Math works. Naturally aspirated on e85, 240whp is reasonable. 320whp is an 80whp gain, or 1/3rd more power. 4.5 psi of boost is approximately a pressure ratio 1.3. 1.3 x 240whp = 314whp. It's reasonable.

 

The turbo size/efficiency (and the rest of the system) matters as well. Boost is just a restriction.

The S2000 made 400 whp at 8.5 PSI and has an instant and flat torque curve (in threshold). At HPR's back straight, I went from a top speed of 112mph while NA and no aero, to 128mph at 4.5 PSI and aero.

 

I'd say 220-225whp is much more reasonable on e85 and a good tune, given a stock F20c makes generally around 200 with transmission and tyre losses. Usually E85 won't net you much more than 10-12% more power without also cranking the compression some too. Even then you're chasing a few more percent.
4.5psi is going to give you around 30% more inlet pressure so that's 30% more power at best - that's 285-295whp max before you even remove your extra flow losses and your turbo inefficiency/drive power.
A pressure ratio of 1.3 is going to be well down on the efficiency map for almost any common turbo - you're probably around 70% if you're lucky.

Some people have very optimistic dynos over there if that's what it said - you might make a little more on a hub dyno of course but still.

(I have a few runs from 4.5psi on mine, on a hub dyno so no tyre losses, it was about 255-270 depending on fuel. And that's a dyno that's calibrated against a standalone engine test bench. Sure I probably have a little more loss in drive but certainly not 60 horsepower. The transmission and belts would be glowing red hot after a run if that was the case.)

 

Yes but that restriction is the rest of your engine, and unless there's some massive changes like you're running race cams, serious headwork and 10krpm+, then that's not going to change a whole lot.

There's a reason everyone else is pushing 8-10psi to make 320whp. It's not magic.

 

Yes, a bone stock S2000 will put down 200whp on 91 octane on a dynojet. But why would you use a bone stock car as the baseline? The car in question is obviously highly modified. Header, test pipe, exhaust, tune, and 220whp on 91 oct is easy on an NA car. 240whp on E85 is quite reasonable. I did a super quick look at the NA section and someone made 260whp in E85 and another made just shy of 240whp on what I assume was 93 octane as they were in Texas. The actual pressure ratio at the compressor of the turbo will be a bit higher than 1.3 due to the pressure drop at the compressor inlet and the pressure drop flowing through the IC piping and IC. We can ballpark that at 1psi because the flow is relatively low. So the actual compressor pressure ratio is closer to 1.4. I looked up the compressor map for the EFR7064. Probably around 56% compressor efficiency at the peak power point. Which does result in a bit more back pressure because of the higher required turbine pressure ratio.

 

I.E, terrible efficiency. Doesn't add up.

 

Yes, the compressor efficiency is 'terrible' at that operating point. However, it's low pressure ratio and relatively low mass flow, therefore the compressor power requirement is low. Which translates into a low turbine power requirement and therefore low turbine pressure ratio requirement. The relatively low compressor efficiency is driving a percentage increase of a low turbine pressure ratio, which is to say, not a large absolute value impact. As compared to the same percentage increase on a higher power operating point with higher turbine pressure ratio. If you think of it, we operate our engines in the 'terrible' parts of the BSFC maps in everyday driving almost the whole time.

 

And the counterpoint to that is since losses are fairly low due to low flow and low pressure - there's nowhere to suddenly find another 40-50rwhp over anyone else's setups at low boost levels regardless of what you do

 

I knew you'd be arguing this, which is why I added the top speed delta down the back straight, which doesn't lie and this log is one of those runs down the straight, showing just how much boost is being run:





When Robert Thorne originally tuned the S2000 below, it made 300whp on 3 PSI (different dyno than I used) and the guy who owns it left it that way for awhile (like me) as it was fun. The last time I tuned it, it made 470whp, but a bit more boost. Now it's got a larger turbo and I am going out to tune it again. The weekend this picture was taken, he took first in class and the class record, IIRC.




The dyno I did my car on, I've actually tuned a lot of cars on and have a pretty good idea on the numbers it puts out. I've also used many other dyno and understand some reading low/high. The one I used here has been one of the most consistent dynos I've ever used. Believe the numbers or not, the track improvement was substantial. Since it's a track car these days, that's all I care about. On the plus side, temps stay low and I can run it all day.


This was the day I did the dyno tuning with my car:

For reference, here are the graphs from both cars on the dyno:

 

I think Buggy might be referring to F20 numbers while the 320whp was from a F22.
For me most US dyno numbers seems a bit exaggerated but I've gotten used to it by now