Best transmission to handle 500BHP SBC?

5000SE · Post by **5000SE** » Sat Dec 22, 2007 5:19 pm

Right, a Dolly Sprint was quoted to be able to do 115mph with 127bhp, which it produced at 5700 rpm.

All things being equal, that means it is indeed a house brick. Brace yourself here, because the gearbox ratio selection is going to be a bit academic unless you can get a LOT more power and a LOT less drag.

In standard body form, you'd need 670bhp to just scrape 200 in ideal conditions with perfect gearing, and that means creeping up there on a very, very long run - like salt flats!!

To get there and actually have enough power to accelerate to the required target speed within anything like a reasonable distance, you'll need quite a bit more power. 750? 800bhp?

Flat floors, low ride heights, tight wheel fit in the arches etc will all help but not as much as you might hope.

You estimate about 400ftlb at 3800rpm and revving to ‘a bit more than 6000rpm’. That would will be delivering somewhere in the region of 360-380bhp.

You’re going to need 2 engines!!

kev_the_mole · Post by **kev_the_mole** » Sat Dec 22, 2007 5:26 pm

I'm happy with my TKO600 but they can whine a bit when new but I can't tell the noise difference between the 'box and the girlfriend most of the time

Lewis · Post by **Lewis** » Sat Dec 22, 2007 5:33 pm

Oof, sorry, forgot those bits!

Wheels - probably 15", say 210/50/15 tyres.....

I found this dyno sheet for a more 'standard' L98 TT, if it's of any help...

Lewis · Post by **Lewis** » Sat Dec 22, 2007 5:37 pm

5000SE wrote: In standard body form, you'd need 670bhp to just scrape 200 in ideal conditions with perfect gearing, and that means creeping up there on a very, very long run - like salt flats!!

To get there and actually have enough power to accelerate to the required target speed within anything like a reasonable distance, you'll need quite a bit more power. 750? 800bhp?

That's perfectly acceptable and not far off what I was thinking! Consider this more a starting point....If I can generate 600BHP and add some nitrous into the equation, potentially....

A similar Dolomite with 600BHP made 186MPH on track (not it's top speed!) without nitrous and pretty standard bodywork, so there is the potential there...

Four figure horsepower is what I'd like to end up with but for the meantime that's a) out of budget and b) totally unrealistic, as the shell couldn't handle it. However, it is 'in the running' as a future development.

.......two engines though.....

Hey, maybe it's time for one of those auxilary jet turbines powering a supercharger

ian.stewart · Post by **ian.stewart** » Sat Dec 22, 2007 5:39 pm

there are a few Mk1/2 escorts hitting the 180 mark running Turbo Cosworths, one reputedly only using 400hp

kiwicar · Post by **kiwicar** » Sun Dec 23, 2007 8:01 am

Just a couple of thoughts I hope might be relevent, as your intention is to go for 200 mph, I think you may want to spread the weight along the chassis otherwise you will have a big issue of stability and a twitchy car. If you went for a gearbox out of a 928 porker in the back it should be able to handle the torque (especially if you are not doing drag launches) and it would help with ballancing the car and increase the polar MI (think skater with arms out).
The other thing is a centrifical crank driven supercharger might give you a better power curve for this application, less peek torque but extending the power curve at the top end so giving the gearbox an easier life but enabling you to hold top gear for a few more MPH, also with crank driven supercharger you could then use bigger inlet ports on the heads which would give you a few more revs for a given cam.
Have fun
Mike

russell_ram · Post by **russell_ram** » Sun Dec 23, 2007 12:06 pm

Lewis,

I don't want to poo poo your plans as everyone wants a monster engine and don't even know if you considered this but, if you're aleady funds limited as you state:

"Four figure horsepower is what I'd like to end up with but for the meantime that's a) out of budget and b) totally unrealistic, as the shell couldn't handle it."

then you need to think about the chassis very seriously.

As far as I'm aware, you'll not be allowed to run on any UK track in any class - even RWYB. A car doing 150mph plus quarters requires compulsory parachute even if you don't use it AND sub 10 quarters requires a fully inspected and MSRA legal chassis design - a simple bolt in 4 point cage is not enough to get you cert and allowed to run.

Russ

Lewis · Post by **Lewis** » Sun Dec 23, 2007 1:22 pm

Thanks Russel - that's new information to me. I didn't intend necessarily to go drag racing with it anyway but it would be something I'd like to do with it at a later date - so I'll bear that well in mind.

I have a budget for chassis development, it's just a separate entity from the engine. That's why I stated that - Yea, I'd love a 4-figure output but 500 is much more sensible and the car could actually take it and be streetable.

On 1000 it'd just grenade, everything - couldn't afford an axle, gearbox, ancilleries to suit, was more what I was getting at!

- and as such I don't want to pursue that avenue - as I could never make it reliable or safe within budget.

500 is probably the top end of what I'd want, so I'm not too worried about that for the time being - I'm sure that'd be fine to run with RWYB? I'm pretty confidient I could make it 'safe' at that level too, with regards to shell integrity and brakes, handling etc.

The Dolly I mentioned previously runs nigh on 800HP now but can't use it - as such it only runs 12 second 1/4s at RWYB, with no 'chute, passing the line at something like 120.

stevieturbo · Post by **stevieturbo** » Sun Dec 23, 2007 3:20 pm

Santa Pod are starting to enforce some new rules that they arent telling anyone about

with regards to 150+ and sub 10s cars.
If only they would just email people explaining exactly what they require, although I know a few people are basically sticking 2 fingers up to them, and shifting their race series over to Avon instead, who are more accomodating.

Although its probably only a matter of time before they too force dangerous additions to road cars, so they comply with their track rules. Its a pity a lot of the rules are based on 50's cars, with no brakes, crap tyres, and big wobbly chassis.

As for your gearbox. Throw a T56 in there and be done with it. It comes with a couple of different gearsets, so I dont see a TKO500/600 offering any real benefits, aside from being potentially stronger.
But a T56 can easily handle 600+lbft of torque in a heavy car anyway regardless of its rating.
So a 1000kg car wont pose any problems whatsoever. Only downside is that it is quite big.

As for getting to 200mph.......good luck. It aint as easy as you might think, and takes a LOT more power than you think to achieve it in the limited space available on suitable locations within the UK.

Lewis · Post by **Lewis** » Sun Dec 23, 2007 4:22 pm

Yea - I appreciate the scale of it! It'd just be a hell of a nice thing to accomplish!

Gotta put my degree to use at some point

Thanks for the advice everyone RE the box - I think, as Stevie suggests, I'll start with a T56 and see how I go!

stevieturbo · Post by **stevieturbo** » Sun Dec 23, 2007 4:25 pm

And while your at it...may as well throw an LS1 in there too

It bolts up to the boxes just fine lol.

Lewis · Post by **Lewis** » Sun Dec 23, 2007 4:36 pm

Tempting but I want to build up my own engine, for kicks, so that's the way I intend to go