8 replies to this topic

[smith1380gt]

As the title says, has anyone tried the 15% reduced size SC pulley on an Eaton M45 supercharged A series?
Results? Problems?

I just bought one off Ebay for a little more boost... 6500 RPM engine speed will give just under 14000 RPM on
the charger. I'm just a little concerned about the extra heat, etc, but need that extra power.

[Sammy D]

The M45 is only any good for 10 psi max really, the pulley probably wont make that much difference at all apart from just generally more boost constantly on tap lower down the revs. Just remember that with a charger the boost is constantly "on" as it runs with the engine speed, unlike a turbo.

It'll confuse your tuning too, you'll have to richen it up a bit more and most likely mess around with the timing, so bear that in mind

[Wil_h]

At that RPM the M45 will be pumping enough air for 200bhp on a 1275.

But don't get too excited, you'll be using around 30 of that to drive the SC, you'll have an 80 deg celsius rise in temperature above ambient minium, but I suspect a lot more as your psi will rise massively.

I wouldn't put it on.

If you NEED more power, bin the SC and buy a turbo

[smith1380gt]

I worked out the pulley size against the one on the SC currently...

My crank pulley is 4.5", SC pulley is 2.5 6500 RPM engine speed = 11700 RPM SC speed
Same crank pulley with SC pulley at 2.125" 6500 RPM engine speed = 13764 RPM SC speed

Assuming (don't know for sure) 8 psi currently as a guestimate, the difference in RPM only brings boost up to 9.4 psi

Is that really enough to be a big problem? I currently don't have much of a heat issue, NO detonation despite running
a decent amount of advance. I expect to change needles again, and maybe dial the timing back a little.

[Wil_h]

Just done some more calculations. I've had to make some assumptions as it seems you are pumping more air than needed if it's only 8psi, but I might be missing something. But even so, the calculation is a comparison, so the absolute values aren't that important.

So, taking into account the increase in inlet charge temperature and increase in load on the engine, an increase to 10psi by increasing the SC speed will give you a net loss of 2 bhp.

In fact, my calculations predict a rise of 15bhp, by decreasing the SC speed to around 9000rpm.

To be honest, I have never done these calcs before, all my maths is based on turbos, and I've just adapted it for SCs, but it is interesting. What I think I'm missing is the relationship between, SC speed, flow and psi. how have you calculated the increase? and what is you guess of 8psi based on?


If it was me I'd get a couple of pulleys and get to an RR to find out for sure, probably not that easy though.

[smith1380gt]

Just done some more calculations. I've had to make some assumptions as it seems you are pumping more air than needed if it's only 8psi, but I might be missing something. But even so, the calculation is a comparison, so the absolute values aren't that important.

So, taking into account the increase in inlet charge temperature and increase in load on the engine, an increase to 10psi by increasing the SC speed will give you a net loss of 2 bhp.

In fact, my calculations predict a rise of 15bhp, by decreasing the SC speed to around 9000rpm.

To be honest, I have never done these calcs before, all my maths is based on turbos, and I've just adapted it for SCs, but it is interesting. What I think I'm missing is the relationship between, SC speed, flow and psi. how have you calculated the increase? and what is you guess of 8psi based on?


If it was me I'd get a couple of pulleys and get to an RR to find out for sure, probably not that easy though.

My estimate of 8 psi is based on a discussion with Stuart Guerr @ VMAX based on my standard Metro cam and pulley sizes. Assuming PSI is directly proportional to speed of the Supercharger if 11700 = 8 psi, then 13764 = 9.4 Moreover, if you take the manufacturer's word for it, the pulley is 15% smaller than stock, 15% of 8 PSI = 1.2 PSI, so you get 9.2 psi that way. I've also been told that the Eaton M45 is OK if kept below 14000 RPM.
If heat really becomes an issue, I've considered water injection. I've used it quite effectively on an MR2 Turbo in the past.

[Wil_h]

I've done a bit more digging and educated myself a bit. Using the Map on the Eton website, it still shows that for 8 psi you only need to spin the thing upto 9000rpm, at 11700 rpm you'll be running around 15psi.

[nurseholliday]

The big power MINI boys are using 15, 17, and 19% reducer pulleys with no problems. What you will need is an intercooler capable of cooling the air enough if you are going smaller than 15%. There should be absolutely no problems with the supercharger's reliability with a 15% reducer pulley.

[Wil_h]

The big power MINI boys are using 15, 17, and 19% reducer pulleys with no problems. What you will need is an intercooler capable of cooling the air enough if you are going smaller than 15%. There should be absolutely no problems with the supercharger's reliability with a 15% reducer pulley.

The problem is the MINI boys don't have 1300cc 8 valve engines, they have modern 16v 1600cc engines, so they have to run it faster to pump the necessary air, but at a lower psi.

An intercooler is a great idea, but unless you are running blowthrough, or injection, it's not really possible.