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Good Gear with 700r4?

10K views 14 replies 8 participants last post by  PHWOARchild 
#1 ·
Searched here and could not get a good answer. I have a 3.36 gear with my 700r4 in my El Co right now. Peg leg and will be going to a Yukon Posi unit I bought. While there should I go with 3.55 or 3.73? I like the idea of running at 2200 at 70. But know that it will only be like 2450 at 70 with a 3.73. Actually less drone from the damn Flowmaster at 2400.

Had them in a Mustang GT with the same .70 last gear in the 4WR70 it had years ago and they were a great blend. In fact less throttle around town means better overall mpg. The Stang had a 3.08 gear and moaned driving it or just not seeming to not work right. Seems the same with the El Co. Just not crisp at lower speeds around town. Stangs Gears are 2.84, 1.54,1.00, .70. Where the 700r4 is 3.06, 1.62, 1.00, .70. Did not see any difference in MPG at 70mph either with the Mustang. Of course we are talking Fuel Injection and better Aero.

I think I am talking myself into them? Can anyone give me some experience with a similar combo? I have a 350, Vortec Heads, Comp 268HE Cam 1600- 5500 range, 10.1 C/R, Headers, 600 Holley and a Jegs high rise.
 
#4 ·
I had an 1986 Monte Carlo SS with a 3.73:1 limited slip (G80 code), and a TCI 200r4 w/stock convertor. Not as low a 1st gear as a 700 and just a tad lower OD (.67), a mild 350 w/260 cam, 600vs Holley aprox. 325HP.
Many times the tires would just break loose on hard accel from stop in 1st when I didn’t want them to. Much worse turning into flow of traffic pulling out of a parking lot trying to get up to speed quickly and can’t because tires are spinning(15” 245s). Gets downright dangerous with just a slight bit of moisture on pavement. Must wait for lul in traffic for ample time to pull out easy.
Made for a pretty good 2nd gear that shifted into 3rd right at 60mph which coincided with the B&M adjustable lock-up kit for the convertor. Barked em in 3rd more than a few times. 70MPH was just under 2500rpm. Visited the gas pumps more often than I liked and that was when it was $1.50 gal. If I could have more consistent traction in 1st I could live with the fuel bill as it was fun to drive.
Good luck!
ssmonty
 
#5 ·
Are you running a stock convertor ?
Convertor and Tire size will play a big part in final cruising RPM

I have a 94 SS S10 with a 5.7L Gen II LT1, Aluminum Heads, Roller Cam, Lifters, & Rockers, 10.5:1 Compression. Built 700R4 Trans, 2500RPM Stall Convertor, 8.5” Posi Rear w/ 3.42 Gears, running 295/50R15's

As much as I would prefer 3.7 gears, the 3.4's are perfect for me because it allows me to cruise at 75 to 80 all day long. Due to my convertor in my case if I went to a 3.73 I would clearly be over revving at 80 even in OD

Example here I am just casually cruising on the parkway at 75 to 80
The 2500 RPM pic is just lightly on the pedal enough to maintain speed in OD. The 1800 RPM pic is when I let off the pedal and let it free wheel off the convertor.

For me this is the perfect gear for my set up because with the high RPM convertor it's really fast and responsive on the street and I can still cruise at 80 on the parkway
 

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#6 · (Edited)
Tires and Converter

Are you running a stock convertor ?
Convertor and Tire size will play a big part in final cruising RPM

I have a 94 SS S10 with a 5.7L Gen II LT1, Aluminum Heads, Roller Cam, Lifters, & Rockers, 10.5:1 Compression. Built 700R4 Trans, 2500RPM Stall Convertor, 8.5” Posi Rear w/ 3.42 Gears, running 295/50R15's

As much as I would prefer 3.7 gears, the 3.4's are perfect for me because it allows me to cruise at 75 to 80 all day long. Due to my convertor in my case if I went to a 3.73 I would clearly be over revving at 80 even in OD

Example here I am just casually cruising on the parkway at 75 to 80
The 2500 RPM pic is just lightly on the pedal enough to maintain speed in OD. The 1800 RPM pic is when I let off the pedal and let it free wheel off the convertor.
For me this is the perfect gear for my set up because with the high RPM convertor it's really fast and responsive on the street and I can still cruise at 80 on the parkway
So 3.42? I don't think that would be a big change from my 3.36. Tires are 215/65/15's. 26" Tall. Yours according to TireRack are 26.7 so both of ours are probably very Similar in the way they drive. My converter is a 2025 Stall. I just have switch to go in and out of Lockup. The revs are pretty good with the Converter just above it's stall at 70 and if don't want to lock it. Only do this if I am standing on it. Then hit the switch and lock up cruise like another gear.

.
 
