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Sun Oct 13, 2013 3:00 pm

...am I right in thinking that a slightly bigger charger that can be spun a bit slower will produce less charge heat than a smaller faster spinning one?

thanks in advance!

Sun Oct 13, 2013 3:11 pm

not necessarily. At low speeds there is more % leakage, while at high speeds there is more turbulence. what is the best place to be? Probably where it was designed to operate, ask the manufacturer or stay similar to the original application

Sun Oct 13, 2013 3:54 pm

Compressing air makes heat, it's the ideal gas law in action. Making the blower larger only forces more air into the engine, making more heat (more air forced into the same size space=higher pressure and therefore more heat). Slowing it down defeats the purpose, and you've effectively taken one step forward and one step back to gain nothing- or possibly having an even worse system than you started out with due to leakage, ect. I'm assuming you mean Roots style compressors. If you want more efficiency (less heat), you're looking for either a screw type compressor ($$$), or a centrifugal compressor like a turbocharger. That, or remove the heat before it enters the engine, AKA intercooling.

Sun Oct 13, 2013 11:34 pm

hmmm.... yeah I thought you might say that.

I am looking at the difference in using an amr300 or an amr500.

300cc per rev and 500cc per rev respectively.

the amr300 would be spinning 3:1 to get enough boost...
the amr500 less obviously.

just figured it might make a bit of a difference.

Mon Oct 14, 2013 12:51 am

yeah, the 300 is clearly too small, it's for a tiny 600cc engine! like I said use similar to the application if you have no specs.

Mon Oct 14, 2013 1:10 am

people have the amr300 on a 36hp with great success... you can spin them really fast... but I think the amr500 will be a better route.

thanks for the input.

Mon Oct 14, 2013 7:14 am

Those things are dinky, you'd be much better off with an Eaton M45 honestly.

Mon Oct 14, 2013 2:02 pm

I have an AMR 500 supercharger in my 181. (stock 1600 DP with mexican EFI running megasquirt)

I also have a mini copper S as a daily so I have a bit of experience with superchargers.

A supercharger should be run in the rpm range it is designed for, especially if it is a roots charger. All roots chargers have some blowby and at low rpm@s are quite inefficient.

The amr 500 is plenty big for a 1600 and can even be used on a 1915. Remember that an aircooled vw engine has quite lower volumetric efficiency compared to the small japanese engines the chargers came from. Use this calculator in order to see how the charger will perform.

http://performancetrends.com/Calculators/Superchar...ulator.php

I use 70% for volumetric efficiency for the vw engine. 80% for the efficiency of the charger. 500 ml for the displacement of the amr 500. 1600 cc for the displacement of the engine. 14.7psi for the barometric pressure. The max rpm for the amr 500 is 16500 rpm and with a redline of 5500rpm, the max ratio it can be driven is 3. plug all that in the calculator and you get almost 25 psi!
The amr 500 is plenty big for a 1600. Even with a 1915 you can get up to 16 psi of boost with a drive ratio of 3.

As for the heat, a roots charger is a simple pump. All the compression is happening at the manifold. In my opinion a big charger underdriven and a small charger overdriven at the same boost pressure will produce the same heat. Best ways to deal with heat is a chargecooler og water-meth injection.