FI with 3.70 rear end and a close ratio best?

[Ridge K.]

Re: FI with 3.70 rear end and a close ratio best?

THANK YOU SO MUCH FOR THAT INPUT!!!!!
I needed someone in my corner!
My 70 Chevelle conv has factory air (it was originally a 307 3sp), a well built SB400 (probably close to a 350hp/396), M-20 and 3.07 12bolt posi. It makes a few passes at the strip each year at Chevellabration and it is DRIVEN to and from the event each year (OKC to N'ville) as well as local crusin' and Interstate driving. The SB400-M20-3.07 combo does just great for all around driving.

Glad to be of help, Tom,.....but...I need to qualify it.
My '67 L68 400hp Corvette convertible now undergoing a nut & bolt restoration is going back with it's original 4:11 posi and close ratio. It will also be a driver, so this will be interesting crusing down Pacific Coast Highway.
I've driven these babies for coming up on 40 years and haven't found a bad combination yet, as long as they had both torque & horsepower. I guess that's why I've always been a big block guy. You always seem to have that spare torque.
Stop by the next time you're over in Tulsa and we'll take it out and smoke the tires with that old 3:08. It'll smoke them in the first three gears.
Ridge

[Stewart A.]

Re: FI with 3.70 rear end and a close ratio best?

Well in 1985 GM brought this weapon out in Aussie Land. A 3.08 rear M21 4 speed and I took it took Calder Raceway and ran mid 13's all day until the clutch fried itself. This car was fast it never got dusted by anything factory. It was a 5 liter 308 cube and an absolute pleasure to drive distances. I used to pull 65 miles an hour in first gear. So to summarize what we have been saying yeah 3.55 3.70 4.11's would of made it a tire fryer but would of killed it's top end speed and driver ability. Stewy
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[Tim S.]

Re: FI with 3.70 rear end and a close ratio best?

hi all, I'm about to get a T10 built for my 59 FI 290 HP and I would like to know if I should stick with a close ratio for the gear set? The rear end is 3.70. From what I can tell from other threads this would be the recommended way to go based on the rear end I am going to use. Thanks in advance!

Provided you are firm on keeping your rear gear ratio, the close ratio trans will probably work the best. You may want to check with one of the specialty companies to see if you can get a overdrive 4th made up (perhaps .90). This would settle the car down a little on the highway.

Tim

[Ian G.]

Re: FI with 3.70 rear end and a close ratio best?

So would that make it behave somewhat like a 3.36 rearend?

[Paul Y.]

Re: FI with 3.70 rear end and a close ratio best?

I just returned from a 1300 mile road trip in southern and western Colorado. I have a 63 FI with 336 and close ratio. It is a pleasure to drive. I would put a 308 in it if I found one. I think the fuel injection gives it more torque and bottom end. I was driving part of the trip with a friend and his 39 Ford Standard coupe with 60 horse engine. I got around 20 mpg throughout the whole trip. 10k and 11k mountain passes require about 1/2 inch of throttle. We're working on our second 80k miles on the car. The car handles city driving quite easily as well. My vote is for a highway gear if you like to drive it.

[Ian G.]

Re: FI with 3.70 rear end and a close ratio best?

I bet that was a super fun trip Paul Couldn't you have taken a picture of your car from the front? I get the idea that its a 63. Just kidding :P
I really love the color. What name did GM give it?

For my car I want to stick with the 3.70 rear-end, which I chose for the best "stock" posi highway gear, based on people's feedback on other threads and my desire to stick to original factory options. So really I just wanted to figure out the best bet for the tranny to work with that rear end... close or wide. I have told my builder to go with the Close ratio based on these responses.

Thanks for all the info! I really appreciate the wisdom!

[Loren L.]

Re: FI with 3.70 rear end and a close ratio best?

Although no C1s came with the wide ratio, wouldn't a wide ratio geatset with a 3.55 rear be more streetable? This would still have good acceleration with the 2.52 first gear, combined with less revs in fourth gear on the freeway.

You might want to make a return visit to whatever you are using as a "Facts Factory" regarding the wide-ratio T10.

[Ian G.]

Re: FI with 3.70 rear end and a close ratio best?

Hey Loren, which C1s came with a wide ratio option? maybe 61/62?

[Barry H.]

Re: FI with 3.70 rear end and a close ratio best?

Bill Clupper is absolutely right, but remember he is primarily driving in Oho, (very flat) My 62 360HP FI came from Indiana, (also flat) with a 3.08 rear end & a close ratio box. In Pa., (very hilly) I changed the gear set to a wide ratio for a lower low gear to extend the clutch life. Remember the close ratio gearbox was primarily produced for SCCA type racing, where acceleration from a dead stop was not important. Back in the day, most Drag racers loved the wide ratio boxes. I am in the process of switching my 65 327, 350HP coupe to a wide gear set, because the 350HP is basically dead at low RPM, & a close ratio is like starting out in second gear. Barry Holmes

[Paul Y.]

Re: FI with 3.70 rear end and a close ratio best?

I bet that was a super fun trip Paul Couldn't you have taken a picture of your car from the front? I get the idea that its a 63. Just kidding :P
I really love the color. What name did GM give it?

