9:1 compression piston (Pros and Cons)

[We're on Boost]

but 9:1 is fine.

Yep 9:1 is OK. Mine is nominally 9:1. People had pretty much figured out how to make ~500 awhp on pump gas by 2007 and I suppose some were earlier. But the best documentation of it that is still online that I know of is the same thread in EvoM that gave me the direction I needed for how to do my car. I wanted ~500 awhp potential on pump gas because E85 stations were disappearing rapidly in my area.
Anyway, people started using larger turbine wheels (for example GT35 instead of GT30) and newer tech compressor wheels, better engine management, and all the other stuff guys above have mentioned.

So read that thread in EvoM here: New record for pump gas, set with the HTA35r
Actually, read post #1, then if you want to skip the dozens of fanboy posts, go to post #15, then #25, then #62 which is the best post in there for how and why, and #62 is where Buschur says the compression ratio was approx 9:1.
BTW it came out later that the turbine housing on this car was only a .63 a/r so they were actually giving away a little top end for some gain at lower revs with that.
The charts that were originally posted in that thread are all lost now but I have some of them saved, if anybody wants to see them.
That Buschur build was obviously an expensive build.
If you want a lower cost build and some amount of safety, keep it down to 400 hp!
For me with a high cost build, I keep my ethanol percent around 40 - 55% for most of the year and boost at about 27 psi. It still makes 550 awhp set like that, and that is my idea of good safety.

 

[1cleangsx]

2004-2024 it’s still a matter of cylinder pressure right? V8 guys make decent power on pump because they have twice the cylinders, there’s half the stress on a rod/piston in a v8 compared to a 4 cylinder making the same power. I personally went with 9:1 because it seemed like the “middle of the road” on compression, not to high not to low, and I will say this, @biglady112 tuned my car on pump ethanol with a positive outcome after saying I came in about 5 degrees to hot on timing with a 6266, 10 years ago I was running 12 degrees more than that on a 16g with no idea what I was doing, my point is weather your 7:8:1 or 10:1 run e85 it’s very forgiving

 

[bastarddsm]

We have better sensors, better fuel injectors, more efficient turbochargers and far better ECU systems and tuning capabilities these days, but that just helps our safety window for tuning. The limits of pump gas are still very real and apply to the 4G63 - we would make similar peak numbers as 2004 with the same lb/min of peak airflow, but turbo technology advancements and better tuning options have created far better response and "under the curve" numbers to go with it. More advanced engines have better knock control strategies with more knock sensors and faster processing, variable cam timing with better cylinder head design and direct injection, which are actual game changers.

None of that are really game changers. I mean vvt adds some area under the curve, but when you bring IVC earlier it builds more cylinder pressure and knocks. Direct injection is better than port for knock behavior, BUT you have to have lots of in cylinder charge air motion, and that kills port flow. And it still rattles. You forget 9/10 things that are done by oem is for emission and or warranty $$. About the best thing I've seen is nissan, insulating the intake air from the water jacket all the way to the valve seats.

Unless I'm missing something the newest baddest stuff is maybe a little better than a stock late evo - And the only real difference between a dsm and evo is slightly bigger cams, slightly bigger turbo, fmic. Same shit we did in 2004.

Like I said before 500hp on 87oct, 2L and it's full boogie from 4-9k on that setup. It's a $500 truck vgt, and small enough cams it would probably early 00's emissions with some time on a 5gas. Imagine what it would do with OEM level development money.

 

[TerminalTalon]

I talked to a friend about the pump gas tuning years ago mainly when Mellon Tuning was running around. Correct me if I’m wrong but wasn’t it just less timing-more fuel?

 

[Rémy B]

Yes, that is part of it, colder air charge, a proper exhaust system with lower back pressure, reasonable oil temperature to keep the pistons at a better temperature , all that helps to keep the combustion chamber at a more forgiving point to run higher static CR on pump gas, and then comes the amount of boost, it need to be at a reasonable level if you want your daily driver to live longer.