what gear box at what boost
Turbo Mini Forums

hello all i was hoping to run 15psi (or as much i can sqeeze and be safe) out of my std gear box with a x pin diff ? anyone know the stats? cheers

What stats?

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

i broke 3 box's and one diff all under 15psi and under 150bhp...
maybe they were knackered who knows?

well worth a x pin diff as if your diff were to bust chances are it would break the casing too..

Ron

Yep,

If the standard diff pin breaks, the chances are one of the bits will get trapped between crownwheel and casing leading to a large hole....

I broke one and wrote off the casing with a standard MG Metro, normal usage, so for my Turbo project, the X-pin diff was first on the list.

I've also been looking out for the DAM 5626 casings (got one now) as these are much stronger than the DAM 2886 casing around the 3rd motion shaft bearing.

Edited by Rod S on 22nd Jul, 2008.

Schrödinger's cat - so which one am I ???

I ran mine for a couple of years on 15psi + and all was good, if its recently been rebuilt and you don't drive foot to floor all the time it should last ok.

A little bit of mechanical sympothy goes a long way!

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1/4mile in 13.2sec @ 111 terminal on 15psi

my engine is a 1310 running a std mg metro cam and i just bought some omega pistons and did the head so i can run 15psi, i have a x pin diff but do i really need sc drop gears or even a full sc box? getting low on cash you see. anyways cheers for your help guys. much appreciated.

the weak link are the drop gears these need to be straight cut ones and the diff next

15psi broke my drops.

It's up to you. Take it easy and hope that they don't implode, or get it sorted for piece of mind.

In the 13's at last!.. Just

false economy not to have uprated diff and drops we all know you dont put a turbo in the car not to plant that right foot save the heartache and do it right buddy. i have gone whole hog with mine sc drops, evo diff and challenge SC gearset. and i only intend to run 12 - 14 psi boost.

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MikeRace, Mini13

I thought that helical drops were just as strong if not stronger than straights as they have a larger contact area.

Is the only reason they break because of the side loading on them?

Finally if you are low on cash, don't chance it. You'll break all manor of things before you get a reliable 150bhp unless everything is new.

yes sideloading is what destroys em i presume a set of hellecle drops with timkin would be an idea.

Ric has hit nail on the head with his last comment

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MikeRace, Mini13

I believe Robert is still using helical drop though...due to the comments he makes when he goes in mine "god your drops are loud"!! Lol

Stand to be corrected mind!

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1/4mile in 13.2sec @ 111 terminal on 15psi

will be running about 9 psi on fast road turbo motor. have a sccr box with sc drops, centre oil pickup, x pin diff.

hopefully will be reliable and give scope for more power in the future.

if you invest i9n a sc box with drops and 4 pin diff then you can do any thing up top.

as 9 psi soon turns into 12 and then 15 ect

always looking for them bigger bunches of bannanas

what difference does the boost pressure make? 10psi on a 7:1 compression is nothing but 10psi on a 10:1 compression is silly power (if you can get it to work)

would it not be better to state what power you were looking for?

last year i did the 1/4 mile in 14.5sec at 17psi of boost. this year i did it in 13.85sec with 13psi of boost. the difference being the compression ratio

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM