What's rear gear ratio are you running?

[samert111]

My 68 C10 has a 12 bolt with a 3.08 gear and a Saginaw 4 speed manual which I really don't care for. This is all behind a GM crate 350 with a Comp Cams Thumpr roller cam, 1:6 roller rockers, Edelbrock Performer EPS manifold topped off with an Edlebrock 600 carb.

I'm planning on swapping out the Saginaw with a Tremec TKX 5 speed with a .72 final gear. This combo should give me just under 2000 RPM at 70 MPH with my 27" rear tires according to the calculator I'm using.

This would all make for a nice highway cruiser but still a little anemic off the line I'm thinking.

The Tremec ratios quoted are 3.27, 1.98. 1.34, 1.00 & .72.
What I don't know is what the Saginaw 1st gear ratio is exactly but from what I'm finding online it could be anywhere from a 2.54 to a 3.50.

I know the Comp Cams Thumpr cam is more for the SOUND and not so much performance but the truck scoots along pretty good as it is now.

So, I'm just curious what others are running for rear gear ratio's with similar setup. Maybe a 3.42 or 3.73 which would put me at 2160 RPM or 2356 RPM respectively at 70 MPH. Still not too bad I don't think.

[MySons68C20]

I have a similar combo only with a 383, 3.42 gears and 29" tall tire. The TKX has a low 3.27 1st gear so I think you should try before swapping in a lower (higher numerical) ring & pinion. When I ordered my TKX (arriving in the next day or 2) Gene at Silver State Transmissions said that would be a great combo.
Hope this helps!

[Keith Seymore]

Sounds like you need a 3.73:1 gear.

K

[Joyridin]

My automatic 6l has a .68 final drive ratio in the trans. I have a 3.73 rear gear with a 28" tall tire. It cruises great down the road. I was contemplating a 3.55 rear gear, but there wasn't enough difference to waste time or money with the change.

[samert111]

Originally Posted by MySons68C20

I have a similar combo only with a 383, 3.42 gears and 29" tall tire. The TKX has a low 3.27 1st gear so I think you should try before swapping in a lower (higher numerical) ring & pinion. When I ordered my TKX (arriving in the next day or 2) Gene at Silver State Transmissions said that would be a great combo.
Hope this helps!

Thanks,
I think that's a good plan. I eventually want to change out the carrier to a posi unit so at least this way I can try out the current 3.08 gears to see how it all feels.

I got my Tremec quote from Jeff at Silver Sport transmissions which I think is the same place as Silver State. Are they located in Rockford, Tn?

[Accelo]

For most street performance applications, a 10:1 final First gear ratio is usually considered optimal.
Unsure where you are at because of the unknown 1st gear ratio. You could get close if you have a tach and the speed in 1st.
Assuming your current ratio is 2;20 to 1 and the diff is 3.08 you have a 6.76 final drive ratio. Way too high for performance usage. However, the same 3.08 with the Tremec’s 3.27 ratio gets you to a 10.07 to 1 final drive ratio.

A TH200-4R overdrive automatic utilizes a First gear of 2.74, a Second of 1.57, a Third of 1.00, and a 0.67 Overdrive. With this transmission's First gear ratio of 2.74 combined with a 3.73 axle ratio, the final drive ratio >> yields a 10.22 (2.74 x 3.73 = 10.22)
That is the performance sweet spot. Many believe it's too low for the street and it certainly would be without the overdrive.
The first gear ratio matters a lot and because it takes little change to make a bid difference. Consider first the two Muncie gear ratios. 2;20 and 2:56. Finial drives are as follows;
Close
2.2*3.08 =6.7
Wide
2.56*3.08 =7.8

