2011 Grandsport Cam Procharger problem

[blazenstyle01]

We just put a procharger and cam on a 2011 corvette Grandsport. Everything in the tune is fine except when we are trying to dyno it. It pulls great until we get to like 4800 rmp it then just drops its power and sounds like someone is putting there hand over the exhaust. after it drops it continues to grow again but not near how it should. The line graph looks like a automatic car when it down shifts on a dyno. There is no change in the boost when this happens. It is still rising. We only have 6psi. Any ideas?

[5_Liter_Eater]

Do you have a dyno graph? From what you describe it sounds like valve float. I don't see anything in the scan that points to a problem which again points me to valve float. When I had it on my blown C5 it was the same thing. Everything looked good in the scan but it felt a little flat. On the dyno it looked like a huge ~50 HP/TQ dip @ ~5000 which recovered by redline. I never re-dynoed it after I put new springs in it but the car came alive!

BTW, the AFR is too lean and that is too much timing for this application. I'm surprised it's not knocking badly.

[blazenstyle01]

I will post a graph as soon as i get on that computer. The afr and timing in that log are not what it is set to, i have the afr at 11.5, and timing at 15 wot. That log file was just one that i had handy and it was a result of trying different things to cure the problem. As for the floating valve, wouldn't you think i would show a drop in my boost?

[5_Liter_Eater]

That would stand to reason but I did not see any loss of boost when my valves floated.

[blazenstyle01]

there is a very noticeable change in the exhaust tone. it almost sounds like when you hit the rev limiter but that's not what it is because the car keeps pulling. Did yours have the same sound

[5_Liter_Eater]

I don't remember that tone exactly but after we tried swapping known good coils and installing a new set of plugs and were doing another pull some customer walked into the shop and said "sounds like valve float". So it didn't sound normal I guess although I did not detect it.

[0260in3]

Sounds like valve float for sure. Seen it many times.

[blazenstyle01]

here is a picture of the dyno run. the green line at the bottom is the boost. Red is HP blue is TQ. I'm sorry for the poor pic having some computer problems

[5_Liter_Eater]

Yep. I'm going with valve float.

[TM-Z06]

Are you running meth? I've seen that kind of graph when meth kicks in and you're not tuned for it.

[JHester]

Def not valve float. Float isnt as abrupt. What does the ETC do? Its not closing is it? Have you raised all of your max airflow tables? Im unable to look at the tune right now.

[DSteck]

If it is happening at about 5500rpm, then you're losing traction on the dyno. Watch your engine speed and vehicle speed spike up from 5400 to 5600rpm.

[IDRIVEAG8GT]

Valve Float and losing traction! I think what we have here is an absolute monster.

[edcmat-l1]

By the explantion of the sound, I would pull the plugs and check the gap.

I wouldn't think it's wheel spin, unless it broke them loose instantly. Usually wheel spin will be a gradual hazing, and won't be as sudden as that graph looks.

Also, if this thing is procharged, it's pretty damn lean, with a good amount of timing in it at the same time. I would say it's blowing the spark out, or worse.

[blazenstyle01]

yea its definitely not wheel spin and its not running meth. I have pulled all the plugs checked the gap all were fine. The thing thats getting me is that its so consistent when it happens, run after run it happens in the same spot and the graph looks the same. I show no signs of anything happening in the log, i dont loose any engine speed or wheel speed when the dip happens, its not showing any knock, and the boost is consistently rising with no effect in it.

[DSteck]

I've never seen wheel spin look consistent. Only reason I suggested it is that's what my graph looked like when my car wasn't strapped down properly, although it was accompanied with a huge spike.

I've seen this exact same thing happen on a Procharged Trailblazer SS with a cam. It turned out the pushrods the previous shop installed were too long, and the valves weren't able to close completely. Literally the exact same kind of drop off, same RPM, every time. Scanner showed no signs. After putting in adjustable rockers and correcting the lash, the engine pulled clean to redline.

[edcmat-l1]

First thing I would do is get the fuel and timing right, and see if that doesn't get rid of the problem. I wouldn't go off on a tangent trying to diagnose it when the fuel and timing are some far off. Keep running it like that and you'll lift a ring land.

[blazenstyle01]

The tune that i first posted was one that i used for one run in trial and error it is not the final tune that is being used nor was it ever used more than once. I have updated the tune in the first post to reflect the most recent tune. It's still doing the same thing.

[Motorhead-48]

At frame 8770 your fuel trims go static with the car at idle...any idea why? Back into Open Loop?

Go to frame 18356. Your Commanded AFR is still 12.72 with your foot buried in the pedal, and your wideband supports that data. You have several spots beyond that where you peak quite a bit above 13.0...I wouldn't go there with a cam'd FI motor.

Most of the run is still showing 19-20 degrees of advance logged even though your tune file seems to show you should be at 16 degrees.

Are you logging injector duty cycle and monitoring fuel pressure?

[Snyper]

Ive seen that happen when an intake sucks shut. It sounds like the car goes underwater almost. Do you have a plastic or rubber intake on the blower?