines but that sensor requires active
electronics to drive it. I've never seen anyone try to use it in an
analyzer application. Since it toggles across stoich just like a
regular sensor, it would have limited utility as a tuning tool.
> As far as spark advance is concerned, as an experiment, I tried
> advancing the base timing setting, with the result that I got
> preignition, particularly at full throttle, with any further advance
> at all. But they claim that they can advance the spark if you use 92
> octane fuel, which will make more power. I have a problem with this,
> especially in this application.
You shouldn't. The ECU has a three dimensional map of manifold
pressure vs RPM vs timing. More advanced ones have a map for each
cylinder. Depending on year model, this map has from 8 to 32 slots
to an axis. The spark is individually tuned for each set of
conditions as part of the mapping process. The chip maker can remap
the ECU to take advantage of of the higher octane fuel wherever
possible. When you turned the distributor, you simply shifted the
whole map forward and added advance everywhere. Kind of a broad-axe
approach to tuning.
> Fuel octane has to be raised if flame spread is fast enough to
> cause pre ignition. Flame spread rate is dependent, among other
> things, on charge density. Charge density is determined by effective
> compression ratio. Higher octane fuel has a more controlled ( slower )
> burn rate to compensate for, and take advantage of higher charge
> densitys. The compression ratio in the 460 EFI is relatively low,
> 8.5:1. It is dificult for me to believe that advancing the spark on a
> low compression ratio engine, then using slower burning fuel to
> prevent pre ignition will yield more power. If this were true, in the
> days before EFI, it would have been a basic hotrodding trick to simply
> advance the timing on your distributor, burn high octane fuel, and,
> presto, more power! I've never read anything to that effect, and I
> read a lot.
Octane has nothing to do with the burning speed. The process of
detonation is complex enough that it has yet to be completely
modeled. Octane is still measured at many refineries by means of an
on-line test engine, though chromatography is gradually taking
over. In simple terms, detonation occurs when the ignition
precursor compounds produced as the fuel mix is heated, first by
compression and then radiatively by the advancing flame front, to
the point where it ignites. High speed in-cylinder photographs show
that detonation almost always originates at the junction between the
head and block where a stagnant mixture is the furtherest away from
the flame front. Octane booster work in a variety of methods.
Tetraethyl lead (TEL) worked by decomposing into tiny particles of
lead oxide which absorbed and/or reflected the radiative heat from
the advancing flame front. Other compounds such as the higher
aromatics like toluene suppers the formation of ignition-prone
precursors. Any detonation control effort is a race between
completing the combustion cycle and premature ignition.
Advancing the spark does make more power in a low compression engine
if done properly. The goal is to arrange the peak combustion to
occur at a time which is least likely to cause detonation while
delivering the maximum force to the piston. The rate of combustion
is an exponential function of pressure. The curve climbs rapidly
after the knee. I high compression engine starts out well up on the
pressure axis and so needs less advance to put the combustion peak
in the right place. A low compression engine starts out lower on
the pressure curve so more spark lead is used to give the reaction
time to proceed at the low pressure. There is a tradeoff where
radiative heat loss to the piston and block while the combustion is
still slow and additional frictional losses due to there being
pressure behind the top ring for a longer period of time balances
against the increased combustion pressure. Just slamming in more
advance by turning the distributor on an old engine doesn't work
because it puts advance in everywhere and not just where it is
I might add that using premium gas where it is not required may
result in less power and mileage. This is because the non-TEL
octane boosters such as toluene, MTBE and other ethers, and the
alcohols have less BTU per gallon than the base stock. It thus
takes more volume of fuel to make the same power. For at least 10
years now the EPA has mandated an additive package sufficient to
keep injectors clean for 100k miles for any grade of gas.
You'll never read about this just looking at the popular hotrod
press written by knuckle dragging Neanderthals who think multiple
carburetors and tunnel ram manifolds and open exhausts still have a
place on the street. But the SAE (Society of Automotive Engineers)
has a huge collection of engineering materials available on the
subject. proceedings of their fuel, engine management and engine
electronics conferences are available, albeit quite expensive.
