Torque capacity calculations

[virgil]

OK, power train sizing question...will a smallish gearbox survive with a very torquey engine in a very light car? I understand you'd need a very strong box for 400ft/lb in 1.5ton car, but in 500kg? 400ft/lb and sierra type nine?...am I thinking on the right lines here...

Take the gearbox and diff both say capable of 200ft/lb. Transfer into very light car (500kg) with bigger engine, say 300ft/lb and find that it wheel spins in 1st gear. Gearbox should survive as the extra torque is just being lost in wheel spin.

Now 1st gear is 3/1 ratio, so gearbox is getting 200lb torque, but diff is getting effectively 600lb due to the gearing. So we know diff is ok for 600ft/lb

In 2nd gear the ratio is 2/1 - gear box still gets 300lb and diff still 600lb - Diff could therefore take power increase from standard to 300lb, and surely the wheels again spin saving the gearbox.

Basically what I am trying to say is that if the very light car is not over tyred, does the wheelspin act as a natural saviourt to the drive train?

Therefore 600ft/lb all gets wasted until 4th/5th where it just accelerates like the proverbial....

[splatspeed]

yes if it spins before it breaks it will save the gearbox

however the wheels will not spin in top giving all the torque to the input shaft and breaking it

does not matter the weight of the car but the power out of the engine

sorry

[GreenV8S]

It acts as a torque limiter to some extent, but beware that the weight on the wheels can vary dramatically. A favorite way to shred transmission is to spin the wheels up while the car is airborn, and then come down hard. (One benefit of traction control is that it prevents the wheels from spinning up in this situation and saves the transmission when you come back down again.)

Also note that gearboxes have different torque restrictions in different gears, and in the higher gears the torque limiting effect of the wheels will occur at such a high crank torque that it won't provide any useful protection.

[virgil]

Thanks for the input...thought it would be too easy to be able to get away with a light cheap gearbox!

Do you think a type 9 box could live with the revs from a bike engine? Wonder if it would would run it far to fast (over heat) when used with a very high geared Diff?

[chuntington101]

are you looking at anything inperticular???

500kg car dont need much power or torque to make them quick!

also what engine are you looking into? is there a gearbox that you could use that is standard that will take it??

thanks Chris

[virgil]

chuntington101 said:

are you looking at anything inperticular???

500kg car dont need much power or torque to make them quick!

also what engine are you looking into? is there a gearbox that you could use that is standard that will take it??

thanks Chris

Currently have a Griff 500 so looking for a VERY quick play thing. Started a lotus 7 type when I was 21 from scratch, still have the Diff, box, dampers, brakes etc but got rid of the Cosworth turbo engine I had (270hp - 500kg - Mmmm) and chassis I'd built as I moved to a flat with no workshop.

Now thinking either light alloy 4 pot turbo, bike engine (or two - have seen this done) or Rover V8. RV8 is kind of fave, as If I start tweeking it, I may be able to them pass on any mod to Griff etc. Also, I kind of like the way a big torquey engine drives. SO looks like it will have to be a T5 box...or even a T6?

Also had thought new alloy ford 4.6 V8 or Corvette L7...

Basically may end up with effectively an engine with wheels !

[chuntington101]

well if your planning on putting the engine in the Griff then id go for a nicely built LS1. as for power levels, well the sky really is your limit, or your wallet! lol. 500bhp is easly achived with a new set of heads, cam, ecu and a good set of heards! 600bhp is a simple strocker away! or you could go for a Magnus blower on a bone stock engine to get REAL gut renching torque!

if it was a 7 style then id look into the Honda S2000 motor! smaller and light than the Civic Type R unit. just need to find one then! lol there is an article in Track and Race car this month about a guy that built a westy with one in for around 14K and it looks amazing! CF everywhere lol.

but then again it would be nice to see a 500bhp LS1 in a Dax or Westty!

as for the box, the UK T5 should take a rover V8 no probelms. for the American mussel id got for the US spec T5 or T56 (the 6 speed equilivent i think). might be worht talking to boosted LS1 on here as he can get complete LS1's with boxes i think!

thanks Chris.

PS take a look on ls1tech.com for more info on LS1's and what the americas are doing to them!

thanks Chris.

[virgil]

chuntington101 said:

well if your planning on putting the engine in the Griff

PS take a look on ls1tech.com for more info on LS1's and what the americas are doing to them!

thanks Chris.

Not for the Griff, but If I tweek a V8 for the kit, then maybe pass the improvements to the Griff.

Looked at Boosted's site already - bit pricey though for a toy. Self breathed on RV8 about my limit cash wise. Nice idea though!

[chuntington101]

have you concidered a ford 302 cubic inch (5 ltr)?? they are old but are cheap! also with ally heasds they aren't that heavy! and you can get good power out of them.

worth a look into.

oh and a guy in practicle performance car has one in hie capri!

thanks chris

[spyder dryver]

virgil said:

Do you think a type 9 box could live with the revs from a bike engine?

Bike engines usually come complete with a gearbox.No type 9 necessary. If your only criteria is speed, as in acceleration,then stick a Blade or R1 type engine in a seven chassis. Blisteringly quick. Not always user friendly though. High revs and noise when cruising. Can quickly become tiring. Limited top speed with some engines unless a suitable diff is used.
But if all you want is speed, a bike engined seven is worth considering.

[GavinPearson]

You size the gearbox to the peak engine torque if you want it to live.

You also need to match the ratios to the torque range of the engine.

It also seems pointless to have an outstanding powertrain and tyres that don't grip.

You're best off buying a proven engine / gearbox combo that works in a particular application properly.

[virgil]

Thanks guys.

302 must surely be quite a bit heavier than an all alloy lump?

May go the bike route, but (and I know this may sound strange) didnlt want the sequential box - wanted a normal one.

So will probably be RV8/T5 or bike jobbie...just got to clear the workshop, fix the couple of grumbles with the TVR and Mrs Virgil out for a nice persuasion dinner!