The Tremec TKX has a 2;87 first gear which will get you movin in a hurry and second is 1:89 which I think I'll like which is close to the M21 2:20 first gear, relatively speaking.
Sounds like you have a nice combo in your car 65air.

 

As R66 stated......I'll be able to " pull stumps at the farm" with first gear!

 

You will have to bring it over after you put the TKX in, we lost several trees here in the woods as a result of the last wind storm. But, if you are racing at the strip, it might be a wheel puller.
I think almost anything you do will require both an differential gear and transmission change to obtain the best results. Once again, you have to design your combination for the optimum torque range of your engine. If high gear in the transmission is too high, you may get 'trailer hitching' or 'rockin' chair' and overall poor drive-ability in my opinion, but I am no expert by any means.

 

Sure, be glad to get those stumps out of the way for ya! I am not worried about a bucking and jerking in 5th, the L79 is a fairly mild cam and even at 2000 RPM still livable.

 

just to clarify, the M20, M21 and M22 ALL have the same rpm drop between 1st/2nd and 2nd/3rd gears. The only difference is the 3rd-4th drop, with M20s being wide and M21/M22 being close .

The M20s larger rpm drop from 3rd to 4th is not as desirable for racing.


IMO, I’d consider both the overdrive TKX and a gear swap, but I’d consider going to 3.08. The lower first gear of the TKX should compensate for the 3,08 nicely.

 

If you want to play, find a road with a slight grade that you normally travel or want to use just for comparison.
Put the car in 4th gear, say at 25 mph or so, then as you are going up the grade and slow down until you get 'trailer hitching. Look at the tach and determine the rpm. Repeat the trial a few times to verify your rpm needed to avoid downshifting.
I think your total advance including vacuum advance can contribute to the trailer hitching, but there are those that may know better..
Ron

 

Your phrase about the 5-speed being "the best of both worlds" is my view as well. I've had a 5-speed in my C2 since 2008, and I think it is the single best change I have made to the car. I've posted a couple articles on CF about 5-speeds in the following thread, and a third article will be posted later this week:

Article on installing a T5 5-speed in a C2 - CorvetteForum - Chevrolet Corvette Forum Discussion

Regarding the gear ratio discussion in this thread, following is my take on why a 5-speed is the "the best of both worlds" (excerpted from the first article):

BENEFITS OF A 5-SPEED CONVERSION

Many people assume that the only benefit of a 5-speed transmission (with an overdrive 5th gear) is the reduced rpm at highway cruising speeds. This reduces engine noise and exhaust noise for more comfortable highway cruising on long trips. However, this is only half the benefit of installing a 5-speed.

The other big benefit is having a lower first gear for improved launch from a standing start. We have all heard that for fast acceleration, the preferred combination for a C2 was a close ratio Muncie and a 4.11 rear. This was great for acceleration in first gear, but the engine rpm at highway speeds was high and became unpleasant on long trips.

For highway cruising, the preferred rear end ratio would be something like a 3.08, but this reduces standing-start acceleration in first gear. I know one C2 owner who owns two differential assemblies, a 4.11 for street use and a 3.08 for long trips. He actually swaps the rear end from 4.11 to 3.08 every time he makes a long trip, and then changes it back to the 4.11 for local street driving.

Now, suppose you could achieve the same effect as changing from a 4.11 rear to a 3.08 rear, but accomplish this by simply shifting into a an additional 5th gear? This is what a properly set up 5-speed does for you. This is much better than physically changing the rear end, and it’s better than having to compromise on a single rear end ratio such as 3.55 that you use 100% of the time with your close-ratio Muncie.

It’s easy to illustrate this with an example. The “effective gear ratio” for the overall drive line is simply the transmission gear ratio multiplied by the rear end ratio. So, a close ratio Muncie (2.20 first gear and 1.00 fourth gear) has an effective first gear ratio with a 4.11 rear of (2.20 x 4.11) = 9.04. With a 3.08 rear, the effective fourth gear ratio is (1.00 x 3.08) = 3.08.

