The V8 Owners Forum -

I am swapping sd1 engine from rx7 to nova grasstracker, ratios on lt77 not working has anyone some suggestions for any other gearbox that will fit with longer 2nd and 3rd gear.

The BW/Tremec T5 was made with loads of different ratios.

What diff are you using?

Tom.

I think you'd need to look at diffs. That will give a much larger change than any gearbox will.

hi thanks for that diff on the mazda is a 4.1 with 16" wheels which pairs up well for ratios but i have a cosworth lsd set up in a spaceframe with suspension ready to weld in nova but its 4.4 and knocks a fair bit of the 2nd 3rd speeds which is the gears i need so i know it makes sense to use rx7 axle.

Hi
Sorry to sound dumb here, but on a grass tracker how many gears do you actually use? all 5 or just 2nd and 3rd? and what overall ratios do you want them to be ie what are you using at the moment and what are you aiming at when you multiply gear ratio by diff ratio? sorry for the questions, but have you considered clutch, and an auto transmission converter to manual valve body? probabaly save a heap of weight, but no good if you need more than 2 or 3 ratios.
Best regards
Mike

hi as a rule you need 2 gears one to get off the line and 1 to race in so usually 2nd gear to start and then 3rd to race in so it needs to be long enough to get down the straight in.
As for the clutch auto thingy wouldnt know where to start weight is an issue as up against cars with 10k engines in, is this what drag cars use

V8 RX-7 wrote:hi as a rule you need 2 gears one to get off the line and 1 to race in so usually 2nd gear to start and then 3rd to race in so it needs to be long enough to get down the straight in.
As for the clutch auto thingy wouldnt know where to start weight is an issue as up against cars with 10k engines in, is this what drag cars use

So if you had a taller diff, 1st and 2nd would work fine ?


Why use such a short diff, when it is appearing to be the problem ?

1st would be a no go its on mud cheers

V8 RX-7 wrote:1st would be a no go its on mud cheers

That makes no sense.

You want to use a 4.4:1 with 2nd and 3rd gears.

So that wont be much different than say a 3.5:1 with 1st and 2nd ?

The gear number doesnt matter. The ratio seen at the tyre is what matters.

You have gear ratios, final drive and tyre size to play with.

Hi
A powerglide, as standard weighs about 200lb (ally case one, don't even look at a cast iron one) with torque converter, strip out the auto bit and replace it with a manual valve body you save 10lb or so, swap out the torque converter and replace with a 7" twin plate clutch, probably another 10 or so replace with lightweight internals and strip out some of the internal clutch plates (especially reverse) probably another 8 to 10.
Ratios wise, 1st is as standard 1.76 or 1.82:1, you can get 1st clusters down to about 2.3:1. they are as strong as an ox, easily take 800bhp on grass. you would need a low final drive may be lower than your 4.4:1 but could be the answer. Top is straight through.
If you want to read up on it then "powerglide Transmission handbook" ISBN 978-1-55788-355-1
http://www.amazon.co.uk/Powerglide-Transmission-Handbook-Carl-Munroe/dp/1557883556/ref=sr_1_1?ie=UTF8&qid=1287079133&sr=8-1
has a description of what to do to use it on grass (well cinder track racing)
Best regards
Mike

auto would probably be an interesting option. Wonder if it would offer better traction ?

Hi
you can set up the valving to soften the change which would reduce shocking the tyres loose so yes it should help. The box would be fully manual appart from that. You can use them without a clutch or torque converter, just pull away using the 1st gear band, however they only do that where you have a rolling start as it leaves you slow off the line as you can't pull away with the throttle fully open.
Best regards
Mike

kiwicar wrote:Hi
you can set up the valving to soften the change which would reduce shocking the tyres loose so yes it should help. The box would be fully manual appart from that. You can use them without a clutch or torque converter, just pull away using the 1st gear band, however they only do that where you have a rolling start as it leaves you slow off the line as you can't pull away with the throttle fully open.
Best regards
Mike

Make it a clutch driven auto. do away with the torque converter, and get a splined input shaft to fit the auto, then fit a clutch and flywheel, so then you can launch like a clutch driven car but with the benefits of an auto, used to be quite common a few years ago, "ClutchFilte" was the generic term for them
http://www.forwardlook.net/forums/forum ... ?tid=22378

"Make it a clutch driven auto"
I think that was what I surgested in my first post on this and repeated in my second
Best regards
Mike