Make sure it's not the rev-limiter. I did everything mentioned on this thread and several other threads but everything ckeckout ok. All things that need to be verified on yours but last year I had the same problem with mine until I replaced the ignition module to one from a 454 mag. Now it runs up to 5050 rpms and hits the rev-limiter. Find the number on the module and verify what it is. Good luck.

PM

For what its worth, my boat is similar to yours, if not even a bit heavier, same motor, and even worse flowing heads than yours (peanut ports). Same carb, etc.., and I can hit 5200-5300 rpm if I use your 23 pitch bravo one, at 62gps all day long, stockfuel lines, etc..stock TV4 ign as well, no limiter. I expect with your heads, I could go even a bit faster. Something is holding you back, but don't think its for lack of power in that motor.

Well keep the ideas coming I am in the process of checking thinigs on the motor everything seems ok. My engine builder has mentioned ign and also he said to step up to a performer rpm air-gap intake. If I change the ign should i go with the crane box and leave my merc dist. in would that help. Thanks for all the ideas so-far I do have a thunderbolt IV that is what is says on the square part of the dist.

Performer Intake is designed more for the peanut oval ports and peak power around 4k or so on a 454.

An RPM will be much better.

However, going solely by your description of going flat and falling on it's face I would strongly think carb calibration or fuel supply issues. Then again, weak spark or incorrect timing can cause the same thing. This intake will cause power loss in comparison to the RPM, but it won't make it fall on it's face at this engine rpm.

A good running TB IV should have no issue at all firing this motor. Make sure that total timing is where it's supposed to be. Bring engine rpm up to 4200rpm when setting timing just in case since some modules aren't all in until this point.

Do a search on Thunderbolt IV rev limiter and you will see that some had them as separate units. Could save you months if there is one at 4700 or so. Just a thought.

PM

If its a 93 its probably a t-5 and has a rev limiter. Get it out of there and try a t-4 from a friend before you spend money. Do the fuel pressure gauge. You've got to know that you have fuel at wot or you will hurt the engine.

Remember, a fuel psi guage won't show if the needle/seat is a restriction. I've seen this a bunch of times...fuel psi guage showing good pressure but bowl(s) running out of fuel.

I do have a tb IV ign. I just talked to a guy in florida who is retired from merc. He told me to set the timing between 3600-4000 rpm I asked about switching to a mag module he told to try this first. He also told me maybe to try an 800 crm carb instead of the 750. Also, mercruiser rev limiters will make the engine quit or (not pull any more). I keep investigating

just pulled the module off it is a TB IV it says V8-24 2K22A those are the numbers on it

If the timing advance doesn't work should i try a different module or just go and buy a DUI distributor i have heard some bad things about an msd system