Tuning or Valve Float? Help

[Maxwell Power]

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 around 6100. 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. This feels like you just plugged the intake or exhaust.

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

[cptinjak]

I'm no expert, but i found this looking through your tune:

[ProTools4]

are you running GM lifters PN 88958689 ?
AKA the CTSVR racing lifter....

over at LS1tech there are several threads about issues with these lifters.
and the LS1tech crowed is split into Pro & Con on theses lifters

I have them in my 96 Impala and they are pitaful in my combo,
they were just added to a very proven and powerfull high reving engine and now the things a turd
they will be removed this week.

as a test move the rev limits above where you plan to spin plus some margin.
then lower it back down when you hit the street.

[flame]

Post a log of it happening showing airflow pids

[planethax]

In the tune you posted the cut is at 6200 rpm

[FastEddy]

Haha, rev limiter is set at 6200... either you posted the wrong tune or are disabling your limiter the wrong way. Also would like to see data logs rather than dyno graphs.

[Maxwell Power]

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!


I posted the tune with the reduced rev limiter because the valves were potentially floating. I'm not going to keep the rev limit at 7500 if the valves float at 6200. As I stated, I already determined it wasn't a rev limiter. I was looking for something else.

I appreciate the input from everyone however. Thanks!
Dominic

[ProTools4]

you did not answer my question

lifter part number!?

[ProTools4]

????????? ????????

[Maxwell Power]

I don't understand why it is so important to you. 120 on the seat, 337 at peak lift of 600 is obviously too low.
The 88 number sounds right, but I'm not in a hurry to go digging through my invoices. They were around 350 bucks for the set on Summit.

I had the lrm gauge that attaches to the rocker and it was way off. We pulled a spring after measuring installed heights and checked the pressure.

[ProTools4]

my guest is that once you fix the seat pressure you will have the same issue.

[Maxwell Power]

my guest is that once you fix the seat pressure you will have the same issue.

well that would suck immensely. I have no desire to get ANOTHER set of head gaskets for this motor.

Which lifters are people having great success with?

[ProTools4]

LS7s are a standard

[ProTools4]

So....

.....What happened??????

[ProTools4]

bump


So....

.....What happened??????

[cptinjak]

bump


So....

.....What happened??????

I think we lost him.

Jack

[DrLoch]

Probably changing head gaskets...

[ProTools4]

Probably changing head gaskets...

and lifters

[Andy0x1]

Re: 88958689 lifters.
I just installed them in an L67 that used to spin 6600rpm no problem, and now I get valve float at just 5000rpm.
Do you have a link to the rant forum?

Is the hydraulic piston diameter for the oil passage in these lifters so much larger, that a given oil pressure nets that much more pump up pressure?

are you running GM lifters PN 88958689 ?
AKA the CTSVR racing lifter....

over at LS1tech there are several threads about issues with these lifters.
and the LS1tech crowed is split into Pro & Con on theses lifters

I have them in my 96 Impala and they are pitaful in my combo,
they were just added to a very proven and powerfull high reving engine and now the things a turd
they will be removed this week.

as a test move the rev limits above where you plan to spin plus some margin.
then lower it back down when you hit the street.

[Maxwell Power]

Fixed mine last week.
Upon installation of the cts vr lifters, I had float around 6100. I gained two hundred rpm when raising my spring pressure... Not enough that's for sure.
I checked my preload last week and it was .080" ... oops. Not sure how I screwed that one up. New 7.350 push rods (old were 7.40) and I'm rev happy.