New props or gear change?
 

I have a 1994 formula 336 with hp465's. It appears that my top speed is on the low side vs. others with comparable power. My best speed run so far has been 67 @ 4900-5000 rpm, down around 5-9 mph claimed from other 336's. It still has the stock 21p non plus mirage 3 blades. The biggest difference in my boat is that it has 1.36:1 bravos. I know my rpm is low so I'm looking into getting the motors up to the 5200rpm area. My main usage would benefit from having a higher cruise speed vs top speed so 4 blade props are what I want to switch to. Would I do better moving down in pitch or swapping the drives to a 1.5:1 ratio and running a higher pitch prop like all the others have with comparable power?

I highly doubt that the claims made by others of being 5-9mph faster are accurate/real GPS speeds.

Your prop slip is only at about 8% which is already extremely low, and realistically, too good to be true for a heavy straight V bottom boat.

Was your speed taken with GPS????

BTW, 4 blades will increase your cruise speed, but decrease top end speed. You would probably need to use REV4 props to get a small enough pitch.

Yes the speeds were gps verified by 2 sources. The on board garmin 741xs and a gps app on an iPhone 6. I guess it is possible the tachs could be off given the slip numbers.

I would say that your engines don't have the torque to turn that drive ratio. I have the same problem with mine. ( I solved mine by adding 89 cubic inches.) I would change the drive ratio and possibly go up 2 inches and then run the 4 blade props. Best of both worlds. The low slip number was because your drive is too deep and you don't have the torque to break the prop loose.

I doubt the 1.36 ratio is an issue. I agree with the low X dim on his boat being an issue.
I spin 24 Bravo's to just over 5000rpms with 502mpi's with CMI's.

Ratio can be a factor. On my boat my 650 HP 509 doesn't have the torque to spin the prop. I lost a lot more RPM than I should have from just the ratio change from 1.5 to 1.36. I figured that I would be able to spin the same prop to close to the same RPM because I went up another inch. From 2 inch shorty to a 3 inch shorty. With the 1.5 ratio -2 shorty I was turning a Bravo 28 to 6000 RPM. with the 1.36 ratio -3 shorty I was only able to get 5400 RPM. SAME MPH.

With 465HP a side, if you changed to 1.5 gears and 25P Mirage you may touch 70 mph. I had 425 a side in my 93/336 with 1.5 and 25P mirage ran 68 @ 4800. Tried 2" shorties with 24P Bravo 1s. Mid range & cruise was great, top end suffered. That combo gave a lot of stern lift and upped the gas usage a lot.

BTW, No 336 with your power is gonna run mid 70s.

A 600 rpm change going from a 1.5 to a 1.36 is the normal difference in rpms.
Raising the propshaft an inch might raise the rpm slightly, but most likely only because propslip increases.

I heard it was only 300 to 400 RPM.
Tried to do the math but can't get it right.

slip stayed the same.

By the sounds of it I'm better off leaving it alone, enjoying it for what it is, and upgrading to a newer and faster boat in a few years. Thanks to all