to raise compression or not to raise compression?

Jungy · 02-02-2009

Okay so here I am sitting on a bunch of parts I've gathered over the winter and now I'm debating if I will really benefit from installing these 10.5:1 je's vs the 8.8:1 wiseco's that I have in my motor now. The only reason I am in a debate is because I'm not sure if the cost vs. benefit is really worth it because im gunna have to tear down my block and get it bored .020 over. So what I want to know is what does everyone else think go high comp or keep it as is?

Super Bleeder!! · 02-02-2009

high static CR gets you better response at the expense of boost.

Low CR is vice versa.

Decide what you want, better response or ultimate overall power. No free lunch!

turbotalon1g · 02-02-2009

HIGH COMP!!!!!!!!!!! ^Good answer, I just want to see it, Would be good if you are keeping it a 2L

Do it. It will be fucking sweet. Plus a lot of us want to do it but won't.

Jungy · 02-02-2009

Ohh yeah the head is already getting machine work done because I'm having 1mm o/s ss valves installed, so what I was thinking was that I would have the head milled to have the comp bumped up 0.5:1 making it 9.3:1 with the wiseco's I have now or 11:1 with the je's.

EclipseGST · 02-02-2009

Quote:

Originally Posted by Jungy

Ohh yeah the head is already getting machine work done because I'm having 1mm o/s ss valves installed, so what I was thinking was that I would have the head milled to have the comp bumped up 0.5:1 making it 9.3:1 with the wiseco's I have now or 11:1 with the je's.

Please dont do this...

Jungy · 02-02-2009

Please expand upon your statement with reasoning. The car is full stand alone via megasquirt and running on e85. I wouldn't think I would lose lose overall power because of the high detonation resistance of e85, I think I would be able to keep my boost pressure up where they are at right now. With the higher cylinder pressure from raising the compression I would be able to make more power assuming there are no issues with knock or detonation at the boost level. I've done reading and volvo's test e85 optimized turbo car runs an 11:1 comp ratio.

**Shane@DBPerformance** · 02-02-2009

Do you want to run 20psi or 30-35psi?

Jungy · 02-02-2009

Right now I have my spec2 set at 24psi and I would like to run as close to that as I can and still be safe and not risk my motor.

**JET** · 02-02-2009

One thing to think about, with high compression via static compression it does not get cooled. If you add "compression" via boost, then you run it through the IC and it gets cooled down. So lower compression has more potential for power and be safer on the engine, but the higher compression will have better low end and spool the turbo a little faster.

Jungy · 02-03-2009

That is another thing that has crossed my mind too. I'm curious, would it be beneficial to run my meth kit in conjunction with e85 if i go HC? I've never heard of anyone running e85 and meth injection because of e85 already high octane and its ability to cool your intake charge on its own. I haven't used this alky kit since I installed megasquirt and went e85.

4g63tcrazy · 02-03-2009

There is a guy running the 16g holding 30psi til redline with E85 and meth injection with NO intercooler. I think with the high compression E85 and meth would work awsome for you.

wheelhop · 02-03-2009

Quote:

Originally Posted by JET

One thing to think about, with high compression via static compression it does not get cooled. If you add "compression" via boost, then you run it through the IC and it gets cooled down. So lower compression has more potential for power and be safer on the engine, but the higher compression will have better low end and spool the turbo a little faster.

I agree: Miller cycle.

While I think that the stock 1g compression is far too low, I think that right at around 9:1 is about perfect. You can negate much of the knock issue with high boost and higher compression by just having more timing retard. Now, at first glance you may assume "well you're still trading up: timing for compression". But a higher CR raises the burn rate which makes MBT, the ideal timing, much later. So you need to have more timing retard to get good timing; since timing is about *timing* and not about advance. If you new at what point the fuel would preignite (different from detonation), then you can run as much CR up to preignition, as long as you know that you'll have to dial in more timing retard for the faster burn rate. There comes a point where the thermal efficiency increase doesn't merrit the cost of more CR.

As well, a higher boost will raise burn rate, and later timing with higher boost seams to do very well. Buschur does something like this with his pump gas builds. MAD timing retard, huge boost. All the fuel/air is still burned. All the fuel/air is still ignited at a point where it will put the most torque on the crank.