Super Charger for a small block chevy

[rholbrook]

I'm thinking I need a super charger for my boat. My Ex-BIL has installed many of them and currently has a very fast blown boat. I took Harrison and all his buddies up boating and my boat needs some more ponys. It has a 305 in it when it should have had atleast a 350. The only reason I bought the boat is because I basically stole it and couldn't pass it up. I have propped it with better props for this altitude but it still needs help. It runs fine at Powell but up here, it needs help. Its a 23.5 ft 2004 Chapparal SSI open bow that is in great shape. It would be perfect if it only had some more power.

I have been thinking about putting a stroker motor in it but am thinking if I could find a used blower that may do the trick too. It doesnt need a ton more power but if I could get 50-75 more hp then that would do it.

Anyone have one laying around?

 

[Cascadia]

I thought you were getting rid of your boat because of your mooch SIL.

 

[sawtooth4x4]

Turbo. Once the boost hits, it'll pop those skiers right off the back. lol

 

[rholbrook]

I thought you were getting rid of your boat because of your mooch SIL.

SIL meaning sister-in-saw. No, I just tell her no. She has already asked me to take her young womens group and I told her to find someone in her own ward. There are boats in their neighborhood.

 

[Greg]

What generation SBC is it? Vortec, etc? EFI or carb? A little supercharger with 5-6 pounds of boost would REALLY wake it up and they're not hard to find used.... the question becomes if it's in good, running shape. Most roots-style superchargers have a wear strip on the edges of the blower's rotors.

IMO the 305 got a bad rap, but it can be a strong engine... better heads, cam and a bit of compression (or boost!) would do wonders.

 

[Greg]

Here's a hell of a deal of a Gen 1 SBC B&M 144 blower for $750/obo... that's a great little blower with LOTS of potential. - http://truestreetcars.com/forums/parts-accessories/70250-sbc-b-m-144-blower-supercharger-obo.html

And one on Ebay, open auction at $1200 now - http://www.ebay.com/itm/B-M-chevy-S-B-supercharger-induction-Blower-/141680092906

 

[rholbrook]

It has a TBI sitting on top of it. I have been trying to find out if there is anything that is different for a marine setup to pipe water through it. I have no idea what needs to be done. My other question was whether or not the same setup would work for a 350.

 

[Toad]

I got a TBI 350 sitting on a pallet ready to go. I think the only difference really is brass freeze plugs.

 

[rholbrook]

I got a TBI 350 sitting on a pallet ready to go. I think the only difference really is brass freeze plugs.

I know the difference between a regular motor and a marine motor. I meant the difference between a marine super charger and a regular super charger

 

[zmotorsports]

I know the difference between a regular motor and a marine motor. I meant the difference between a marine super charger and a regular super charger

The biggest difference between a marine supercharger and a street supercharger is the belt drive and pop-off system. The marine supercharger uses a serpentine style belt and does NOT have a pop off valve. This is so in the event of an overboost the pop off valve does not open potentially releasing a flame into a sealed compartment, the belt will merely slip.

On a street supercharger they usually use a Gilmer style of drive belt and have a pop-off valve to release the energy in the event of an overboost.

I had a B&M 250 on my 40 Chev with a SBC and it ran great. I ran the Gilmer style belt had run it in a slightly underdriven ratio. Come on strong and pulled hard. Ran low 12's in the quarter.

When I built my brothers two motors in his boat I ran the same B&M 250 superchargers with the serpentine belt setup and it ran great. His was carbureted and it took a bit to get them dialed in to where I was happy with the performance. I had done a lot of internals though and they were both 350 cid. On a friends boat, I pulled the 305 and replaced it with a built 350 and he was very happy. I tried talking him into supercharging it as well but he was happy as it was. I don't know how I got talked into working on boats. I hate boats and hate working on them even more.

Personally, I think the Weiand superchargers are better, but this is from about 15 years ago when I was racing. I don't have as much experience with them lately.