Check out http://www.sae.org. You can buy the papers online,
delivered to you in PDF format. There is also a good handbook
available on fuels.
> In diesel engines, particularly in heavy trucks and marine
> applications, EGT is often used as an indicator of engine load, most
> often being the limiting factor on how much power can be produced.
> This same theory should hold true for gas engines. I've been trying to
> research acceptable, and maximum EGT for gas engines in general, and
> the 460s in particular with little success. It doesn't appear to be an
> area of much interest, and maybe I'm reading too much into it, but if
> you know of any scources of information, I'd sure appreciate hearing
> about them. I have an EGT meter on my rig, and have some interesting
> observations, if anyone is interested.
EGT is only moderately useful for an electronically controlled,
emission-controlled engine with a cat downstream. part of mapping
the ECU is making sure the cat stays hot enough (but not too hot)
under all conditions. EGTs will do apparently crazy things as a
result. One technique that is frequently used is to take advantage
of the additional valve overlap that modern 3-way cats allow to
carry extra fuel through the engine to the cats to keep them warm.
What your EGT does depends on whether the manifold is hot enough to
sustain burning in the manifold or not.
From: John De Armond
Subject: Re: Compression ratio, fuel octane , and aftermarket chips
Date: Mon, 04 Oct 1999 05:42:25 EDT
Robert Hiebert wrote:
> >I can understand the chip maker's reluctance to disclose chip
> >contents. This information is generally NOT available from mfrs. I
> >once reverse engineered the ECU maps on a Mitsubishi GT3000 in the
> >process of hotrodding it for a customer. I spent literally weeks
> >with the ECU on the bench, dummying in sensor signals and watching
> >on a logic analyzer what locations were being accessed in the PROM.
> >That was for one model of one car. Imagine having to do that for
> >every model across a single brand's lineup.
> As I mentioned, the fact that the chip contents are not available is
> probably justifyable, and I can understand that. I would
> think,however, that it would be in the chip company's best interest to
> supply before and after torque and horsepower curves as part of their
> advertising. This information surely would be a result of the
> developement process, and certainly couldn't be viewed in any way as
> some trade secret. The fact that it's not available, and only general
> HP gains are, makes me very nervous.
> >Chips generally are NOT needed for minor modifications and for
> >fairly significant modifications to ECUs that use a mass air flow
> >meter. The ECU can learn new parameters on the fly. This applies
> >only to non OBD-II ECUs. OBD-II ECUs can learn too, but they'll
> >drop codes much quicker when things change per the federal mandate
> >for OBD.
> My point was that the advertising literature would have you believe
> that for a stock engine, an off the shelf chip will work. Any
> modifications that increase flow would require a custom chip. But the
> reality is that only major internal modifications require a custom
> chip. This may be nit picking, but it all is part of the credability
Actually I'd commend them for not quoting "horsepower at the word
processor". If they guarantee satisfaction or your money back,
that to me is much more genuine than promising a given increase or
worse (like Jacobs Electronics) guaranteeing a specified number of
HP increase for any engine.
For engines built to production tolerances, a variance of 10% or
more in HP would not be uncommon. Even engines built to after
market racing specs vary quite a bit. One of my clients, a well
known engine builder who shall remain nameless, actually had me
install a control on his dyno so that he could dial in the desired
HP. This shop is not being dishonest because they don't promise any
specific power. But his customers who have bought racing engines
for years expect to get dyno slips reading exactly the same HP as
the previous engine. And even though they may be winning with the
engine, if it is down 5 HP, they'll complain. So this shop simply
gives them what they want. A number. I commend your prospective
vendor for not doing that.
