[JSH]

Originally Posted by ZL1Atlanta

And then dives down again before he gets off the gas. I'd be interested to see what the dyno plot looks like.

For some reason he did not print the chart (?!)

[ZL1Atlanta]

Originally Posted by JSH

Both the shop owner and the tuner drive modified LT4 cars. The owner's is PI with 1000+ and the tuner's is DI Ethanol that runs 9s up here.

We've made three changes from the 965 hp SAE build one or more of which have most likely caused this:

1. from 103 to 112mm
2. new belt
3. from 3" to 2.75" snout pulley

Blower speed is 15% greater now.

Could it be something as simple as the TB blade not fully open even though HPT shows 100%?

I was seriously leaning toward a faulty 112mm that is being forced closed with the extra air pulling in, but that shouldn't happen on the hit. I had this happen and had to get one with an upgraded motor/actuator. I assume any new since then (almost 2 years ago) wouldn't have the issue. Belt slip should show in the logs, but I've also had it where it not, but when going to a 10 rib we magically picked up boost with no other changes.

[JSH]

Bottom section of HPT:



I don't see where HPT captures back pressure at the exhaust valve, which might be helpful here.

[JSH]

Originally Posted by Katech_Mike

The flat portion of the exhaust isn't your problem.

Could be a number of things. I would guess it's fuel delivery related without seeing a log or even dyno graph.

Shot in the dark guess is if you log the pid for high pressure fuel pump delivery angle you'll see its maxed at 130 degrees.

Log shows 94 degrees

[ZL1Atlanta]

Originally Posted by JSH

Bottom section of HPT:



I don't see where HPT captures back pressure at the exhaust valve, which might be helpful here.

It does seem like at some point the car should have registered more power than before. The dyno plot would be nice. The MAP plot is good, fuel is ok enough (just rich), TPS seems fine, but the spark dancing like it does obviously isn't right. I can only think of something in the torque mgmt or traction systems causing that looking at the other data. Admittedly, I'm not a tuner, I just look at a lot of my own logs and consult with guys much smarter in this area than me and learn from that. Lol.

[JSH]

Kong's first guess was slipping belt, but he had not seen the log and the MAP curve.

Originally Posted by ZL1Atlanta

It does seem like at some point the car should have registered more power than before. The dyno plot would be nice. The MAP plot is good, fuel is ok enough (just rich), TPS seems fine, but the spark dancing like it does obviously isn't right. I can only think of something in the torque mgmt or traction systems causing that looking at the other data. Admittedly, I'm not a tuner, I just look at a lot of my own logs and consult with guys much smarter in this area than me and learn from that. Lol.

[ZL1Atlanta]

Originally Posted by JSH

Kong's first guess was slipping belt.

You said it gained boost and the graph doesn't show any variances as you go up in RPM. It just goes higher as it should. I'm going to say that's not it. If boost was lower than before that would make sense, or if it had peaks and valleys. To my previous point, I could show you a MAP plot before the 10 rib that looked fine and then after the 10 rib with no changes and MAP peak was higher. But in your case, its already consistently higher than you had before the change.

[Katech_Mike]

Post the actual log file as an attachment.

If the throttle body was being pulled shut you would be able to see it in commanded vs actual in the log.

Someone mentioned earlier that you may have cats? Is the true?

[KingLT1]

MAP shows an increase through the curve all the way out to limiter. Doesn't look like belt slip.

Timing 21-22 degrees from 4000-6750rpm, should be making plenty of power with that.

Fuel is rich, but not killing power. Just unnecessary strain on the fuel system. It's running about 5% richer then commanded so the MAF needs work.

Throttle might be closing but I would think you would see a drop in KPA when that starts to happen.

Crimp section isn't hurting much. It's flattened but widened so overall it's not much if any smaller in diameter vs the rest of the exhaust. I would still remove it.

If it still has green cats, they are likely junk. I think I remember you saying that they were removed.

Need to be logging more PIDS in plotter. MAT, Rail / low side psi, and Wideband should be plotted.

Your SOI seems low for a Cam car. Might be causing the EOI to be a little on the low side? With your injector MS around 4.8-5ms range I would expect to see EOI in the 170-180's not 140. 140 is what I typically see with injectors in the 5.7-5.8ms range.

Either way I don't see any of that causing that big of a loss in power. When you start talking about losing 100+ whp with more boost and potential flow, I think that indicates something more on the mechanical side vs tune.

[JSH]

Originally Posted by Katech_Mike

Post the actual log file as an attachment.

If the throttle body was being pulled shut you would be able to see it in commanded vs actual in the log.

Someone mentioned earlier that you may have cats? Is the true?

Site won't let me upload a .hpl file. I'll email it to you.

No more green cats. They were mangled so we scraped them out.

[s346k]

965 @ 7k
850 & 5800

what power did it make @ 5800 on the first dyno?

[JSH]

Originally Posted by KingLT1

MAP shows an increase through the curve all the way out to limiter. Doesn't look like belt slip.

Timing 21-22 degrees from 4000-6750rpm, should be making plenty of power with that.

Fuel is rich, but not killing power. Just unnecessary strain on the fuel system. It's running about 5% richer then commanded so the MAF needs work.

Throttle might be closing but I would think you would see a drop in KPA when that starts to happen.

Crimp section isn't hurting much. It's flattened but widened so overall it's not much if any smaller in diameter vs the rest of the exhaust. I would still remove it.

If it still has green cats, they are likely junk. I think I remember you saying that they were removed.

Need to be logging more PIDS in plotter. MAT, Rail / low side psi, and Wideband should be plotted.

Your SOI seems low for a Cam car. Might be causing the EOI to be a little on the low side? With your injector MS around 4.8-5ms range I would expect to see EOI in the 170-180's not 140. 140 is what I typically see with injectors in the 5.7-5.8ms range.

Either way I don't see any of that causing that big of a loss in power. When you start talking about losing 100+ whp with more boost and potential flow, I think that indicates something more on the mechanical side vs tune.

Will adjust MAF. Removing the crimp. Cats are gone. All of OIDS are in the log file. I can send it to you. I don't know about SOI stuff.

It essentially rolled over about 175-200 hp short of expected peak. Never seen this before. Lots of fuel, lots of air.

[JSH]

Originally Posted by s346k

965 @ 7k
850 & 5800

what power did it make @ 5800 on the first dyno?

905/820 at 5800

Too bad we can't see back pressure at the exhaust valve.

Might it do this if traction control was on?

[18.2SS.1LE]

What transmission? Clutch/trans slip?