A full point difference in ratios!
A friend mine has the exact set up you have, Tremec with 3.27 and 3.08 gear in his Chevelle. He considers it too low of a ratio for the street. He changed his differential from 3.55 because he thought he was driving a tractor (11.06 ratio ) and didn’t like it at all. He considers the 3.08 barely tolerable and would have preferred a higher gear for first.
In review I am guessing you are not dragging your truck and just want a street-able ratio I suggest you aim for something in the 8 to 9 ratio. We are not 18 anymore, well I am not but occasionally dive like it. On a "Closed loop course!"
The Tremec is also available in more than one first gear ratio. Consider this as you can see the 3.27 ratio is really low, as far as first gears to, and it’s designed for more modern vehicles with higher final drive ratios.
I am including a chart with the different first gear and differential gear. The final drive ratios are given for first gear.
Happy ratios.

Tremec
3.27 3.08 =10.0716
3.27 3.70 =12.099
3.27 3.55 =11.6085
3.27 4.11 =13.4397

700R4/4L60
3.059 3.08 =9.42172
3.059 3.70 =11.3183
3.059 3.55 =10.85945
3.059 4.11 =12.57249

4 speed (close)
2.2 3.08 =6.776
2.2 3.70 =8.14
2.2 3.55 =7.81
2.2 4.11 =9.042

4 speed (wide)
2.56 3.08 =7.8848
2.56 3.70 =9.472
2.56 3.55 =9.088
2.56 4.11 =10.5216

Saginaw 4 speed.
2.54 3.08 =7.8232
2.54 3.70 =9.398
2.54 3.55 =9.017
2.54 4.11 =10.4394

[MySons68C20]

Originally Posted by samert111

Thanks,
I think that's a good plan. I eventually want to change out the carrier to a posi unit so at least this way I can try out the current 3.08 gears to see how it all feels.

I got my Tremec quote from Jeff at Silver Sport transmissions which I think is the same place as Silver State. Are they located in Rockford, Tn?

My bad....It is Silver Sport duh!

[MySons68C20]

Originally Posted by Accelo

For most street performance applications, a 10:1 final First gear ratio is usually considered optimal.
Unsure where you are at because of the unknown 1st gear ratio. You could get close if you have a tach and the speed in 1st.
Assuming your current ratio is 2;20 to 1 and the diff is 3.08 you have a 6.76 final drive ratio. Way too high for performance usage. However, the same 3.08 with the Tremec’s 3.27 ratio gets you to a 10.07 to 1 final drive ratio.

A TH200-4R overdrive automatic utilizes a First gear of 2.74, a Second of 1.57, a Third of 1.00, and a 0.67 Overdrive. With this transmission's First gear ratio of 2.74 combined with a 3.73 axle ratio, the final drive ratio >> yields a 10.22 (2.74 x 3.73 = 10.22)
That is the performance sweet spot. Many believe it's too low for the street and it certainly would be without the overdrive.
The first gear ratio matters a lot and because it takes little change to make a bid difference. Consider first the two Muncie gear ratios. 2;20 and 2:56. Finial drives are as follows;
Close
2.2*3.08 =6.7
Wide
2.56*3.08 =7.8

A full point difference in ratios!
A friend mine has the exact set up you have, Tremec with 3.27 and 3.08 gear in his Chevelle. He considers it too low of a ratio for the street. He changed his differential from 3.55 because he thought he was driving a tractor (11.06 ratio ) and didn’t like it at all. He considers the 3.08 barely tolerable and would have preferred a higher gear for first.
In review I am guessing you are not dragging your truck and just want a street-able ratio I suggest you aim for something in the 8 to 9 ratio. We are not 18 anymore, well I am not but occasionally dive like it. On a "Closed loop course!"
The Tremec is also available in more than one first gear ratio. Consider this as you can see the 3.27 ratio is really low, as far as first gears to, and it’s designed for more modern vehicles with higher final drive ratios.
I am including a chart with the different first gear and differential gear. The final drive ratios are given for first gear.
Happy ratios.

