Superchargers vs Turbochargers.

[kneegrow]

Having been fed a diet of tuning books to make up my own mind about forced induction. I settled on supercharging as a method of going for about 150hp from my old mini. I plan to go the route off a 750ml pass Eaton M45 blower. Not being a big fan of lag (after all minis are about going around corners really fast, I don't really want the boost to kick in half way around the corner), I felt at home with my choice to not go for a turbo.

However, I have been made aware that turbo developments have come a long way since my books were published. How far can we overcome the lag?

I was looking at the supercharger figures and it takes 30hp to produce 10psi at 6000 RPM. Basically, this sort of means that I could have more with a turbo.

Lets have a good debate about the latest of both technologies and see which is the best for each purpose.

[kneegrow]

What I am going to do myself is to run a stock MG Metro non-turbo engine with turned pistons and scooped out chambers, about 8:1 CR, open the ports right out, use a 260 inlet 285 exhaust cam, standard valve sizes, high lift rockers. Looking like having a suck through setup....due to space.

Antilag looks like a bad thing. Rally cars get rebuilt regularly. Turbos seem a compromise of getting the power/lag balance right (offset by lots of gears-narrowER power band). Superchargers, from what I gather are limited at the top end, due to the power consumption associated with the resistance of the inlet tract/valve timing. I'm looking at getting as much as I can out of my engine (below 7000rpm) thus avoiding the need for EN40 crank, etc, etc.

[kneegrow]

GreenV8s,

Good info about Rootes blowers. That has got me thinking seriously. I will have another look. A T2 turbo is a good choice but unless I plan to do some pretty novel siting of everything, it ain't gonna fit. I'm not going to start sawing my bulkhead about. The volumetric efficiency dropping off is probably why the guy who sells kits uses them on serious overbores/higher compression engines.

I will have a think about the maths and see what 12PSI should get assuming I have an ultimate cyl head.

I like the idea of efficiency and a cool charge.

Thanks guys.s

Whilst you're at it, anyone know a model of screw blower roughly equal to an M45?

>> Edited by kneegrow on Friday 24th September 20:44

[kneegrow]

I went to "le pub" with my engineer mate last night. We had a chat about pressure drops, loading and heating of rootes pumps. I initially thought that it would be a good idea to fit something like an M62 instead. But, the pressure differential actually causes direct loading on the rotors. As the area would be bigger at a lower RPM (To achieve the same boost) if anything, the resistance would be bigger. Rootes blowers are not the choice for anything over pretty limp boosts. This will have a brilliant effect, but I am looking for something which I can develop without having to alter all my gubbins for.

Looking for screw blowers is very difficult. They are astronomically expensive. I saw an Autorotor one come up ages ago but I have forgotten the model number. The websites are quite scanty as to which model does what. Whipple only go down to a 1.2L pass which is too big. A Mazda Millenia has a 1L pass which at 1:1 would give scope. But, I think it has a load of crap cast with it. They are also cheaper than Bini blowers. They are a bit on the big side. I might have to go with the M45 as they are cheap and I am probably going to destroy it anyway.

How about using a Wankel motorbike engine as a supercharger? I also though, an old church organ in our village was powered by a "Supercharger" I think it was a shorrocks! (They binned it)