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I have a 1966 coupe, BP38318, 3.73, standard rear wheels, with a bad M21. I have driven it about 3,000 miles since the BP38318 was installed. The 383 likes the 3500 to 5500 range for power. If you listen to the motor you can hear it smoothing out in the 3,000 to 3,500 range. I was thinking of using the TCET 17722 with 2.87 - 1.89 - 1.28 -1.00 -.81.
Currently 70 mph is about 3500 rmp. The .81 will change that to about 2835. A .68 5th would be about 2135 rmp. My thinking is the .68 would be to high a gear fo use with out shifting down to 4th when I want the power. Yes?
Another question. I have the C3 crossmember on the stock frame. Will mounting a TKX on a C3 crossmember instead of the stock crossmember be a problem ?
I love cruising in 5th (.64). Particularly with a side pipe car, top down. Yes, big drop in revs, but 5th for me is not about performance, it's just pleasant on a country drive with my wife.
I love cruising in 5th (.64). Particularly with a side pipe car, top down. Yes, big drop in revs, but 5th for me is not about performance, it's just pleasant on a country drive with my wife.
I have a stock World Class T5 in mine with the .63 OD and a base 327 and a 3.36 rear. It is not a powerhouse in 5th but I use 5th only for highway cruising and its fine. If my anemic 327 can drag my car along in 5th, your 383 & 3.73 should have no issue. I can cruise at 65-70mph and go from the middle lane to the left to pass someone without leaving 5th and have no issue, and I always have the option of dropping into 4th if I want to be more aggressive. Having that big RPM drop when cruising to reduce noise, heat, fuel consumption and wear & tear is awesome - that is what overdrive is supposed to do! My trans is out of a 3rd gen Camaro - GM literally built hundreds of thousands of these Z28s & TransAms with .63 OD, a 3.42 rear and a 205 HP engine and they were all fine!
I did almost the exact same thing OP is thinking about except with a C1. I have a 3.70 rear and had an M21 in my car. While I liked the close ratios once moving I always felt the first gear was too long to get moving easily from a stop. You have to remember that the TKX 'close ratio' has a shorter first gear than an M20 'long ratio'. I put in the TKX 'close' with the .68 OD and couldn't be happier. Cruising around at 55 in 5th is at 1800 RPM (and yes I'd have to drop it several gears for any "power" but I'd get 18mpg compared to 16mpg on the M21. On the expressway, however, (70-80mph) I average around 2400 RPM in 5th and am in a much better engine efficiency range so my mileage jumps to 24.5mpg (WAY better than the M21). I chose the .68 because I feel 5th is for "loafing" along rather than any use for power. My engine doesn't come close to producing any kind of "power", as one would put it, until slightly above 3000 RPM.
Do you have a complete C3 crossmember or a C2 crossmember with C3 removable ends attached to it? I put C3 removable ends on my C2 crossmember and my TKX went in fine. I’m guessing you would need a C3 mount if you have a complete C3 crossmember but not sure if you would have issues with the body.
Other than having a more stout transmission...or for road racing.... I never understood a 0.81OD. There's nothing better than climbing to 60-65mph on a highway and shifting to 0.64OD in my Tremec 600 . I also have a BP 383 and it has plenty of torque to handle highway cruising . Since my rear had to be rebuilt having 4.11's out back now makes the spirited fun +2 and still maintains low-mid 2000's on highway. With the gears I'm around 2150rpms at 60mph. The 0.064 OD makes 70mph highway runs easy & fun. To each his own!
American Powertrain has the complete C2 Tremec conversion kit and they also sell a removable cross member for easier install and/or if for whatever reason one needs to pull the transmission.
I have the same rear set up in my 66, An L-79 with a 4:11 rear. First gear is so low I can walk it into gear and pull a tree stump out with it. By 30 feet, she is all done. I do love the overdrive on the highway. It also makes the side pipes more tolerable on the highway. Jerry
I have the same rear set up in my 66, An L-79 with a 4:11 rear. First gear is so low I can walk it into gear and pull a tree stump out with it. By 30 feet, she is all done. I do love the overdrive on the highway. It also makes the side pipes more tolerable on the highway. Jerry
Tremec TKX's can come with a 3.27 first gear in them...Possible you have this first gear..
The close ratio TKX with the 2.87 first gear and the .68 was my choice after applying the calculator. My 69 Camaro had a 2.64 first gear Super T-10 and 4.10’s in the back giving an overall first gear of 10.824. I really like this combo for stop sign to stop sign driving. I was looking to duplicate that with the TKX in my 64 coupe. With 3.73 installed and the 2.87 first gear of the close ratio TKX it gives a 10.7 overall first. Close enough. And with the .68 OD, the overall final drive is 2.54. Pretty much the 1970’s solution for 400 cu inch V8 sedans and highway driving. IMO, the .81 just doesn’t get the final drive down low enough at 3.021 effective ratio.
Cliffs Notes: get the .68 OD. The .81 would leave you wanting more IMO.
