9.0:1 or 9.5:1 on 91 is no problem anymore. As stated the ability to fine tune is much better than before. The thing behind going to a higher compression is you need to run less boost to make what the 8.5:1 engine made on more boost. Higher static compression helps with low, mid and spool times.

 

Actually, higher static compression does not decrease spool. This is a common misconception.

 

correct. although it does increase low rpm power which fools people into thinking its spooling faster.

 

what would be the wtq differance at 550whp from a 8.5:1 compaired to a 10:1

 

Why not go with 11:1 compression? Wouldnt this also benefit people running other than e85 or two maps?

This is just a guess and a made up example:

If your running 93 octane on 8:5 motor boosting 25 psi making 330 whp. And then you change to 11:1 motor same octane couldnt you also make the same power but less boost and a re-tune complementing the higher compression?

What I'm trying to get at is, if your going to make the same power with a higher compression motor at less boost, wouldnt that be better over all? (with a good "reliable" tune off course)

 

8.5 compression is good to get more boost and high power on pump gas ( 91 oct ) as what my tuner said to me

 

i just built a 2.2 and put in 9.0 :1 cr pistons..i wanted between a high rev 2.0 and 2.4..so i figured id go with 9.0:1 cr and 2.2..thinking mild boost and a slight cr bump would be fine for road race and mid range power..so i wouldnt have to overdue my turbo or motor .efficiency wise.thinking 85% turbo efficency and 85% in motor..something like that ..then if i want i could turn up boost later ..tuned right of course...e85

 

Theoretically, about 5% net at the wheels, all else being equal, and assuming one can achieve MBT ignition timing with the higher compression ratio - the chances of which become less likely as torque increases.


It depends. With a fuel of limited octane, the lesser the power target, the more practical the higher SCR becomes, and vice versa.

 

9:1 is the best, the high compression stuff is mainly for e85. It is true I ran the 2.2 out to 30psi on 92 octane but it doesnt work for extended pulls as well as you'd think. The 4% (per full point, 9:1 to 10:1 for instance) power gain from higher compression and the inability to make good pump power isnt worth it in my mind UNLESS you are on good fuel, not pumpgas.

I currently run a 9:1 2.4 and am not going to be considering higher any time soon.

Mikeys car will never run on 93 and 10.5:1 on anything more than wastegate pressure.

aaron

 

I'm pretty happy with my 2.0 10:1 BR motor, 93 octane 600awhp at 30psi and the car feels much peppier at low boost, it's wicked on the street with 460tq. I had to back the timing off about 3* and 2psi vs my 9.5:1 motor to make the same power.

 

With my 8.7:1 motor, I recently discovered that I am able to push it to 40 psi with 93 octane, and still run 20+ deg of advance in the upper registers, with zero knock. I feel I need not explain the significance of that, but I'll say that generating cylinder pressure with air makes more power than doing it with aluminum..

 

Mark S would be proud that us Yanks got it figured out finally

Congrats Ted that is awesome. I'd like to see your knock voltage logs sometime of that pull but to me it illustrates the importance of the cylinder head/cam combo for big boost on lower octane fuel.

aaron

 

Yes, props to Mark S for reminding me to ignore popular paradigms and use my brain.

I'll gladly share those logs with you when I can tweak things a bit further, but right now, Drifto and I are doing a bit of machine work on my turbine housing in an effort to eek a bit more efficiency from it. We'll see where that puts us.

Finally, I should remind everyone that 22 years ago, BMW churned out 1350bhp from a stock block 1.5L engine using a large twinscroll turbo, 8:1 SCR, with fuel that was around 95 octane.

 

Based on your experiences, which would you recommend for an E85 car that would also run not necessarily a record breaking 93 octane tune, but like an average reliable power?

I would like to think 11:1 but lowest 10:1 or for HTA green setup...

 

http://www.youtube.com/watch?v=skly2gsdbyU

We've been running high compression for a LONG time. We've run as high as 11.5:1 on straight pump gas at up to 34 psi of boost, no issues and great results. Video speaks for itself. Making power on pump gas, high compression blah blah, is nothing new around here.

The topic question, 8.5 compared to 9 is such a small increase/decrease I wouldn't put any thought into either.

Most of the engines we are building now are 10:1, very few exceptions.