low compression

Ntyvirus1 · Post by **Ntyvirus1** » Thu Oct 16, 2008 9:50 pm

would it be "safe" to run 8:8.1 pistons in a n/a car before boost?

excon · Post by **excon** » Thu Oct 16, 2008 11:42 pm

I assume you mean 8.8:1 compression.

Yes, you could run that, but if you are running that low n/a you'll be producing less power. I'm not even sure what would happen.

You would also use more gas (in theory) because it would take more gas/power (than it would with 9.3:1) to get you to where you were going. not much though...

Post by **jonnymopar** » Fri Oct 17, 2008 9:20 am

LimeStrat is doing just that right now. He's got a 2.4 with turbo pistons installed, but no boost yet. It's weak, but it runs ok. He drove quite a long way to the 2GN meet in July on that setup with no problems. You should be fine if you wanted to do that.

Ntyvirus1 · Post by **Ntyvirus1** » Fri Oct 17, 2008 11:29 am

thnx and srry bout that excon, i got a little switched around with the symbols.

slow2.0ts13 · Post by **slow2.0ts13** » Fri Oct 17, 2008 11:36 am

j/w out of curiousity ntyvirus1 why do u want to lower compression?

Post by **occasional demons** » Fri Oct 17, 2008 12:22 pm

slow2.0ts13 wrote:j/w out of curiousity ntyvirus1 why do u want to lower compression?

Ntyvirus1 wrote:would it be "safe" to run 8:8.1 pistons in a n/a car before boost?

I'm assuming he is building the engine for a turbo/SC set up, but will be driving it for a bit before the turbo/SC is installed.

slow2.0ts13 · Post by **slow2.0ts13** » Fri Oct 17, 2008 12:38 pm

oh, so lower compression is better for turbos and i guess higher compression for n/a's?
idk im a noob.

Danteneon · Post by **Danteneon** » Fri Oct 17, 2008 12:40 pm

You are correct. High compression with forced induction makes things want to go boom

Ntyvirus1 · Post by **Ntyvirus1** » Fri Oct 17, 2008 1:19 pm

yea evntually i plan on getting a turbo setup goin but money wise ill prolly end up rebujilding the bottom end with the MPX rebuild kit before i can afford/install teh turbo.

slow2.0ts13 · Post by **slow2.0ts13** » Fri Oct 17, 2008 1:52 pm

fyi: when i was pricing some things out (idk if ur looking at the kit from modernperformance.com) you can build your own kit for about 200 less.

Ntyvirus1 · Post by **Ntyvirus1** » Fri Oct 17, 2008 4:04 pm

not the bottom end kit

OB · Post by OB » Fri Oct 17, 2008 4:32 pm

Compression has nothing to do with turbocharging. Boost is the issue. The higher the boost, the higher the overall cylinder pressure. Pressure = heat. Heat = detonation. With the right amount of fuel and a healthy amount of spark retard, higher compression engines can make reliable turbo power. The reason people use low compression is to keep a theoretical 'safety net'. However, with the right equipment and tune, pretty much any engine can be turbocharged successfully, regardless of compression. Low compression is the easy way out and allows for mistakes in the tune and a lot more abuse. A good idea for the average driver. Many people think that compression is something that has to be addressed for a 'properly built' forced induction engine, but this is not the case. That's not to say that the low compression idea is a bad one, but I just wanted to clear that up.

Oh and lower compression should actually reduce fuel consumption due to the lower cylinder temps. Detonation is less of an issue, so a leaner burn can be achieved without worrying about heat. On the flip side, power is lost from the smaller amount of air and fuel in the cylinder that is ignited. This is why the 9.3:1 engines were used on the newer Neons. Better fuel economy. They were able to make up the small amount of lost power with tuning, since the compression difference was only half a point.

LionheartedSXT · Post by **LionheartedSXT** » Fri Oct 17, 2008 8:39 pm

^^^
that was very useful info OB, good stuff...

Donkeypuncher · Post by **Donkeypuncher** » Fri Oct 17, 2008 8:45 pm

That is all very correct. It's just a good rule to stay under 9.0:1, especially since most people up the boost down the road. Most people I know stick with 8.6:1, but a lot of the stock 420a guys run a turbo just fine with 9.6:1. Of course that is with the correct fuel setup and proper tuning. There were plenty of guys that toasted their engine due to detonation though. Mainly because they went cheap and tried to tune with injectors and a safc controller.