Dumb question

[2010_camaro]

OK so I built my engine for boost compression ratio came out to 9.8:1. I've always been told to lower compression for boosted cars.
If a car with 10.5 CR makes 650whp on 10lbs And it's twin that has 9.5 CR it will make less power on the same boost.

So to make the 650whp you turn up the boost.

My question is why bother dropping compression?
Isn't cylinder pressure linear to horsepower?
So even tho you are less compression you have to run the same boost to make the same power so you'd be at the same cylinder pressure.

[Unreal]

Dropping compression is from the 60-70s when they had no ecus, no knock control, crappy port and head design, etc. For some reason it just keeps going.

Lowering compression just makes car lazier, less efficient and lower power off boost. Then on boost you crank up boost to make up for it. Basically you want compression low enough so part throttle and low end stuff can take some decent timing and run good.

Friend just finished his corvette. 11.5:1 with 25psi or so of boost. Runs amazing. My car is ~10:1 and if heads ever come off I'll bump it up.

Higher comp spools turbos quicker, gets into RPM quicker.

[2010_camaro]

My turbos come on at 2k and spool fast. Car runs good. Just always beenadvised to drop compression some.

[blake-b]

10.5:1 and twins going together here.

[CamaroDreams76]

Definitely not a dumb question. I'm glad it was asked and explained. I didn't know the reason why people drop compression, now I know it's unnecessary.

[Unreal]

There is a lot more too it.

Now a 10:1 piston compared to a 11:1 piston could be a companies forced induction piston, that has thicker ring lands, crown, etc for boost. So there could be very good upgrades that make lowering it worth it. It also gives 1/2 ass tuners more safety room, and more ability to half ass stuff since more compression means tune has to be better.

[christianchevell]

Boost pistons are made different than regular pistons or stroker pistons, or many other types that's why the variable compression ratios along with the fact a real race car is going to have a huge cam also with the larger stroke from the cam lopes coming into play with the valves opening farther thus valve reliefs and lower compression ratios also, the lower the compression ratio also the more boost allowed and the higher you go the more money you have to spend on things like head gaskets, fasteners, head bolt/studs..etc

You in fact are boosting the compression with forced induction and forcing in more air to accept more gas and the resulting explosion/flame over makes more power from that power. Its not just old school, look at a zl1s compression ratio, even it had lower compression and forged crank but could use forged con rods and pistons. The increase in clearance inside from the lower compression ratio also has the effect of giving it a larger cylinder volume to fill.....thus making more room for that gas air mixture to explode, kind of like why Forced induction often leads to larger heads/porting for more flow; ZL1 guys wish they had larger superchargers/ forged internals through out also to handle better boost with out a weak link like the piston or con rod..... And boost is kept low with only a 1900 cfm blower not a 2300 or 2900 with hypereutectic pistons.

SO lower the compression for a lot mean= turn up the boost, add the nitrous LOL, plumb that METH.... Me I am still pissed they did not do a 427 in the ZL1....LOL live up to your name GM, there is still time to make 7 liter for the zl1......!!!!!!!!!!!!!!!!!!!! Bump it up screw the EPA, give us a monster 800 hp factory Camaro with a 7 liter and a good rear and then call it the friggin ZL1 ZL1.....LOL

[Olddudesrule]

Originally Posted by CamaroDreams76

Definitely not a dumb question. I'm glad it was asked and explained. I didn't know the reason why people drop compression, now I know it's unnecessary.

Got to second this^. I too thought this was still an important, necessary step. Just another example of why these forums can be so damn useful and informative. I'd gladly read another ten "what's the best oil" threads to bump into a thread like this every once in a while. Thanks for asking OP, and thanks for the very straight forward answers.

[BlaqWhole]

With a built engine and higher compression, you'll make more hp per # of boost than a built engine with lower compression. But you'll also have more limitations...depending on the tuner and several other factors. Lower compression engines will have more of a safety net. These days you have E85, meth injection, better ECUs that do more stuff, and better engine internals. So it isn't always gonna be quite a yes or no answer. You're really better off talking with your engine builder and/or tuner to see what is the best bet for you.