> >With unleaded fuel, that means almost nothing. Unleaded fuel does
> >not leave deposits on the plugs to pick up the color. As a broad
> >measure, the shell at the base of the insulator can be read. A gray
> >ring means the mixture is close enough not to harm the engine. The
> >ONLY way to tune a modern engine is on a dyno using a data
> >acquisition system and and a wide range exhaust gas analyzer.
> Page 23-5 of my Ford motorhome chassis service guide has a spark plug
> inspection chart, which among other things, relates plug colour to
> mixture. Page 13-17-11 of my 1992 Ford engine Service manual has the
> same thing
Go back several years before unleaded gas and see if that same
picture isn't in the service manual for that year. I see that a
lot. The after market manuals (Haynes, etc) are even worse.
> >>To back this up, in open loop, below about 4"
> >> manifold vacuum, my exhaust gas oxygen meter indicates full rich.
> >Unless you have a wide range EGA (if you paid less than $1000 new
> >for it, it is not a WREGA.) These low cost "EGA" sold by Summit
> >Racing and the like that read a standard oxygen sensor are really
> >frauds. The standard oxygen sensor only has a range of lambda = 1
> >+_ perhaps a tenth. Lambda=1 is stoichiometric. The sensor is
> >essentially a toggle device, indicating either rich or lean. The
> >transfer function looks like a "Z" with the leg being almost
> >vertical. The ECU toggles the mix back and forth across lambda=1
> >because a) it is the easiest control modality and b) oxygen storage
> >cats work better that way.
> >Honda uses an oxygen sensor that is wide range on the lean side of
> >stoich on their lean-burn engines but that sensor requires active
> >electronics to drive it. I've never seen anyone try to use it in an
> >analyzer application. Since it toggles across stoich just like a
> >regular sensor, it would have limited utility as a tuning tool.
> This is interesting! My EGA is by "Autometer" and is a 20 LED DC
> voltmeter, with a range of about 1 volt in 50 millivolt increments. I
> believe the HEGO produces a voltage of between .1 and 1.1 volts. I
> also believe the limits of combustion of an air fuel mix are about
> 20:1 lean, and 11:1 rich, stoich being abouot 14.7:1. I had assumed
> that 50 milivolts would represent about 20:1 mixture, and 1volt would
> represent about11:1 mix. If I understand you correctly, 50 milivolts
> probably represents 16.2:1, or leaner, and 1 volt represents13.2:1, or
> richer, and I would have to agree that it would be extremely limited
> as a tuning tool. With only plug colour to go on,it's quite possible
> that my mixture could be improved on.
I've scanned a page from the SAE paper # 860408, "Air-Fuel Ratio
Sensor for Rich, stoichiometric and Lean Ranges", <bunch of japanese
names I don't feel like typing :-)> Go to
http://neonjohn.4mg.com/files/car/wrego.gif This paper can be
bought in PDF format from the SAE site. It is part of the
proceedings of the Sensors and Actuators symposium (document SP-655)
at the SAE congress in 1986. Whew! This page contains a whole
bunch of information.
Lambda is defined as the ratio of the mixture strength divided by
the mixture strength at stoichiometric. A stoich mix is lambda =
1. A 12:1 rich mix would be 14/14.7 = .952. A lean 15:1 would be
The conventional narrow range sensor (one wire, not counting the
optional heater wires) generates a voltage proportional to the
oxygen partial pressure on either side of a zirconium oxide
barrier. The barrier is coated with platinum to catalyze the
oxidation of any unburned HC or CO to make sure the oxygen available
is truly representative of the combustion conditions. Figure 2 at
the top left of the page shows the transfer function of this type
sensor. The curve is labeled "O2 sensor output E(lambda)". As you
can see, this is practically a toggle function.
