What would cause engine break-up at 5200 RPM?

spirockp · Oct 3, 2007

I purchased a 275 HP motor from "an engine shop here in NJ" The RMP range is up to 5500 RPM but when I just about reach it the motor breaks-up. It sounds more electrical than mechanical. I have a "Ready to Run" MSD distributor which is good up to 9000 RPM. Any idea what I could be looking for that would be causing this?

Thanks.

Peter S.

mrmustangman357 · Oct 3, 2007

valve float possibly. check your valvesprings as they may start keeping the valves open at that rpm. Another possibility is your fuel pump may not be giving adequate flow at that rpm (also may be filter, etc). I have been surprised more than once the power increase i got from changing a fuel filter

65 fastback · Oct 3, 2007

Do you have a fuel pressure gauge? Check to make sure that you have constant fuel pressure at the upper RPM range. I had this problem with my similar horse power 302. The stock fuel pump could not feed it past 5,000 rpm.

Tim

spirockp · Oct 3, 2007

Fuel pump, interesting.

I'm running an electric; Carter 6psi 72gph.

Any idea if that too small?

68RCodeConv · Oct 3, 2007

Could be the coil or just a loose connection on the coil.

BullittStangV8 · Oct 3, 2007

What shop here in Jersey? If you dont want to post it here, could you PM me it?

spirockp · Oct 3, 2007

It was the "EngineFactory" I just didn't want anyone to think I was just asking a question to plug a shop.

jcode68 · Oct 3, 2007

Are you possibly running a rev limiter that is set a little low?

C0V3R · Oct 3, 2007

spirockp said:
Fuel pump, interesting.

I'm running an electric; Carter 6psi 72gph.

Any idea if that too small?

I'm running that pump too with a dyno proven 250rwhp so no I dont think that will be an issue for you.

D.Hearne · Oct 3, 2007

Breakup? Ice Bergs ? Did it blow up or just quit running or something else?

65 fastback · Oct 3, 2007

spirockp said:
Fuel pump, interesting.

I'm running an electric; Carter 6psi 72gph.

Any idea if that too small?

You should be getting 5-6 psi at 5200 rpm. Get a cheap gauge from Summit and install it on your fuel feed line to your carb. Have someone take it up slowly while you keep an eye on the gauge.

I was running the stock mechanical pump, so your electric pump probably isn't the problem.

Tim

jake2582 · Oct 3, 2007

i would guess coil if you still use the stock one. either that or module maybe?

hungrymonkey · Oct 4, 2007

what is your cam specs and valve springs?

mikethebike · Oct 4, 2007

What about your spark plug heat range? If you overheat them you will break up at higher rpm. Also check your fuel ratio at wot (EGT's are good for this).

302 coupe · Oct 4, 2007

I had a similar problem once. I had the right springs for the cam, but put them in at the wrong installed height. Engine always started breaking up at about 52-5300 rpm. I added some shims under the valvesprings to get the correct installed height and it cleared right up.

jake2582 · Oct 4, 2007

i doubt the valve springs are the problem. (no offence)
if the engine was built by a reputable shop then i would highly doubt they dont know what they are doing.

Dbiscayne · Oct 4, 2007

Do you get a full 12+ volts to the fuel pump all the time? It should be wired with at least 12 ga wire coming from a relay that's getting power straight from the battery.
Have seen problems when wired up with just 16 ga to a switch then to pump.

Other than that, what everyone else said could definitely cause it.

phast69 · Oct 4, 2007

Not sure about your problem bro but just so no one jumps ship The Engine Factory built my motor also...302/350 about 3.5 years ago and the only problem I had was my cam tore the living hell outta my hardened brass gear on my distributor but we got that fixed and it's ran great ever since.

Good luck. You may wanna call the guys at the factory....they were very helpful when we were trying to diagnose my problem.

mfp4073 · Oct 5, 2007

I was having a similar problem to that. I chased it for a year. Then I found that my thermostat was hotter than I remembered (or I got the wrong part in the right box). Car was preignitioning at around that rpm at about the same place on the 1/4 mile. Basically it would get to a certain temp that I didnt get in reg driving. I solved it by dropping the thermostat and going with a higher octane fuel. Never did it again.

probably not the problem you have....but there are just so many things!

jasonn · Oct 5, 2007

Start with the basics. Pull the plugs. Are they new? Did you bump some so that the gap is closed? How about the gap being too big. If you do not have a real hot ignition setup, I would gap them around .025-.030. Any more and your ignition may not be able to jump the gap. How about wires. New? Open the hood at night and see if you see any wires arcing out. How about charging system. Alt. charging around 14 volts? Is the coil seeing full voltage. Coil new? What carb? Done any jetting? It may be something like coil springs, but I ALWAYS go back and check all of the little things first. 99% of the times it is something stupid that we ALL overlook sometimes.

What would cause engine break-up at 5200 RPM?

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