Ok Gentlemen, I’ve had conflicting advice from some eminent gearbox reconditioning firms and so I need a straw poll from the streets –i.e. your opinion.

I’m putting a 157Bhp highly tuned (and peaky) 1700 Crossflow into a 550Kg Caterham-alike kitcar. I ran a Type 3 box (from a Cortina MkII 1600 GT so it has nice close ratios) with a 110-120 Bhp Xflow no problem, but will it last under the power of the new engine?
The box is as shown on this page:
http://www.zetecinside.com/xr2/gearbox.htm

2 of the gearbox firms reckon the box it will only handle 140-150Bhp tops.
A 3rd firm reckons it should be OK up to 160-170 Bhp.

What do you reckon, and what power have you put through a Type 3 box?

 

If this is the 3 rail gearbox as used in my old CORSAIR 2000E ?, then it will take 170 all day long as mine did, one of the best gearboxes I ever used!!
tabetha

 

It's actually the single rail 2000E box which is rather different. However, I'm impressed at yours handling that sort of power!

 

I did over 15,000 with it.
If it were me now though I would use a TOYOTA/PORSCHE P50 gearbox, goes on without too much hassle and will take 300 all day.
tabetha

 

Its not the brake horse power that breaks them but the torque, and with your engine you only going to have a max of 140ft/lb

that said it needs grip to break it, Newtons laws of opposite and equal.
If you can only put down a certain amount of torque and its lower than the breaking point then its safe.

Of course if its grippy and you have some really high ratios then you may come into problems.
(A)
150 ft/lb x 1st gear 2.9:1 = 435 ft/lb x the CWP ratio 4.1:1 = 1783.5 ft/lb.
(B)
150 ft/lb x 1st gear 2.4:1 = 360 ft/lb x the CWP ratio 3.54:1 =1274.4ft/lb.

500 ft/lb diference

The reason why some cossied powered Escorts dont break the english axles is because they cant put the power down, they can on the rollers but thats done in 4th with a gentle drive up the revs, and they are strapped down. The Torque they supply is far in excess of what the tyres can grip, a spinning wheel and you have no grip.

(C)
400 ft/lb x 1st gear 2.9:1 = 1160 ft/lb x the CWP ratio 4.1:1 = 4756 ft/lb
(D)
400 ft/lb x 4th gear 1:1 = 400 ft/lb x the CWP ratio 4.1:1 = 1640

3000 ft/lb difference

so you see in 4th when the power reading are done the torque is a lot less.
and if you can spin the wheels with 170bhp x-flow you spin them with the cossie at the same rate, and for longer,

You have a light low grip car, thats easy to change the box mounts on, so go with that box you have first and see what happens, i doubt you will break it on street tyres.

 

Awesome -many thanks for the excellent talk thru.
What does CWP stand for, BTW?

I guess I'll be visiting your website in due course after the quality of the above!

 

CROWN WHEEL PINION.
tabetha