if Lloyd did the heads, then they are fine. The heavy rockers aren't helping. You need to verify the pushrod length too. If 7.4" was too long, 7.35" may be too long as well with the Harland Sharps.

It won't take much to throw some stock rockers on there and see what she does...

 

I would try different rockers first, checking pushrods again to be sure wouldn't hurt, and if those turn up nothing if it were mine I would send off an oil sample to see if there are signs the cam is going flat.

When my cam failed the car ran good, just started getting lazy at the track

 

The car is at the shop right now, having pushrod length and valve lash double checked. The shop is an LS specialty shop that also does dyno tuning. I asked about the rockers and was told that roller rockers costing HP is a myth. They've tested them back to back vs stock style rockers. While I'm not picking up any HP with the rockers, I'm also not losing any.

Frank

 

I didn't mean to imply they cost power (or gain it), but heavy rockers often lead to instability at high RPM on these engines unless the heads are equipped with lightweight valves (like the sodium filled ls6 valves) or the cam lobes use a ramp rate designed to aid in control and stability.

The comp xer lobes, if I recall correctly, are among the offenders (anyone feel free to correct me there)

Good luck and hopefully they can help you get her lined out though! Should make for a healthy setup once the bugs are lined out.

 

The XER lobes are definitely aggressive. The valves are just standard stainless valves. I'm keeping the rocker theory in my head though. Thanks.

Frank

 

What valve spring? What are the lifters preloaded to?

 

Lunati spring kit that Lloyd installed... 73925 spring.

155 lbs on seat, 390 lbs open.

I just got a call from the shop. Pushrod length and valve lash are correct. I do have 1 rocker that's touching the inside of the valve cover that they're "clearancing" for me.

I'll have to go back through my old info to check lifter preload.

Frank

 

That's not enough spring for those Harland Sharp rockers. You need at least 450lbs open.

Those springs sound like they were spec'd for the stock rockers.

 

If they just checked the pushrod length, they should have been able to tell you the preload. Don't bother with your notes, what is the preload they're setting the valvetrain up to?

 

They're actually Scorpion rockers.

Frank

 

Ah you're right. That was someone else who had Harland and similar valvetrain stability issues.

I'd suggest throwing a little more spring at it so it doesn't flatline like that uptop. The preload may be wrong as well, but the valvetrain going unstable from lack of spring pressure will cause similar issues uptop. If you have stock rockers, I'd still suggest using those first since you do have stock heads, which are designed with the stock rocker geometry in mind and have powdered metal guides. Depending on preload/pushrod length, it may just be a simple swap to the stock rockers to verify the upper RPM issues may be due to valvetrain instability.

Once you have that result in hand, you'll know if that was the issue or if something else is causing it. If it does correct the issue, then you can choose to either stay with stock rockers or swap out to a different spring, like the BTR Max Pressure, PRC EHT springs, or Vinci springs designed for roller rockers, and keep the Scorpions.

 

Consulting with Lloyd and the shop now to look into possibilities.

Thanks,
Frank

 

Lifter preload is .060"

 

Probably thinking about my issue.

 

Nice car Frank

Those lobes are fast and your open spring pressure is not enough to control them especially if you have stainless aftermarket valves they are heavy

I would change the cam out,get 3/8 pushrods + the intake needs to be ported then you should be at 450rwhp+ if the motor is sealing up good

 

I just talked to COMPs tech line. The springs they suggest for this cam has 430 LBS. of open pressure. But, he said that the 390 LBS. should be sufficient. This thing has no audible signs of valve float though.

Frank

 

It has signs on the dyno of valve float, though...

I'm telling you, you don't have enough spring for that combo. Those Lunatis are designed for stock rockers.

 

Going to try a set of stock rockers.


Frank

 

any updates on this?

 

Did a trunion upgrade on a set of stock rockers and installed them. Went from 386 to 388 HP... In MUCH cooler weather. Kinda busts that whole "roller rockers cost horsepower" theory all to hell.

Frank