amount of boost vs compression

[nholm325e]

I am going to turbo a m50 engine for street use. 300-350whp.
Im sure theres alot of variables that play into my questions but im just looking for generalizations...

The motor is stock 10.1 compression, how much compression can the m50 take while keeping it somewhat reliable?? 11.1-11.5??

So say its stock compression 10.1, and i boost 5 psi, what would that bring the compression about too?? 10.5 or somethin??

[ForcedFirebird]

I am going to turbo a m50 engine for street use. 300-350whp.

So say its stock compression 10.1, and i boost 5 psi, what would that bring the compression about too?? 10.5 or somethin??

Try 15:1 or more. 5psi will add about 30% hp over the same engine N/A.

[mops]

it's not easy to say.
some motors will handle more. eg. my friend has a stock NA 10:1 SR20 with turbo manifolds on it and 7 psi is no problem on pump gas.

things that will greatly affect detonation (in no particular order - some are more effective in preventind detonation than others)
-camshaft specs
-manifold design including
-wastegate plumbing
-turbo sizing
-intercooling
-water/meth injection
-exhaust backpressure in general
-combustion chamber design
-quality/type of fuel used
-ignition timing

m50 run 10.5:1 static compression. What's more important is dynamic compression and it depends mainly on cam. Lower your dynamic compression (with hot cam) and make extra free flowing exhaust manifold/wastegate/system and large size turbine housing, combine it with good tune and water/meth injection and huge intercooler and you might be reliably making 8 psi on stock motor. this is all speculation really...
worst case scenario you can be using 10% toulene in the fuel.

[matt]

M50 runs 10:1, M50TU (with VANOS) runs 10.5:1

10psi on a stock one shouldn't be a problem. What are you doing for tuning?

Tuning is the MOST important part of the equation.

[ForcedFirebird]

M50 runs 10:1, M50TU (with VANOS) runs 10.5:1

10psi on a stock one shouldn't be a problem. What are you doing for tuning?

Tuning is the MOST important part of the equation.

I couldn't agree more. I could link you to a site that has a 10sec K Car (yes a reliant) that was pushing 32psi on cast pistons.

10psi seems like a lot for a stock tune, you mean with no RRFPR(FMU) and stock injectors as well?

[mops]

I couldn't agree more. I could link you to a site that has a 10sec K Car (yes a reliant) that was pushing 32psi on cast pistons.

10psi seems like a lot for a stock tune, you mean with no RRFPR(FMU) and stock injectors as well?

if the compression is poor then you can run even 100 psi on stock pistons but that wont be making any significant power.

and yes, it might last as long as you dont abuse it and use short bursts of boost and generaly be cautionus about going on boost. but normally you have to build something that handles reliably some amount of abouse.

[matt]

I couldn't agree more. I could link you to a site that has a 10sec K Car (yes a reliant) that was pushing 32psi on cast pistons.

10psi seems like a lot for a stock tune, you mean with no RRFPR(FMU) and stock injectors as well?

No, sorry. I meant a stock motor. The motor won't last very well at all with stock engine management at any PSI.

[ForcedFirebird]

if the compression is poor then you can run even 100 psi on stock pistons but that wont be making any significant power.

and yes, it might last as long as you dont abuse it and use short bursts of boost and generaly be cautionus about going on boost. but normally you have to build something that handles reliably some amount of abouse.

Did you boost your e30?

[mops]

not yet, but i got most parts sorted out... you wouldn't believe but finding a siutable radiator proves to be most difficult thing for me right now. Once that's sorted, it's just a matter fabricating exhaust and bolting all the parts in....

[ForcedFirebird]

not yet, but i got most parts sorted out... you wouldn't believe but finding a siutable radiator proves to be most difficult thing for me right now. Once that's sorted, it's just a matter fabricating exhaust and bolting all the parts in....

Radiator or intercooler? I see e30's in the wrecking yard all the time, many places can repair them.

My wife doesn't want me to boost the e30, she said that's what my Firebird is for, lol.

[mops]

radiator.... over here e30's and bmw in general are pretty rare on the wrecking yards.

[ForcedFirebird]

radiator.... over here e30's and bmw in general are pretty rare on the wrecking yards.

Perhaps I could help you find one, although shipping might be a pain.

[mops]

Perhaps I could help you find one, although shipping might be a pain.

Thanks for the offer, but you are right. Shipping will make it cost-prohibitive.

However, I found this awesome website... www.a1radiators.net.nz - it has all the pics and detailed dimansions for every make and model radiator for cars commonly found locally. as soon as i get a change to browse it up I'm sure i'll come out with something that will work for me :)

[techno550]

10:1 static CR and 5psi of boost gets you to around 13:1 effective CR.

I have a M50TU (10.5:1 static) and run up to 13 psi on pump gas. just under 19:1 effective.

300 rwhp is not too hard to do on the M50 based motors. the M50TU is a better motor to do it on. You'll need ~9 psi to get to the 300 mark. ~14 to get to 350 rwhp, and its getting touchy on pump gas in that range.

[Nütz]

8 psi -----------10.5:1 CR

9-10 psi -------10.0:1 CR

11-12 psi ------9.5.:1 CR

13-14 psi ----- 9.0:1 CR

15-18 psi ------8.5:1 CR