Brett.. I need a little help

[myscarab30]

I have done some upgrading and will be running about 425hp and want to be max 5050-5100 rpm they are genIV 454's with 1.5 TRS drives. I was running 23p Mirage with extra cup (not the +) at 4600 @60-62 mph before the new stuff.. What would you recomend..Thanks

[Griff]

What power did you have before to turn 4600rpms????

Why limit yourself to the 5100rpms?? A 500rpm increase would be like adding 100HP or so. Those engines also should easily turn 5300+rpms. I would test what you have now first.

[myscarab30]

They are the 330's with cast internals...Dont want nothing to come apart

[Griff]

Good move to keep the rpms around 5k with the cast bottom end. I would still try your current props to get a baseline. They should be pretty close. I upgraded a 454mag from the stock 365hp to about 420hp and picked up about 400rpms.

[bbladesprops]

Hi,

I agree with a 400-500 window of growth, the current propellers will be sufficiant for testing. Griff's rpm increase per his hp increase is a little higher than what we typically see. There are always variations. With a 200 hp increase like you are suspecting, we would expect 2 inches of pitch increase to maintain the same rpm as you currently have. Or in other words, your rpm should grow 400 if you keep the same props and indeed gain 200 hp.

[myscarab30]

Thanks brett I have 3 sets of props Ill try all of them and see what happens

[Griff]

Heck, you think thats a lot of gain, you should see the boat now. The new owners replaced my engine and put a 525sc in it. Went from a 23" Mirage+ at 5400rpms and 65mph on the old engine to a 27" Hydromotive at a best of 77mph so far:shock: This is in a 24 Outlaw.