700r4?

[1LowToy]

What's the final drive ratio of a 700r4?

I've checked on a gear ratio calculator and found I can lower the RPM @6o by about 250 rpm by changing from 342 to 308:1. Just wondering what a 700r4 would get me. Anyone have any info on this? Who knows I could gain some fuel mileage in a box

[Jonboy]

700R4 OD is .73. It will also gain you a lower 1st gear (3.08, vs. 2.52 in a TH350) to get your truck moving. Try to find one '87 or later to get the upgraded pump and auxillary valve body.

[foamypirate]

If I'm not mistaken, the 700R4s OD is actually .70, I believe.

[Jonboy]

On second thought, I think you are right. FYI, the 3.42 is almost ideal for the 700R4, IMO.

[glock35ipsc]

Originally Posted by Jonboy

FYI, the 3.42 is almost ideal for the 700R4, IMO.

I agree. That's the combo I'm running (4L60E, but same ratios) and it's perfect all around.

[gchemist]

My ZZ4 gets 18+ MPG at 70 with 3.08 gears and 700R4. Tires are 255/60R15 all the way around. Tire size is important. On a stock engine, you want cruise RPMs near 2000. Different tire sizes and rear ratios will achieve 2000 RPMs.

[1LowToy]

I've been tinkering with this gear ratio calculator www.csgnetwork.com/multirpmcalc.html

I may be just under that sweet spot of 2k rpm with my 275/60 tires and maybe a little underpowered with an I6. Does anyone know what gear ratios came with the I6/700r4 combo? Mine is an 80 model that has I6/TH350 and 3.42:1. I have an 86 700r4 and all the attatchment goodies but need to decide if I should go ahead and get dirty doing it.

[gchemist]

OHV Six-cylinder 250 cid. (130) @ 3800 rpm - 1980
OHV Eight-cylinder 305 cid. (155) @ 4000 rpm - 1986
OHV Eight-cylinder 305 cid. (160) @ 4400 rpm - 1986

The I-6 is under powered. You should run RPMs higher to use the OD gear. 3.42 gears should work great with higher RPMs. It would be nice to know the peak torque RPM. A factory manual or sales brochure should have it listed.

[1LowToy]

It runs at 2800 @ 65mph now. Here in California I,m gettin runover on the feeways. When their not back logged in traffic speed are a wee bit higher than posted

[D13]

250 L6 was never offered with 700R4 as far as I can tell. usually TH350 with 2.97 or 3.08 gears and 225 15" tires.

4.3 700R4 came usually with 3.08's and either 225/75R15 or 235/75R15

The lugging torque of the 250 should let you run 3.08's at 60mph or so, probably won't be happy at under 2000 RPM at 70 (wind resistance gets nasty over 60mph). I'd aim for 21-2200 RPM minimum at 70 with a 250. Realistically that means 3.23's with a 700R4.