Griff

I would go with a 250 for sure. Roots type blowers and whipples make torque all through the rpm range. Centrifugals have to spin up and don't make good torque at lower rpms.

You need to find out your comp ratio.

thedonz

you stated you didn't want to remove the engines or pull the boat......before you can even determine if you can safely add a blower....of any type, ....you need to know what your starting compression ratio is.....if you do not have a low compression engine, with blower friendly pistons, you cannot SAFELY add a blower because the engine will not last....thus, you WILL end up pulling the boat and pulling the engines.........everything else is an academic exercise until you answer the initial compression question first......good luck

HTRDLNCN

if those really are custom high torque cams they may
be too advanced or detonate too easily with a blower.

Bajapred

iTrader: (1)

FYI..the 525sc was a 454ci that used the weiand 177 blower..the 575sc was a 502 that used the weiand 256 blower..and the 600sc was a 502ci with a b&m 420mega blower..just thought it might be good info for you

Swamplizard

thanks - keep coments coming

I found out that the front gear can be flopped on the 177 and 250 so it can run backwards for the counter-rotating motor.

The compression is stock 502 8.75:1 and the exhaust valves are stainless so it would probably survive low boost. IT's a rolle rmotor with strong internals and I would not push it much over 4000 rpm ever.....but if the torque doesnt show up down low, it might not be worth the effort.

rdoactive

The 250 is a good size for the 502.
Flipping the front of the blower will reverse it.
You'll probably need a new cam and ignition module.
The trans will have to be upgraded to a 72C. The 71 is rated at 310hp, the 72 at 475, but can be upgraded a lot. The tailstock gear reduction is only rated to around 500hp.
My $0.02
Gary

Swamplizard

310? What happens if you feed it (the BW71c Trans) 420hp? does it overheat or do parts break or does it just "slip"? I had no idea these things were rated so low. This boat originally had 500HP motors in it.

Bajapred

iTrader: (1)

Well, you can also take this with a grain of salt but here are my .02cents........... your outdrives will prob be ok if you just take it easy on them...the biggest problem with shelling an outdrive is coming out of the water and re-entering with the throttle still wide open..this will blow about any outdrive...take off out of the hole in a feathering manor and don't get stupid with the thing and you will most likely get by with what you have....on the other hand, your engine.....1st your engine is not the ideal setup for a blower install...compression ratio is 8.75:1.. 7.5 or 8:1 would be much better, you will have a "'possible" detonation problem with your 8.75 ratio..you will just need to make sure you have plenty of fuel and fuel pressure getting to your carbs..2nd your fuel pump will need modified or you will need an electric pump good for around 110-130 gph or so. 3rd, If you do not plan on running over 4000 rpms, you will never really benefit from a supercharger, that is about when real boost starts kicking in..so keep all this in mind.....or not

One more thought..the fact that you really do not want to run this thing hard, it would be best to buy a supercharger that was a bit on the bigger side so you could run it slower but get the same amount of boost from it, compared to running a smaller SC & spinning its a$$ off..just a thought though

cuda

If his Arnies are anything like my Kaamas, there is no such thing as feathering them out of the hole. I have to spin mine to almost 4000 rpm, with the props cavitating, then you'll feel the props bite, and it will jump up on a plane. You start getting off the sticks rather quickly when it comes up.

Swamplizard

yeah - mine was a bit like yours cuda until I added ventilation snorkles - now it is not quite as all or nuthing. My boat is much heavier than your and the HP is down on it so it takes a while to get up on plane and I dont have to rev it much over 3000 rpm before it starts to bite and slowly gets up on plane.