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Why Summit? I got pricing from all of the prime suppliers. They all wanted to supply a complete kit but I'm sure they would have sold just the trans. I wanted to source all of my own stuff as I had most of what I needed (clutch pedal/linkage, driveshaft, bell housing, cross member). They all had their own proprietary clutch and I wanted to make that choice on my own. Like I said I believe they would have sold just the trans but Summit was cheapest with no shipping cost - just the $9.99 oversize fee. Not knocking the companies that supply these kits - I think any of them would be great to work with - Summit Racing just worked well for my situation.
 

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3.23- 3.42s would be my choice. I have no issue running the highway with 331s, but do stick to speed limits.
 

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1969 Chevelle SS ZZ 502
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37 Posts
I have a mildly modified 327 mated to an M21 with a 4.11 rear end and some really stuffy World Products S/R heads (not even the torquers). It is running a 3863151 vintage performance cam (222/222) that makes power between 1500-5200rpm. I plan on upgrading my heads to something that can breath, and going with a 480/230 cam in the future to bring my hp up to somewhere around 350ish and the power band would move up to 1800-6500

I really enjoy driving the M21/4.11 around town, but don't take it on the highway because in my city you have to be doing at least 70 to keep up with the slow traffic, and 70mph is about 3500rpms with the M21 and 4.11. It sounds fantastic, but gets old on longer drives...not to mention I can watch my gas gauge go down on the highway.

I am going back and forth between transmission options for the future. One option is the Tremac TKX 5spd, the other is keeping the M21 and adding the Gear Vendors overdrive unit, and a third would be lowering my final drive ratio down to something like a 3.73...or even lower. The TKX seems like the pedestrian easy option. The Gear Vendors unit is really cool, but really expensive, and lowering the rear end ratio just seems like the boring way to go.

I've also thought of the idea of keeping an entire rear end with brakes and everything set up with something like a 2.73 that I could just bolt up to the car if I were going to go on a road trip.

I've used the calculators out there and I have seen the numbers, but I would like some real life feedback. Has anyone had a chance to compare any of these set ups? Can the TKX take the same kind of gear banging abuse that the muncie can? Is it as fun to drive? I really like the muncie, but I really want an overdrive.
396, M20 , 4.10 rear 14 in tires 3500 RPM = 55 mph. I went to 15 in. tires helped a little, G/V overdrive 2200 rpm 70 mph better ( after beating the tunnel to make it fit ) Loved it BUT my ZZ502 too much for the M20 , JEDS said this Richmond 5 spd. with 5th being overdrive will work in my Chevelle and I called Richmond and they told with just cutting 1 or 2 inches at the rear of the shifter hole it would fit LIERS
Save yourself a lot of time , money , grief , and get the TKX . And get rid of the linkage CRAP. I wish I DID !!!
 

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I put a gear vendor unit behind an M20 in a 68 last fall. Had to beat the crap out of the tunnel and notch the floor brace to make it fit. I didn’t think that was ideal. Plus the wiring is a cluster F for it.
I’d go TKX.
I was seriously considering a GV unit but after hearing this IDK.
I'm running a TH350 in a 66 chevelle.
I wonder if it'd be the same cluster F problem you had with an automatic
 

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I have an M23W with under 250 miles I want to sell. Asking $2250 plus shipping. Went to M23Z - W has 2.56 1st gear vs the 2.99 1st in the Z.
 

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I love my M23Z box. Loud sob tho. I've had folks ask what that whine is!
 

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I was seriously considering a GV unit but after hearing this IDK.
I'm running a TH350 in a 66 chevelle.
I wonder if it'd be the same cluster F problem you had with an automatic
I helped a friend install a GV unit behind a TH400 in a '69 nova. We had to cut out braces to get it to fit in there. in a '66 chevelle, the drive tunnel that far back is really small and i dont think teh GV unit would fit well at all. Be aware a TKO TKX is going to require tunnel mods as well, so you are cutting sheetmetal no matter which way you go. I personally find the OD of the GV unit to be not as useful as the OD in the TKO TKX and therefore prefer the TKo TKX
 

