7.4 only turns 3800 rpms

Knot L8te said:
The MPH is off of GPS and RPM has been checked with timing light. I agree the boat has to be around 23+ mph to stay on plain. If I have a 3-4 adults I can get on plane fine but any more then that I have to move most everyone towards the bow. It just seems like a little over a half throttle the boat just stops pulling. To me it felt like timing but after rechecking that and also trying to power tune it while under WOT it is at its max on timing advance. Just lost for ideas.
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I asked before….how many hours are on this engine. Is it the original engine?
 
Was thinking a possibility of a flat cam but I believe this is a roller cam in the MPI which makes me think its very unlikely. I did find one exhaust flapper partially wedged and thought it may have been the issue but I replaced both sides and it didn't change it. Could anything else in the exhaust be causing the issue?
 
Scott215 said:
We would only take street big blocks up to about 6800 rpm maximum where we could spin a small block 7500 8 grand no problem.
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A street small block V8 will not rev to 8,000 rpm with “no problem”. If the valves haven’t begun to float before that, you have surely oil starved a significant portion of the motor.
 
You know what I mean a built right small block with titanium valves, good springs , stud girdle, compression,heads and cam. It's not hard steel crank good rods you know . Just good parts
 
Sorry I should have said a motor built for it my apologies. Don't want to argu with anyone
 
Anyway back to the guy struggling with the big block. One of two things is true: 1) this engine has not pulled over 3800 since it was installed 2) something is off in the engine.

Since you have done all the obvious things…..what does Jasper say regarding adjusting the valves?

If the engine used to pull beyond 3800……it would be a likely source of a performance issue. It would give you a chance to check the cam and see if there is an issue with the two 140 cylinders.

I know it is a lot of work but there aren’t that many things left. Also can you get the build/dyno sheet from Jasper? That would be helpful in determining how they configured it.
 
I used to shift my street Nova my 70 Nova with a 40 over 350 a hydraulic flat tappet cam a set of 202 heads ported and polished , 456 rear end gears, and a turbo 350 I used to shift it at 7200 and go through the lights at 7400 and that was a roller nothing.just different valve spings. Trust me man I'm not trying to argue with you I've been there I've done it I street raced for 30 years so have a little experience. That was a daily driver.
 
When you replaced the gimbal ring you didn't touch anything on the engine, when the outdrive went back together did it go very very smoothly, it wasn't rough at all, did anything have to get forced on or in in other words was it a struggle or did it go back together nicely
 
Did you ever get a fuel pressure gauge on as scoflaw had suggested at WOT
 
How did it have 70 lb of fuel pressure at idle in 40 at 3800 RPM You sure that's not backwards
 
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