Rotrex supercharger on P38 engine

[ChrisJC]

Evening All,
I'm pondering adding a Rotrex supercharger to my P38 engine. I'm thinking that with a low amount of boost, the standard Motronic system will be fine.

Has anybody every fitted a Rotrex supercharger?, which one did you use?, did it work?

Chris.

[stevieturbo]

What application ?

Centrifugals don't offer a lot low down in the rpm's, so if that's where you spend most time, you may not get great results.

I don't know much about the Motronic system, but adding boost of any kind and just hoping for the best, is a bit of a stretch on most systems. Although if it has an airflow meter and you are passing all air through it as it would normally expect, maybe it might tolerate some. Or it could max the MAF out and then it won't have a clue what to do

[ChrisJC]

It's in a SWB Land Rover, 4.6 engine with ported heads.

I would set it up to suck through the MAF and blow into the Thor inlet manifold throttle body.

I believe that the Motronic works fine up to a bit over 300BHP, and can probably be mapped to more if needs be. That sort of number is going to be perfectly adequate I think.

On the surface of it, it looks like a simple matter of getting the right pulley size and right version of the Rotrex unit.

But I confess to being a bit unsure how the engine can suck through it when it's not pumping as much as the engine needs, e.g. floor it at idle.

Chris.

[stevieturbo]

On the surface of it, it looks like a simple matter of getting the right pulley size and right version of the Rotrex unit.

But I confess to being a bit unsure how the engine can suck through it when it's not pumping as much as the engine needs, e.g. floor it at idle.

Chris.

How can an engine suck through a turbocharger ?

A blower is always spinning, it's always moving air....although at idle, the engines need for air is rather little, even if you did go WOT.

But if you're expecting big things from a centrifugal blower at idle, you've got the wrong idea about them. They will largely aid performance higher in the rpm range.

if you want off idle boost/torque, you need a Roots, Screw etc type blower.

Not quite apples to apples, but still a decent visualisation. ( gearing also skews the test a little )





I'm not saying a centri will offer nothing down low, it can still be a little better than n/a, but don't have high hopes.

For a heavy off road application where I assume you don't rev it much ? I'd be looking for a screw type blower, lots of cheap variants off Jags and other cars these days if you can adapt them to fit.
No idea what sort of full kits are out there though

[SuperV8]

I'm using a centrifugal supercharger on my Rover 4.6.
Using a procharger - rather than a Rotrex, just what I found for a good price at the time.
I'm sure I have some posts/pictures about it if you search my name.
This post has most of the history:
https://forum.daxsportingclub.com/phpBB ... php?t=4305
Using megasquirt 2 so can't comment on GEMS suitability.

The difference is amazing - even when only just using a little boost - even from idle, very noticeable (in my 600kg car - so maybe a Rangy might blunt this feeling?)
My procharger failed at the drag strip (marketing BS claiming 80,000rpm max when they used <20,000rpm capable bearings!) - so I took the belt of and drove home, what a difference it was making, and that was early on and only a few PSI - engine felt so flat/slow - and that was a 4.6 in a 600kg car!

Rotrex are great - but expensive - and tend to be aimed at smaller higher speed engines - so more boost and less flow - where as American centrifugal chargers are aimed at bigger/slower engines so less boost but more flow - different pressure/flow maps.

From "memory" I think I calculated around 10psi in my engine was around 400hp - so you would pick a blower which could deliver 400hp mass of air at 10psi.

Obviously need to make sure your fuel system can deliver enough fuel for your power goal?

If I was to start from scratch I think I would go turbo route - couple of small turbos, or one bigger one - would be much cheaper - and in a rangerover you have plenty of space. I already had a very expensive stainless exhaust which I wasn't about to cut up - and not to mention space in my Dax Rush is rather limited! - so a centrifugal charger fitted my requirements better.