Tremec
3.27 3.08 =10.0716
3.27 3.70 =12.099
3.27 3.55 =11.6085
3.27 4.11 =13.4397

700R4/4L60
3.059 3.08 =9.42172
3.059 3.70 =11.3183
3.059 3.55 =10.85945
3.059 4.11 =12.57249

4 speed (close)
2.2 3.08 =6.776
2.2 3.70 =8.14
2.2 3.55 =7.81
2.2 4.11 =9.042

4 speed (wide)
2.56 3.08 =7.8848
2.56 3.70 =9.472
2.56 3.55 =9.088
2.56 4.11 =10.5216

Saginaw 4 speed.
2.54 3.08 =7.8232
2.54 3.70 =9.398
2.54 3.55 =9.017
2.54 4.11 =10.4394

Great info Accelo, thanks for the weighing in!
BTW, this site rules!!

[AcampoDave]

I have a 3.08 rear with a Muncie M22Z. It has a 2.98 first gear and I am very happy with the launch ratio of 9.18 It really hits the sweet spot with a 30" tire.

[Accelo]

I noticed the other 1st gear ratio for the TREMEC TKX 5-Speed is 2.87.
My buddy, with the Chevelle, wishes he would have gone with this ratio instead of the 3.27's.

Here is what he said:
"You end up short shifting it. Like two gears before you get through the intersection.
The 3.27 would be way more tolerable if it was an automatic".
His recommendation, not mine.

2.87 * 3.08 =8.8396

Right at 9-motor revolutions to 1-tire revolution.
I consider 10 to 1 better only when performance is more important than drive-ability.

Cheers

[samert111]

Originally Posted by Accelo

I noticed the other 1st gear ratio for the TREMEC TKX 5-Speed is 2.87.
My buddy, with the Chevelle, wishes he would have gone with this ratio instead of the 3.27's.

Here is what he said:
"You end up short shifting it. Like two gears before you get through the intersection.
The 3.27 would be way more tolerable if it was an automatic".
His recommendation, not mine.

2.87 * 3.08 =8.8396

Right at 9-motor revolutions to 1-tire revolution.
I consider 10 to 1 better when performance is more important than drive-ability.

Cheers

Thanks or the follow up. I see your friends point and now I'm questioning which 1st gear rato to go with now. I called the vendor and he specifically selected the 3.27 1st gear based on my current gear and tire size. So I think I need to have another conversation with him.

[samert111]

Originally Posted by AcampoDave

I have a 3.08 rear with a Muncie M22Z. It has a 2.98 first gear and I am very happy with the launch ratio of 9.18 It really hits the sweet spot with a 30" tire.

I'm currently running a 28" tire and plan to drop to a 27" tire to get the tire width I'm looking for so the 2.87 first gear is looking more like what I would need.

[AcampoDave]

I'm currently running a 28" tire and plan to drop to a 27" tire to get the tire width I'm looking for so the 2.87 first gear is looking more like what I would need.

I would agree as long as the overdrive doesn't come up being too deep with a 3.08.
Edit, you also have a 350 and I only have 283, so your bound to have more torque at any rpm than I do.

[samert111]

Originally Posted by AcampoDave

I'm currently running a 28" tire and plan to drop to a 27" tire to get the tire width I'm looking for so the 2.87 first gear is looking more like what I would need.

I would agree as long as the overdrive doesn't come up being too deep with a 3.08.
Edit, you also have a 350 and I only have 283, so your bound to have more torque at any rpm than I do.

I need to find out what my current 1st gear is. Right now I would like it to be a little more aggressive from a stop so If I have something like a 3.0 or less then I think the Tremecs 3.47 1st gear is going to be what I'm looking for.

