Ken: When I mentioned the re-working of the head, that was a very real and valid point, that has a direct cause/effect relationship on modifications and the power levels that you are trying to obtain from your engine. Because you are wanting much "better" than stock, naturally aspirated engine performance, as well as the capability of, in the near future to be supercharged. Kind of a "dual" role, in engine design, and certainly a "paradox", from a building standpoint. Because of the performance "parameters" of high torque at lower RPM's, that you want, while at the same time dealing with the limiting factors of the block/head design, long stroke, RPM limitations, and rod ratio.
Moderate head/port preparation will considerably improve the intake and exhaust flow rates of the production 292 head. Making the runners taller and wider is a real plus. You can remove much more material from the floors and roof, than from the walls. Do not be conservative with the combustion chambers. Build it up with weld, as needed in the low spots and smooth it out, lots of blending. These chambers are very thick and rough, and almost anything you do, will improve flow. Smooth all the edges around seats, and blend. The chamber is tapered, so you want to open up the small side a little, and more smoothing to help prevent any secondary combustion (detonation), from this squish area. In the valve area, bowl blending is all important, make sure to form a smooth radius from bowl sweep to floor of runner.
All this head work is important, because it has direct relationship on flame-front, cam selection and cam timing, flowrates, velocity, and backpressures.
You also need the head prep done first, so as to ascertain the CR. Need to know: bore, stroke, head gasket volume (thickness), head combustion chamber volume, piston dome volume, piston deck height. I feel you would not want to go more than about 150/160 PSI static compression maximum! Not knowing all your variables, the basic formula goes something like this:
EFFECTIVE COMPRESSION RATIO
static CR= x2psi x4 x6 x8 x10 x12psi
7.0-1 8.0 8.9 9.9 10.8 11.8 12.7
7.5-1 8.5 9.5 10.6 11.6 12.6 13.6
8.0-1 9.1 10.2 11.3 12.4 13.4 14.5
8.5-1 9.7 10.8 12.0 13.1 14.3 15.4
9.0-1 10.2 11.4 12.7 13.9 15.1 16.3
9.5-1 10.8 12.1 13.4 14.7 16.0 17.3
This chart shows the various levels of boost (PSI) and the effective compression ratio. It is based on averages, so is only approximate estimates. Can be used for 4, 6, or V-8 engines. For most "street" engines, the effective compression should be kept at/or below 12.1 CR maximum, when using 92 octane pump gas. When using 100 octane "blended racing gasoline", the CR should be kept at/or below 15.1 . In both cases, even if using "lead" additives, DO NOT exceed these compression limits. It is recommended that a "boost-sensitive" timing retard
system device be used to prevent "DETONATION"!
The dynamics of airflow sure does change things. It will be difficult for you to have a high torque NA engine, unless you jack up that CR. But if you do that, you will have to drop it right back down to run a blower. I would suggest you stick with a CR something around 8/8.5 . Any more than this and it will be too high for blower. Any lower and you won't have any power NA!
Just a decent compromise in the middle.
For a NA, you can find cam with a narrower LDA to give you better throttle responce, and better low speed pull. With the blower, then you can go with the wider LDA split duration cam to assist in clearing the additional exhaust volume. Got to get rid of all that extra air you jammed in there!
What you need is an adjustable cam drive on that 292. Then you could run a dual pattern cam and retard timing with the blower use. Something like a"Jesel" set-up for the Chevy BB, but mounted on the front of that 292. That would be MOST cool!
Don't know what type fuel delivery system you plan on using, carb or injection? If using carb on the blower, you may need 2 of them because of 50% more airflow into engine/carb with blower, you can see that soon run out of carb CFM flow and might require 2 carb's.
If going the injection route, you should not have the problem. A cool set-up that I have seen on blower motors is multiport injection by Electromotive. It uses its own computer module which is programmable. The unit replaces the carburetor, distributor, and needs no other ignition sources. It has its own crank fired direct ignition system built in. Check it out at:
www.electromotive-inc.com Have fun and good luck!
Think Chevy!
:rolleyes:
:p
