How does e30 gain its power on the stock turbo? Tuners referred

[Stkid93]

Fellas, hope y’all are doing well.

my question is, where do the power gains come from when using e30 specifically talking about the fist?

we really don’t raise the boost much at all when using e30 on stock turbo. I get about 26 psi on e30 and 24-24.5 on my 93 tune although some tuners keep the boost exactly the same. And those are peak numbers from the mid range.

So is the power difference is basically all from timing and e85’s cooling ability. I just looked over dizzys Dyno sheets earlier today, and he went from 208/257 on his stage 2 93 octane tune all the way up to 232/320 on e30. So 25 wheel horsepower and 65 wheel torque just from e30!

If we dramatically increased boost it would make a lot more sense but your lucky to get an additional 2 psi on e30. And again that’s in the mid range. No matter what boost will fall off towards the top of the revs.

 

[Dialcaliper]

It’s all about about timing plus air density. Heavily boosted engines on pump gas are heavily octane limited in the timing advance they can run. Late timing means less pressure buildup and more energy vented out the exhaust valves.

It doesn’t help that the hilariously undersized stock turbo is running off it’s efficiency curve even on the stock tune, and so for the same pressure, the air coming out is HOT and less dense. You could gain back some of the loss by running a huge oversized intercooler (at the cost of throttle response) but you’d still be octane limited.

The ethanol in E30 provides cooler charge air through evaporation so even though the actual pressure isn’t higher, the total airflow going through the turbo and into the engine is effectively similar to what it would be if you were running higher boost.
Its important to remember that even though it seems like the intake tract is a closed system that stops at the valves, the whole system through the exhaust is still constantly flowing, so the in-cylinder effects actually act on both the intake and exhaust as if it there were no “blockages” in the sstem

The ethanol also means a significant octane boost (somewhere between 94-97 octane), which allows additional timing to be run, meaning more cylinder pressure and more power.

A third effect is that the in cylinder cooling *also* affects the exhaust manifold pressure - the exhaust exits cooler, denser and and at lower pressure, which means the turbo and pistons don’t have to work as hard to push the air through especially during the valve overlap - reduced pumping losses means more airflow, less parasitic heat loss and more. Less loss means higher “volumetric efficiency” which really just translates to more energy going out the crankshaft.

In other words:
Cooler air + higher octane -> more air mass at the same “boost pressure” + less pumping loss -> more powah!!

Boost pressure alone is a terrible surrogate for power, because what actually matters is MASS of air which depends on not just pressure, but also temperature and total volume flow (PV=nRT or PM=drT for any physics/chemistry people out there).

Timing of course is another variable, which affects BMEP (mean effective cylinder pressure), basically the average pressure on the piston over the stroke.

Hope that wasn’t overly complicated, but the takeaway is that there’s a lot more going on in an engine than just “boost pressure” going in.