Table one outlines the 4 types of wide range oxygen sensors
investigated. All these sensors depend on doing work of some sort
on the oxygen. The type sensor that has been developed since this
paper came out is illustrated in slot 3 of Table 1. This sensor is
know as an oxygen pumping sensor, or as the article says, "oxygen
cramming". This is the sensor used on the Horiba WEGO meter (About
$2000) It has either 4 or 6 wires depending on whether it is
self-heating or not. This sensor uses electromotive force to pump
oxygen ions across a zirconium solid state electrolyte barrier. The
more oxygen present, the more work per unit time is used pumping
it. This is converted by the electronics to a practically linear
voltage vs oxygen partial pressure, and thus lambda curve. Figure 3
shows the transfer function for the oxygen pumping sensor(solid
line) and a related sensor, the oxygen biased sensor. According to
a 1990 price sheet from Hitachi, the sensor alone costs $500. It
requires active electronics to drive it, unlike the single wire
sensor which simply generates a voltage. I imagine the price has
gone up since then - the price of the Horiba sure has!
BTW, let me know if you have trouble viewing that page. Some people
have told me they have been denied permission on some attempts.
I've only had this site up a couple of weeks so I'm still learning.
> I guess I worded that wrong, this quote is what I meant
> "A high compression or turbocharged engine operates with much higher
> charge densities and
> consequently faster burn rates. The high octane fuel permits these
> rapid burn rates because it has far
> less tendency to autoignite and detonate under these conditions. As a
> result, high compression and
> turbo engines cannot realize their full hp potential without high
> octane fuel."
> This is from the tech page of what I consider to be an excellent site
He has that kinda muddled. Fast burn rates, as induced by modern
high swirl combustion chamber designs result in LOWER octane
requirements and less spark lead. If the swirl makes the combustion
proceed faster, it needs less "head start" (advance) to get the peak
pressure at the right point. It is important to remember that the
combustion rate is an exponential function of pressure. This means
that things truck along at a leisurely rate until the knee of the
curve is reach. After that, the reaction rate curve goes straight
up. The implication is that what happens back down the line isn't
too important to the ultimate outcome. Consider a doubling series
where we double the previous number each second:
The shape of this series is equivalent to the rate of combustion vs
pressure. In these two series, I've changed the starting value by a
factor of 5 (1 vs 5) but it only took a couple less seconds to
exceed 1 million. The same thing applies to combustion. The
reaction rate can vary over a wide range and have very little effect
on knock. Vastly more important is the amount of time spent at
elevated temperature that breaks down the fuel in the far corners of
the chamber into compounds that easily explode (detonate) - the
so-called knock precursors.
Part of the confusion comes from the fact that knock can also be
controlled by means that DO slow the reaction rate. Water injection
and exhaust gas recirculation are two techniques. Both techniques
have power penalties associated with their use.
There is an excellent book available that covers this topic in
excruciating detail including the calculus for those nights when
sleep just won't come. Titled "Internal Combustion Engine
Fundamentals" by John Heywood, ISBN0-07-028637-X, McGraw-Hill,
available also from the SAE bookstore. This is a graduate level
textbook but it is a fairly easy read if the math is mostly
ignored. Lots of data and graphs.
> >I might add that using premium gas where it is not required may
> >result in less power and mileage. This is because the non-TEL
> >octane boosters such as toluene, MTBE and other ethers, and the
> >alcohols have less BTU per gallon than the base stock. It thus
> >takes more volume of fuel to make the same power. For at least 10
> >years now the EPA has mandated an additive package sufficient to
> >keep injectors clean for 100k miles for any grade of gas.
> I think this is a key point here. The question is, does advancing the
> timing on a low compression engine require premium gas to make more
Reverse the cause and effect. Given a higher octane fuel, one can
extract more power from a given engine by use of more compression
> It makes sense that timing has to be tailored for the complete curve,
> but, isn't timing on the 460 all in by about 2000 RPM, and most power
> is made above that?
I can't talk specifically about any engine other than the ones I've
built but in general, the most advance is in the region of low
cylinder pressure and high speed - cruise. Timing is typically
backed off a few degrees at WOT because that tends to make more
power. A typical timing map looks somewhat like a topo map. This
is because each combination of RPM and manifold pressure is
optimized individually. If the intake and exhaust are resonating at
a given point resulting in better cylinder filling, less ignition
advance will be needed there than immediately adjacent points when
no resonance supercharging is occurring.
