6 replies to this topic

[JamesL]

Hi All,

I've recently returned to the mini fold having owned a Longmans built 1380 many years ago.

My new purchase is a 1999 MPI Cooper with a VMAX supercharger kit including stage 3 head, roller rockers, Emerald K3 ECU, charge cooler etc. It is supposed to be around 140bhp but it feels slower than my old 120 brake motor.

There is a problem with the gearbox, second gear syncros are knackered so I need to pull it out for a rebuild.

The current box has a close ratio straight cut gearkit with straight cut drops. I'm not sure what the FD is but assume it to be the std 2.7

I've been talking to Stuart @ VMAX who will be doing the box overhaul and the recommendation is to switch back to a standard helical setup and change the FD to a lower 2.9 ratio.

He says that the SC close ratios don't really suit the supercharger setup and I will get more driveability out of a std helical gearset.

The lower FD will also make it feel a bit quicker as it feels a bit lethargic at the moment.

The car is used as a second/weekend toy mostly on A/B roads. There is the occasional need to take it on the motorway (around 60 miles) but not more than once a month.

For those of you with a similar setup, what would you recommend I go for? Should I rebuild the current SC box and just swap the diff for a lower FD - if so which one - should I go as low as a 3.44. Otherwise is the helical setup the answer?

I don't have loads of time/money to keep swapping the engine in and out so really need to get this right first time around if possible.

Thanks in advance to anyone who can give me some feedback.

James

[Guess-Works.com]

There's some substance to what VMAX are saying regarding the ratios however...

My inclination would be to leave as is, well apart from getting rid of 'le crunch'.

A supercharged system should be well capable of pulling a 2.7 final drive and running the long 1st gear in a SC gearset. Not from personal experience, but I know someone who converted a stock 1275 motor, and that had a 2.7 with a Metro challenge gearset which has an even longer 1st gear @ 2.3:1 ( the std helical 2nd gear is 2.2:1 ) and that had no trouble at all... would easily pull 60 in 1st.

So my suggestion would be, make sure the 'claimed' 140 is actually what you're getting.

and of course, changing the long final drive to a shorter one, 2.9/3.1 or even shorter will give you the quicker acceleration, at the expense of that cruise speed.

[Dylan8660]

I run a 2.9 but not in such a powerful motor, it's a nice compramise that will give you 75mph @ 3500 rpm for motorway and for A's & B's once your rolling 2nd and 3rd is all you'll really need, 2nd up to 60, 3rd up to 85. If your pockets can take it have a quaiffe put in as well, it's the best money I spent on mine.

[johnnysti]

I run a 3.44 in mine which is great for acceleration but not the best for motorways/dual carriageways. I also have s/c c/r gears and have no problem with them whatsoever. When i converted to blow through, i had the s/c drops changed to helicals as the novelty of them soon wore off and any sort of motorway driving needed ear defenders. Now though, the sound has been replaced with the supercharger whine but i can cope with that!

My advice would be to do it right first time. It may be a little harder to front the costs now but its a hell of a lot cheaper than doing it twice!! I would get a final drive somewhere in the middle and would also advise s/c gears. S/c drops or helicals is up to you. Also a nice strong diff.
Doing it all right now means that if you wanted to upgrade for more power in the future, the gear box should be in good enough nick that it won't need strengthening saving quite a bit of money for other areas of the engine.

[JamesL]

Hi Guys,

Thanks for your feedback. I am going to pull the box out, work out exactly what ratios are in there and probably have the current SC setup rebuilt but lower the final drive to make the acceleration better. (depending on what is in there) Whilst it's in bits I will also remove the SC drops and revert back to helical so she's a little more ear friendly in the cabin.

In the short term I will take it for a spin this weekend with a passenger making notes as to rpm vs speed so that once I've established what fd is currently fitted, I can then gauge which lower ratio to go for.

Quaife diff sounds like a good idea but a little beyond budget at the moment, definately something to think about for the future. The current 4 pin diff will have to make do for now.

Cheers
James

Edited by JamesL, 10 February 2011 - 07:52 PM.

[NG007]

I think a 3.1 is the best of both worlds not to high not to low..

i would not go below 2.9 on any engine.. or it would be a total slug.

[Matrix]

My car runs a 2.9:1 with 10" wheels and a sc cr box... fantastic on the motorway and pulls like a train 1st gear is good for 60mph if I push hard
forgot to add...and a quaife LSD

Edited by Matrix, 14 March 2011 - 02:40 PM.