Supercharger Questions ?????
Turbo Mini Forums

I hope these questions are new, I have searched but without success.

Q1) All of the aftermarket supercharger kits I have seen have a new alloy bottom pulley. Now ignoring the fact that I am not convinced about alloy pulleys, none of them have harmonic dampers. From the searches I did all seem to agree a harmonic damper is required, so how does this work???

By the way for my conversion I have sourced an MPI poly vee pulley and was planning some sort of serpentine belt to drive everything but this is a pain and if a harmonic damper is not required then I will make up a pulley to suit.

Q2) What sort of boost / drive ratio combinations are people getting? Every book / web site seems to give a different formula for calculating boost vs drive ratio and for my target of 10psi I am getting anything from 1.4 to 1.9 and all points in between. So I thought I would get some real world examples and verify some of the formulas.

Have fun,

Matthew

Have a look on here, it will give you some idea of where you need to be.

http://www.rbracing-rsr.com/turbosupermaps.html

Regards
Dave

This calculator seems to give the right sort of answers:



You can select the Eaton M45

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Here's a picture of mine striped down.
I think the pulleys are ford ohc one's which give the charger a 2:1 ratio and produce just under 10 psi @ 7k engine speed

Picture never got added! selected add attachments and selected it.

http://www.turbominis.co.uk/index.php?p=20&id=3448

Link to my pics

Thanks Mini23

This confirms my thoughts, the Sprintex calculator for the Eaton M45 gives a drive ratio of 1.53 for a boost pressure of 10psi. If you actually have 10psi of boost at 2:1 then it brings into question the accuracy of the Sprintex calculator.

Out of interest the Sprintex calc gives a HP rating of about 140 how does that compare real world?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

PS Nobody has answered the forst question about harmonic dampers?

I would always use a damper. You could use the MPi pulley as you say or maybe you could fit an S type damper ring onto the alloy pulley you have in the kit?
http://www.minispares.com/Product.aspx?pid=36125

Regards
Neil

I think the figures from the Sprintex Calculator tie in pretty well with the graphs for the M45 in the link I provided above.
The 2:1 ratio at 7,000 rpm is taking the M45 right to the top of it's operating limit and is not to be reccomended in terms of best efficiency.
ie 25 HP to drive it and outlet temps very high.
If you feed sensible figures into the Sprintex spreadsheet and then transfer the figures to the eaton graphs it should give you a feel for what is happening.

Regarding the crank damper, my views on the subject are as follows:-
The damper was designed for a standard engine used in the normal Rpm range and as soom as anything is changed ie lighter flywheel , the damper will not be at it's optimum. I would not know where to begin to calculate what modifications to do to the damper to make it operate at the required rpm after the engine has been modified.
Some 998 & 1100 engines run with just a pulley and seem to last very well.
I do know a few people who have run 1275's without a damper and no problems followed.
Why can't you run with a damper and fit the pulley in front of the damper, it shouldn't be too difficult.
Regards
Dave

Beware of the Sprintex calculator as it give 0.65L per rev for the M45. Eaton themselves give 0.75L per rev.

Thierry

Mini British Open II 1275 SPI Full Stock
working on SSpi project

what is 45 cu in when converted to cc's
regards
dave

One litre equals 61.02cu ins.

So 45cu ins is 737cc

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

or 16.387cc x 45
well spotted Thigre
Regards
dave

Edited by danboy on 27th Sep, 2007.

I will have a look to unlock the tab, so I can modify the value.

Thierry

Mini British Open II 1275 SPI Full Stock
working on SSpi project

Already tried but I can't do it.
Best of luck
Regards
Dave

Ok, it's done...thanks to Google

here is the unlock file with 0.75L/rev M45 blower.

Hope it help.

Thierry

EDIT: can't attach the xls file, but i can mail it (PM) or if someone can host it...

Edited by Thigre on 27th Sep, 2007.

Mini British Open II 1275 SPI Full Stock
working on SSpi project

Here it is...

http://www.davecoxon.co.uk/Blower_Calculator.xls

Edited by turbodave16v on 28th Sep, 2007.