mikevanky

Water meth inter-cooled stock 4.8, 76/68 aft on point and spark is around 14* br7 plugs

power falls off up top and this log shows it. Really cant figure this out, at lower boost it has no issues pulling to 7,000.

cylinder air mass falls off, injector duty cycle levels off and rpm and mph you can see a clear plateau

Id like to make it to the track Sunday for the first time this season....

smokeshow

iTrader: (16)

Not enough turbine, too much cam, and/or something compromising charge density...based on what you're saying. Can't view the file but likely one of those things. Those turbines are known to be quick spooling but early to choke, so there's that. Will also make a setup sensitive to an oversized cam. A small turbine/housing will cause power to go asymptotic at any boost level, albeit later in the RPM range at lower boost. Too aggressive of a cam will show up as an odd characteristic in a torque curve, for example an early RPM torque peak followed by a leveling off or decrease in torque, again followed by a very high RPM torque rise. If boost is falling off at high RPM, it could be an air filter or turbine issue. If boost remains the same but cylinder air mass is decreasing, it could be excessive IAT or again too aggressive a cam. All of these effects could be combined as well... That should get you started.

Atomic

iTrader: (42)

^ blah blah blah....get a bigger turbo, yours is done

mikevanky

The cam is a stock 1998 Camaro cam, so nothing crazy there.

I am wondering if I am maxing out the flow rate of the turbine.

I am also concerned about the pressure in the exhaust system after the turbine getting too high. Although I would imagine a lower differential pressure across the turbine would present its self as boost pressure falling off and thatch not occurring. My bud made a dump pipe last night to test that theory out...

mikevanky

That's what I was a afraid of!

Is this how a maxed out turbine usually presents its self?

BudRacing

iTrader: (3)

What valve springs are you running?
If they're stock the boost is likely creeping past the closed valves. I didn't even see the dyno chart but on a 4.8 a 76mm turbo shouldn't be falling off like that.

Atomic

iTrader: (42)

Theres a lot of different "76mm" turbos out there. The turbine is the expensive part of the turbo, hence cheap turbos usually have small turbines. That spools fast but dies off at higher power (airflow).

Choked turbine is usually power falling off up top regardless of boost. You can move vertically on the compressor map but not to the right. Im sure backpressure is close to 2-3:1. Not necessarily bad, just depends what you want. Higher backpressure gets you fast spool at the cost of top end power, so which do you want?

BudRacing

iTrader: (3)

Since I don't feel like downloading something to view a .hpl attachment.

How many psi when it falls off? and at what power level and RPM?

mikevanky

Yeah nailed it, cheap on 3 turbo with only a 65 mm turbine

I was actually thinking about tapping into the hot side to bring that data into my PCM, I think I can do that through an AC pin?

I have fuel pressure sensor I could use with a heat sink... would be really interesting to see how that plots and if it goes exponential...

mikevanky

Interesting you bring up the springs, I was thinking about this myself.
They are just LS6 springs so I could be asking too much of them at that RPM and boost lvl. I am not sure how to determine if that is the case or not.


Boost pressure is 13.5 in first and 15 in second.

RPM where power lvl falls off is around 5,500.
I am not sure on the power lvl currently I would guess 550 - 600 crank? I'm maxing out 53 lb injectors with a rising rate regulator and HP tuners torque estimates put it closer to 650 HP