> >EGT is only moderately useful for an electronically controlled,
> >emission-controlled engine with a cat downstream. part of mapping
> >the ECU is making sure the cat stays hot enough (but not too hot)
> >under all conditions. EGTs will do apparently crazy things as a
> >result. One technique that is frequently used is to take advantage
> >of the additional valve overlap that modern 3-way cats allow to
> >carry extra fuel through the engine to the cats to keep them warm.
> >What your EGT does depends on whether the manifold is hot enough to
> >sustain burning in the manifold or not.
> On my engine, secondary air is not introduced in the manifolds at all,
> but rather just in front of the cat, at mid point of the cat, or
> dumped to atmosphere. Also secondary air only goes into the system at
> or near WOT, down stream of the thermocouple as well. Would not EGT be
> quite significant in this case?
I don't know that particular engine so again, generalities. The
excess fuel would pass through the engine from the injectors.
Therefore it could burn under the proper conditions in the exhaust
even without air injection. I just can't predict what the EGT will
do. I use individual EGTs on each cylinder when tuning on the dyno
but I use the information to see if the cylinders are matched and
not the absolute temperature. Indeed, the SuperFlow dyno (most
popular one in the US) thermocouple input block is not even
reference junction temperature compensated. The apparent temperature
will vary with the temperature on the reference junction block.
Since they all vary together, that doesn't matter much.
> If I'm understanding you correctly, you feel that an aftermarket chip
> can be of benefit in general, and my engine in particular.
> OK, what would be a realistic expectation as to power gain, and at
> what point in the RPM range?
> Is this likely to stress the engine to the point that reliability
> could suffer?
> How do you chose a manufacturer without graphs, or specs to compare?
I can't tell you about your engine. What I'd do is find a vendor or
vendors who offer a money-back guarantee with no restocking fee and
try them. If you want to test scientifically and don't want to rent
dyno time, guy a G-Analyist (~$125 from Summit, JC whitney, etc.)
This device contains an accelerometer. After you plug in the
vehicle's weight and calibrate its drag curve (by letting the
vehicle coast in neutral from various speeds), the gadget takes
acceleration and computes horsepower vs RPM and displays it. It
actually works fairly well.
From: John De Armond
Subject: Re: Compression ratio, fuel octane , and aftermarket chips
Date: Mon, 04 Oct 1999 18:19:02 EDT
Robert Hiebert wrote:
> >names I don't feel like typing :-)> Go to
> >http://neonjohn.4mg.com/files/car/wrego.gif This paper can be
> >bought in PDF format from the SAE site. It is part of the
> >proceedings of the Sensors and Actuators symposium (document SP-655)
> >at the SAE congress in 1986. Whew! This page contains a whole
> >bunch of information.
Well, I just read this article when it came back in and found the
link to be broken. Figured out what is happening. This free web
site wants you to see their ads so they only allow one in via my
home page. Go to http://neonjohn.4mg.com and then click down
through files and car to wrego.gif. That will work.
> I have a G-Tech-Pro, which I assume is a similar instrument, and have
> used it to quantify changes when I installed my aftermarket ignition,
> and headers. Dispite its limitations, I'm very happy with it.
Kewl! I've never used one of the pro versions. I'd like to hear
how it works. Several years ago I built an interface to a laptop
computer and wrote some software that takes the doppler signal from
a police radar, extracts the acceleration data from it and makes
similar calculations to the G-Tech. I found the two to agree
remarkably well. The radar works better for low acceleration rates
where the signal from the G-tech accelerometer is small. The radar
also handles vehicle pitch much better because it is actually
reading ground speed. And finally, it can be used from outside the
car. Nifty for snooping on your competitors :-)
> Thanks for all the information, and your opinions. It's been a real
> pleasure, and I look forward to talking with you again some time.
You're most welcome.