Top end power fluctuates??? Gonna kill myself, I swear...
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Top end power fluctuates??? Gonna kill myself, I swear...
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.
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.
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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...
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...
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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.
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Originally Posted by 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.
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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.
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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.
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.
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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?
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?
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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.
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.
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??
Originally Posted by bboyferal
This is the second front-mounted LS1 with a T-67 losing power up top here recently... Solved by reducing boost.
*thinking*
*thinking*
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??