Can somebody help me with advice about the gear ratio that is the best for me .
I have a sonic 358 and just bought two chief engines sc 620 hp
carburated . I need to do the upgrade from bravo I to bravo xr .
What gearratio 1 / 50 or 1/36 .

1.50

That's a tough question. A lot of factors are at play for this decision. From what I understand, if you can hit the rev limiters with a 32p prop with 1.50:1 then you should go to the 1.36:1 ratio and smaller pitch prop's. But since yours is a new setup it's hard to guess.

I suggest you go to the technical Q & A section and do a search on drive ratios. There's a lot of good information over there that will help you make a decision.

that's what i've heard,if you run out of pitch with 1.50 ratio then the only option is to go with the 1.36 ratio and then maybe you can still use your old prop's,maybe pitch'em up.i guess you just have to try it.kinda in the same boat(no punt intended)jus smaller.i put a 420 mega blower on my prowler and it's all trial and error cause i don't think there's anybody else out there running bigger horsepower in the prowler's.goodluck,dave

I would think that you could stay with the 1.5 ratio that came originally on the 358's. I have a 358 with 525's and Hydromotive P-5X's 27 p and it runs 82 which is faster than the 30 Bravo 1's that originally came on the boat. If you have not run Hydromotive 5 blades you should try them. They made a lot of difference in handling, nose bounce, accelleration without cavitation, top speed, and fuel economy when compared to Mercury Bravo 1's. The Hydromotives are available up to 34 pitch. I think with the 1.5 gear ratio you would probably run 29 to 30 pitch props that should run in the 85 to 90 range. With the horse power increase that you are getting over my 525's I calculate your new speed to be 87 based on a formula posted on this webb site that I have tested on several boats and it seemed to be pretty accruate.

So a 31 Sonic with 1.5 ratio bravo ones and 26P props spinning 5100 with 140 gallons of fuel going 74mph. On gps ... how much horse power do I have?