RW99

The install that will never end continues.

Now, with new (unburnt) wires and plugs, there's a weird power wobble up at the top end. Sorry, no pic of the dyno run, but basically the power comes up nice and fast and even to 3k rpm... but as the rpm's climb from there it begins dipping and peaking giving this wavy trace to 6500. Same thing for torque curve. Overall, it looks like it's costing maybe 70 rwhp/rwtq or so, limiting the T67 to around 550 on average...

A/F is rock solid steady throughout the pull, as is the boost at 10-11 psi. An Eboost2 is used to produce VERY stable boost traces; I am pretty sure air delivery is not the problem. Fuel delivery is on overkill, twin pumps... and the solid flat A/F would suggest that's not the culprit, either.

Any ideas, guys? Ideas in play right now:
--check valvesprings, maybe one's bad?
--compression/leakdown
--some sort of misfire?

Basics: PTK T67, FMIC, FAST 78 mm, AFR 225's 72 cc, forged/dished 346, 224/224/114, Alkycontrol, custom single pipe exhaust. 2bar SD tune.

Going out of my mind. Thanks for any help.

98turbls1

iTrader: (17)

You didn't include the type of valve springs... Are they stock, 918's, Patriot dual gold?? Or other ones??? I'm thinking that you may have a little bit of float...You may check your compressed spring pressure...See if one is odd or looks unlike the other ones...

Got Me SOM

iTrader: (2)

RW99 you're in Fla right? who built your car? my guess is valvesprings too but who knows.. post up the dyno sheet.

MIGHTYMOUSE

iTrader: (59)

what is your timing. when mine wouldnt make power it was too low of timing, and it felt like it came and went

RW99

The springs were the "upgraded" set that came with the AFR's. I'll need to check back into the paperwork to confirm the specs exactly.

I'm in the east bay/San Fran. Whatever the problem is, I'm pretty sure we'll get it solved right about the time the rain starts falling nonstop.

Timing is at 14. And the behavior is the same with or without methanol (which is being sprayed fairly conservatively)

Thanks, guys...

HellRaiser

iTrader: (9)

Maybe a stupid thought but you may have a air leak somewhere? Intercooler pipe's or BOV is leaking?

RW99

Wouldn't that cause a drop in my observed boost though? The boost trace is really flat throughout the range where the HP/TQ are fluctuating.

MIGHTYMOUSE

iTrader: (59)

i dont mean look at the commanded timing, i mean look at the actual timing

HellRaiser

iTrader: (9)

Might, but then your e-boost might be keeping it from dropping to.

parish8

iTrader: (6)

i have had kr kick in and my timing drop from 15deg down to 11deg or so and couldn't really feel it but i am sure it would show on the dyno. last year when i was coming up on 20psi i could feel the power come and go up top while running down the track, i ended up needing a little more dwell on the coils and since then it was been running good.

RW99

Thanks for the ideas; KR has been disabled. I'll see if there's a log for the actual timing, too.

You can actually feel the uneven power up at the top while on the street at WOT, too. Not much, but definitely there.

As for the Eboost compensating for a leak somewhere, I know that the installer had to dick around with the Eboost to achieve that flat boost from spool-up all the way to top end... but as long as I'm seeing steady pressure at the top, the air delivery shouldn't be the problem, right? And we wouldn't expect the power to dip AND come back? I dunno.

MIGHTYMOUSE

iTrader: (59)

you have to physically check the actual timing on the crankshaft

RW99

I am told that the springs all look good.

My belt used to be a six rib but it walked a little when we swapped the stock PS pump for a Turn One unit and pulley. So now it's a "custom" 5-rib.

Is there a chance that at high rpm the belt isn't functioning correctly and this results in the alternator (relocated stocker) getting a little funky? And that's causing imperfect spark?

TransAm6383

iTrader: (1)

no that doesnt sound like it...that wouldnt make the car perform like that.

RW99

So the problem has been solved: reducing boost smoothed out the top end, although HP peak is lessened a bit and TQ doesn't stay as high as I'd like up there. I will post up a couple of graphs once I get them from the shop so this thread has some documentation with it...

I'm happy with the car now, fully spooled at 3000 rpm and pulling very hard. Thanks for all of your suggestions.

I think I'll drive it for a while and consider a T76.

bboyferal

iTrader: (9)

This is the second front-mounted LS1 with a T-67 losing power up top here recently... Solved by reducing boost.

*thinking*

Darren P

iTrader: (1)

what was boost and what was it reduced to

Old Geezer

iTrader: (3)

Turbo operating on the wrong side of the surge line??

I think that just because the springs "looked good", that they may not be suspect. Were they actually tested for correct pressure, on the seat, and at max lift??

Ari G

iTrader: (25)

Have you checked fuel pressure?

HellRaiser

iTrader: (9)

Glad you got everything work right. Once you have these setups dialed in you can enjoy the car for once.