High Compression Boost?

[Gorgishmork]

I'm not sure that I understand why people say that you can't make the hp gains running high static compression with the gains that a low compression higher boost application can make. I mean isn't a 10:1 motor with 2psi of boost still 167psi chamber pressure at TDC, while a 8:1 with 6.1psi also 167psi? Doesn't that mean that equal displacement engines, will make the same amount of net power? The fuel is still being compressed to the same pressures at the same air/fuel ratio. Help please.

[4-G-rim]

compression is how tightly packed the air is in the engine. say your engines compression ratio is 10:1(10 to 1). this means that the pistons compressed the air/fuel mixture 10 times its original pressure. the higher the preesure, the more excited the molecules get, resulting in a more violent explosion.

this is why low compression pistons are used in turbo engines. the air pressure going in is already pretty high, so if the pistons compress it anymore, it could explode prematurely, causing a condition known as "knock". this is bad, because it will cause the piston to move the opposite way when it is not supposed to causing your engine to go BOOM. so not only do you use lower compression pistons, you use a higher octane fuel. a fuels octane rating is its resistance to burn, so a higher octane fuel also helps in preventing knock.

Though this is not saying you can't build a high compression turbo motor...it just takes a bit more tuning and the right parts too. My friend was able to make 600awhp on his Galant VR4 on a fully built 4G63 with 10:1 custom made pistons with a GT35r at only 23lbs of boost.

[PharmEcis]

It's about the proper combination of parts and a very good tune. You can have the best tuner in the world but have complete and utter failure if you didn't select the correct part combination.

9:1 is a great street engine for boost. You don't sacrifice off boost performance and it will perform great under boost.

Make sure you are doing your calculations. Just because a piston manufacturer says a piston is 9:1 doesn't mean it will actually be so in your car. Head swaps greatly affect static CR depending on the combustion chamber volume. Thicker head gaskets and shaving of the block and head can also affect your CR.

Do the math or your CR is just a guess.

[Galanttuner10]

It's about the proper combination of parts and a very good tune. You can have the best tuner in the world but have complete and utter failure if you didn't select the correct part combination.

9:1 is a great street engine for boost. You don't sacrifice off boost performance and it will perform great under boost.

Make sure you are doing your calculations. Just because a piston manufacturer says a piston is 9:1 doesn't mean it will actually be so in your car. Head swaps greatly affect static CR depending on the combustion chamber volume. Thicker head gaskets and shaving of the block and head can also affect your CR.

Do the math or your CR is just a guess.

alright continuing on track here,, its good to know that 9.0 is a good cr.. and yes the head swap changes the cr but these pistons are made for the 64 block with the 7bolt 63 head so it should be almost spot on

and to straighten things out you can boost a high compression motor but it wont be as efficient as a lower compression motor especially when running a larger turbo.. correct?

[Galant306m]

Galanttuner are you factoring the difference in compression from the 63 to the 64?

[Galanttuner10]

Galanttuner are you factoring the difference in compression from the 63 to the 64?

i dont have to factor that in.. i know stock compression is 9.5 and with the head swap ill be around 10.. why would the 63 compression matter??? cuz thats their pistons but we run our pistons.. and the 9.0 pistons are made for the 64 block with the 63 head

[PharmEcis]

alright continuing on track here,, its good to know that 9.0 is a good cr.. and yes the head swap changes the cr but these pistons are made for the 64 block with the 7bolt 63 head so it should be almost spot on

and to straighten things out you can boost a high compression motor but it wont be as efficient as a lower compression motor especially when running a larger turbo.. correct?

Running higher compression is always more efficient. The problem you run into is that you will eventually run into a boost limit due to cylinder pressures and the ensuing detonation that will occur.

If you want to run high boost, high compression is not for you.

[Galanttuner10]

Running higher compression is always more efficient. The problem you run into is that you will eventually run into a boost limit due to cylinder pressures and the ensuing detonation that will occur.

If you want to run high boost, high compression is not for you.

yea i wont be going high on the 14b like 12 psi max

[PharmEcis]

on a 9:1 motor you can go way higher that 12 psi especially out of a 14b.

The turbos you guys deal with aren't performance related turbos per se. A lot of the 9:1 builds I've done have run 30 pounds of boost out of a 35R. Heck I even did a 9.8:1 that ran 24 pounds off a 35R hybrid.

[Galanttuner10]

on a 9:1 motor you can go way higher that 12 psi especially out of a 14b.

The turbos you guys deal with aren't performance related turbos per se. A lot of the 9:1 builds I've done have run 30 pounds of boost out of a 35R. Heck I even did a 9.8:1 that ran 24 pounds off a 35R hybrid.

after the headswap ill be around 9.8:1 or 10:1 and im not going to go 9:1 until i run a much larger turbo.. but even with that high of a compression i should be fine.

[xd_01]

are you doing a full build or just swapping out heads?

[Galanttuner10]

well its pretty much just a swap for now, 3g lifter, new valves and stuff ill upgrade everything later when i upgrade the turbo

[xd_01]

sounds cool, should be fun to swap out. gl

[Galanttuner10]

sounds cool, should be fun to swap out. gl

o it is cool and im sure it will be tons of fun.. thanks

[xd_01]

i dont know if you know about DSM talk.com but ill give you a link to a thread that has alot of good info on the 2.4 hybrid motor that might be useful to you.

http://www.dsmtalk.com/forums/showthread.php?t=175027

[Galanttuner10]

i dont know if you know about DSM talk.com but ill give you a link to a thread that has alot of good info on the 2.4 hybrid motor that might be useful to you.

http://www.dsmtalk.com/forums/showthread.php?t=175027

ive been through everything and i have many dsm guys helping me with this build when the time comes