I have a 1966 coupe, BP38318, 3.73, standard rear wheels, with a bad M21. I have driven it about 3,000 miles since the BP38318 was installed. The 383 likes the 3500 to 5500 range for power. If you listen to the motor you can hear it smoothing out in the 3,000 to 3,500 range. I was thinking of using the TCET 17722 with 2.87 - 1.89 - 1.28 -1.00 -.81.
Currently 70 mph is about 3500 rmp. The .81 will change that to about 2835. A .68 5th would be about 2135 rmp. My thinking is the .68 would be to high a gear fo use with out shifting down to 4th when I want the power. Yes?
Another question. I have the C3 crossmember on the stock frame. Will mounting a TKX on a C3 crossmember instead of the stock crossmember be a problem ?
I have a 3.70 rear in my '67 and have used that rear with three combinations of engine/transmission:
1) TKO 5-speed with .82 5th gear and stock 300 hp 327
2) TKO 5-speed with .82 5th gear and 424 hp 383
3) T5 5-speed with .68 5th gear and 424 hp 383
With your 3.70 rear and 383, I would definitely recommend the .68 5th gear. Even my stock 300 hp engine seemed like it could easily use more than the 0.82 5th gear. The 383 has no trouble with the .68 5th gear. Both configurations could comfortably drive as low as 40 mph and still accelerate without downshifting.
For any stock V8 Corvette (except maybe those with the high overlap 30-30 cam), I think the 0.82 5th gear is only appropriate for rear end ratios of 3.08 or 3.36. Unless the cam in your 383 is really aggressive (more than 235/235 duration on a 110 LSA), I think your 3.70 rear is just fine for the 0.68 5th gear.
Regarding the rear crossmember, the center area for the C3 transmission rear mount differs slightly from the C2 center area, and the bolt-on rear mount bracket is different. To get a C3 crossmember to work for a TKX conversion in your C2, all you need to do is order the C3 rear mount bracket instead of the C2 bracket.
I think there are two schools of thought on the 5 speeds. Some want one more gear and want it to feel just like the shift from 3-4th. Those guys want the lower overdrive, .82 so it feels like one more gear. I think most want the overdrive to cut noise and help with MPG on long trips. For me I prefer the taller overdrive of .68 or even .64 to help with a quiet 70 mph + cruise. Each to their own on this decision.
When I ordered my Tremec I requested the 2.87 first gear. I believe she'd wound up in mid 5's by 45mph. But...I don't Red Light Grand Prix the car & I only low roll raced it once in 10 yrs starting around 20mph in 2nd. Then I felt guilty LOL ! If ordering knew just be sure to ask the questions that give you the gear ratios you look forward to.
I have done several of these with the .64 OD with 3:73 and 4:11 gears…
The .64 is too much drop. The .81 still seems to turn new parts into old parts faster.
I have a new .68 ready to install with 3.70 gears.
I do believe that .71 or .72 would be interesting to test but I think the .68 will likely be fine. I have side pipes so right now at 75mph the rpm’s are 3500 ish and it is roaring.
The .68 should clam things a bit and if I need to go, I can always downshift:-)
Silver Sport is the company I was recommed to go with. They gave a very good detail of the parts to be sent. They are sending a C3 transmission cross member mount. That should match my C3 cross member I had installed on the new frame bought.
I used the Tremec calculator and my physical tire size is 25.5 inches.
The M21 is 3200 rpm at 65 3675 rpm at 75 mph
.81 is 2575 rpm at 65 2950 rpm at 75 mph
.68 is 2100 rpm at 65 2500 rpm at 75 mph
I live very rural and expect to be driving about 70 mph most of the time at about 2350 most of the time. Only city driving would be Lincoln or Omaha. Not to often. Long trips at 2500 sounds better than 2950. Yes ?
Go look at the torque curve on your BP 383. It is fairly flat and is mostly all-in at 2500rpms.
So as you are cruising in 5th you will have good acceleration without downshifting and if you want to hammer down, you can grab 4th and be gone. The strokers are great for the OD transmissions because they make good power down low.
So in my opinion, the .68 is prolly the better choice for overall drive ability.
I think the .81 is good if you need to keep the engine wound up for something like auto crossing. But if you aren’t auto crossing, I see no need to turn the rpm’s higher than necessary.
When I recently went to order, I called Silver Sport and talked to Shane and he had good thoughts about the different OD specs and how to think about them and how they execute. I too was dead set on the .81 and backed off to the .68.
Nelag.....I was on my first cup of coffee staring at these ratio numbers. Gotta Love This Stuff.
TKX has .068 5th gear OD . Tremec 600 offers 0.64 5th Gear OD.
Then we have different engines ...rear gears ...tire diameters all which effect highway rpm.
My BP 383 has the Tremec 600 with 0.64 5th OD + 4.11's out back.+ a bit taller rear tire.
It has no problems on a highway with the Tremec 0.64 OD. I'm in 5th gear around 65mph due to the ratios below:
At 60mph it's at 2000 rpm
At 65mph it's at 2150 rpm
At 70mph it's at 2350 rpm
At 75mph it's at 2500 rpm
Tremec's Website has a Gear Ratio vs RPM vs Tire Height calculator:
It's a plug & play that calculates all the factors including different Tremecs for each set up: https://tremec.com/aftermarket/resou...io-calculator/
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Another TKX question.
