Need a back axle PROJECT :)

Pah!

The Rover V8 is a pile of s**te compared with the Alfa V6. It's just not right to put that ancient heap of an engine in an Italian Car.

Reply to
SteveH
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So your younger brother was putting 430bhp through it then ? Mmmmmmm..........wonder why it failed.

Reply to
Bob Sherunckle

Not that it'll ever happen anyway...

Reply to
Bob Sherunckle

From a Maserati or Ferarri?

Douglas

Reply to
Douglas Payne

If you _really_ want a V8, then a Thema 8.32 engine or Montreal engine would be the best bet.... but rebuilds wouldn't be cheap.

Reply to
SteveH

Absolutely. It'll rip the engine mountings straight out of the chassis. And it wouldn't be right not having a cambelt that's near impossible to change.

Reply to
Dave Plowman

I would have thought it would have been more than that, 4.9 V8 iirc.

Reply to
Theo

Cos they are crap?

Reply to
Burgerman

The TR7 back axle is narrower than the SD1 it is designed like, and can take

300 horses fairly well. Oddly enough, the four speed car is the one to take it off, because that has a more useful 3.45 ratio compared to the 3.90 you'll find on the five speed cars.

Dunno how you would fit a V8, gearbox and diff in front of the axle, and still leave space for a driver, in a Punto.

Reply to
Sales!

sit on the roof. a la mr bean

Reply to
Theo

Thought the TR7 4 speed back end was the Marina/ Dolly 1500 - 1850 one? Now a Sprint back axle could be up to the job, as it's got TR6 internals, IIRC.

Engine off to one side? Or maybe Reliant Robin style, with the engine sitting where you'd expect to find the radio :)

Reply to
Stuffed

Probably ;-) Are they really - honestly, I haven't a clue.

Reply to
Bob Sherunckle

Well what breaks is not the crownwheel or pinion but the small "diff" gears that run in the middle. What causes it is crap suspension allowing the wheel to bounce about like a ping pong ball as it spins when you change from 2nd to third or fourth...

Cosworth "quafe" steel gears help a bit but the break too...

But in a lighter car it should be OK unless you are an animal with too much nitrous, and bag of cement in the boot...

Reply to
Burgerman

You may well be right there, now I come to look it up. Ok, forget the 4 speed, the 5 speed is the one to have, and change the internals if you don't intend to hillclimb with it. :)

The 5 speed is up to the job, it's taking 220 here and I know of a 5.0 engine with reportedly 400 bhp that is driving through the regular axle.

By contrast, the sprint engine is well under that sort of power and I believe came with a regular diff and gearbox, given that both are basically the SD1 box and diff with a different final drive to aid acceleration of the smaller engine. As compared to the rover v8 engine they were usually driven by, of course. :)

Quite. ;)

Reply to
Sales!

IIRC, only the '5-speed' is the same design as the SD1, and 3.45 SD1 diffs are common and cheap. IIRC again, the 4 speed one isn't as strong.

Reply to
Dave Plowman

Time for some physics!!! at least rear drive physics...

Axles don't break because of horsepower. They break because of torque. The maximum torque you can put through one depends on the vehicles grip and the weight or weight transfer on to it. (This weight transfer CAN be greater with more power though...)

So provided you can dump the clutch in your 1.3 and get a squeal from the tyres it really shouldn't matter how much power your 5 litre motor has beyond this because the wheelspin is a torque limiting safety valve.

Thats why a 1.6 / 2.0 litre transit has a HUGE diff, and the same engine in an old cortina has a crappy small 6 inch one!

The max torque the axle sees depends completely on to gear ratios too. A gearbox is simply a torque multiplier. And bigger motors generally have taller first and second gears as they already have the motor torque to pull it... So there is not so much of a torque increase at the axle as would be expected. The greater aceleration comes from each gear accelerating you to a higher final speed.

So that helps even things out too.

So if the cars light, and a 1.6 can spin the wheels in first gear then a big nitrous V8 can "only" do the same. Once wheels spin, weight transfer and torque actually decrease. But it goes on for 3 miles and 4 gears further!

So I wouldn't worry too much...

What really bust all my diffs was a) more grip because of wider tyres and lower pressures than stock. b) more rearward weight transfer due to crap soggy suspension! (on purpose for grip) c) Heavy and hard gear changes from 2nd to 3rd because I like to feel it squirm and see the smoke at the lights...

The suspension/weight transfer/grip thing is closed loop and really helps it "hook up" which is the reason for breakages...

Reply to
Burgerman

Ah right.

See - I was talking about using the diff in a proper twin wishbone setup ;-)

As a matter of interest, what will the durability of the ex Crapi axle be like in my locost - 500kg -ish and 110 bhp at the back wheels - centuries I would imagine.

Reply to
Bob Sherunckle

Yes several I would think, but its heavy?

Reply to
Burgerman

Yes - certainly heavy, especially considering the overall weight of the car. I would have probably opted for an IRS or de dion setup, but it works well enough for clumsy old ham fisted me.

Reply to
Bob Sherunckle

Sorry, meant to follow up, not email.

Yeah, the 5 speed is the right one, the 4 speed is probably a Marina one like the box and not worth using for anything like the gearbox isn't.

Reply to
Sales!

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