Wow... i am shocked by how pompus that was! I apologize for not comprehending your post. Obviously it wasn't all that CLEAR. And perhaps that is why i mentioned that a 19% is a different story.

 

That perhaps turbos do better at higher boost levels than positive-displacement superchargers?

 

the interest is the ratio of drive to driven pulley, transmitted by the belt.
if the drive pulley turns 360 degrees, this means the belt moves a length equal to the circumference of (pi)x(dia1+.200). The ratio of degrees turned by the pulleys is then (dia1+.200)/(dia2+.200)

(I should have used (dia+.200), or (rad+.100), not (dia+.100) in the earlier post)

 

depends on the compressor wheel, exhaust housing, and engine displacement... turbos are quite complicated... however... being that it is a factory application im sure that all of these factors are optimized for that particular car and boost.

 

I understand the belt issue but it's just not that simple in reality. All that matters is the speed that one pulley's shaft turns relative to the other. Keep in mind that a 15% pulley from manufacturer X is different than Y which is different than Z. Same goes for crank pulleys. Belts are just as different (stock, NAPA, Goodyear). What you can do is note the boost made in different configurations and get a good idea of what combinations do what.

 

Originally posted by Andy.


#17
12-02-2004, 01:08 PM
andy@ross-tech.com vbmenu_register("postmenu_432405", true);
6th Gear
Join Date: Oct 2002
Location: Lansdale, PA
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Here's an interesting little snippet from the Bosch Automotive Handbook about pulleys. For a standard 6-rib DIN 7687, the effective diameter is the diameter of the pulley peaks plus 3.2 mm (0.126" for you sliderule types ). This of course applies to both the drive and the driven pulleys.

So, stock:

(5.460+0.126)/(2.58+0.126)=
5.586/2.706 = 2.06

This matches up nicely with the MINI tech documents.
__________________

 

i disagree; you do need to incorporate the belt to calculate the exact ratio

 

That would reflect how efficient that particular design is which is not a reflection of the base design differences.
Centrifugal superchargers/ turbos being compressors are more thermally efficient.

I'm assuming that was Scott's implication.

 

absolutly they are more efficent without a doubt! however, mismatched pieces can yeild inefficantcy just like a supercharger... taking an m45 and spinning it too fast will cause excess heat and it will become inefficent... same with a turbo...

also many people think that 15psi out of one turbo and 15psi out of another = the same power.... that is not true... but i don't want to hijack this thread anymore than what has already taken place.

 

That, and the fact that the added heat from a positive-displacement supercharger makes them pretty much self-defeating once the boost gets into the high teens.

To claim that 14-16 psig of boost on top of an 8.3:1 static compression should be no problem at all for a Roots-type supercharger is misleading at best. Those numbers may be easy for a centrifugal supercharger or a turbo, but they're getting close to the limit for a Roots-type blower.

Scott

 

rpm and size is what determines efficency

 

True, but since there are only a limited range of supercharger sizes that will work with any particular engine, you don't always have the option of putting on a much bigger blower to reduce the rpm significantly. (In other words, if you have a small-block Chevy with a Roots 6-71 blower, and you're getting excessive intake heating, you can't simply replace the 6-71 with a 14-71 to reduce the rpm without running into other problems.)

I stand by my original statement - 15 psig of boost from a roots blower with a static CR of 8.3:1 is *not* trivially easy, as some have stated.

Scott

 

As you should stand by your original statement. your argument/point (or whatever is e-friendly) is true... you can't just bolt a 1271 on a MINI thats for sure! But i guess i just get sensitive to blanket statements because i just don't want people to be misled in basic knowledge. There is a whole world of cars out there and i throughly enjoy them all! Anyways, yes the supercharger choices are very limited for the MINI cooper.

 

The belt is designed to run on the outside circumference of the pulley. If you figure the low part of the groove, the belt rides about 1/8" above the lowest point but that realy does not effect the interference where the belt rides on the pulley ( it does not run on the inside ). The ratio can only be outside C to C.

 

this whole thread just made me realize the importance of math in tuning cars 0_o

 

All, this thread is an extraction from the "Works GP Intercooler upgrade" thread. I did this in order to "clean up" the other thread so it remains on-topic.

I want to make it clear that dmh did not actually start this thread, but his post was the first one I pulled into the new thread, so it appears that he did.

Yes, I know these are old posts, but they should have been separate a long time ago.

 

It's good info thanks for breaking it out and giving it the bump!

 

Ok so I have read all these posts and I am getting more and more confused the further into the thread I got.:impatient

Question:
I am running Alt 17% and Alta 2%. I am in the SF Bay Area. Is anything negative going to happen? I do not and am not going to track my car.

 

Mini Tyler-

Its very difficult to ask that type of question here. Few will come out an tell you that you're not going to hurt something, when in fact, you might. The only reliable response you can pull from is listening to others experiences with similar setups.

That said, in my opinion, as long as you're not tracking the car or keeping it in the high rev's for extended periods, you should be fine.

enjoy.

 

Thanks for the info, I can sleep better now.