Quick Supercharger Question

First: what is the highest compression piston you want to run with a supercharger ?

Also does that differ from 4 cly ,6cly etc

2:By changing the pulley ratio can you gain more ? also if so,,at what point will you have gotten all your going to get out the SC ?

Thanks

 

roots type supercharger?

Roots type is called "positive displacement", because it moves a given amount of air per revolution.
What size? straight rotors? stock helix? high helix? Stripped or not stripped?

yes, the blower rpm is determined by its drive ratio.

how much air the engine can process is as important or more important than how much the blower can pack into it.

engine static compression is one part of the equation, but...what fuel, what intended use? FINAL compression ratio needs to be counted too.

 

oh just make things complicated why don'tcha

Its a small roots 4 straight vanes ,, I will assemble the details and try this again

 

Short answer: It depends.

How much boost you get depends on the relative displacements of the engine and blower, and the relative speeds they turn, plus a lot of other variables. How much boost the engine can take without detonation depends on the compression ratio, chamber design, fuel quality, plus a lot of other variables.

If you run 5-10 psi boost you should run about 8:1 compression. Maybe more, maybe less.

 

the first paragraph is right,
but don't get hung up on "boost". I would suggest that boost isn't the answer. The same blower and drive ratio on a 454 vs. a 283 will yield different amounts of boost, even if both engines are 8 to 1 compression, because the engines are able to process different amounts of air. Want more boost? Smash your headers flat!

 

Can there also be to little boost ?

 

in a manner of speaking. If you put a little Judson off a VW on a big block Chevy, likely you can't pump enough with it to create much boost. In an extreme case like this, if the engine can naturally draw more than the supercharger can push, then the supercharger actually hurts performance by becoming a flow restriction.

what engine are you thinking of "boosting", or is this a theoretical question?

 

Less than zero is too little, you don't want that.

And boost increases as rpms go up. So while you might make enough boost at higher rpms to do something, it might be too little at the bottom end and hurt performance.

A supercharger that is too small just has to work harder (spun up faster to make more boost). But, my understanding is the the faster it spins, the more heat it makes and is less efficient. There are optimum sizes for blower size to engine size and for intended use. If you want to drag race the motor wants to be at full rpms for the most part. That is different that trying to drive it on the street and needs to run well at low rpms too. Too big of a blower takes too much power just to spin it and is a big parasitic drag on the motor especially at lower rpms.

But, I am no blower expert, I just play one on the internet. So, be careful following my advice, I have learned to.

 

Less than zero is too little, you don't want that.

True.
A blower too small for the engine, or turning too slowly, actually restricts air intake rather than providing pressure.
However, if the blower produces less vacuum in the manifold than the carburetor set-up, there is more power. Whether it's more than needed to drive the blower is another question.
Then, the cross-over point is where the extra power is significantly more than the blower drag and additional weight (6-71 = boat anchor).

 

Gasoline? Alky? Nitro? Other? Street on gas probably 8-8.5 to 1. Lippy

 

FWIW- boost is MUCH easier to change than CR..................

While not the S/C you are using, Magnason did have charts showing boost vs efficiency, that should give you ballpark ideas.

Boost #'s will change with other systems (intake/exhaust)
a 'better' intake will raise boost, while a better exhaust will lower it.

 

The motor that you are putting the supercharger on will also limit how much boost that you can make.
I run a 471 on a slant six and according to the Dyers chart, a stock slant will only take 17 pounds of boost. In other words, that is all you can physically stuff in this motor with this blower. Put the same blower on a small block and the numbers will change.
Robert

 

i built a 406 with a 6-71`30% overdrive 13:1 compression pistons on alky it all relative depending what your doing

 

good good,,wondered about that as well,,thanks