zt260

I found a 1999 Donzi with a 454 Mag 385HP. The owner runs it at 5400rpm. Is this a safe rpm for a stock 454 mag? Seems like the valves would have trouble.

Thanks in advance.

H2Xmark

unless the factory rev limiter has been raised it will not turn 5400rpm's, maybe his tach is off.

Vinny P

I have been told, the rev limiters are set to 5050 on those motors. Why would you want to spin a stock 454 that high anyway? I would pitch up a bit and drop some r's..

H2Xmark

you are right, 5050 to 5080 on the rpm's is where the rev limiter kicks in,

Payton

The older, 365 mags, didn't have a rev limiter.

futz991

As the others have said, the rev limit on the 99 454mag is between 5050 and 5100. That said, running it at 5400 is not a problem for that engine. It has all the good parts in it to allow that RPM. Unless his tach is off, he ha dto have the ECU re done to hit that RPM

zt260

He said the ECU was reprogramed. So that should explain the rev limiter. I just did not think the stock springs could handle 5400rpm. Valve float is no fun for the seats. I didn't want a motor with a bad valve train from running to many rpm.

blue thunder

I would be happy to spin that engine to 5400rpm if the valve train was fresh and correct. The problem I see with floating vlaves is not so much beating the seats up as over heating the valves at extended WOT blasts. They don't get enough seat time. If you limit the 5400rpm blasts to 15-30 seconds max and the engine sounds good up there, I'd say you are fine. BBC really sound nice in that rpm range.

Dave

aTX427

I second the tach as a possible cause - try getting a clip on digital like they use on motorcycles - Lockhart Phillips makes one for about $80 the wraps around the plug wire or swap yours out for a Nordskog.