Mike.

 

[rholbrook]

Thanks Mike, do you have to run water through some sort of inter cooler for a colder air intake or just pull the engine compartment air?

 

[Jesser04]

Russ if it's a top mount the supercharger will sit on top of the intercooler. The front mount will have a box/intercooler that between the supercharger and the intake. This is one of Randy's the polished aluminum is the intercooler right below the supercharger. If it were me I'd look into a 496 swap we are putting one in dans pontoon boat right now. I think he is into it maybe 6500 bought it blown had hunter machine rebuild it and we are installing it.
I sent randy the pic with the comment big power he replied back with the pic above.

 

[zmotorsports]

Thanks Mike, do you have to run water through some sort of inter cooler for a colder air intake or just pull the engine compartment air?

Russ, I did not run any inter cooler on the ones I built but they were not pushing more than about 6-8 pounds of boost so it was not as necessary. More boost will heat the air up more and would require cooling, and fuel. The engine must be built with better components when you start pushing much more boost than that, plus you will want to run less compression.

Five to 6 pounds of boost on a fairly stock engine is fine. Cast pistons can take that no problem and the heat will be minimal.

In my 1940 blown SBC I was running forged pistons and pushing around 9-10 pounds of boost with no inter cooler. I had also dropped my static compression some to compensate, if memory serves my static compression was low 8:1 range.

I believe that 305 marine engine is going to be in the 8.5-9.0 compression ratio range so it should handle 5-6 pounds of boost without issue. Just be certain to get the ignition and fuel ratio dialed in as the OEM pistons won't be as forgiving to a backfire as a forged piston.

Mike.

 

[rholbrook]

Thank You, great info

 

[Greg]

I think the big question here is how much money to you have for this project? Boost gets expensive, fast... especially if you want to do it right. If you only want/need 50-75 more HP and it's a simple non-Vortec marine 305, I would suggest building a 350 with Vortec heads, a quality roller cam and a tad more compression... It'll cost a few thousand, but be a little simpler. Or you could put Vortec heads and a better cam on the 305, leaving the bottom-end alone, for less overall cost. It won't make as much torque and power as a 350, simply due to more cubic inches.

I'm not sure what a marine 305 is rated at, but I'd guess somewhere around 250 HP? I'm not sure what heads are on that engine either, but if they're not Vortec heads there is a huge gain to be had there.

 

[zmotorsports]

I'm not sure what a marine 305 is rated at, but I'd guess somewhere around 250 HP? I'm not sure what heads are on that engine either, but if they're not Vortec heads there is a huge gain to be had there.

First off let me preface by saying I am not a marine guy. I have built marine engines but I hate marine/boats. So basically I am saying "don't quote me". I believe the marine 305 cid engine is rated around 205 or 210 horsepower. I know the stock Mercruiser 350's were rated @ 260 HP.

Greg brings up some good points about other options that could potentially be cheaper. I say potentially because it is dependent on what you use/find for a supercharger.

That said, I have a huge sign in my shop that I used to point to when I was racing and people would ask about how much to go such and such speed. It read "Speed is a matter of money, how FAST can you afford to go". I love that sign.

Mike.

 

[Greg]

I'm not a marine guy either, so I know nothing about the additional cooling requirements that marine engines are equipt with!

 

[rholbrook]

I think its rated at 300 HP right now. When I get back home I will open it up and see what it all has in it for sure. I dont know what heads are on it but I did think about heads and a bigger cam or just a 383 swap which in hard parts cost and machine shop time I will be in it probably $1,500 to $2,000 depending on computer reflashing and misc other stuff but I will have some of that in a super charger setup as well. There will be a lot less work with a super charger. I dont want to sink a ton of money into this project because at the end of the day, its a 2004 Chapparral 230 SSI, a very clean 2004. I just need a few more ponys would make me really really like it more.