[Formulajones]

Originally Posted by amcmike

Well high 11s would be in the 115mph range. If he had a 6-6.2k rpm redline, theoretically he'd be able to cross the finish in 2nd gear (assuming 26" tall tires and stock 4L80E gears). That would eliminate time loss normally to shifting into 3rd (maybe .25 to .5s?).

lol I'm thinking more about the sluggish 60 foot he'll have with a 2.56 and a 2.48 first gear (yawn) which will kill ET, not to mention a loose converter will hate it. But what's worse is with an overdrive, there is no need to even have that 2.56 in there.

I'd like the effective ratio better if we had a low 1st gear. This thing needs a 6L80 with a 4.03 first gear, lol.

[77 TRASHCAN]

Originally Posted by geeteeohguy

I'm running a 2.56 safety track in my '67 GTO behind a TH400. Compared to a 3.36-3.55 gear, the ring gear on the 2.56 is super thin, and the pinion gear is a huge diameter. The 3.55 ring gear is a LOT beefier. While I love the 2.56 gear on my street car with it's low highway rpm and high fuel mileage, it would not be a choice for dragstrip operation at all.

When I made my earlier post, I was wondering what would go first on a 2.41, 2.56 gear. Rip the teeth off the ring gear, or rip the flange off the gear carrier???

[Formulajones]

Originally Posted by Slick

Mark (HIS) is a very, very smart guy, and a very nice guy.

Please don't try and figure out the why of 4L80E AND 2.56 gears. Nor figure out the need to run 87 octane. It makes my head hurt trying to understand.

If I guessed that his design goals are maximum fuel economy, longevity (revolutions/mile) and performance, it would still probably be wrong.

Did Mark mention that he is running a Dominator?

Add that up!

Okay so that wasn't a typo??

[jonathonar89]

Originally Posted by 77 TRASHCAN

When I made my earlier post, I was wondering what would go first on a 2.41, 2.56 gear. Rip the teeth off the ring gear, or rip the flange off the gear carrier???

Every transmission worm gear set I’ve seen gets stronger the closer you approach 1:1. This can be seen when you look at Tremec transmissions, for instance. As an example, TKO600 is stronger than the TKO500 due to gearing.

How is this different with rear end gears?

[Skip Fix]

With my 2.56 and a 265-50-15 I could run most of Texas World Speedway roadrace course in second! The little stock 180 HP 400 could only pull 4000 in the long straight but that was 130s.

[Mr Anonymous]

Originally Posted by ta man

He picked up 1 second with a gear change? Any more details?

It was a whole bunch of years ago (more than a dozen), and I don't recall the whole myriad of parts we threw at it, i tried to forget it. It was hard on torque converters, and that in turn was hard on the thrust bearing. It screamed "do the gear first, dummy", and we eventually listened. We had a lot of junk parts, and we ended up making junk out of some decent stuff too.

[JLBIII]

Wow Thought I was one of the few with a 2.56 safety track rear. Second gear on the TH400 really winds out. Still learning the ins and outs on this Firebird. Really looking forward to an all day cruise instead of just the local 15-20 mile runs.

[Formulajones]

Originally Posted by JLBIII

Wow Thought I was one of the few with a 2.56 safety track rear. Second gear on the TH400 really winds out. Still learning the ins and outs on this Firebird. Really looking forward to an all day cruise instead of just the local 15-20 mile runs.

I've got a first gen 400 firebird 8.2 rearend here with factory traction bar mounts. Crazy as it sounds, it's a 2.56 saf-t-track.

[JLBIII]

Originally Posted by Formulajones

I've got a first gen 400 firebird 8.2 rearend here with factory traction bar mounts. Crazy as it sounds, it's a 2.56 saf-t-track.

Sounds like it's for a 67.

I stopped over at a friend's house today. He wanted to hear my car as I left. I hit WOT from a slight roll and the tires broke loose in 1st and into 2nd.

[Formulajones]

Originally Posted by JLBIII

Sounds like it's for a 67.

I stopped over at a friend's house today. He wanted to hear my car as I left. I hit WOT from a slight roll and the tires broke loose in 1st and into 2nd.

Yep I think it's mono leaf. I haven't looked at it in a long time.

[geeteeohguy]

Originally Posted by JLBIII

Wow Thought I was one of the few with a 2.56 safety track rear. Second gear on the TH400 really winds out. Still learning the ins and outs on this Firebird. Really looking forward to an all day cruise instead of just the local 15-20 mile runs.

