Higher Compression Vs. Lower Compression

[lawdaman]

Got a question for you DSM wisemen here. I'm looking into turbocharging my engine. I know my stock internals can handle about 10psi at the max. Now here's my situation. I'm trying to build a quick spool system. If I were to rebuild my block for a higher compression than stock, i know I'll raise my engine's HP which will let it push the turbo harder, allowing for a quick spool. But at the same time I know I'll be limiting myself on the amount of boost I'll be able to run without blowing a hole in my block. Of course lowering the compression will allow me to raise the boost on the system, which will give me a higher overall HP potencial, but then I would be relying on the turbo most of the time to get going.

I'm not looking to 11's (mid-12's would be nice ), which set-up would best suit my purpose of building a kick-ass, reliable, dailey driver?

 

[Ghost1984]

as far as raising the compression and wanting to turbo the car, is not really the best idea.....detonation will be sure to happen, if your gonna rebuild the engine your better off just getting forged pistons like 8.5:1 so you will be able to run higher boost, which yea you would be relying more on the turbo, but if you have to much compression with boost your engine is more likely to blow up in the long run, so i think your better off just keeping the compression low and set it at a good safe boost level.

 

[lawdaman]

DAMNIT! That's what I assumed, but I was hoping I was wrong... This means I have to install the turbo kit running on 8-10psi for a while, then have the block rebuilt, because I'll be damned if I'm going to ride around on a lowered compressioned NA car for several months until I can get the kit...

 

[timloomis]

ahh!!!!compression dusnt mean crap!!!all a turbo does is raise compression basically.u can run 12:1 and be ok as long as u have the fuel system to back it up.the more compression,the less boost u havta run to get the same low compression power.u just gotta make sure u have the fuel system to back it up.u will not detonate if u run premium gas,a big fuel pump,big injectors,and fuel control.why do u think the lancer evos make so much power?they run 8.7:1 compared to 8.5:1 on 2g turbos and 7.8:1 on 1g turbos.l8r.

 

[TalonSpeed]

First off, getting a car with 12.1 compression to run on pump gas will be kinda difficult, especially if you are in CA. Nissan, Toyota, Mitsubishi, Subaru, and Chrysler all use lower compression turbo charged engines. They do this for a reason. i would expect their engineers to know more about compression and boost than 99% of the people on this board. 8.6:1 is ideal for turbo cars. If you want more get up and go before boost kicks in try getting a 2.2 stroker kit.

 

[Initial DSM]

9:1 compression has been done to death by many 4G63 owners. I dont see why this would be a problem in a built 420a engine with turbo, so I say go that route. You can still run high boost as long as you have correct fuel setup as previously stated. There are even a few people on 2GNT that are planning on running turbo on 10:5:1 , so yes if thats the case, get a e-manage or stand alone like megasquirt or a used DFI 6 off ebay for fuel control and you should be straight.

 

[E-CLIPS97]

Go to vtengines.com and get the fully built block. The use CP pistons which can be made into any compression you want. Get them made in stock compression size. That way you will have forged internals, yet wont sacrafice your daily driving with lower (slower)compression pistons and yet will still have room to turn up the boost when your ready.

 

[Cesar]

Don't lower compression. Make sure you use high octane fuel. Keep the intake temperature low.(intercooling). Make sure the fuel system can keep up. Find a way to monitor knock. Forged internals are good protection against detonation. If you have no detonation, you do not need forged internals.

 

[TimG]

Originally posted by Cesar
Don't lower compression. Make sure you use high octane fuel. Keep the intake temperature low.(intercooling). Make sure the fuel system can keep up. Find a way to monitor knock. Forged internals are good protection against detonation. If you have no detonation, you do not need forged internals.

Amen... someone with a brain. And look, another Canadian.

The turbocharger condenses and flows more air going into engine. I actually know someone up here in ca.dsm.org who runs 10:1 compression pistons on a 20G at 18psi.

Most people would think that is insane. Yet when you take a look at his datalogs, great fuel trims and no knock, you have to be impressed. His car hauls ass.

Just make sure you have a good logging system and you read on how to tune your fuel system for the most efficiency out of your engine. If you go forged internals, you will have more lee-way with the amount of boost and mistakes you can make tuning at high boost. Key is no knock, good timing, good fuel trims and no knock (yes again).

 

[Cesar]

TimG
Are you not the one with pistons for sale?

 

[DSM-ZERO]

the comp. ratio will not effect spool time only the turbo will do that, ie ball bearing. But higher comp. will give you more off the line but you won't be able to run as much boost on pump gas UNLESS you have an EMS and C16 then anything is posiably. I say 9:1 or 10:1

 

[farey34]

could you run 8.8:1 compression on a nt? thinking about a turbo kit later but would that just suck for a nt? have it apart to replace a burned valve! Damn NOS!

 

[lawdaman]

You can run as low as 8.5:1 on a NT. I dont think theres a limit to how much you can actually lower an engine's compression ratio. The only question is "why go any lower?" Your pistons and head gasket are the main determinors of your compression ratio. It all depends on what you want. So yes you can go as low as 8.8:1. Me personally, after reading the responses from this topic I started I've decided to go with a 9:1 or 9.5;1 rebuild. Low but not too low where i'll be relying on the turbo too much. Lag's a b!tch.