Now, let’s consider a representative T5 5-speed with a 2.95 first gear and a 0.68 fifth gear. If we combine this T5 with a 3.70 rear, the effective first gear is (2.95 x 3.70) = 10.9, while the effective fifth gear is (0.68 x 3.70) = 2.52.

Compared to the close ratio Muncie, the T5 5-speed and a 3.70 rear yield better standing-start launch than the Muncie with a 4.11 rear, and lower highway rpm than the Muncie with a 3.08 rear. It’s the best of both worlds.


You mention some concern that your car presently has its original drive train, but the TKX kit from Silver Sport is a 100% bolt-in solution that does not require any cutting or welding that affects the originality of your car. You can always swap the Muncie back in if you want to restore the original drive train.

The T5 conversion that I have been developing is also 100% bolt-in. The only reason to prefer a T5 conversion over a TKX conversion is that it costs less, and provides a lower cost option for people who want "the best of both worlds" with a 5-speed.

 

Great article joe, I am thinking, after much research that the TKX with 2:87 1st and .68 OD with my 3:70 rear gear will be my "best of both worlds". I am dealing with American Powertrain, they offer a veterans discount but have not pulled the trigger yet and have not checked with Silver Sport.
L78 I would think going to a 3:08 would drop my Rpm to much in my L79 with a .68 5th gear, 3:36 maybe!!
Thanks

 

Heck, even with BB torque 3.36s behind an M21 is a bit doggy. I converted my transmission to M20, which helped a bit. If the OP wants to keep an original driveline, converting the transmission is an option. All you need is a main drive gear and countergear.

 

You already have the correct setup, and the 327 loves to run at 3400 RPM's.

 

I think Silver Sports shifter is a little different than AP’s. You may want to check that out. I would go with Silver Sport.

When I first installed the TKO 600 10 years ago I was pleasantly surprised at the acceleration in first gear. It felt like I had 50 more hp. I feel the gearing with a 3.70 rear gear is perfect.

 

I think keeping the 3:70 rear and the TKX will give me all the first gear acceleration I need (don't intend to drag race this baby) and with the .68 OD turn 70 to 75 mph around 2200 to 2500 rpm, sound about right all you knowledgeable gear heads out there?

 

I agree that that a 2.87 first gear and 0.68 fifth gear is pretty much "the best of both worlds" when combined with a 3.70 rear.

When I ordered my TKO-600 (predecessor to the TKX) in 2008, I selected a 2.87 first gear and a 0.82 overdrive to use with my 3.70 rear. This gave me an effective first gear of (2.87 x 3.70) = 10.62. I think that a first gear equivalent ratio of around 10 is a good overall goal if you want strong standing-start acceleration.

My only regret was that I did not order the 0.68 fifth gear. I got the 0.82 overdrive because it's very common for traffic on the interstates in the Boston area to have to slow down briefly from 70 mph to 50 mph and then accelerate again. I wanted to be able to speed back up from 50 mph to 70 mph without having to downshift to 4th gear. As it turned out, with the 327/300 hp engine I was running at the time, even accelerating from 40 mph worked fine. That engine has a lot of low-end torque.

For the T5 conversion project I'm working on, I have temporarily installed a T5 that has a 0.68 fifth gear. I find that it's a nice improvement over the 0.82 that I had in the TKO. Since my current engine is a 383, I have even more torque now and no reason to worry about having to downshift if I hit a slow spot in traffic on the interstate.

Regarding the choice of vendor for your TKX, I think Silver Sport is hands-down the best choice. If you look through the discussion board archives, you will see a lot of positive reviews. I would strongly recommend buying your TKX from Silver Sport.

 

Checked with Silver Sport yesterday and Jeff had the better deal for the complete kit for my 67 and was a great guy that answered all my tech questions even though they are very well outlined on line, but I always like to talk to someone. So that said, with the very helpful info from you guys and a couple weeks of research I ordered the TKX 2:87 with .68 5th gear.
Joe I think your right these guys are the ones to go with!
Thanks to all, Mel