Thread: Domed pistons and quench?

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"Is this because the domed would cause too high of pressures and not be dependable and go kaboom ?"

Yep. In the case of the supercharged motor, here's a chart from Blower Drive Service showing the limits of scr versus boost for use with pump gas:
http://www.blowerdriveservice.com/techcharts.php
It clearly shows the "8 for 8" rule (8:1 for 8 lbs of boost with pump gas). On alternate fuels, you'd be limited by the components you chose for your buildup. You could use a very high scr with nitrous or a blower, but it would be a matter of which component would fail first. Will it break the crank or split the block in half first?

"If that is the reason then would it be proper to say that domed pistons and superchargers are just two ways of skinning the same cat?"

Yep. You can use high scr naturally aspirated with no power adder or na with nitrous or low scr with a blower although you'll make more horsepower with either nitrous or a blower than you will just naturally aspirated with a high scr. By the way, some guys consider a nitrous motor to no longer be naturally aspirated. I disagree because the air going into the motor is still being pushed in there by atmospheric pressure although there is fuel and an oxidizer under pressure at the port.

"But then chooseing which one would be based on 'class rules' or upon whatever would be practical for a street vehicle?"

Yep.

"what would determine whether I would use 10:1 or 13:1 ? Is this all based on cam spec's. and whatever power I want the motor to make? If so,,,then why doesn't everyone that builds a race motor run 13:1 or much higher?"

Making horsepower is a matter of moving air through the motor. The more air you move through it, the more horsepower you make. Spinning the motor faster dictates a long cam and the long cam dictates a high scr. But spinning the motor faster means using the best components money can buy so they can withstand the tremendous forces generated with very high rpm's. Any cam grinder can grind a cam that will feed any motor at any rpm's, but the cost of the components will require a second mortgage on your home.

The stumbling block with building a high scr, low rpm motor is the cam. Let's say you want to build a 13:1 motor, but don't have the coin for the high buck components. You figure you'll keep the r's down. Problem is, the cam that will work with 13:1 is going to make power from about 4,000 r's to about 8,000 r's.

Can you see how all of this fits together? You must sit down and figure out your combination before you start to build a motor. If you're planning to make big power at low rpm's, then start with the largest motor you can, 500 inches minimum. If you plan to make big power at low r's with a small motor, then include nitrous or a blower in your plans. When I say low r's, I'm referring to a motor that will see a limit of about 6,000 r's.