31SS Sonic- more power, bigger props??
 

Last summer my '88 Sonic 31SS ran 75 (GPS) with 23" props, 1.5 Bravo's. I only had 485hp (x2) then but now have 555hp & 540# torque @ 5400....... What prop pitch should I need??
I have some 26" & 28" from my Formula. Will they be enough??

Are the 26 and 28's 4-blades? If so,absolutely won't be enough...30 - 32 4-blades...I'm running 32 labs on my 31 and 30 on the 386

Yes, 4 blade Bravo 1's. I also have a set of "special" 29" 14.5 diameter to try. I never dreamed I would need props that tall! Guess I'll have to hit up some of my cat buddies for props to try...... I would guess those would put me into the
90's???? :evilb:

We need more information;
What rpm did you run with the old motors and props at WOT?
It had to be in the mid to high 5000's to get 75 mph with 23 pitch props.
At what rpm do your new motors develope max HP?
This rpm will determine what pitch prop you will need.

Yes, it was in the high 5000's, I don't remember exactly. I was also running alot of trim at the time... actually too much!

My max power is;
588 hp @6000 514# torque (stated above).
555.6 hp @5400 555# torque.
Hope that is helpful!!
George

My guess is your 26 Bravo 1 props turning 6000 rpm should be good for about 83-85 mph. This is assuming the hp numbers are accurate for the old motors and the new motors.

The 28's may be a little too tall for you, this will bring the rpm down to about 5600 or so.

The hp#'s are accurate. They came from a dyno run just before tear down when we found 3 valve guides had fallen out of the heads. I now have Brodix heads.... that is the reason for the bigger power.
Thanks for the info. I feel better about my chances with the props I have for testing. Keeping my fingers crossed!!!

I'm running 525sc's in my 31...I have the boost turned up to 7#'s... we came up with 600 hp doing the "40hp per pound of boost rule"... I have a set of 30p labs that are worked to 32's...I've seen 89(gps)... I was running 5400 rpm's with the 30's before I had them worked and The 525's run better around 5200 as yours will run better around 5800(guessing)...what I would do is watch the gps throughout the rpm range...more rpm's usually mean more speed, but not so in my case...the speed never moved from 5200-5400...hope this helps,Mike

You have 2 sets of props to test with! These will give you great baseline numbers to work with. Then let us all know what your actual speed is. I hope you get the results you are looking for.

Thanks. It will be a couple of months yet to test... I have recovery from shoulder surgery in April to deal with.... then the LAKE!!:drink: