From: Dave Baker
Subject: Re: Blueprinted engines
Date: 30 Oct 1998
Excellent article Bob and correctly refuting those who think blueprinting is
something to do with building to factory tolerances. It is building to the
tolerances set by the man who designed the engine before the limitations of
production engineering reared its ugly head.
As an engine builder who does build to tolerances that the engine wants rather
than what the factory can achieve I would like to throw my tupence in.
99% of the things that people believe make a difference to the way an engine
performs and nearly everything that has been mentioned in the thread actually
make almost no measurable difference at all.
The engine that I build most of is the Ford 1600 CVH engine and most of these
over the last 5 years have been for a race series which calls for engines to
remain at standard Ford spec. Any horsepower gains to be had therefore call on
very careful engine work because no porting, camshaft, carb work etc is
allowed. This has given me the opportunity to study some 40 engines over the
years and to try different things and to get feedback from dynos on what makes
a difference to power.
The only thing that makes any measurable difference is the difference in
cylinder head airflow between different castings.
You can mess about with piston/bore clearances, bearing clearances, balancing
things to 0.1 gramme, boring exactly at 90 degrees to crank centreline and see
no more than 1 or 2 % in power improvement.
Over that range of engines I have hundreds of flow tests and the difference in
flow between the best and worst standard cylinder head is more than 10 bhp.
When you buy a standard production car they range between lemons, good standard
and the occasional flyer. Nearly all of those differences are related to
airflow not internal engine tolerances IMHO.
To build an exceptional engine for customers with deep pockets I got them to
search scrapyards and send me as many cylinder heads as they could find. I
flowed them all and put the highest flowing head on the engine. Over the years
I developed computer programmes that analysed flow data and related that to
power figures. I can now predict engine power on a range of engines to as close
as 1% (with certain limitations which I won't go into here). Power is directly
and linearly related to inlet valve airflow. Every engine that I tested gave
the power that the airflow predicted despite the fact that thousands of other
things like exhaust system, oil viscosity, internal tolerances etc should have
been affecting things. I believe that all these other factors made minimal
difference and also just tended to average out of the equation.
The only other "blueprinting" type exercise that I would say makes any major
difference is the exact way that the bore is honed so as to seal to the piston
rings as well as possible. The grade of stone, cross hatch angle, depth of cut,
type of plateau finish etc can greatly affect power and oil consumption. One of
my engines which produced 86 bhp at the wheels went to another engine builder
when the car owner sold the car to another driver who didn't know who had
originally built the engine. This "engine builder" knocked the power down to 78
bhp at the wheels on the same dyno by what I can only describe as completely
fucking up the bores with a cheap flapwheel type glazebuster tool rather than
using the correct honing equipment.
I found this out when the engine came back to me a year later after the new
owner found out who had done the original build and wanted to regain the
performance it once had. For those specialists out there who will understand
this - the bare bottom end, no cylinder head, had a turning torque of 30 ft lbs
even after a seasons running with this awful bore finish. The pistons had to be
drifted out of the bores with a club hammer because there was so much friction
against the rings.
As to all the other stuff, if you stay within factory specs on bore & bearing
clearance and all thrust tolerances the engine will be fine for most
applications. For very highly stressed uses it can become more important to
ensure that bearing clearances (especially big ends) are spot on if oil
pressure is to remain good.
As to the cost of blueprinting I fail to see why it should be expensive as
people suggest. To have cranks and bores machined to an exact size and to
balance all parts properly costs next to nothing over an average "chuck it
together" engine build. For an average 4 cylinder engine I charge about £300 to
do all this work to race tolerance rather than road tolerance so where on earth
the figures of thousands of dollars come from as have been suggested I have no
Dave Baker at Puma Race Engines (London - England) - specialist flow
development and engine work.