Troubleshooting question: valve float or what?
Thread Starter
Teching In
Joined: Jun 2012
Posts: 8
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Troubleshooting question: valve float or what? Hey guys,
here's the situation I'm having. I can't figure out what is causing this sudden power drop at 6100 rpm.
As many of you know, the rev limiter is a fuel cut. I set it to 7600rpm in this car (in all the maps) and the power still stops suddenly. It doesn't feel like the fuel cut rev limit. I can lower it to 6k and it does the normal fuel cut rev limit.
As you can see by the graph, it falls rich and power dives HUNDREDS of HP at the wheels in only a few hundred rpm.
The setup:
Lunati 60512 cam (282/288 with .599/600" lift)
Lunati double valve springs with over 200 psi of pressure at the seat.
GM Performance Roller lifters. (the more expensive model tested to 8k rpm)
Crane Roller rockers 1.72 ratio.
Built bottom end, pistons rods blah blah
This problem was happening at 6400 rpm before, but we collapsed some lifters and spun a bearing after about 5 hours. Turns out the moroso pickup wasn't sealing properly. We fixed the pickup issue, put the OEM pump on it (smaller), installed the GM lifters because the Lunati lifters had collapsed (over half of them). Now we have 75psi at 6k rpm and the problem is worse. Now it's right at 6k.
Anyone? I am at a total loss.
You can see by the AFRs that whatever happens isn't fuel system. It's like air just stops going through the engine. It almost sounds like valve float, but the seat pressure is high, the cam isn't THAT big and the springs are beefy.
Any help would be appreciated.
Thanks,
Dominic
here's the situation I'm having. I can't figure out what is causing this sudden power drop at 6100 rpm.
As many of you know, the rev limiter is a fuel cut. I set it to 7600rpm in this car (in all the maps) and the power still stops suddenly. It doesn't feel like the fuel cut rev limit. I can lower it to 6k and it does the normal fuel cut rev limit.
As you can see by the graph, it falls rich and power dives HUNDREDS of HP at the wheels in only a few hundred rpm.
The setup:
Lunati 60512 cam (282/288 with .599/600" lift)
Lunati double valve springs with over 200 psi of pressure at the seat.
GM Performance Roller lifters. (the more expensive model tested to 8k rpm)
Crane Roller rockers 1.72 ratio.
Built bottom end, pistons rods blah blah
This problem was happening at 6400 rpm before, but we collapsed some lifters and spun a bearing after about 5 hours. Turns out the moroso pickup wasn't sealing properly. We fixed the pickup issue, put the OEM pump on it (smaller), installed the GM lifters because the Lunati lifters had collapsed (over half of them). Now we have 75psi at 6k rpm and the problem is worse. Now it's right at 6k.
Anyone? I am at a total loss.
You can see by the AFRs that whatever happens isn't fuel system. It's like air just stops going through the engine. It almost sounds like valve float, but the seat pressure is high, the cam isn't THAT big and the springs are beefy.
Any help would be appreciated.
Thanks,
Dominic
Thread Starter
Teching In
Joined: Jun 2012
Posts: 8
Likes: 0
Figured it out Got it figured out.
My gauge was incorrect. I actually only had 120# at the seat.
At least the fix is relatively easy. Thicker shims and call it a day. I need about 070" worth of shims for the right seat pressure. So I'm going to do 80 thou.
Thanks for reading though!
My gauge was incorrect. I actually only had 120# at the seat.
At least the fix is relatively easy. Thicker shims and call it a day. I need about 070" worth of shims for the right seat pressure. So I'm going to do 80 thou.
Thanks for reading though!
If you only have 120lbs on the seat and are colapsing lifters, you have some major issues.
If you are trying to turn 7500RPM I would highly suggest getting rid of the GM lifters for some short travel's to prevent them from pumping up at the high RPM's.
Also you should not need any more that 180lbs on the seat to control that up to 7600RPM. Make sure you have 400+ over the nose with a dual spring.
If you are trying to turn 7500RPM I would highly suggest getting rid of the GM lifters for some short travel's to prevent them from pumping up at the high RPM's.
Also you should not need any more that 180lbs on the seat to control that up to 7600RPM. Make sure you have 400+ over the nose with a dual spring.