[geezer#99]

I’ve run a sag with the 3.11 first gear and a 3.7 rear gear.
First gear was a quick flash to 6 grand. Not ideal but super easy to get moving.
You can tell the first gear ratio by the rings on the input shaft. Info in this link.


https://www.chevyhardcore.com/tech-s...transmissions/

[AcampoDave]

I suppose you already know about the Sanginaw and their identifying "rings" etched into the input shaft. I used to run a 3 ring with the 3.50 first gear and that thing was too low for a 3.08 even. I used to run a 2.76 rear with it and it was well suited upon take off, but it was just too much gear for a 283 in the hills. 4th was like being in OD.

Edit: that's a good article Geezer.

[samert111]

Originally Posted by AcampoDave

I suppose you already know about the Sanginaw and their identifying "rings" etched into the input shaft. I used to run a 3 ring with the 3.50 first gear and that thing was too low for a 3.08 even. I used to run a 2.76 rear with it and it was well suited upon take off, but it was just too much gear for a 283 in the hills. 4th was like being in OD.

Edit: that's a good article Geezer.

I knew about the input shaft rings but not the breakdown. Unfortunately, the trans is still in the truck and although I can see the clutch and bearing assy thru the inspection cover, I don't think I can see the rings without pulling the trans back at least.
I need to slip the clutch a bit to get it going so I'm thinking it's got the 2.54 1st gear.

[Accelo]

Just post the rpm and speed, in first gear, while cursing steady. If you speedometer is correct I can approximate the ratio from the tire size and gear ratio which you have already posted. No need to pull the transmission.
Cheers

[samert111]

Originally Posted by Accelo

Just post the rpm and speed, in first gear, while cursing steady. If you speedometer is correct I can approximate the ratio from the tire size and gear ratio which you have already posted. No need to pull the transmission.
Cheers

Thanks,
We're gone for the winter and not back until mid April. Once I get back I'll do as you suggested.

[Tom]

3.42 with a .70 overdrive or whatever a 4L60E runs. Excellent daily driver combo.
In my 78 its 3.73's with 1:1 final. I don't take it on the freeway lol.

[Accelo]

Consider how far modern cars have taken this.
2006 corvette has;
2.56 diff ratio and a 4.02 first gear in the automatic. (For a 10.29 final drive ratio)
Not much difference in the first gear final drive ratio is there?

On the top end a lot of difference.
2.56 with a .67od ratio is a 1.72 final drive. (4L80E transmission)
With the Muncie and others it's just the 1* the differential ratio or just the diff ratio.
Say 3.73's, if you cut the Corvette's ratio in half it's still a higher @ 3.43.
Ultimately the motor is turning less than half the rpm of the average 60 car.
One can't run a 60's motor this slow without fuel injection. It would buck like a horse.
Simply put typically the newer the transmission the lower the first gear and the more gears there are.
Cheers

[Chevy nutcase]

My 66 c10 that I bought last year came equipped with a 3:73 posi rear and a brutal sm420 tranny. I swapped the rear out for a 5 lug and rebuilt it with new 3:43 gears. It helped the screaming problem at 55 mph but after driving it around for a while now I think the sm420 has to take a hike. 1st is 7.06:1 2nd is 3.58:1 3rd is 1.71:1 and as you might guess 4th is 1:1. I've heard hardcore offroad rock crawlers love these ungodly low geard boxes but its unpleasant as a driver. 1st is so low its useless unless pulling out on a steep hill as it will get you to 3 or 4 mph before the engine detonates. I can pull out in 2nd very easily but I have to wind it way out because 3rd is so high. Was thinking a tremec or even a T5 out of a mid 80s to early 90s s10. Yea I know they were never built to take gobs of hp but I have no plan for that

[Ziegelsteinfaust]

I have a 73 C10 with a hot LT1 350 backed by a Th700r4 with 4.88 gears, and 31 " tires. Or 285/65r17.

It's ways got the passing power.

[tdangle]

1970 C20. Mild 350, 7004R with 2400 stall and 4.10 rear. 31.5" tall tires.

[D.B]

72 C20 with a 511 BB, T400 2200 rpm stall, Gear Vendors, 4.10 gears with locker and 33" tires.