M90 drive ratios

[quadcam boat]

I ran my M90 Eaton bown lexus engine and my max boost was 2.94psi!
I was hoping for 8psi.
Run the blower drive calculator off sprintex website (www.sprintex.com.au)and you just need to fill in 4 ltr engine, 7000rpm max and pick Eaton M90 from the supercharger list. I played around with the Boost required figure and found out the following

Drive ratio required to get 55kpa (8psi) = is 1.92

Drive ratio is 1.7 with the current pulleys I am running, so I played around with the boost required figure and found out that 37kpa (5.4psi) should be produced at a drive ratio of 1.7 It also says to increase boost or max RPM.

Thinking about that, the blower probably isn’t spinning fast enough and is operating inefficiently at the current low speed. That probably explains why the boost is lower than works out on the boost calculator, because the blower is spinning too slow and has too much leakage around the rotors at this speed. I don’t think to blower drive calculator takes this into account.

The difference between the 2 calculated pulleys is --

73mm diameter for 8psi

82mm diameter (current pulley) for theoretical 5.4psi which is 3psi actually.

THis is working on the drive pulley being 140mm (all pulleys measured on the outside of the grooves)

That’s bugger all difference for a huge effect!!!

Anyway will get one made with a drive ratio of 2.

Hope this info helps others doing the same thing.
Cheers,
Andrew

 

[Lextreme II]

Boat,

There are couple of things that will cause a drop in boost.

1. High flow exhaust system like headers, cats, pipes and mufflers
2. Decompression.

I would go to about 2.62" to get about 8-9 psi.

 

[quadcam boat]

If I used that size pulley and ended uP with a drive ratio of 2.1, I would have to rev limit it at 6650RPM or the blower would overspeed. Also, I'm a bit worried about belt slippage.
Cheers,
Andrew

 

[quadcam boat]

O.K. Lextreme, you win. I am getting a 70mm and a 62mm pulley made tommorow. On the blower calc, 62mm will give me 2.25 drive ratio with 6235RMP redline. Oh, thats at 11.9LBS!!
I don't really think thats practical, I'm going to start with the 70mm pulley which gives me drive ratio of 2 with 7000RPM redline. 9PSI.
I am making an interchangable pulley hub and got the 2 idler pulleys off the shelf at REPCO. We are going to machine the middle out of them to fit the hub. I ended up with the 62mm one because there was one sitting on the shelf. . May have to get a custom made one to get something in between if required. A mate of mine is going to do it for me after work.
Also found a really helpfull guy in Australia who does custom pulleys for Eatons. Had a good talk to him yesterday and got lots of advice. He offers a exchange service where you send your front housing to him and he will press whatever size pulley you want on. Or he can make interchangable hub setups if you want. Also can supply different length snouts can rebuild Eatons and supply parts. Phone Matt on 043 8756782 Excellent prices.