UPDATE: Took the car back to the same dyno with hot tires and strapped the crap out of it. It took a couple pulls for it to hook. I added a little to much fuel to the last pass up top but here are the results:



So I built a guy a LSX 454 for his 06' Z06 after the exhaust valve decided to vacate the motor out of the side of the block. The first graph is over MPH and shows the problem. The second graph is another Z06 I am doing with H/C to really show the problem. I tuned both of them less than 30 minutes apart. I expected the 454 to make 620/560rw. The thing makes 460rwtq at the hit and doesn't get any better till the end of the run which makes no sense to me. I designed the motor not to exceed 6,500 rpm since the SS intake valves and springs coupled with the FAST just won't allow power to be made much above that on this size motor. Just for perspective, a 15' Z06 with full exhaust, pullies, CAI and tune only put down 630rw on this dyno. I think he said 15lbs of boost but don't quote me. The runs start at 2,750 rpm and end at 6,750.

Does this look like clutch slip, spinning on the dyno, something in the drive train? The 454 was run second and there is nothing in the logs to indicate anything is wrong at the motor. KPA is good 101-98, DynCyl follows on both although the 454 only peaks at 1.11 like the 427 but doesn't drop off like the 427. The 427 ends at .94 at 6,800. I am not sure if an exhaust restriction would show in the logs though. I am not sure where to go with this. Any suggestions would be greatly appreciated.

454 mod list: 600 miles on motor
TEA/TFS 260 heads
BTR STG IV cam 246/254 111
8.75 DCR
Lunati lifters - 3/8" push rods .0030" preload
Haltech 108
Ported FAST 102 and NW tb
OBX 1 7/8" catted LT's with stock cat back
60lb injectors
Monster LT1 Twin

427 mod list:
FRH ported LS7 heads
bullet 242/248 114
8.5 DCR
3/8" push rods
Vararam
Ported FAST 102 and NW TB
TSP 1 7/8" headers with stock cat back
stock injectors
McLeod RXT Twin

We are adding a custom cam, U/D pulley, EWP and some other little things to the second Z. Numbers coming soon.

 

Do you have a multi choice crank sprocket? I seen them 6 degrees off and taking lots off at the wheel reason I stay away and use GM sprockets only.

If using GM crank sprocket my next suspicion will fall on degree-in the cam, pls let us know what is was good luck
David.

 

Yes, I degreed the cam. I do the at .050" method and I check the valve timing of the intake and exhaust lobes just to ensure that there are no manufacturing defects. All was within a degree with this one. And that is probably just human error. I see where you are going with that though. That cam in that motor should peak at 6,100 or so and carry to 6,500. I had a very similar cam in my 416 and it peaked at 6,100.

 

To me, the torque curve looks to flat on the first Dyno pull. i am used to seeing slope changes on a cammed car, and that pull is pretty flat.
So maybe clutch slip is the issue.

 

Clutch is kind of what I am looking at as well. Just hate to think a brand new $1,200 clutch with 600 miles on it is slipping on the dyno. And just to clarify, the second graph is the two motors overlayed. Run 5 is the 427's final pull and Run 10 is the 454's final pull.

The rpm would jump from 2,700 to 5,800 extremely fast and then slow down pretty well for the rest if the pull. I tried some quick hits in the lower gears to spin the tires on the dyno to heat them up but the results seemed to be about the same either way.

 

What kind of clutch?

 

McLeod RXT Twin.

 

Sorry, his has the Monster LT1.

 

I don't think it's clutch slip as power continues to climb, but does the it smell like it's slipping after the run? Does the pedal get soft? My initial thought looking at the graph was the cam was off a tooth on the install, have seen that happen from guys who bring cars to get tuned on the dyno though I that doesn't sound like the case since you built this one. I personally haven't seen a set of obx c6z headers, how long are the runners or have you used them on any other 600+ rwhp builds?

 

I verified with the customer that we did degree the cam for sure. I was hoping I still had it marked on my degree wheel but I have done a few builds since then. IIRC it came in 1* advanced like the last ten comp cams I have done. I was also wondering if it was tire spin since it was really cold that morning but I can't really see it on the logs looking for RPM or MPH spikes. The runs were strange though and it could be due to the tq this motor puts out. As soon as I would go WOT it would hit 5,500ish almost immediately and then slow down significantly for the last 1K rpm or so. The dyno owner is the one that pointed that out.

The OBX headers are a dead rip off or LG LT's. Same length and all that. I am going to pull the driver header again to ensure that when the motor went something didn't get lodged in that primary. I am just wondering if an exhaust obstruction wouldn't show up in the logs.

I am also seriously considering pulling the balancer and degreeing this thing again just to double check. It is just an ATI and a huge PITA.

I don't remember smelling the clutch and it doesn't seem to be slipping on the street. But the pedal is soft on this car no matter what. I am attributing that to the geometry change on the pedal due to the relocation of the Tick Master drive rod.

It could have been a dyno quirk that I am way over thinking.

 

That isn't clutch slippage or tire spin, you typically see erratic spiking if the clutch/tires lets go on the dyno. That thing is dead flat.

I'm with the other guys, we've seen this a few times with the cam being off. Of course headers can play a part but I'd start by pulling the timing cover and revisiting the camshaft timing.

 

I can't see that clutch slipping either but I didn't break it in. I do my best to advise people on proper engine and drive line procedures but I am not there. I couldn't find any spikes on my logs. It wrapping up so quickly and laying over is what had me leaning that way.