The car needs to be put on a dyno to see what is happening after 6000rpm. It wouldn't be the first time one of LE's setups has experienced valve float. At the very least, have the springs tested to see if their pressures are in spec. Get your power back above 6000rpm and put gears on that match the power band and there should be a massive difference.

 

There is no reason that cam with those heads should be falling off around 6000. That is a big cam, and Lloyds lobes are aggressive. I dont think you are down on power up to 6000 rpm, but you are leaving alot of hp on the table by shifting so early. 114 is hotcam trap speeds...

 

I changed the spectre to a K&N cone filter at the end of the season and it didn't seem to help much if at all. One of the main things I have yet to check is fuel pressure when the car starts to die off in the RPM range. I'm running a stock LT1 corvette pump. I now wonder if the engine is demanding too much being as it uses 30lb. injectors and is tuned for all the mods which I would think would demand a lot more fuel. What do you guys think? The only reason I thought that is b/c I was told a cc503 setup is almost maxing the pump out but I'm not 100% sure.

 

If I don't shift at 6k the engine falls on it's face. It won't pull anymore after 6k, it just revs out and doesn't make any power. Pulls hard right up until 5500 then it starts to fall off.

 

These are not actually LE heads from what I was told. He just sent the flow specs to me when I asked for them before I bought them.

"All Flow #'s are at 28" H2O on the same flow bench, operated by the same person.
Ported Flow:

Lift: = Int/Exh:
.200 =134/104
.300 =190/144
.400 =235/172
.500 =257/191
.550 =265/195
.600 =265/200 "

 

That could be a tuning issue or the valvesprings. You are probably making the right power up to 5500, are your springs 918s or pac 1215s? I would really upgrade them to dual springs anyways. Lunati just came out with a nice looking dual spring for a reasonable price. That is a pretty huge cam and the RPMs it is expecting to be shifted at, its not worth it to run behives, duals give you piece of mind in case of failure. Sell the behives, put the money towards duals, fix your intake, and see if that solves your "fall on its face" issue, then we can start blaming it on tuning.

 

Is it even a possibility for the fuel pump to not be able to supply adequate fuel so power dies off?

 

They are the Comp 918's.

 

BOOOOOOOOOOOOOOOOOOOOOOOOOOOO. What year? And they are too small regardless. But there were a few years of horrible mexico failures.

 

Are they really too small? I was under the impression they were fine... Well that kind of sucks, haha. If that is the reason though man will I be one hell of a happy camper! I bought them in late 2010 early 2011..... With the failures I keep reading about I think I might just go dual springs to be safe.... What would you recommend for a spring that won't cost a crap ton of money?

 

Stick a gauge on it and go drive around, see what the pressure is at.

 

Looking back in my old messages to Lloyd Elliot he said the beehives (918's) would be fine. Do you really think it's the springs? There are a lot of people running the 918's over 6700 rpms with no problems. I'm not saying your wrong but I don't want to have to buy new valve springs if I don't have to. It's a good amount of work to do the valve springs. (especially if I don't have to). I wish I would have datalogged it! I feel stupid that i didn't, I have no idea why I didn't.

 

I want to bring this thread back to life as I am in the process of trying to figure this problem out again. The power literally drops off at around 5700rpms. I have run the car past that point but all it's doing it making noise, the power/pull is gone. I have only tried to around 6200rpms but that is still within the power band of the cam. I feel I have valve float problems and want to know if anyone can recommend a replacement valve springs for the ole' LT. If anything it will give me peace of mind as I got these Comp Cams 918 beehives used. The car doesn't gradually drop off power-wise, it literally just drops off... The car is also in the process of getting 3.73's so that's another good thing! Finally I can do some work to the car again after a few years of just driving her as is.

 

The 918's can easily handle that cam you have. You say they aren't LE heads, but you do have the flow chart. Who assembled the heads? Are the springs at the correct install height? You can check them with a simple tool like this:

http://www.summitracing.com/parts/pro-66902/overview/



Lots of guys never check. They just slap them on and think it's good to go. The 918's can't go beyond .600" lift. So if the install height has them compressed a tiny bit, they will go into coil bind. You can fix the install height with different locks and/or retainers, or by checking the shims underneath the springs.

I ran the 918's for 3 years on a 350 LT1 with heads that flow around 255-260cfm, and the XFI468 cam (242/248). The car would pull clean to 7k every time.

 

Wouldn't the engine always run like **** if it was binding? I mean the lift never changes so why wouldn't it show down low as well?

 

Well I am updating this thread again. I'm pretty sure I found my high rpm power loss problem. Lloyd Elliot recomended to me an installed height of 1.740-1.760". I just measured my installed height at 1.900". Lloyd mentioned that even at 1.800" you can get valve float. I'm VERY happy I found out what the problem is! I should have measured the installed height originally but I just never did. No idea why.

 

Wow... get that fixed and you're gonna be lovin' life.

 

I cant even imagine how much better the car will run! Got 3.73's in last week and now this fix. I was leaving A LOT on the table with power dropping off at 5800rpms. The cam should run easily to 6500rpms. I can't wait to have the car fixed! haha

 

So how do I shim a valve spring 0.15"? The Comp cams recommended shim kit I have seen sells .015", .030" and .060". I would need to stack (5) .030" shims on every spring? That's a lot. Do they sell thicker shims?

 

You could also do 2 .060" and 1 .030".....

1.9" installed height seems high. If that is accurate I could see you having the issues you are having. That would put you at about 87lbs on the seat vs 144lbs on the seat at 1.750".

If you shoot for a 1.750" (2-0.060" and 1-0.030" shims) installed height, your seat pressure should be 143.6lbs (65% increase) and your open pressure should be 358lbs (versus your current 302lbs). And you'll have 0.072" clearance from coil bind.