What is the difference between porting the blower, and overdriving it?

sizemoremk

Registered User
I was curious what the difference is in having the blower ported, vs running a smaller pulley?

Does the ported blower run any cooler?

My understanding is that the 94/95 blower was opened up, and created more boost, meaning that a larger pulley is required for the same ammount of boost. (ignoring the teflon rotors for this discussion)

I'm just curous what the benifit of porting vs 5% or 10% pulley is...

Is it that the ported blower has less drag on the engine than the early model, giving more boost, and more power from less drag?

If I was to port an early model blower/inlet plenum, and use the same stock pulley, would that give me more boost, or just less drag on motor, or both?


Thanks guys!
 
Well I'm no big city lawyer, but basically here is the short of it.

Porting the blower in many cases is to either smooth out the insides of blower so there is less friction and the air should move with better velocity. Sometimes you would port something if you want it bigger. In the case of the SC blower outside of the inlet and outlet I don't know if there is much to port. Some of the experienced guys I'm sure can talk more about that. As far as the 94/95 Supercharger my reading on here seems to point to the fact that the 94/95 blower has a bigger pulley, teflon coated rotors and a bigger opening on the intake of the blower.

Putting on an overdrive pulley is simply putting on a smaller pulley that allows the blower to spin faster which in turn helps generate more boost. The downside to this is more heat. What I plan to do after exhaust is to get a pulley from a 89-93 SC and use that as that gives roughly a 5% boost to the newer blowers and likely install an intercooler fan to help with the heat.

Ultimately they are pretty different approaches. If you want the easiest way to gain some power I'd suggest the pulley as it's far easier and typically cheaper to do that than have anything ported (unless you know how yourself).
 
I agree with what Cowtown said. I'll only add that on an M-90 most of the gains from porting come from increasing the size and position of the inlet. The late model m-90 has a larger opening and is positioned a little higher. The MPII reworked M-90 case takes it one step further making the opening a little bigger still and raising it a bit more (requires an MP plenum).

Depending on how much air your motor wants/needs, you may need porting and overdriving. Usually overdriving the blower too much will give you more bottom end torque but at the expense of top end HP. A ported blower flows more air at the same rpms and boost level. Keep in mind that higher boost doesn't always mean more air. Since air expands when heated the boost can be higher and there can still be less oxygen getting into the cylinders because hot air is less dense.

David
 
So porting it for moire air would likely be more efficient than spinning it faster.

But are you saying that porting it doesn't create more boost?
 
sizemoremk said:
So porting it for moire air would likely be more efficient than spinning it faster.

But are you saying that porting it doesn't create more boost?


Yes porting the blower is more efficent than overdriving it.

Porting the blower may or may not create more boost at a given rpm. It really depends on your heads, cam and exhaust system. Similarly it won't help much to run a ported blower and choke it with a stock TB and MAF.

On my car I was running a heavily ported early model blower with matching plenum made by ESM. I had ported heads, MP FMIC, 75mm TB, 76mm MAF a big cam and 50# injectors and every other bolt on you can imagine. I was overdriving it about 23% and making about 319 rwhp.

I switched nothing but the ESM case and plenum to an MPII case with the MP plenum, and the car gained 50 rwhp and 70 rwtq spinning it the same speed and making the same boost. How ??....I'm assuming a cooler more oxygen dense intake charge and less power pulled from the crank to turn the blower.

David
 
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