How does combustion chamber size affect performance?

the smaller the combustion chamber the higher your compression

the only thing is the smaller your combustion chamber the harder it is to fit larger valves in there due to the edge of the chamber being right up against the valve and causing shrouding


also when you have a smaller chamber on top of the benefiut of higher compression you are also running into a situation called squish

squish is where the piston and the head (not the combustion chamber but the flat surface of the head itself) come real close to each other which pushes the intake charge more to the middle of the chamber and helps tumble things around so your flame front burns a little more even and faster... all in all letting you make more power with less timing and reduced chance of detonation

Ok.....now, is there an alternate way of lowering compression other than using a larger combustion chamber?

yes, dished pistons.

how do you know which pistons and what size combustion chamber have a given compression ratio? I'm sure there are math formulas for it, but I'm just starting to get into engine building

just out of curiosity what is your application here and why is it you need to reduce your compression?

trying to figure out how to build a 350 for max power on 87 octane, since my other thread on the topic didn't really go NEARLY in-depth enough

well compression ratio is a weird thing

I have seen it where some cars running 10:1 NEED 92 octane

but then again I have seen it where a12.5:1 compression ratio motor ran on 87 octane


running alum heads will give you a little better compression ratio but since they absorb more heat it's kinda a trade off cause heat builds pressure and pressure makes power


going with a fast burn style heads ( as far as I know you might want to check around though) is your best bet
they have lot of squish built into the head mixing the air/fuel intake charge up which causes that better burn. again more power and more resistant to detonation.



what is it you have setup right now or at least planned in your build?

I havent' gotten so far as planning anything much more than my goals: max power/torque in a NA 350 on 87 octane with decent drivability/gas mileage.....

I'm undecided as to carb vs FI, no clue what sort of cam to run, etc. about all I know for sure is it'll be a 350 block and the heads will be ported/polished

As for which heads, in another thread I've asked for flow numbers for both the FastBurn and Vortech heads....

I have a fairly decent idea of how to get the power to the ground once I've got it built, though

your best bet would be going with FI


they are able to give you better fuel metering and atomization of the fuel

that will allow you a little more give as far as octane req

also the fuel injection system doesn't work on vacume like a carb does so it will work over a wider range of rpms


problem is cost, and tuning.

now if you are going for a bang for the buck go with the carb also the carb will be a little easier to tune being you don't need to bust out the laptop if you run a stand alone or send your chip off to get it retuned if you are using a stock GM chip

bang for the buck is a Good Thing, but would FI or a carb be lower maintenance once properly tuned?

Also, what sort of FI systems should I look into (more make/model than *type*....ie Holley vs Accel rather than TPI vs TBI)?

FI would prolly give you the least hassle once setup

but as far as which product to buy I can't help you there


I know the theory behind it and so forth just do not have the knowledge as far as parts and numbers...

Ok. I'll check on the FI boards.

Thanks