#7 · (Edited)
Convertor wont matter for cruise rpm, so long as you use a lockup unit. Only tire HEIGHT, rear gear ratio and high gear ratio will affect cruise rpm with a properly working lockup 700r4 trans.

I agree with ProStreetRobs recommendations as they are the same as mine, except he uses the lower height around 26" 295/15 tire, while I run the 28" 275/60/15 and 325/50-15, both of which are 28" tall tires.
3.73 is great with a 28" tire
4.10's rev a bit too high for 70mph cruising on the freeway, but great for drag racing
3.42 are great for 70mph cruising, just a bit high for drag racing, again with 28" tires.
All with a 700r4 with a lockup TC.

I suggest a 4.3 V6 with codes DCLF or DBLF, if you are sticking with a stock TC. On my stock longblock L31's(Vortec 350's) it gives about 2800-2900rpm of stall speed. Less rpm drop at WOT upshifts, it helps to reduce the massive rpm drop experienced in the 700R4/60/60e transmissions. Obviously better performance can be had from a performance TC, but you are going to pay double-quadruple the price as we..

Good read here.
http://www.corvettefaq.com/c3/THE HERD Torque Converter Upgrade.htm

You'll get more acceleration bang for buck from a good torque converter than from gearing IMO.

peace
Hog
 
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#9 · (Edited)
Gears and weight.



Yes you are correct the 65 El Camino's have the wimpy 8.2 in it and 3.55's are the next step. I finally hammered it from about a 10 mph roll and I don't know? It lit up the peg leg with 3.36 and got a solid 2nd gear rubber as well. I bought the trans from A&A in Independence MO and it has a shift kit and a bunch of other mods to make it more heavy duty correcting all the short comings of them. Motor is pretty stout and the car is pretty fast so I my just stay with the 3.36 for good mpg as I am going to drive it on some rod runs of around 600 miles round trip. Still think the 3.73's maybe OK. Never can get enough of more performance!!

Weight. I think many people group the 65's in with the later 68's to the fat *** Laguna's. The 65 El Co's are fairly light at 3235. 700r4 maybe another 50 at most as those years you have the powerglide and the M21 4 speed. That is as light as most new "high tech light cars". My C5 Vette is about the same weight as well. For your viewing pleasure... I have copied the weight spec for the 6cyl and 8cyl models and pasted this below from the official Chevy spec page :
 

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#10 ·
I recently sold my 67 Elky with a ZZ572 in it, I love the early years :thumbup:

I have a non lock up convertor so no matter what MPH, RPM, or Gear I'm in, if I give it any gas I'm at a min of 2500 RPM +

On my Fords with 4R70W or 4R100 OD Trans as long as your running a lock up convertor you can run 3.5 or 3.7 no problem.
 
#13 · (Edited)
Ford Over Drives



Had a 97 Mustang with a 3.73 gear and a 4r70W. Loved that combination. Now the first gear in the 4L60 or 700r4 is 3.06 to the Ford 2.84. So I am assuming it would make it more like a 4.56 gear with the 700r4.

4R70W - 2.84 x 3.73 (Ring and Pinion) - 10.59lbs of torque X 100 lbs delivered = 1059lbs
700R4 - 3.06 x 3.55 (Ring and Pinion)- 10.86 " " " " = 1086lbs
2nd Gear is also interesting -
4R70W - 1.55 x 3.73 - 578lbs
700r4 - 1.63 x 3.55 - 578lbs
Same 3rd gear
4th gear @ .70 ratio the 3.55's will run about 100 rpm slower on the highway at 70.

So with 3.55's in a car that weighs around the same and 700r4 it should shift and drive much the same as the Mustang I had with 3.73's. Just makes sense. I have original peg leg 3.36's now. So the 3.55's look like would mimic the Mustang GT. May stay with the 3.36's when I add the posi unit. 350 has more torque than the 4.6 or 281 Ford. 3.55's are high price - 280.00. 3.73's are like 179.00.
 
#11 ·
The Stang had a 3.08 gear and moaned driving it or just not seeming to not work right. Seems the same with the El Co. Just not crisp at lower speeds around town. My converter is 2025 stall. Comp 268HE cam (???)
The low stall converter is prolly causing that feeling... need about a 2500 - 3000 RPMs stall lockup converter with a Comp "268HE" (??? XE 268? 268H?) cam. The engine at low RPMs is low on the cam's torque curve and feeling weak before it 'comes up on the cam' and starts pulling hard...
 
#15 ·
Plug & chug some ratios into an RPM calculator for 3rd and OD and see what the numbers look like. The 3.55 is not that big of a jump from the 3.36 you have now. 3.73 should be about right, I would do 3.89 and 4.11 just for comparison. I run a 3.89 in my car with a 28.9" tire, 4th gear is about 3200 RPMs at 70.
 
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