I assume you are aware that there are material limits to what can be done
in the alloy head. If the intake and exhaust valves are already
"unpocketed" to a proper degree, there is precious little metal left for
further reliablilty factors and I would NOT suggest trying to find more
removal in the region behind the valves.
However, you could do well by removing a wedge shape portion of the bottom
face of the head which angles away from the actual present chamber vertical
wall, on the side "away from the valves.
This would then be a relief "over " more of the piston crown and would also
likely improve the incomming flow somewhat, at the expense of losing some
"turbulence" affect.
Without proper lab testing, this is all based on experience and personal
opinion.....not on proved results.
Also, any amount taken off the chamber wall in this manner will have some
affect at reducing total "clamping" affect against the gasket and this may
lead to gasket failures.
I suggest obtaining your desired CR by looking at your pistons to see if
they have nice thick crown area which would allow the piston tops to be
machined down a bit to provide the CR desired. If the answer is NO or is
questionable, then the alternative is obvious........design and obtain
custom made forged pistons (which you should have in any case).
You are going to make some serious BHP and forged pistons are going to be
almost mandatory ! Venolia, J&E, Jahns and others can accept this job for
making you proper pistons.
Also, your cam grind can now be very mild but with increased lift. The
blower action will stuff really huge volumes in the cylinder with a high
lift mild overlap grind. As a matter of fact, you would NOT want lots of
overlap or you will be pushing mixture out the exhaust valve. Let this
engine make great gobs of BHP and torque at mid range and yp to perhaps
6500rpm. This will give reliability. Gear the rear end properly and you
will have a fantastic accelerating car...if the tranny can take it. Sounds
like you are thinking in the 185-200bhp range?
Finally, I will mention that many vehicles these days are turbo and
super-charged. Quite a lot have very high CR into the range you are worried
about.
By using electronic knock sensors and boost monitoring and wastegate
systems, engine damage is prevented. I would like to suggest you keep
your 8.93:1 CR and go for equipment which allows it to work. This CR
will give you better power off the mark before the blower starts to do a
job affectively !
Go see Buick (which uses a supercharger) as well as other marques.
Possibly the parts people as well as mechanics will let you study up in the
shop manuals and learn how high comp is handled in SC and TC engines.
Contact the mfr. of your blower for max advice and data.
Also......drop by the local hot rod shop and see a copy of the current
magazine type manuals covering turbo and super charger installations.
As a last tip, call or fax Turbonetics Inc. 805 529 8995; fax 805 529 9499
and request their catalog on Garret TC's. This is well loaded with
requirements, charts etc. as well as their line of hardware.
Many mfr's make wastegate systems which will control your boost easily and
names like Rajay, Deltagate, Garret etc. all supply lots of info..free.
While you perhaps did not intend to go with an "intercooler" this would
also be another subject worth learning about.
There is something to be learned from all these sources, both on the book
and mfr. level.
If you think to write me again and try to get more data, don't bother. I am
too busy to become involved in this project but would enjoy seeing a report
when you have things running..or when you make ongoing decisions. I might
take a minute to reply briefly.
I am retired now. I don't have connections with the industry any more and
besides I am at least 104 years old (still working on this problem) and may
not be around even to answer you back.
Dick T.
This archive was generated by hypermail 2b30 : Tue Sep 05 2000 - 09:59:56 CDT