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I helped a friend install a GV unit behind a TH400 in a '69 nova. We had to cut out braces to get it to fit in there. in a '66 chevelle, the drive tunnel that far back is really small and i dont think teh GV unit would fit well at all. Be aware a TKO TKX is going to require tunnel mods as well, so you are cutting sheetmetal no matter which way you go. I personally find the OD of the GV unit to be not as useful as the OD in the TKO TKX and therefore prefer the TKo TKX
Yeah the GV sounds like a bad plan for my car anyway then .
I wasn't looking for the OD as much as a final gear in a quarter that is shorter than 1:1.
I want to say the GV unit would have given me like a 1.2:1 in 2H Which would have been nice .
I've searched high and low for a company who makes a shorter than 1:1 gear for a 3 speed automatic and I'm comin up craps.
Maybe I go 3:55 gear with my 2.75 first in my 350 tranny and then see if a good converter can see me to around 6600 at the end of a quarter
 

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Recommend a tko or tkx from American Powertrain. My 66 has the tko with 373 gears and does everything well.
 
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Recommend a tko or tkx from American Powertrain. My 66 has the tko with 373 gears and does everything well.
I did the same. I have a S60 Strange with 3:73 gears and a TKX with .68 OD. Great setup for the street.
The only cutting in a 64-67 is directly behind the shifter hole to raise the trans 1/2" or so.
The ideal shifter position (forward and to the left) is being developed by Jody's transmission and others.
This new shifter should eliminate the cutting of the tunnel.
68-72's require no cutting.
 

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1967 Chevelle SS 396 L78 (Sold in 1970)
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My ‘67 SS L78 had 4.10 posi with the M20 and my round trip to Florida from Illinois in the Spring of ‘68 was a drive to remember! It was all good....had no problems whatsoever and anyone who whines about having that power and torque on the highway doesn’t deserve a muscle car! 👍. You’re getting soft! 🙃
 
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My ‘67 SS L78 had 4.10 posi with the M20 and my round trip to Florida from Illinois in the Spring of ‘68 was a drive to remember! It was all good....had no problems whatsoever and anyone who whines about having that power and torque on the highway doesn’t deserve a muscle car! 👍. You’re getting soft! 🙃
Or maybe......
Too young and dumb in '68 to know any better ?
LOL
 

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1967 Chevelle SS 396 L78 (Sold in 1970)
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Or maybe......
Too young and dumb in '68 to know any better ?
LOL
Yeah, I had that coming, but I grew up real fast when I had to deal with the draft during Vietnam! That’s why I sold the car! That being said, if you are easy on a low geared car it will serve you just fine & I stand by that! If you want a highway cruiser buy something else! Chevelles weren’t built to cruise on the highway! That’s why the L78 couldn’t be ordered with A/C....I got exactly what I wanted, so maybe I wasn’t all that dumb!
 

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Even Alot of the grocery getter cars from way back then were short gear ..

Btw thanks for your service
 

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1966 Malibu, 327, Muncie, 3.55 posi
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182 Posts
This year I watched a few episodes of "Route 66" for the first time. I know it's a TV show but it sure made cruising the highway, at 1960's speeds, with a classic Vette, and probably a similar motor/trans/rear combo look like it was business as usual.
 

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Yeah, I had that coming, but I grew up real fast when I had to deal with the draft during Vietnam! That’s why I sold the car! That being said, if you are easy on a low geared car it will serve you just fine & I stand by that! If you want a highway cruiser buy something else! Chevelles weren’t built to cruise on the highway! That’s why the L78 couldn’t be ordered with A/C....I got exactly what I wanted, so maybe I wasn’t all that dumb!
I think there's room for both types. When I had my 66 SS396 Chevelle in the 1980's , I always wanted an overdrive.
And I had the mild version - 325 hp. Before I sold it I built a nice 427 for it . Managed 13 mpg with 3:55 gears and 4 speed.
The thing I like the most about an overdrive is the noise reduction. Long trips in a loud car gets old real fast.
 

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1966 Malibu, 327, Muncie, 3.55 posi
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The thing I like the most about an overdrive is the noise reduction. Long trips in a loud car gets old real fast.
Tranny and gears can help reduce pipe noise on the highway. One noise that never goes away is gear drive. Years ago, I installed Pete Jackson's in my 69' Camaro. They sound cool in the other guy's car but I had no idea they got so annoying when you have to live with them.
 
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