Sizing Superchargers for the A series. All the books and the web talk about correctly matching a supercharger to the engine. Yet I am unable to find anywhere how you do it. Is it based on engine displacement or cylinder head flow or just what will fit under the bonnet?

So far I have seen on an A Series
Autorotor or Link kit (40cc of air per rotation) using a Lystrom supercharger

SC12 kits and SC14 chargers positive displacement roots-type superchargers fitted to the 4A-GZE. See here:
http://autospeed.com/cms/title_The-4AGE-Guide/A_2733/article.html

The Bini Eaton M45 superchargers. When fitted to the Bini
It turns 2.06 times engine speed, (which works out to 14317 rpm at the 6950 rpm rev limiter.) Done by a number of tuners such as VMAX, SC Components and others.

Costs aside, Which one is best for A series 1275?

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1970 Mini Deluxe - 1275, Weber, Clive 346 cam, MS 4-pot slotted discs, Megajolt ignition Now with new improved Mambas... almost on the road
1966 Van with Traveller rear seat conversion
2008 Prado GXL
All in various states of repair...

For positive displacement it is really easy:

Step 1 work out the displacement of your engine eg 1.275 l

Step 2 find out the displacement of your supercharger eg 0.6 l per rev

Step 3 Decide how much boost you want say 7 pound (= 0.5 bar)

Step 4 work out speed ratio:
To get 7 pounds your charger needs to flow 1.5 x the amount of air your engine does. Remember your engine is a 4 stroke so it pumps 1.275 l per 2 revolutions, or 0.6375 l per rev. So, 1.5x0.6375 = 0.95625 is what the SC must put out per crank rev. Divide this by SC capacity 0.95623 / 0.6 = 1.59. This means the speed ratio you need is 1.59.

Step 4 Check for over-revving.
Peak engine speed = 6500 rpm say. Drive ratio = 1.59. So SC speed = 10335. Check that this is less than peak speed.

Shazam. You're done.

You can get the Eaton M45 data from the web. That's what is on a BINI.

EDIT: Flow ratios: 7 lb = 1/2 and atmosphere = 0.5 Bar over the top of the 14 pounts of 1 atmosphere that is at sea level.
If you want 14 lb of boost you need 2 atmospheres so a flow ratio of 2. etc.


M

An M45 is a big and heavy charger for a 1300. It is perfect for a 1600. It is out of it's peak efficiency on an 1800.

M45, SC12 and SC14 are not very efficient so they heat up the air too much for how much boost they make. But Meh... I've got an M45 on my MX-5 and it gives 35% more power from idle to red line at just 5 lb of boost without an intercooler.

Newer Eatons are much more efficient but they are only available in the BIG sizes so far. Great for your Walkinshaw Commodore but not your mini just yet.

Screw compressors are more efficient than these simple Roots types but $$.

I reckon an SC12 is the right cost, weight and displacement for most minis. Adding the availability of Ben's kit and why bother with anything else??

M

I know these things have a peak operating speed but do they have a recomended operating speed?

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1970 Mini Deluxe - 1275, Weber, Clive 346 cam, MS 4-pot slotted discs, Megajolt ignition Now with new improved Mambas... almost on the road
1966 Van with Traveller rear seat conversion
2008 Prado GXL
All in various states of repair...

If you look at the performance curve for an M45 you'll see there is a speed at which it runs at peak efficiency (speed and boost). You should aim for there but really, as long as you don't overspeed it, and you won't on a 1300, you're laughing.

If anyone is interested in web hosting it, I have an Excel sheet with all the correct calculations in it so you can just plumb in your capacities etc and it will give you the projected boost (based on 100% volumetric efficiency) and pulley sizes, CFM etc.

It's just a basic little equation but we use it all the time for working stuff out on the burnout car.

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-Wasabi
1972 Clubman - Daily Driver
1962 850 - EW1 Powered

theres also the amr300 and amr500 chargers that would work

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1962 850,Frog