My '67 GTO ragtop with the 2.56 rear gear and the TH400 shifts from second gear into third at 105-107 mph at WOT. Cruise is 2450 RPM at 80 mph, delivering 21 mpg at that speed. 90 mph is 3000 rpm even. If I loaf it along at 65 mph, mpg goes up to 23 mpg. The car is an absolute joy on long, all day drives. Runs cool and sips gas, and is very quiet and smooth. Top end is strong, but limited to about 130-135 mph due to poor aerodynamics and the front end getting really light. With my stock diameter tires and at redline, the theoretical top end is 158 mph.

[dragginwagon406@hotmail.c]

Originally Posted by Half-Inch Stud

Has anyone run a 2:56:1 Posi into the 11s. Asking for me.

Although not Pontiac, I accomplished this in a 1970 Monte Carlo with a stroked 454 on 225/70-15 Cooper Cobras. I used the factory 1970 small block TH350 converter too.

https://youtu.be/gANPkATqPmA

[lust4speed]

Getting back to what gears are weaker, the 2.56 rear will have more teeth in contact between the ring and pinion. A 4.56 rear has a really small pinion and few teeth engaged, and the smaller pinion tries to climb out and away from the ring gear. The huge 2.56 pinion does more pushing with more teeth.

Any rear gear with slicks and good hookup is going to have the same torque output from the trans on launch. Driveshaft torque doesn't change and it would seem that trans and converter life should be the same.

[Formulajones]

Originally Posted by lust4speed

Getting back to what gears are weaker, the 2.56 rear will have more teeth in contact between the ring and pinion. A 4.56 rear has a really small pinion and few teeth engaged, and the smaller pinion tries to climb out and away from the ring gear. The huge 2.56 pinion does more pushing with more teeth.

.

This is highly dependent on the diameter of the ring gear. Which is why it's really not recommended to put a really high ratio gear in the smaller rearends. I never liked them much on anything 8.2 and below.
When you get up into the 8.8 rear, the 8.875, the 9" etc....(even the 8.5 isn't horrible) It's really not an issue how small the pinion is because the larger ring gear diameter really helps the contact patch.

Ran into this with the whimpy 7.5's that GM used decades ago. Even just trying to run 3.73's and 4.10's in those rearends only left about 1.5 teeth contacting the ring gear, and made it pretty easy to strip the teeth, which is why they kept those rears to a 3.42 max.

[ta man]

Originally Posted by lust4speed

Getting back to what gears are weaker, the 2.56 rear will have more teeth in contact between the ring and pinion. A 4.56 rear has a really small pinion and few teeth engaged, and the smaller pinion tries to climb out and away from the ring gear. The huge 2.56 pinion does more pushing with more teeth.

Any rear gear with slicks and good hookup is going to have the same torque output from the trans on launch. Driveshaft torque doesn't change and it would seem that trans and converter life should be the same.

Less stress on the transmission with 4.56 vs 2.56 gearing..think about riding a bike in too tall of a gear vs a shorter gear

[Formulajones]

Originally Posted by ta man

Less stress on the transmission with 4.56 vs 2.56 gearing..think about riding a bike in too tall of a gear vs a shorter gear

Yes, everything involved. More rear gear just makes life easier on transmissions, driveshafts, joints, axles etc... Even the engine itself. Simply because you have more mechanical leverage to get the car moving.

[grandam1979]

Originally Posted by dragginwagon406@hotmail.c

Although not Pontiac, I accomplished this in a 1970 Monte Carlo with a stroked 454 on 225/70-15 Cooper Cobras. I used the factory 1970 small block TH350 converter too.

https://youtu.be/gANPkATqPmA

That’s very cool did you cross line in 2nd gear? That’s big mph for a high 11. You said it’s a stroked 454 how much stroke is it?

[77 TRASHCAN]

Originally Posted by ta man

Less stress on the transmission with 4.56 vs 2.56 gearing..think about riding a bike in too tall of a gear vs a shorter gear

Ernie, You done racing for the year???

[ta man]

I hope this weekend..been a tough year to get out..trans has been out for over a month..finally have it back..total rebuild. The tranny builder was surprised it will still almost dipping into the tens still the way it was! Don't want to hijack this thread much..but the condition of the trans may explain why the UCC convertor didn't work out well..plan is to try and get out before the tracks are closed with it and see what it does..goal is still 10.5 this year

[steve25]

Sorry, but I don't concider any car with less then 3.08 gears to be anything but a station / food store vehicle, even if you have a 4.500" arm in the short block.
I once had a 70 350 Lemams with the 2 speed TB300 trans, that was replaced within two weeks with a TB 400 due to its depressing level of acceleration !