Overdrive vs tall rear gears?

[Hemi Joel]

Is there any disadvantage with regards to strength or durability to using a 3.23 or a 3.0 rear gear, with corresponding deep 1st - 4th gears in a 5 speed trans? As compared to using 4.11 or 4.56 gears in the rear and an overdrive 5th gear?

[squirrel]

It probably depends on what you're doing. I just went on a trip with my new 2.47 gears behind a blown big block....no problems. But I'm using a slushbox, not a weak 5 speed trans.

[Hemi Joel]

I've got an old Doug Nash 5 speed in my 67 Olds 442, backed up by a 2.75 geared 9'', and it works great. But it's probably under 450 horse and I don't pound it to hard.

What I'm talking about here would be a Drag week car that will run 9's, maybe quicker. Probably have a Jerico or a G-force 5 speed with a 1:1 fifth and a deep 1-4 gearset.

[squirrel]

The torque at the driveshaft and those parts that are directly connected to it (ie trans output shaft and rearend pinion gear) will be higher with the deep low gear trans. On the other hand, the driveshaft won't have to spin as fast.

I have pondered this quite a bit, and I've noticed that as time goes on, production cars are going to steeper overdrives. There must be a reason that they do this, since it seems to be adding drivetrain friction/inefficiency under normal cruising conditions. But then again, they aren't building race cars.

[milner351]

Joel - will you run the same tires track and street? I ask because especially if you run the coupe fenderless - or leave yourself some room - you can run short slicks and tall street tires to help out the gearing situation - this is what the poison gas car did last year.

I think you're going to walk a fine line between what 1st gear ratio will blow the tires off no matter what the track prep, and on the other end of the spectrum - going through the traps in the middle of third gear or something like that.

I have a spread sheet in excel I put together to calculate out the gear ratio, tire size, engine rpm (assuming no slip of course)
It's pretty simple - I'd be happy to send it you if you like.

[JeffMcKC]

Deep gears on either end mean one big gear one small small= weak

[squirrel]

Torque converters seem to be a good way to get rid of small weak gears

[JeffMcKC]

If you have the right converter you can "ride it" we have a 4.10 rear gear with 103 inch rollout tire on Docs car still at 3500 plus pounds a 1.23 60'

A Manual trans guy has to not bog the engine and does not have anything but gears for TQ multiplication the newer Clutches help a lot but its a fine line to get up on the tire with the right amount of tire slip.

[Hemi Joel]

Joel - will you run the same tires track and street? I ask because especially if you run the coupe fenderless - or leave yourself some room - you can run short slicks and tall street tires to help out the gearing situation - this is what the poison gas car did last year.

I think you're going to walk a fine line between what 1st gear ratio will blow the tires off no matter what the track prep, and on the other end of the spectrum - going through the traps in the middle of third gear or something like that.

I have a spread sheet in excel I put together to calculate out the gear ratio, tire size, engine rpm (assuming no slip of course)
It's pretty simple - I'd be happy to send it you if you like.

So far, the plan would be to run the same tires for street and strip. Hey, the fastest guy on Drag week does it, why can't I? Yes, I'd gratefully accept a copy of the spreadsheet. My email is [email protected] - just be sure to use my name in the subject to get past my spam filter.

Yes, in some ways running a manual trans can make it to harder to get the job done. Still, sometimes, it's worth it to me to sacrifice performance or convenience to acheive other goals. I Just have to do things the way I like, it's the only way that i't's worth the time and money. And I just flat out love shifting gears!

So I have to figure out how to make the car work as good as possible, with a manual trans.

I usually run an Advance soft lock clutch. But I will need to have it tight so it won't slip on the street. I could re-adjust it for loose at the track and tight on the street, or try to find a compromise setting. (Squirrell - an infinetely variable stall speed)

So Jeff, stronger ratio in the rear = weaker trans?

THanks for the input!

[MR P-BODY]

I went with the steeper rear end gears but with OD... I went
with a 4.10 in a 9" but with .69 OD so I can cruise at 3000 rpm
or less at 75 mph ... this puts my engine at 7000 crossing the line
which is what I built the engine for at max... it peaks 6600 rpm

[v869tr6]

I put around 900 hp to a set of Ford 2.50 gears but I have a auto, bunch of people have told me its a lot tougher to break a 2.50 or 3.00 gear.

[BlueCuda340]

I put around 900 hp to a set of Ford 2.50 gears but I have a auto, bunch of people have told me its a lot tougher to break a 2.50 or 3.00 gear.

Thats true, the pinion is much larger in those ratios than say a 4.88. but the higher torque required to turn those gears puts more stress on the trans and driveshaft.

[squirrel]

but the higher torque required to turn those gears puts more stress on the trans and driveshaft.

What are you "holding constant" when you make that comparison? The torque on the driveshaft is the engine's torque, times the transmission gear ratio. If the engine is running wide open, and the tires are hooked, then the torque on the driveshaft is the same regardless of the rearend gear ratio.

If you run a steeper low gear in the trans, and a milder rear gear, then there is more load on the driveline in low gear.

[BlueCuda340]

Its harder to turn the pinion because it doesn't have a mechanical advantage as good as say a 4.56 gear. I could be wrong...but thats the way I see it. If its easier to turn the driveshaft, its going to be easier on parts.

[quick 52]

seem like alot of cars use a gearvendor