My 396 lays down at 5700 RPM. It' like hitting a rev limiter and power falls way off. It has a Comp. XE274H which should be good to 6000. It has 820 iron heads and Crane Gold roller rockers. I called Comp's tech line. The tech. said that the 924 springs I'm running should be good to 6000 RPM. He also said that it could be detonation. Why would it pull strong to 5700 and then lay down at that point? Wouldn't pre-ignition problems show up sooner? At first I tought it may be a fuel supply problem, but I have plenty of volume and I've richened the carb. Do I need more octane? Less timing (36 degrees total now)? Please help. I need some input here. Thanks.

I'm no expert here but I think you should post your total parts combination, carb, comp ratio, exhaust, ignition, intake, etc. 36 degrees total timing isn't a lot for most engines IMO.

Here's the combo. 396 .060 over, TRW L2242F60 pistons which should yield approx. 10.25 to 1 SCR, Comp. XE 274H cam (.230/ .236 @ .050 and .550/ .552 lift), Crane Gold roller rockers, AirGap intake, Edelbrock 750 carb., Pertronix Flamethrower distrib., Hedman 1 3/4 headers, 820 cast iron heads with mild pocket port, 3" exhaust to mufflers then 2 1/2" out the rear, fuel supply via Summit fuel cell, steel braided line, 140 gph electric pump w/90 gph Fram canister filter. Any input would be greatly appreciated.

Originally posted by jarsmith2:
Pertronix Flamethrower distrib..... Try another ignition. I have not been too impressed with these guys.

And how are your valves lashed....

What problems are you aware of with the Pertronix distributors? Pre-load is 1/4 turn past zero lash.

I bought an inductive pickup module from them, and it was junk. Your lash sounds good.

I had the same problem almost same combo except I had a 454, 820 heads, HEI, RPM intake and a 280H Comp Cam. about 5500 RPM it would just quit pulling, I change fuel pumps, Carbs and Distributers. Checked Valve spring pressure, only when I went to put in new Comp Cams Pro Magnum Anti-pump up lifters did I see that I had 3 lopes worn off the cam with less than 200 miles on the motor. Might have been my fault though because I had about 20LBS extra of spring pressure after I tested them that Comp recommended. But I installed a Crane solid with similar spec's and now she pull's hard to 6500.

Does it happen in every gear exactly the same way? If so it's not fuel. Normally I would say a bad set of valve springs but take a good look at your ign.

If it's making any kind of noises up at 5700, it's probably ignition. If it stops reving, I'd say your springs are to lite. If it just slows down, it's fuel. You can change the timing and see if that is it. No comments needed...

Who set your springs up. Comps tech line can really put out some BS as far as springs go.
The 924 spec of 115 on the seat might work. But that's assuming you still have 115. Typically you can loose 10 lbs on break in. Even with my limited experience, I'm skeptical about the 924's 296 open spec on a BBC. Especially on an XE cam.
I doubt any machinist would do their own motor that low. I'd shoot for 120/320. Which requires research to find that spring.

My 383 did the same thing at 5800. 2 diff cams/springs, one set on the low side on the seat/open pressure, but still within card specs when corrected for 10% breakin loss. Turned out my tach was 500 rpm low.
Found out the hard way to go with the builder specs regardless of what the tech line says.
6300 rpm is still to low for float, and the motor never made a funny sound. None...
I had 105/305 after breakin on a 4* bigger cam than yours in a SB.

See if you can get Wolfplace to comment.
He's helped me a lot. And his prices are good too..

Oh, anything else abnormal you didn't mention.
A number of people remote diagnosed a guys ign. problem for 10 days & 30+ posts until someone asked if his motor mounts were loose. "Well it does make this clunking noise when I get on it"

I appreciate all the input, and I'm still trying to locate the source of the problem. So, more input is welcome. I retarded the timing after installing an MSD HEI distributior that I borrowed from a friend. I also put better gas in. This helped slightly in first gear (emphasis on slightly and I may be imagining it), but no noticable change in second. It's hard for me to belive that it's a fuel supply problem, but I know that that's still a possibility. I asked Edelbrock if it was possible that I needed the high flow needle and seat for the carb., and they said that with my combination (displacement, cam, engine speed, etc.) that was not necessary. Any input? Thanks. John

If there are any restriction in the fuel line, like a kink or clogged up sock in the tank, this could cause what you're experencing. If the springs are too light, you might be able to shim them. I did that recently and picked up 20# both open and seated with a .060" shim (obviously, you'd need to check for binding). Unless the timing is more advanced than you think or the CR is higher than you think or there is a hot spot in the chambers or the carb is too lean, I think you can rule out detonation.

Thanks for all the input and suggestions. I found the problem. The main connection from the fuel cell was leaking air. I didn't discover this until it began to drip fuel. I tightened the fitting, and it remedied the problem. This fix yielded a new best ET and MPH, 13.076 at 106.32 MPH on BFG TA's. I hope 12s are in the near future. Thanks again.

John

Glad you got it fixed. graemlins/hurray.gif I've heard of the sucking air problem before. Often the leak is too small to leak gas but will let air in. Thanks for posting the resolution.