Gearing for performance TH700R4 + 3.73 ?

[Logbed]

Thanks for the very good insights. The trans&gearing mod is not for free nowadays, but sounds like worth it. I might even go for the suggested 4.10 gears as there's always the option to go back a little in overall gearing by changing the tires to higher profiles (which In my eyes fit well to a longbed truck that rides on stock height).

With the current TH350 and 3.43 I need to reach 30mph to reach 3000rpm and before that its waiting for the engine to wake up. According to my dyno curve, the 4.10 gear & 700r4 & 3000stall would lift the rpm at 0 to 22mph speeds from 2000 to 3000 which would bring the power up from 100 to 155hp at rear wheels. That should make a difference.

Of course there is the option of keeping the TH350, changing the gear to 3.73 and converter to 3000 stall. A lot cheaper, but would it work for my goals at all?

 

[Logbed]

Had the same setup in an 85 el Camino. World Product 305 heads, 700 and 3:73 gears. Despite my comments about 305's, it ran pretty darn good. The 3:73 we're a perfect compliment to the 700.

Ordered an upgraded TH700-4r trans, will be installing it next month. Now thinking about the gearing... How big were your rear wheels in the El Camino? I was toying with a gearing calculator and noticed that if your tire size was anywhere near normal El Camino, my truck with 275/60R15 or 255/70R15 would have equal overall gearing with a 4.10 (compared to what you had with 3.73 and smaller wheels)?

 

[SquareRoot]

The rears were 255/60/15. Would have to Google the diameter.

 

[hogdaddy]

I have 3:73 rear w/ Eaton posi in my 86 Scottsdale w/700 r4 and feel it's perfect.

 

[Matt69olds]

I’m betting with 4:10 gears and a 700 with the converter locked, you will be almost identical cruise rpm as with the non lockup 350 and the current gearing. Keep in mind, he non lockup 350 has about 250-300rpm of slippage at highway speed.

I bet a decent 305 with 4:10 and a 700 will run pretty well.

 

[Logbed]

The rears were 255/60/15. Would have to Google the diameter.

I checked the diameter and used a gearing calculator. Your 3.73 El Camino gearing was indeed almost excactly the same as 4.10 with 255/70R15 tire size.

 

[Big Ray]

went from 3.42 to 4.10 in my 89 with a 700r4.
Much more usable as a truck. Imo...

 

[82sbshortbed]

Just git mine back this week with new 700r4 2,200 and 3.73 posi rear end. I gotta tell you it's much better than the th350. It shifts pretty hard with no shift kit. Low 1st is nice and I can run 65 mph at about 2,200 rpm. Just what I was looking for. 275/60/15 too. Posting on my phone is getting fcking irritating as it's all fcked up. Mods come on I'm not the only one. Need this fixed. It's on and off but mostly fcked up and I have to keep going back and fixing it. I can't post paragraphs because when I hit enter to separate them it puts a mile of spaces and jumbles the words. I can't even post a fcking smiley face either. Grrrrr!!!!