The V8 Owners Forum -

Hi,
I've tried searching through old posts looking for info on centrifugal superchargers installs but they seem to mostly concentrate on roots type superchargers which are a very different animal from centrifugal superchargers!
I have a 4.6 rover V8 and a centrifugal supercharger (procharger C1) and i've been thinking about boost limits and expected power outputs.
I have fully mappable fuel and timing using megasquirt, knock sensor, widband lambda sensor, large air to air intercooler, piper 270 cam (not the regular 270. The V846BP270 for non dizzy engines. Less overlap) ARP head studs. It will be in a Dax Rush (700Kg) used for weekend blasts, 1/4 miles and the odd track day.
The only thing is my compression ration is 9.5:1. (as measured) The head and block have been skimmed after a full re-build using top hat liners.
I know idearly i'd have a lower compression ration but that is what I have to work with! There could be a possibility of buying low comp standard pistons but that would be a right pain and expense, BUT as the engine is still on the engine stand NOW would be the time to change if required?
As long as I stay away from detonation what would limit the max boost/ power could I expect? I wont be extending the RPM limit.
My biggest question would be how much more power would I get going to the lower comp pistons from the 9.5:1 that i'm currently at, is it worth the expense/ hassle?
There are lots of max PSI figures flying about but these all seem to be with roots blowers which are rather less efficient.
Any thought/ ideas/ opinions and recomendations would be very much appriciated.
Tom.

Welcome to the forum!

A centrifugal is basically just a crank driven turbocharger so I assume you want to look at a good turbo set up interms of engine setup. Obviously pulley ratios etc will depend on the compressor map.

Rovercraft did a 700 lb.ft 4.6 Rover so 400+ should be fairly obtainable. I am sure some of the guys with turbo rover experience will be able to point you in the right direction.

9-10 psi would be realistic.

Boosted LS1 wrote:9-10 psi would be realistic.

mmmmmm thats handy to know

Boosted LS1 wrote:9-10 psi would be realistic.

That seems a little low...

We used to run 15psi on a 12:1 compression supercharged bike engine. That was with a Lysholm which isnt too far off a centrifugal in terms of efficency I seem to remember.

^ bet you had a tiny bore diameter.

SuperV8 wrote:Hi,

As long as I stay away from detonation what would limit the max boost/ power could I expect? Tom.

Cylinder pressures or charge temps imo. When they get to high you'll detonate.

What head gaskets are you using? You may be able to lower the compression ratio a bit there...

I'm running 9-10 psi into a standard small block chevy, although with ally heads running 9.25:1 compression.
I have switchable maps on the megasquirt which pulls out a little more timing when under boost, I use this on hot days or when using standard fuel.
They say you should pull 1 to 1.5 degrees of timing per pound of boost.

I go from 36' to 25' @ 150KPa for my high octane map 36' to 18' for my normal octane map which is about 1.8' per psi.

I do sometimes get a little tinkling on the high octane map, looking at the figures I assume i need to get down to about 23 ish @ 150kpa.

topcatproduction wrote:What head gaskets are you using? You may be able to lower the compression ratio a bit there...

I never think that's a good idea though as you'll lose both squish and quench so off boost the engine will be a bit more inefficient. That said lots of people do use thicker gaskets and get along fine. Better to keep the gaskets and add intercooling or water injection?

Yep water injection is always an option, not silly expensive or involved either is it?

topcatproduction wrote:Yep water injection is always an option, not silly expensive or involved either is it?

You can usually get kits for a few hundred quid. Trouble is you have to keep filling up a tank of water!

Intercooling would probably be more sensible... plus the plumbing with a centrifugal isnt too difficult. Though having said that... the air temp rise on a centrifugal wouldnt be that high would it as its not a positive displacement pump?

If Elliot is running 10psi on his motor, then if you had 8:1 plus the smaller bore you could probably squeeze a few psi more out... especially if your air temp rise is lower.

O/P states that he has an intercooler.

Thanks for all the hints/ tips.

Yes will be using an intercooler. This shows my old set up



3.5 supercharged. It went really well even though I was only getting 2psi boost. I was using a v belt and getting lots of belt slip and I think pressure was leaking past my injector seals in the manifold. The pockets weren't deep enough, I could still see the o-ring so I think it was fine under regular driving (mostly vacuum) bet leaked with boost. Very hard to actually confirm thought!!!

I would be happy with 9-10psi. I was thinking of making my own water injection system controlled by megasquirt to only come under extreme conditions. Very hot day/ poor fuel.

I have a standard composite head gasket I was planning on using.
Does any one know a company who make none standard head gaskets?? IE thicker. Probably won't go down that root but would be interesting to research it a little.

I'll let you all know how I get on.

put some fairy liquid and water solution around the injector o-rings. if you get bubbles, they are leaking on boost

Looks like a pretty compact but nice setup. yeah V-belts will be useless for a supercharger unless the tension is very high but that would destroy your alternator bearings etc