FogOfWar

Hi,

Basically I have tried everything, but still have fluctuating power after 5-5.5K rpm.

Build:
all forged 5.3, 317 heads, LS9 cam, PT4788, dual 60mm WG, E100 fuel.
918 springs, rev-kit, headers, LS6 intake.

On the dyno, it showed 650hp @ 9psi @ 5000 and a second later drumroll... 350hp @ 5500 during spoolup. Like driving to a concrete block.

Already covered:
Valve-train: is up to the task, when I blew the tranny the engine was 3+seconds at 7300 and zero damage. The 918 springs are shimmed about 0.100 up leaving only the suggested clearance from coil-bind. Installed lb is ~150 like that and this is not the issue. Also the rev-kit removes the lifter mass from the equation.

Coils and Plugs: AR3932 heat range 10, truck coils, dwell tried from one end to the other, resistance checked on wires. No issues. 0.024 gap. Like new after a run, ignition advance strip in correct place on the ground electrode.
Running wasted-spark.

Fuel: Tuned correctly for 10.6-10.8 on gas scale. Ethanol will not lose power till 10.5 so fat and happy. No leaky injectors, tested.

Spark: 16deg at the top end. Checked to be correct.

Compression: checked, 10+ on all, 5% diff in cylinders.

Lifters: Changed out to GM Performance ones, no change. Preload at 1-1/4 turns.

On the logs I see that the fuel injected is raising correctly with boost, so the fuel and air does go through the engine but no power.

I'm completely out of ideas what could cause this. Excessive crankcase pressure? Too fat oil(10W50) and lifter pump-up? Spark blow-out? Injector clogged What else?

Is there anything else to check?

LT1PWRD

iTrader: (2)

Why such a crazy thick oil? Should be 5-30 to 10-30 in these engines with the the clearance they're designed to run at. I've experienced too thick an oil causing pump starvation @ high RPM, I had a tight clearance engine and was thinkin old school. I'm thinking the opposite of pump-up, possible lifter collapse @ high RPM from starvation, causing a dramatic loss in lift. Were you able to watch/log oil pressure @ 5500? Happens very quickly and have to be watching for it. Just throwing it out there from the info you've provided.

CBM Motorsports

iTrader: (2)

I would check ECU voltage when it starts cutting out. Seen bad alternators/too small of charge wire do the same thing.

ls3fox

Is the converter slipping under power

SPRAYED 01

iTrader: (22)

What cam and what lobes. I have similar issues and have pretty much narrowed it down to the xer lobes.

Never mind just re read the thread.

FogOfWar

Oil pressure is nice and constant the whole rpm/load range in the log.
30-45 at idle and 70-80 at redline depending on temp.

No alt, race oly build on bat only. 11.5-11.7 volts the whole run, no fluctuations.

It would go to the moon then, PTC custom made unit, 15 runs from new.


I looked over the logs and it seems also possible that the trans might starve for oil maybe and lose friction on the 2nd clutches. I'll have to check that.
Shallow pan glide.

necrocannibal

iTrader: (5)

I had a similar issue and it turned out to be excessive back pressure. It was 3:1 after 5800 rpms and power dove really hard.

Forcefed86

iTrader: (4)

+1 for checking back pressure, could have blockage somewhere?

I'd get a better spring in there. The LS9 cam is more aggressive than most think. Dual spring BTR's are the best route IMO, even if thats not you're issues at the moment.

Did you degree the camshaft? Many have had issues with the gen4 crank key way positioning. You need to degree the cam on the newer motors. (not saying that's the problem) I gained 12mph at the same boost level by simply degreeing the camshaft on my LC9. (was installed dot-to-dot originally)

Those aren't resisted plugs either. May look into the standard BR7 plug. The non-resisted plugs can cause issues with RF noise. ESp at RPM. They did on my megasquirt ECU, but not on the AEM.

Fat Jesus 808

iTrader: (5)

SO i just had a very similar issue. Car would make 600hp no issue. Turn the boost up and it would spool fine, then drop to 500hp, i switched back and forth between boost levels 3 times, and every time low boost made 600ish, more boost made 500ish. Put in new plugs(even though old looked fine) opened the gap to around .027 and instantly the higher boost made 675. Just a thought

Sleeperls

Sounds like a restriction issue. What type of flex joint? Collapsing filter or hoses?

Dyno Junkie

I wouldn't call that a thick oil at all.
In our N/A LS3 that revs to 7,000rpm I use Castrol 10w-60,
Run the same oil in LS2 with 7,200rpm limiter.

kevin87turbot

iTrader: (2)

The springs are the problem. A good friend of mine just had the exact problem with his combo. His was fine on low boost, but wasn't good at all under high boost. He is now at 185 lbs of seat pressure with his dual springs. It puts down a little over 1000 rwhp with the good springs.

LT1PWRD

iTrader: (2)

I'm sure you could spin an LS2 or 3 with 75-140 gear oil to 7K,but it doesn't mean you should....

Forcefed86

iTrader: (4)

What are the main/rod bearing clearances? Factory Oil pump?

FogOfWar

Attached log from Sunday.
Stripe is at transbrake release.

I'm going to cut open the converter today, RPM drop after launch, oscilliating rpm up top and rpm drop below t-brake after gearchange told me to.

Edit: Converter checked out to be good also. Bah.

FogOfWar

For others having similar problem.

Converter opening and closing plus I changed the plugs from AR3239 to BP7EFS.

Problem vanished. Clean pulls to 7000.

7.8 @ 171 @ 15psi @ 1630lb

Fat Jesus 808

iTrader: (5)

New plugs winning

greenvortec97

iTrader: (1)

Is this what it was doing? Mine does this and I've yet to figure it out.

SPRAYED 01

iTrader: (22)

What does "converter opening and closing" mean?

FogOfWar

Cutting it open to check for damage and welding back together. In the process the tolerance changed a little inside. There was something like Bef: 0.52 Aft: 0.62 written on it when I got it back.