Why not use a centrifugal Supercharger?

Johnathan · **Postat:** 2006-06-12, 14:20

Why do most car manufacturers not use a centrifugal superchargers on their cars?

I was thinking about making a kit to bolt onto mine, and making it from a turbocharger unit. I really dont see why it cant be done, but why is it not done on other cars?

I think it would produce a proportional boost effect, and could be geared with the pulleys to produce peak boost at a lower rpm .. yes/no?

I realise it will not be like a normal positive displacement supercharger kit, and that it will not run set boost over the entire range, and will gradually build up.

Can this be done, has it been done??

The centrifugal superchargers use the same type of compressor impeller as a turbocharger and the faster they spin the more boost they make and it is not linier. If you double the speed of the compressor you quadruple the output. The problem is that they only make peak boost at the engine's redline and tend to make very little boost at lower engine speeds where they are mostly operated.

liquidvice · **Postat:** 2006-06-12, 17:10

I think that its a noise and reliability issue. Generally roots type blowers tend to need little to no maintinence and are reletivly quiet compared to centrifugal type superchargers. Just my 2c

-Greg

Johnathan · **Postat:** 2006-06-12, 17:15

No mate, thats great keep it coming.

anyone with any ideas, or suggestions, or just tell me it wont work, and why!

i would love th hear it :)

A · **Postat:** 2006-06-12, 21:24

It takes a lot of power from the engine since it is powerd by a belt from the engine so it is usually not woth it unless you are looking at a lot of power so it doesent matter if you lose some to the sc.

Brillko had a centrifugal Supercharger on his Le Mans.

Baka · **Postat:** 2006-06-12, 22:56

if you are going to have a belt/pulley system under the bonnet, its
A going to be larger than a regular type of supercharger, and
B going to have alot more moving parts...

Johnathan · **Postat:** 2006-06-12, 23:48

So in effect, if you were going to make your own from a Turbocharger unit it would not be worth it unless you had a big enough turbo?

Thats actually the only decent argument i have had for not using the turbo i had in mind! It still seems like a very good project though, especially if you could get it geared correctly with a big enough blower

cheers for that guys!

Baka · **Postat:** 2006-06-13, 00:05

to be honest. it probobly is feasible. but you have to think large, larger or largest.

would probobly be big enough

*joking*

Johnathan · **Postat:** 2006-06-13, 09:27

hehe :)

I think the plan i had would work. With my turbo (T3), it would give me enough boost to make a difference to my small 2.0 engine, if not just make it run with a little bit more get up and go.

Taking the back of the turbo off (the exhaust side), and placing a single pulley on it was my plan, but i think this would create an adverse load when tensioning the belt to a level where it would provide enough torque to run the newly made supercharger bodge up.

This is something i will try at a later date i think, but maybe on a bigger engine, with a bigger turbo.

SaabJohan · **Postat:** 2006-07-20, 06:56

A centrifugal compressor is lighter and more efficient than a roots blower, probably more reliable too. The centrifugal compressor was the most common supercharger on for example military piston aviation engines because of those reasons. Usually they were gear driven from the crankshaft and had one or two stages.

The problem with the centrifugal compressor in cars is driveability. With boost increasing with supercharger speed it makes it very difficult to produce a suitable torque curve. Take the BRM V16 engine as an example. To use different gear ratios is in most cases very difficult, it's easier to go with a different supercharger type instead.

A compressorwheel from a turbocharger is in general unsuitable as a mechanical supercharger, they are designed for higher speeds. What you need is a larger compressor wheel designed to operate at lower speeds, while the peripheral velocity of the wheel still is high. Boost is related to the peripheral velocity of the compressor wheel.

Johnathan · **Postat:** 2006-07-20, 09:24

Aha, now thats an answer!

Thank you :)

faj · **Postat:** 2006-07-20, 10:47

Most (all of them?) centrifugal superchargers have internal gearing, stepping up the drive ratio between the belt pulley and the compressor wheel about 1:4 times. As SaabJohan says, a turbochargers compressor wheel needs higher speeds (100.000 rpm?) than a normal centrifugal supercharger (50-60.000 rpm).

So to "build" a belt driven centrifugal supercharger from a turbocharger you would have to make the internal gearing of the unit about 1:10? I think that would make it to heavy for the belt to drive. Creating belt slippage.

Save yourself a LOT of work and time and just buy a used supercharger unit :)

Johnathan · **Postat:** 2006-07-20, 11:50

Yeah this was one of my main worries.

I had actually managed to work out that the homemade unit would be very inneficient because of this. Obviously it would take an awefull lot of time and effort to get anywhere near the gearing on the back of a normal centrifugal blower, and even then it would be wrong. Belt slippage was going to be a real pain with this, as would tensioning it!

Its a shame though, if it were not for the availability of already very good units, this would be a great project!

SaabJohan · **Postat:** 2006-07-20, 20:30

Supercharger of a Packard built Merlin.

Johnathan · **Postat:** 2006-07-20, 21:05

yeah, i think i'll leave it now :)

Thats awesome though! Merlin as in, Rolls Royce Merlin aviation stuff?

SaabJohan · **Postat:** 2006-07-21, 06:01

Citat:

Ursprungligen postat av Johnathan

yeah, i think i'll leave it now :)

Thats awesome though! Merlin as in, Rolls Royce Merlin aviation stuff?

Yes, Packard built the U.S. version of it.