Ok guys, i've got a stumper for ya. A guy brings me a 2006 Corvette LS2/M6; i put some TEA TFS 225cc heads with 62cc chambers, an entire off-road Billy Boat exhaust (Route 66? the one with mufflers), an XE-R lobed 232/234 112 + 0 cam, and a K&N intake. Also, a set of adjustable PP Harland Sharp rocker arms.

When the car is done, it gets dyno tuned - the biggest pull of the day was somewhere in the low 430's, with a 10hp jump from 6050-6100, then the power falls off after that and the car stops pulling hard. The torque curve is very flat (good), but has trouble breaking 400 RWTQ. Also, when we started, we were able to use about 25-6 degrees timing @ 6000rpm with no knock retard - netting the 432-ish RWHP number. As the day went by, the timing numbers went down to around 20 degrees total timing, as we kept seeing more and more knock retard. The power also worked its way down into the 420-425 rwhp @ 6050 rpm range, with the torque never breaking 400.

WTF?! SO. The car comes back to omaha and we tear it down. compression check, 2 cylinders were at 215psi, 4 at 220, and the other 2 @ 225. Leakdown test in the 1-2% range, and the cam installed straight-up as it's supposed to be, the lobes are exactly as they were spec'd.

Today i had the injectors flowed, and they turned out fine. We tried running it lean, rich and everything in between to no avail. One last ditch effort i'm going to try is running a 7.700" pushrod with a non-adjustable rocker arm to see if there's some harmonic associated with the adjustable ones. When the adjustable rockers went on, i had to do a TON of clearancing work as they really wanted to hit the valve covers. .

The car pulls knock retard around 4k-4800, and then again starting at 5900 until we get to around 20 degrees @ 6300.

Can someone please give me an idea what else to check on this car?

Mike/Brian @ TEA have been really helpful, Brian mentioned a name of someone to talk to @ Vengeance that could help me out but I wanted to exhaust all of my resources before i use up a favor

 

Hey Steve, I found the name of the guy in CA I was telling you about. Here is a link to his post and results, he may have some advice for you as well.

https://ls1tech.com/forums/showthrea...9&page=4&pp=20

 

im really curious to see how this turns out as i was going to order my 215's. i have the exact same cam but i was hoping to mill to 61 and run a .040. seems to me the car should dyno way more than that as im at 394hp right now thru a dana 60 4.11 rear and steel nitrous ready ds.

 

I seen crazy things like pinched fuel lines/Regulators and clogged filters cause weird problems. If its detonating lowering the water temp/Plug Heat Range may help.

 

Are you sure it's KR and not some kind of burst knock?I had a similar problem with a LS2 SSR but it was the computer throwing burst KR in it for no reason except maybe noise from the Cam/valvetrain.

Did you happen to take the car off the rollers,drive it for 10 miles or so and put it back on the roller's? If you can run the 26 degree's of timing again without KR the computer is doing something. Vette's are known for this in the past.

 

What type of valve springs are you running?

 

The only info i have on the springs is what i remember when i ordered them, (maybe a NexTek?) anyhow 140lbs on the seat, titanium retainers etc. I'd be surprised if it were a valvespring. It's already got TR6 plugs, IMHO they're too cold already!

I did not drive the car in between dyno pulls at all. What are some things i can do to identify burst knock? I can all but guarantee the knock is false...

 

was the AFR goin leaner the more pulls you made ?

 

No, i was actually surprised at how consistent it was for how much was going on with the car...

 

I have had issues with tuning on the dyno, some cars need to be shut off and restarted after a tune one to two times to get into PE again. One time we had to run a vehicle on the dyno for a minute or two like we were street driving and then shut it off then restart then make a pull. We did this every time we put a new tune in it.

 

Get some octain buster and put it in. If there is knock it will be false. I would make sure on the valve springs. If they flot it will fit the story. What is your a/f ratio 12.8?or so. Then move it from there. What are you measuring the A/F with and how. Before the cats? ot after? If you have that much timing pulled I would not think that u got the HP you did. Try timing from 28 to 30. How thick is your head gasket? .040

 

Do some test and look for false knock. I have seen cars act really funny though with valve float. I know Futral had a problem with on TFS car and it was due to the valve springs. Of couse the car he was working on would not pull past 5600 rpms I believe.

 

No cats, we tried 12.2-13.5:1 AFR; are using stock GM Head gaskets, i suspect the adjustable rocker nuts contacting the valve cover at high RPM.

 

i would think that would be pretty noticeable...how was the engine temp for the rest of the runs ?

 

175-180 (160 STAT) at the beginning, around 190 once the rollers stopped. Nothing really seemed too far out of the ordinary though?

 

[QUOTE=stevewix]The only info i have on the springs is what i remember when i ordered them, (maybe a NexTek?) anyhow 140lbs on the seat, titanium retainers etc. I'd be surprised if it were a valvespring. It's already got TR6 plugs, IMHO they're too cold already!

Try checking valve seals used.
I have seen people use the O.E. hat seal with Dual Springs.
Big Bozo No No! The Dual Springs need a standard metal clad viton seal.
The inner spring does not clear the hat seal.
Could be the cause of your problem.

Tony

 

I would hope the valve seals are for a dual spring, they probably don't even put umbrella style valve guides in TFS heads do they?

 

We are the manufacture for TFS guides. They take a 343530 seal. (.343 x .530 ). Hope someone did not install the O.E. Hat seals.

Tony

 

You mention a valve train harmonic, are you running 5/16 pushrods? Depending on the spring setup, the longer pushrod length requirement may benefit from a 3/8 pushrod to stiffen them up since they are longer.

 

Are you sure about that? I know that PEP is in Las Vegas....and I know the TFS guides are made by someone else...who is not in Las Vegas...

The TFS guides use a stock GM seal (8mm x .500), and that is what the heads are installed with, Dart is the only manufactuer that I know of that ever put a 11/32 (.341) valve in a LS head, but I think even they used a .500 boss on the guide. (.343 x .500)