Let’s talk.

We can all use our Turnpike Cruiser Rear end, No?

Super T-10 that is.

 

Sounds good to me.

I recall reading years ago about better acceleration of a low rear gear rear vs. a high rear gear + a low 1st gear trans. The author argued that a low 1st gear ratio in the trans allowed good takeoff while providing slower driveshaft and pinion bearing speed once in high gear (cruising speed). The lower rear gear gave higher driveshaft and pinion RPM at cruising speed, even with an overdrive trans that dropped engine RPM, which results in increased drivetrain wear.

 

Just realize that the torque capacity of the T10 with such a low gear is quite low. With 8620 gears, the 2.43 is about the lowest that has good strength for performance use. That is why I went with 9310 gears when I got a T10 with 2.88.

 

To add to what Joe wrote, check out this fact sheet about the various Super T10 versions.

https://www.richmondgear.com/wp-cont...hmond/RG26.pdf

 

2:56 gears, good for Bonneville or a top end speed mile. (:•》

 

The rear end ratio by itself doesn't tell you anything. It's the effective final drive ratio that matters. As the OP has figured out, 2.56 gears with a 3.42 first gear ratio in the trans is 8.76 effective final drive in first. That's exactly the same as if you had a 3.42 rear end and an M20. Other than the issue Joe D brought up about trans strength, there is no difference from a performance standpoint. In fourth, you have 2.56 with the T10 vs 3.42 with the Muncie - or basically the same ratio on the highway as you would with a GV behind that M20. The only downside is the RPM drop between gears with the wide ratio T10. With the T10 and 2.56 gears, final drive in second is 4.89. With the M20 and 3.42 it's 6.43. That's a big drop; how bad that is for performance depends on the torque curve of the motor. Unfortunately, this is the problem with wide ratio transmissions, which is why we have five and six speed manual transmissions.

 

Soooo,

I am feeling pretty good being able to leave my rear end alone on my conversion from automatic.

I've had this car for 16 years and my usage has only been cruising to shows etc - no rough stuff anyhow.

 

Yeah, nearly a 100 ft/lb drop rating for the 3.42 first gear T-10. Are the Richmond trans the weaker 8620? Pretty low ratings for an aftermarket trans.

 

Yes they are 8620, as are most gear sets and regular differential gears. The T10 ratings might be on the conservative side, I don't know. I do know that the gear gets very small as the ratio number gets bigger, and that is the critical part. Some other manual transmissions have larger gears to accommodate steeper first gear ratios with more strength.

 

1974-’77: 2.43
1977-’79: 2.64
1979-’81: 2.88
1980-’82: 3.42

https://www.hemmings.com/blog/articl...10-four-speed/


Something to keep in mind, when the factory paired up these transmissions with a engine etc. The transmissions torque rating stayed 25 lb ft above factory engine rating or better.

For example, take a look at 2 of the most powerful cars money could buy in the late 1970s.

1980 Corvette L82 with 230 HP and 275 lb ft, it was paired with the 2.88 ratio trans with 300 lb ft rating. Not the 3.42 ratio with 286 lb ft rating.

1977 400 CID Trans Am with 200 HP and 325 lb ft, it was paired with the 2.43 ratio trans with 375 lb ft rating. Not the 2.64 ratio with 325 lb rating.

If you have the same 350 I have our engines should only be paired with the 2.43 ratio trans... if you want to play it safe.

1968-1970 Oldsmobile High Compression 350 rated at 310 HP gross and 390 lb ft gross is 240 HP net and 330 lb ft net, when true dual exhaust.

 

264 first gear with a nodular main case will handle a big block with nitrous I have built 6 units and all have survived the track and the street