Well after the 357 swap has been completed, I'm looking to start giving it a little extra kick. Don't have many details about the engine itself, but I can say that it has a 10:1 comp ratio. The old TBI from the 305 needs to come off now, and I want to go carb'ed with it. A nice roots blower seems like a nice way for me to go as well. My question to you guys is, What blower would I need to look at? Would I absolutely have to lower the comp ratio? What size carb would be needed? What would the hood clearance look like, what size hood would be needed. Money is not too much of a problem, but I would like to keep the costs reasonable. I will ask about switching from TBI to Carb on the Carb board. Any help and other information you can give that I missed is greatly appreciated. Thanks for your time.

-Russell-

 

A motor with a high compression ratio can be supercharged but requires a high octane fuel to keep
it from detonation. Methanol comes to mind ....
Intercooling will help. Allows more power/compression/ boost/ timing for the available fuel.

Water/ alcohol injection will again allow more boost/power within the available fuel.

You could install the supercharger and restrict the boost
to about 3PSi for street use on pump gas with 10:1 cr.
Then change drive pulleys ( boost) and run racing gas for
use at the track where you can make use of the extra power. 110 octane would allow 10+PSI boost and lots of power.

But for all practial purposes a non-intercooled supercharged motor
that runs on street pump gas needs to have a low(er) compression ratio. Somewhere around 7.5:1 /8.5:1 is the most practical overall. Allows more boost which make smore power than say a 9:1+ motor.

You could replace the cylinder heads with ones with larger combustion chambers to lower the compression ratio. If you have restrictive low performance heads now
(TBI swirl port) it is highly recommended.
On a 350 flat top pistoned motor you want a head with about 80cc's.
Stock 487x casting from a 70's 350-400small block fit the bill. other 76cc 350heads can be opened up a bit with a die grinder (deshrouding) to 80cc's too.
These heads will respond nicely to porting and larger valves simular to my famed 305 heads, but with low compression. Casting #441(X),336,414,920, come to mind. Avoid late light weight casting like 624 and 882.
If your budget allows:
Dart, Protopline, World products all make good high perf head available with larger 72/76cc chambers that also can be enlarged.
The better the head the better the power.

The other alternative is to install dished pistons.
Forged pistons are available and recomended for high boost. As are larger top ring clearances.

What cylinder heads are on the motor now? (casting number) {under the valve cover}

 

Cylinder heads are whatever came on a stock 350 from a 91 GM truck I am assuming. As for the heads, they would be stock too I am guessing. I can get dished pistons if needed, keeping it at a high compression is not a big deal, I am just trying to stay at a reasonable cost. Currently the pistons are forged flat tops I believe. Heads can be replaced just as easy, too. This will just be for a nice high performance street rod, keeping in mind decent gas mileage. From what youre saying, I do not need an intercooler with a lower comp ratio, correct? Also I have a serpentine belt setup. Would a weiand 142 work with my engine? Again, all comments are greatly appreciated.

-Russell-

 

Yes a low(er) compression ratio allows you to run significant boost without intercooling.
Its the easiest, most practical method for a street blower motor.

I would go with the cylinder head swap route and kill two birds with one stone. Lower compression and improved breathing.

I would go with an after market high performance large chamber head. Like a set of 200ccport 72cc protopline or Dart cast or aluminum heads. You could easily open up the chambers a bit to get the cr just right.

Yes a Weiand 142cc street blower can be intergrated into the serpentine belt drive system.
There is someone on this board that has done just that on his third Gen. You'll have to do a search.

A holley 3310 750 or a Edelbrock 750cfm carb will work well for a Weiand blower.
Secondary jetting can be increased a few jet sizes
and the accelerator pump will need tweeking for the blower. A high-output hi-flow fuel system (pump+fuel lines) is nessessary.
A Blower friendly Crane HMV 278-2 cam will enhance the blowers performance a provide easy street performance.
278-290-222-234@.050-.467"-.494" 114LSA

A combination of 8.5:1 compression or less and 8psi boost is a good setup for a street car.

From one Russell to another, good luck.

 

Thanks for all the help so far, you have no idea how much less stressful you are making this for me. Few more questions however. What size pump would you reccomend stepping up to? Should I keep the current pistons and go with only the heads? Thats all I have for now. I hope to start throwing out some pics soon. Thanks for all your help, Russell

-Russell-

 

If you now have high perf flat top pistons (hypereutectic or forged) in good condition then I would go with the head swap. Like I said you'll kill two birds with one stone. ( compression ratio and breathing ability) Blower motors like good cylinder heads. Good bang for the $$$.

If you build the motor just as I outlined with the cam and heads and 8psi boost you'll be making 460 to 490 bhp.
You'll need a fuel system that can provide a constant 50 gallons/Hour at 6PSI to the carb.

Any good 110GPH+ rated fuel pump (mechanical or electric or a combination) fed through a 3/8" - 1/2" fuel line will do the job.

Holley , Carter, Barry Grant are brands that come to mind. Edelbrock has some new stuff out too.

This is a very good mild/ moderate street blower combo.
you'll like it.

 

F-bird, I tried to send you a PM, but you are not accepting. I was wondering if it is ok to send a message to your e-mail box?

-Russell-

 

Here is some good info and charts http://www.holley.com/HiOctn/TechSer...fo/SCTech.html

 

Sure,,, would rather get an email than a PM

russ_q@hotmail.com