ok i went to the dyno today and at 5200 rpms it fell on its face it made 300.9 hp and 349.5 tq and at 5200 it just droped off this is a 400 sbc its 30 over trw flat top pistons cr is 10.8 to 1 5.7 rods motown heads with 205 int and 1.60 exe 220 intake runners a comp nos cam 230 244 @.05 487 501 with 113 lsa and a edelbrock torker intake a 750 edelbrock carb the power range on the cam is 2400 to 6500 any suggestions on why it is falling at 5200 rpms btw it has a 2in spacer between carb and intake heres a web site with the same cam and it putting out 441hp and 434 tq at the flywheel thanks



http://www.compcams.com/Community/Ar...?ID=1649445315

 

I am not sure of your problem but i really dont like to take mine over 5500 rpm. Ive been to 6000 a couple times. 400's are not that high of a reving engine they are mostly torque. IMO

 

Could be any number of things.

A NOS cam running NA won't build the same amount of power as a similarly ground NA cam.
Not enough fuel. Either a bigger carb, bigger needle and seats or bigger jets (needles and hangers).
How old are the valve springs? What's the seat and open pressures?
Ignition timing. Don't rely on the timing pointer unless the cam's been degreed and the timing marks are zero'd in with an adjustable timing pointer. The pointer could say you're at 36* when the timing could be at only 30*.

Dyno tuning is more than one or 2 pulls on the dyno. To find the best performance, you should be spending at least a full day on the dyno so you can change things to see what works the best.

 

Any time power quits like that, 1st thing to look at is fuel pressure, 2nd is the valve springs.

 

how in the hell do you figure? How high a motor rev's is relative to the cam and heads you have in the car. Theres no reason you cant rev a 400 to 7000 rpms as long as your cam and heads are designed to work at that rpm.

 

People also say a BBC shouldn't rev that high. I cross the finish line at 7150 rpm. The correct internal parts just help it stay together longer at those high rpms. A stock 400 only has a cast crank plus many other weak parts. Using high performance parts will help an engine survive high rpms. I know of a 434 SBC in an altered. He buzzes the engine to 8500. It also has 2 dominators carbs and run 7's in the 1/4 mile.

Another thing I would have suggested is valve lash but that's a hydraulic cam. Perhaps the lifter preload isn't set properly or the lifters are pumping up.

 

the motor will rev to 6200 be for it floats the valves but it loeses power the a/f is 12.4 so it seams to be fine on fuel the hole motor only has 800 miles on it. the springs came with the cam.we spent 6 hours trying every thing. jeting the carb and moving the time curve and Ignition timing . thanks

 

I was thinking the same..

 

When a combo mysteriously "hits a wall" at a given RPM you're running out of one or more of the following things:

1. Fuel (always have a fuel gague hooked up where you can see it while you make a pull)

2. Valve springs (are they at the right installed height, even if they are the correct ones for the cam? Are you absolutely sure? The number of times I've seen people screw up valve spring installations is a lot)

3. Ignition (usually accompanied by lots of popping and hesitation before it actually noses-over but there can be subtle things like having an ignition retard box kicking in when you don't think it should for some weird electrical/wiring reason, etc, etc.)