For my car I want to stick with the 3.70 rear-end, which I chose for the best "stock" posi highway gear, based on people's feedback on other threads and my desire to stick to original factory options. So really I just wanted to figure out the best bet for the tranny to work with that rear end... close or wide. I have told my builder to go with the Close ratio based on these responses.

Thanks for all the info! I really appreciate the wisdom!

Thank you. The factory called that color Saddle Tan. It was still there after I stripped eight other colors off of it. I was quite happy to get a Saddle Tan color. Here is a front end picture for you. HaHA

[Ian G.]

Re: FI with 3.70 rear end and a close ratio best?

So what I'm wondering is what is the negative to using a wide ratio with the 3.70 rear end? Keeping in mind my car is a Fuelie.

I keep hearing folks say they use it, and they like it, but WHY? It seems like it would work better having a lower first gear for more acceleration? Is the close ratio, just more visceral -- sound and feel better once it gets going? I don't really care if I can smoke the tires but I want it to have good pickup.

I live in Northern California and its not out of the realm of possibility I will take it into the hills...

Thanks again everyone!

[Duke W.]

Re: FI with 3.70 rear end and a close ratio best?

Remember the close ratio gearbox was primarily produced for SCCA type racing, where acceleration from a dead stop was not important.

Not completely true! Yes, the CR was targeted at SCCA racers, but up until sometime in the mid-sixties, SCCA races were run from a standing start, so the race to the first turn was basically a drag race from a dead stop, but since Corvettes had more displacement/torque than the competition, a tall first gear was okay, and it was designed to be used in very low speed corners, like 30-35 MPH with a 3.70 or 4.11, which usually provided enough top speed to not "run out of revs" on the longest straights.

The trouble with the CR four-speeds is that a short rear gear provides good all around performance, but it's like a five-speed with no fifth on the highway. With a tall gear for good high speed cruising it's like a five speed with no first!

Remember, back in that era there were no interstate highways, and most two or four lane highways had 55-65 MPH speed limits, so sustained high speed cruising at 80 was not part of the typical driving environment.

Anyone considering a complete rebuild on a vintage T-10 should find out if the "wide ratio" Super T-10 gear set (2.64, 1.75, 1.34, 1.00:1) can be installed in a vintage T-10 case. This gearset, which has the biggest gap between first and second (which is much more transparent than a big gap between third and fourth as is the case with the vintage T-10/Muncie wide ratio set) with a 3.36 or 3.08 axle will provide good around town performance and relatively relaxed highway cruising - the best of both worlds without having to install an aftermarket five-speed. I'd recommend a 3.36 for a Duntov-camed 283, but a SHP/FI 327 should pull a 3.08 with no problem.

If the above can be done at a reasonable cost, that's the way I'd go.

Keep in mind that my 340 HP SWC has a close ratio, and I special ordered it with a 3.08. I was not into drag racing, but I made a few runs at Puyallup going through the lights in second gear - mid 14s at a little over 100 MPH. In street racing I would try to avoid any faceoffs below 40 MPH (where first gear put me at a little over 3000 revs), and if there was enough road in front of me I could never loose because any "muscle car" of the era would run out of revs long before I hit my top speed in the mid-150s at 6000-6200!

I still remember being neck and neck with a 440 Charger when his lifters pumped up as we approached 130. I just shifted into fourth gear and walked away.

Duke

[Michael H.]

Re: FI with 3.70 rear end and a close ratio best?

I suppose the original question would probably gather as many different opinions as a question like "what color should I like".

IF... I were to change from a 3.70/CR, I would probably go with Dukes recommendation with a 3.36 rear and 2.64 1st gear with the close ratio/big ratio spread between 1st and 2nd. (I would never drop all the way to 3.08 though)
No matter what rear ratio I had, I would not even consider a conventional wide ratio transmission.

I still think I'd stick with a 3.70/2.20. That 3.70 number is roughly half way between the lowest and highest differential ratios available. (not counting a 4.56, if it was available in 1959) The best of both worlds AND, you already have this combination.

[Loren S.]

Re: FI with 3.70 rear end and a close ratio best?

You might want to make a return visit to whatever you are using as a "Facts Factory" regarding the wide-ratio T10.

Woops, forgot about the 62s, meant to say 2.54, my bad.

[Stewart A.]

Re: FI with 3.70 rear end and a close ratio best?

This is why we have 6 speed gears these days. 5 gears is enough but 6 just ticks over a little above idle on the highway and first is really low which is awesome. Unfortunately we only have 4 forward gears to play with. Paul well done you use your car and probably have a pretty good attachment to it especially after a great ride like that. I often wonder why people take a photo of the rear of a 63 ? Is the front of them that ugly. I should start taking photos of the back of my misses ? 3.36 gears would of just been acceptable with a major drive like that. Great photo's Paul
What's with Americans and these crazy gears. Is there that many traffic lights over there, you need a better road layout if your cars all need 3.70 and 4.11's. Or is it you guys never really drive your cars a lot.
Ian 3.70 will absolutely fry the tires if you have a real 290 hp with those razor blade tires. I can lay rubber in 2 nd and even a chirp in 3rd with 3.70 you will have fun with them just watch the cops !!!!! But if you do a trip like Paul take your everyday drive the revs will do your head in. Stewy