Topic

Having snagged myself a very well priced gen5 Bini supercharger today, my engine plans have become somewhat more real.

I'm still mid research and costing but the charger was a steal and the money rotrex chargers are fetching is large - 12 psi from the Eaton m45 will be enough to start.

Anyway, the point of the thread.. What gear ratios would be best suited to a high revving charged engine, I'm not really chasing numbers and have no idea what to expect in terms of bhp and torque and I'm not that arsed, I just fancy getting into engines and having something I can build in the warm spare room.

Suggestions on gears and what box(es) to source them from would be really helpful.

Also can a lightened Elise fly wheel be machined to fit a clutch from a t series? I can find a picture of the difference to tell.

Not sure high revving is the way to go for a charged engine as they suit normal revs just with extra grunt.

Chargers tend to deliver at low to mid revs and top out before your revs do.

You could alter the pulleys so that the charger is delivering at higher revs, but I'm not sure what you would gain from that.

Look up eks on xpower forum. He makes flywheels for the k and kv6.

A B4 box just sold on e bay for 500 odd quid

Get yourself a decent C4 and a Quaife or Torsion diff and some steel caged bearings

The best source of info I lnow for the PG1 gearbox is www.rovertech.net

The standard vvc box (c4) is good enough for most people. The lotus owners prefer the b4 box (and pay a fortune for them) as its what Lotus sold as the close ratio box.

If you're going to have an engine with a lot of revs, a shorter box would be better, but its expensive to do as you'd need an aftermarket gearset and/or final drive.

It's the torque which kills gearboxes, so consider rebuilding with uprated bearings.

I prefer the K gearset with a diesel 5th for motorway which I'll be fitting with my charged engine. This is the same 1st,2nd and 3rd as the b4 box.

Cheers QS - I'll do a bit more reading up on the gear boxes and the ratios but I like the idea of a taller 5th too as I'm only ever up that high on a motorway. Do you know the difference between the elise / MGTF fly wheel and the Freelander one?

CJJ, I was looking over the Eaton M45 specs during my lunch and in it's OEM Bini guise it runs a 65.5mm pulley that at an engine RPM of 6950 (I need to find the Bini's pully size from the crank granted) the charger spins at 14317 RPM. Various tuning forums suggest the M45 unit is good up until 17500 RPM, which on a Bini is somewhere in the region of 53.7mm on the charger pully (again at 6950 engine RPM). I need to measure up the MG TF alternator pully to do the maths however instinct tells me that on the standard pully, the M45 will still have some RPM to spare when on the Kseries?

M45 pully wheel chart at the bottom here:
http://www.kavsmotorsport.com/mini-tuning-products/mini-cooper-s-supercharger-tuning

The difference in the flywheel is to drilling/dowelling for the clutch - Freelander uses a 228mm clutch which is the same fitment as the t-series setup.

Can the KSeries clutch be machined to fit do you know? I'm thinking gearbox setup would be (and correct me if I am wrong, I'll openly admit I'm into day 3 of gearbox education now!) VVC box with a Diesel 5th, elise parts lightened fly (machined to fit a Tseries clutch), OEM T-Series clutch, steel cage bearings and finally a LSD (although I need to read more on those and their suitability for rear wheel driven charged cars).

I'm not a supercharger expert.... but from what i recall, the physical design of the rotrex is centrifugal - meaning the faster the airflow, the more rpm of the blower = more power. its essentially a turbo on the inlet side.
However, the Eaten is a 'screw' type, which (depending on its design) means it has a very definitive 'peak', where it will produce max airflow, and can then become a restriction if engine RPM airflow requirements exceeds this.

But, ive probably picked up an apple and a pear there, and tried to compare. Im an NA man, not a FI! lol.
What im getting at, is i was of the belive Eaten was designed for low-mid RPM power (mainly because of design limitations at high rpm). Rotrex were for high RPM, 'replacing' turbos as they do not suffer from the same high intake temperatures design flaw.


As for gearboxes - There was a chap at the last dyno i was at that that had a 6-speed fitted to his F/TF. Im SURE i heard the word Toyota mentioned in the conversation... although i was only evesdropping, and didnt get the whole thing.

The 6 speed box was in Highflyers car (Paul)

Give Jon Norris a bell as he has my ex eaton and engine in his car.