Supercharger pulley dimension.
Turbo Mini Forums

Ok here we go again.

As posted some time ago I am building a M45 on a 1293 engine.
I thought I could do 14ish psi but I was adviced that 10ish would be more sensible. ( And that saves me a lot of grinding out of the combustion chambers :) )

Now I did some calculating which I would like to run past you people for some advice.

This calculation was done according to a formula I found on the net.

To achieve 10psi (lets say 0,7Bar) I need,
(1293/2)x0,7= 452,55cc extra volume
This added to the volume/crankturn totals (1293/2)+452,55=1099,05cc
To get this volume from a M45 (750cc/turn) compared to the crank turn, the ratio will be 1099,05/750=1,46

So when the diameter of the (Mpi) pulley is 113mm the diameter of the pulley on the SC should be 113/1,46=77mm

Now this all makes sence to me however this all is pure theoretical; are the cylinders filled for 100%?
I am using an MG metro cam which has an 45 degrees overlap during which the air pushed in through the inlet valve directly out the exhaust valve... Or is this also highly theoretical and is this inreality negligible?

Your (more experienced) help is appreciated...

Thanks in advance!
Rgrds, Han

Dazed and Confused....

http://www.amazon.co.uk/AUTOMOTIVE-SUPERCH...18988208&sr=8-1

That's the book I rate the highest. Expensive but worth every penny. It's a theory book, not an advertiser of gimmicks.

As they say, you want to create flow, not boost. Essentially, you spin the blower to displace a given amount of air and then use it to overfill the cylinders at a given rev range. The residual pressure in the inlet manifold will be proportional to the amount being allowed to flow, which is dependent on the same factors as an N/A engine.

I personally think that Bini blowers don't like high pressure ratios, so try and get the most out of it by higher revs/longer cams. Have a look at the compressor map for an M45. You realise that they aren't high performance things.

The MG cam is a fine item as (in my opinion) you want to keep the overlap down a fair bit but allow increased exhaust flow. Hence why all the best cams (Kent, MG, Ph2) all have longer exhausts.

I assume you are going for the conventional placement for the blower?

For road cams, at highish operating revs at normalish boosts, you'll see near enough the boost you calculated with your pulley ratios, which are about right.

The cylinders are overfilled, which is why you get more than the best hp/L of a N/A engine.

I'd say at higher pressures you might get a bit of a pass with the MG overlap but it will offset any emissions by having less time sucking and will keep oil the right side of the valve seals/rings.

Looking at the chart, the max you want to go for is about 12PSI across the rotors before things get stupidly hot.

Bugger off, I'm getting there.

Thanks very much for the reply Hedgemonkey.

Maybe I should have added that I am using a blowthrough application with intercooler (Cosworth) and programmable ignition.
It will be setup on a dyno.

I'm not looking for the maximum HP that I can squize out of a 1293cc, this is more of a 'can I built it project' (yes I'm an engineer ) in a mini that is used for weekend drives.
Rev's won't be high, I think I will set rev-limiter to 6000rpm but will not go there much (probably never at all except for dyno)

I'm planning to make CR 9:1

Thanks again for your reply.

Dazed and Confused....

Interesting. I'd be interested in seeing how you bracket it up and compare that to mine (in bits again). I'm assuming you're rigging it OO and removing a bit of the bonnet catch panel. You need to take out about 8mm IIRC.

Bugger off, I'm getting there.

Dont worry about blowing the intake charge out the exhaust. That theory is over-exaggerated.

All it will do is make you use a little more fuel, unless it is a massive cam.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Ok, perfect, so a pulley sized 75mm will give about 10+ psi.

Actually my setup is more like the jonspeed/vmax; same location but the charger is rotated 90 degrees so push side is facing rear.
From there a tube will be running to the front to the intercooler, located next to altenator. This is possible because dizzy is replaced by programmable ignition. Then to HIF6 carb (I need to rebuild) up and over brake servo back to the head....

Sorry but I don't get the abreviations OO and IIRC..

Not there yet by far, but getting there (slowely, because 3 weeks ago our beautiful baby girl bas born!).. :)

Send me an email, I can send some pictures also curious to see what you built.
han_vr@hotmail.com

Cheers,
Han

Dazed and Confused....