Manual transmission gearset selection

[CTX-SLPR]

Howdy,

Well I'm messing with my first manual trans vehicle. A '78 Regal with a 3.8L 2bbl and a Saginaw 4spd. The 3.8 is dead so I'm going to be dropping in my 4.1L V6 since its pretty much a direct swap and it will be nice to test the engine out in a smaller and lighter car. I don't know the ratios on the Saginaw or how well they work but I'm wanting overdrive and a shorter rear gear so a T5 is in the works. Since its a straight bench car, I'm going to be using an S-10 tailhousing and coresponding mainshaft. I'm going to build it from the ground up so I'm wondering if I should get a 2.95, 3.35, or a 3.50 first gear sets. Of course the 2.95 is the strongest and lowest but I'm not sure the NA V6 (its only 8.3:1 compression with ported heads and a 212/212 cam) would work well when paired with a 3.42 rear end. Ford puts the 3.35 with its V6's in the Mustang while GM put the 3.50 with the 3800 V6 in the last gen F-bodies. I'm using an electronic speedo so I'm using a WC case so it opens the gearset selection. Advice, thoughts, comentary?

Thanks,

[min301]

Re: Manual transmission gearset selection

Given the lack of torque(it 's a V6, after all), I'd pick the 3.50:1, and you still enjoy the benefits of overdrive.

[squirrel]

Re: Manual transmission gearset selection

saginaws had something like 2.5 to 3.4 first gear ratios available, I think. there is a list somewhere on the internet, you count the grooves on the input shaft. Extra wide ratio was used in the Vega, close ratio in Chevelles and stuff with medium sized V8s.

[CTX-SLPR]

Re: Manual transmission gearset selection

I'm bettering on a 1 stripe with a 2.84 first, thats the second closest ratio box, but I could very easily be wrong. I know people hated the 3spds.
I'm leaning towards the 3.35 gearset since its likely to be more common being the standard Mustang ratio for years. The 3.50 with a 3.42 would make 1st gear rather short with 20mph coming at almost 3000rpm. But then again I've never owned a manual so I don't know how far you are supposed to get in 1st.

[Two Lane Blacktop]

Re: Manual transmission gearset selection


The 2.84 & the 3.42 would a good choice. <-- 2.84 first gear w/a 3.42 diff


A 3-series 1st-gear would be a great clutch-saver if you are in hilly country and/or carrying loads.



The Regal has what ratio now? 3.42? <--Has what *rear* ratio now?


What necessitates an S-10 diff swap?
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May not have been clear first-time around. ---

[CTX-SLPR]

Re: Manual transmission gearset selection

Stock ratio is 2.73 with the 4spd Saginaw. If it was the 3spd Saginaw it would be a 2.93.

[CTX-SLPR]

Re: Manual transmission gearset selection

Well the stock car is set up like this:
2.73:1 rear axle, silly 14x7in wheels with 25.5in tall tires
The transmission I think is a 2.84:1 low Saginaw but Saginaw's were made with 2.84, 2.54, 3.11, and 3.50 low gears. I think its either the 2.84 no stripe or the 3.11 2 stripe unit.

I'm thinking 3.42 or 3.73 rear axle depending on the 1st gear ratio and an upgrade to 15in wheels with around a 26.5in tire. The S-10 stuff is in the transmission, the S-10 has the most forward of the T-5 shifter locations that isn't a remote linkage and the mainshaft is needed to match to the speedometer gear location. The F-body shifter location is right under the leading edge of the bench seat so thats not as usable. With the turbo cam and the increased displacement, I think think I should be seeing decently near the 3800 in the F-body type of power levels despite being just over a point of compression down.

[CTX-SLPR]

Re: Manual transmission gearset selection

BTTT, any comments?

[Eric68]

Re: Manual transmission gearset selection

Unless the engine has a narrow power band I would opt for the deepest first gear you can get -- the 3.50 1st and the 3.73 rear gear would be my choice. Mainly due to the lack of TQ your 6 banger will have compared to a V8 -- gearing will help that.

[Saltfever]

Re: Manual transmission gearset selection

You said you wanted to go to an overdrive. So go to the lowest 1st gear you can get and lower (numerically) the rear gear. That way you get a great starting ratio but when your in 4th you are in overdrive! Also, 4th gear (direct 1:1) is more efficient than any overdrive.

That trans sux. Weak front main bearing. See if you can substitute the thin (narror race) automotive ball bearing for a commercial wider (race) bearing.

[CTX-SLPR]

Re: Manual transmission gearset selection

Well my choices for overdrive are basically the T-5 or an AX-15 and I don't think this engine has quite the powerband needed for a wide ratio low rear gear setup like you are talking. This is a very low budget project since the transmission is there to support the engine as a cheap test bed vehicle on powertour. I'm planning on upgrading the bearing and retainer to an aftermarket unit. I'm really thinking of getting which ever 3.35 or 3.50 gear set is cheaper than then picking the rear axle to match. This engine is going to do most of its power in the low rpm range since the turbo cam really limits overlap I'm going to get good, well for an 8.0 compression, cylinder pressure down low and its limited to 5500rpm. Any commentary? I know of 2.95, 3.35, 3.50, 3.9#, 4.03, and the insane 2.5L 4cylinder 4.30 low ratios.

[TheSilverBuick]

Re: Manual transmission gearset selection

Unless the engine has a narrow power band I would opt for the deepest first gear you can get -- the 3.50 1st and the 3.73 rear gear would be my choice. Mainly due to the lack of TQ your 6 banger will have compared to a V8 -- gearing will help that.

After driving a beat 231 in a '77 Skyark with 3.23's and a 200R4 (.68 OD) the engine had no problems for the most part in overdrive (lugging). Going up decent grade hills it'd have to go to third but wasn't all that bad. Overall I was happy with the gearing for the output the engine had, but it was by NO means fast. For a little more performance I'd have to agree with Eric, unless you plan on putting the Turbo on in that car then a taller GN rear gear of 3.42 would probably be just right for quickness and mileage.

[CTX-SLPR]

Re: Manual transmission gearset selection

hard to compare an auto to a stick isn't it?
I'm thinking 3.50 and 3.42 (11.97 low ratio, 2.46 OD) or 3.35 and 3.73 (12.50 low ratio, 3.29 OD). Though I think you can mix and match the OD gear sets as long as you stick to GM or or Ford sets.

[Saltfever]

Re: Manual transmission gearset selection

CTX. I'm confused, you keep talking about an overdrive but you said you had a Saginaw 4-speed in the first post. The 4-speed did not have an overdrive. The 3-speed could have an overdrive. I was talking about the 4-speed (4th is 1:1 direct).

You know your driving environment. You probably know your torque curve. If you have a 4-speed I would gear it for use as a 3-speed in the city and go direct (4th) for highway cruise. That means to gear the rear accordingly. Put your ratios in excel and plot rpm vs the engine torque curve. I would set the rear gear so 4th rpms slightly under the peak torque (Max VE and efficiency) at the cruise speed you will be using on the highway.

[CTX-SLPR]

Re: Manual transmission gearset selection

It has one now, I'm not planning on keeping it.