What is boost?

[Lith]

However after your last post I had considered that there may be a negative P in action on the NA (after all 300hp, crank from a 3.5ltr may not be 100% VE). This combined with an oxygenated fuel of higher octane (slower burn), may be the discrepancy I'm seeing.... but it still looks odd. What appears to be well under double the O2 creating well over double the HP.

It is a shame that you didn't do a same fuel equivalent tune. What ECU do you run? Did you have it tuned NA versus boosted?

If you have an NA versus boosted E30 tune and a curious (/ geeky ) enough, then I recommend having a look at the fuel maps as if it is tuned well then it should be able to start painting a bit more of a picture.

Assuming you have a Link - the G4 software bases more or less bases it's fuel calculations using the fuel table values as P compensated % pulse widths. If you get curious - take look at your NA and FI fuel tables (~100kpa MAP for the NA and ~180kpa for turbo) and then scale the numbers for the FI fuel table to accommodate for target AFR.

For sake of ranting, I've just put some rough numbers that should be accurate enough still to give an idea if you decided to give it a crack and put your own numbers in place:

NA: 13.0:1 AFR target on BP98 (~.88λ with stoich = 14.7)
FI: 10.6:1 AFR target on E30 (~.82λ with stoich = 13.0)

To scale the pulse width % - scaledFuel = Fuel / (13.0/10.6)

Do it for the rpm you reckon you may be around 100%VE on the NA setup, divide "scaledFuel" by that number and you have an suitably rugged estimation of the relative VE of what your engine is running under boost.

Again, just a thought of something to play with if you are at all curious to get even a rough impression of what flow dynamics are happening when you start throwing boost through the motor.

Anyway, I've got too carried away... I've broken my own promise to myself not to get involved on forum threads like this but this thread got interesting, I'll bow out from here but I at least reckon it is worth getting curious and scientific about investigating this stuff directly instead of just believing what the odd magazine article and forum/internet post says - a lot of it is overly generalized and sometimes misguided (but seemingly plausible) conclusions from too few variables considered... the rabbit hole goes deep

[strx7]

Do you know why do you have drop in torque at ~4500rpm?

its some black art flow characteristic of the 3rd Gen head, I've never seen one that doesn't have a drop or flatspot there.

even custom inlet manifolds & aftermarket cams still show a dip there.

[fivebob]

Do you know why do you have drop in torque at ~4500rpm?

its some black art flow characteristic of the 3rd Gen head, I've never seen one that doesn't have a drop or flatspot there.

even custom inlet manifolds & aftermarket cams still show a dip there.

maybe this might help explain it.

Essentially a stock Gen III, with 2.5" exhaust, ARC cold air box and Motec ECU.
Yellow line is the actual manifold pressure reading, red is the 10 point smoothed average.

[strx7]

not quite sure how to read that data, looks like at approx 4600rpm the manifold pressure drops, almost like its wastegate delay/boost control related

[Scottie]

Do you know why do you have drop in torque at ~4500rpm?

its some black art flow characteristic of the 3rd Gen head, I've never seen one that doesn't have a drop or flatspot there.

even custom inlet manifolds & aftermarket cams still show a dip there.

maybe this might help explain it.

Essentially a stock Gen III, with 2.5" exhaust, ARC cold air box and Motec ECU.
Yellow line is the actual manifold pressure reading, red is the 10 point smoothed average.

is the yellow line showing every time a runner fills/empties? normal map sensor location?

[gt4dude]

I have no idea, I've also heard that all 3s gen3 heads have that same dip. My manifold,turbo and wastegate setup is unlike any other 3s setup also

[strx7]

I have no idea, I've also heard that all 3s gen3 heads have that same dip. My manifold,turbo and wastegate setup is unlike any other 3s setup also

likewise, self built inlet and exhuast manifolds, and it was nothing to do with the wastegate as it was on full boost long before then. In my dyno its only a subtle dip between 4300 and 5000rpm but it is there....

[pc]

@ Redmist's question. Is it possible that more than double the air makes it into the cylinder with the NA vs 1 bar boost comparison?... and could this be tested by measuring fuel used on each setup vs O2 exhaust readings?
I never studied anything in this area, so don't know.

Edit: does an exhaust/inlet valve overlap make the initial flow before the downward stroke different in a boosted engine?

[fivebob]

not quite sure how to read that data, looks like at approx 4600rpm the manifold pressure drops, almost like its wastegate delay/boost control related

Nope no wastegate delay, wastegate control was set to constant duty cycle from about 8psi onwards. Anything seen here is most likely to related to the efficiency of the engine, not to any external factors like boost control.

[fivebob]

is the yellow line showing every time a runner fills/empties? normal map sensor location?

Possibly, never been quite sure why the yellow line separates from the average except for 3000 & 6000rpm. One possible explanation is the resonance of the intake manifold occurs at 3000rpm intervals allowing for a more efficient flow at these point. The other possibility is that it's an artifact of the logging resolution, but I'm bot sure that this is the case as it was logged at 200hz so I wouldn't expect it to follow the 10 point average for such a long period

One thing I do know is at 6000rpm I had to take a couple of degrees of timing out of the map to stop detonation.

Normal map sensor location in the plenum.

here's closer detail at 4500 & 6000rpm

[strx7]

since the only constant is the head and the valves it has to be some kinda of flow/resonance inefficency at those rpms. My engine is a 91mm stroker. Would be interesting to know if a heavily ported head, and a head with larger valves both show the same dip. It would appear that different cams seem to smoothen the dip out somewhat.