How much torque will this gearbox handle??

Post by **Johnny A** » 29 May 2007 07:47 pm

The 1.7 5-speed manual 340 gearbox, how much power can it handle??

Would it take 170ft-lbs do you think??

Cheers.

Post by **Chris_C** » 29 May 2007 08:23 pm

Hope so, I'm looking at about that

Husky is putting a lot more than that through his, and hasn't had any trouble that he's mentioned.

Post by **classicswede** » 01 Jun 2007 01:17 pm

The box should be fine with that.

Torque is what causes problems with the prop. The std prop will take a lot of BHP but increasing the torque is what doe sthe prop in.

Post by **filthyjohn** » 07 Jun 2007 12:07 pm

Does anybody know the absolute limit for the box? Also maybe an approximation of how much torque you need to shred the rubber bits of the prop? I might take my prop out and get one custom made, working from the original rather than wait for it to die.

Post by **classicswede** » 07 Jun 2007 12:57 pm

I've only ever had trouble with teh splines.

Post by **germ** » 07 Jun 2007 02:16 pm

^^in what way? the rear end droping off? or shearing?

Cheers
will

Post by **foggyjames** » 09 Jun 2007 11:44 am

The 360 prop is plenty strong, John....if that's what you mean. The only weak spot on that is allegedly the 'link piece' from prop to gearbox input shaft. The 340 prop is a different matter, although people manage to shred them on B14 cars, so maybe it's nothing to do with power?

The M4x series gearboxes are known to take 300-400lbft of torque, depending on usage. The weak link on the transaxle version is supposed to be the diff, but I'm not sure anyone here has done and first-hand destructive testing. Once upon a time M46s (in the larger Volvos) were commonly considered to only be 'rated' to about 250bhp. Now people are putting 350bhp through them without blowing them up.

If you want a 'safe' limit, I'd not run more than about 250lbft of torque through a M47R. More is probably possible, but unless you drive like a tool, 250lbft shouldn't be enough to toast one. The 340 prop? That's anyone's guess. If the engine is a low-torque revvy little monster like the Renault 16v units everyone's going crazy for, you'll get away with a lot more than you would with an 8v turbo unit of the same BHP rating.

cheers

James

Post by **filthyjohn** » 10 Jun 2007 11:22 pm

Aye sounds good mate, those sort of numbers are upper-level of my plans, though after a passenger ride in a scoobaru today, i wouldn't mind having 300+ to wipe the smug smiles off some of their owners' faces (and expensive haircuts).

Post by **foggyjames** » 11 Jun 2007 12:22 am

250 from a fairly 'normal' redblock turbo (i.e. with boatloads more torque) should see you keep up with 300bhp scoobs in a straight line - they weigh craploads. Ryan's 740 at 15psi (250bhp?) is faster than a 2006 STI Type UK...whatever the hell that is!

cheers

James

Post by **Makkiver** » 11 Jun 2007 09:55 am

The horsepower doesnt matter, its the torque!

M47 will explod at 440Nm allmost instantly!

The 47R that was in my 360 did not break even whit 435Nm torque (370Nm Backwheel Newtons)

Propably because the power came whit so hi revs around 4000rpm?
But if the power is there allready in about 3000rpms the gearbox will propably break?

Post by **filthyjohn** » 12 Jun 2007 09:51 pm

So which box do I have? ('89 360 glt).

Post by **sven360** » 12 Jun 2007 11:09 pm

All 5 speeds are m47's if my memory serves me. 4 speeds are m45's.The R denotes it hangs at the back as opposed to "normal" RWD configeration.
Are you around at the weekend so I can get the screen off ya?

Post by **filthyjohn** » 13 Jun 2007 10:33 pm

I see. Yeah mate, I'll be available this weekend, evenings are better, say 5pm or later. My unit's 2 minutes from the wear bridge, which way are you planning on coming in? Should have that diff off for your brother too, it's being a bit of a pain so I'll have to grind it off

Post by **foggyjames** » 14 Jun 2007 01:48 am

If you're trying to remove the diff casing from the box, and you have all the bolts out....er....smack the crap out of it around the tabs near the flange (presumably there for this very reason). Sometimes they're really stuck together, but a good bit of action from the variable pressure applicator will help

cheers

James

Post by **Johnny A** » 03 Jul 2007 11:16 am

Sorry for the late reply.

Power will more likely be 200ft-lbs+ made at very low rpm (I am a supercharger fan so it's more likely than fitting a turbo)

Think it will be a case of suck it and see