[MidnightAuto]

Well, it seems I am going to bite the bullet and replace my M20 with at TKO 600. I've researched all the 5 speed options and believe this is the best path for me. I've got 3.36 gear with a 26.5 in tall tire.

With that said, I am waffling between the .82 or .64 5th gear. I've been playing with the speed analyzer on American Powertrain web site and it makes me lean towards going after the .64. At 2K RPM with the .64, I'd be going 73MPH on the highway. As opposed to the .82, at 2K RPM I'd be going 57. Seems like a no-brainer, but I am curious of folks opinions? I suppose the shift from 4th to 5th could be a bit of a dog dropping so much with the .64?

But I am really only using 5th for cruising, not top end racing. I also don't think I will even hit 5th gear in the 1/4 mile?

For reference, I've got a mild 421 with a tripower.

Opinions welcome. thanks for thoughts.

[b-man]

Definitely the .64, or why bother?

[JLMounce]

The only time you choose the .82 ratio is if this car is being road raced on a big bore track that you need extra gear for more MPH on the long straight.

If you’re doing the swap to get an overdrive, go with the .64

If you want or need both, that’s when you go to the t56 6spd.

[Scarebird]

As the others have said - 0.64

I have the 0.82 with 3.08's - it is not bad but the 3.42's I had first would have been better with the 64's - 3.42's were quite quick off the line.

[MidnightAuto]

thanks guys. Yeah, .64 seemed right to me, but this is an expensive endeavor and it would really suck to not be happy with it. Just wanted to make sure I was not missing anything...

[4dblnkldude]

I agree with all the above. You wont even wind out fourth all the way in the 1/4 mile with 3:36's.

[Formulajones]

Absolutely .64 is the only way to go. Otherwise the expense and effort of overdrive is pointless. All the TKO's I swap are with the .64 and it works well with a variety of rear gear and engine combos.

I've even shown the naysayers how well it works with one of my own cars my wife daily drives. A little DZ302 that makes very little if any bottom end torque, with a 254 @ .050 cam, and I run a 3.55 gear and 27" tire on it.

I use 5th gear all the time with it. It'll lug down to 30 mph and idle along, and pick up speed without complaint, climb the mountain grades around here no problem and gets 22 mpg doing it.

Your 3.36 would work fine with a bigger Pontiac engine making plenty of torque.
Even with that said, probably my favorite gear with this transmission is 3.73's

[amcmike]

For reference, if you're redline was 6k, with your setup you'd have to be doing 140mph before you'd need to shift out of 4th. That's low 10s/high 9s in the quarter.

With the 421 Pontiac torque, you should have no issues using the .64 overdrive even down at 55mph. As JLMounce said, the .82 is meant for road racing on long tracks where you might actually use that gear at heavy load (assuming a numerically high rearend ratio that would actually get you fast enough to use it). Or maybe someone who's running a really low 2.73 or 3.08 rear gear that doesn't need a lot of overdrive (which still, they'd still be better off replacing the rear gear and doing the .64). It'd be silly to spend all that money for a measly 18% overdrive.

[fastekibeast]

I did the same swap few years ago, one of the best upgrades I ever made.
I have 3.55 rear and I bought 0.64 od transmission, I suggest that you keep in mind what kind of cam you have in your engine, because it will dictate alot.
I had a Lunati #07702 cam in my GTO and if I remember right the rpm range was 2200-6500rpm.
If I drive 95-100km/h with 5 gear, the engine rpms was about 1800-1850 and the motor didn't spin easy it was "working" constantly but if I drive about 120-125km/h it run like a charm the engine rpm was about 2100-2200 and was a really fun and easy to drive, these was no any effect that engine was working.

Janne

[428goat]

I used the .64 with my 67. Loved it.

[David Jones]

.64 with a 3.73 in mine.
Perfect.

[MidnightAuto]

Thanks again for the feedback. My one question I am wondering is what my setup will feel like going say 65. That will put me at 1800 rpm in 5th. I don’t know the cam specs from PO. I will be getting car out of storage soon and will remind myself what 1800 rpm feels like in 4th at the moment. More to come. Thanks again for all the thoughts. Definitely helping me sort out

[Formula8]

Originally Posted by fastekibeast

I did the same swap few years ago, one of the best upgrades I ever made.
I have 3.55 rear and I bought 0.64 od transmission, I suggest that you keep in mind what kind of cam you have in your engine, because it will dictate alot.
I had a Lunati #07702 cam in my GTO and if I remember right the rpm range was 2200-6500rpm.
If I drive 95-100km/h with 5 gear, the engine rpms was about 1800-1850 and the motor didn't spin easy it was "working" constantly but if I drive about 120-125km/h it run like a charm the engine rpm was about 2100-2200 and was a really fun and easy to drive, these was no any effect that engine was working.

Janne

X 2. When I had the 455 with the smaller cam, all was good with the .64OD. With the smaller engine and bigger cam, there is a much smaller window to tune for driveability in OD. I have not been able to get the 433 to drive in OD as nice as the 455 did yet and I don't think the displacement has as much to do with it as the cam.

[Formulajones]

It's all in the tune up. The more rambunctious cams like the 254@ .050 in my 302 just takes a little trickery in the idle feed and transition circuitry, along with a proper timing curve that works in conjunction with the vacuum advance that will make the engine happy at all rpm, even lugging.

I don't think anyone here runs a cam on the street, especially a daily driver that is as radical as what I'm doing here when comparing the size of the engine. In a 455 with 150 more cubes you'd need the equivalent of a 260+ @ .050 cam to see the same result and affect.

[Formulajones]

Originally Posted by MidnightAuto

Thanks again for the feedback. My one question I am wondering is what my setup will feel like going say 65. That will put me at 1800 rpm in 5th. I don’t know the cam specs from PO. I will be getting car out of storage soon and will remind myself what 1800 rpm feels like in 4th at the moment. More to come. Thanks again for all the thoughts. Definitely helping me sort out

65 is easy peasy, and the example I talked about above is about 1800 rpm at that speed. That little 302 will climb the mountain from near sea level to over 7,000 feet over a span of about 6 miles, and easily holds 65, and will gain speed if needed, without downshifting. I cruise around town with it at 30-35 in 5th all the time. 45-50 mph is also very nice cruising in 5th so the rural roads are nice too. If the engine is tuned right and happy you'll find you'll be using 5th more often than one might think.

If a 302 with that cam will do it, a Pontiac shouldn't have a problem.

These overdrives completely change the character of a car. 5th gear they just go to sleep. Not only that but you are also gaining some 1st gear multiplication that is better than any Muncie, making the car much easier (and easier on the clutch) to drive around town. It's really a win win. There is no down side and no sacrificing one end or the other.

[tom s]

I have a 421SD (434) in my 63 Lemans with a OFII cam.I have 3.90s in the back with the .64OD and am going to swap to 3.64s next week.I know the engine can handle the 3.64s but was not sure if I went to a set of 3.42s.The engine has a Bathtub tunnel ram with a pair of 750 SD AFBs,also 28 in tire.NO issue with using the OD in street traffic.Tom

[i82much]

put some 4.33' s and an M22 in it, ya sissy!

just kidding

[Formulajones]

Originally Posted by i82much

put some 4.33' s and an M22 in it, ya sissy!

just kidding

Friend of mine used to say, "put a gear in it and be somebody" LOL Most of the guys I grew up around with cars wouldn't run less than a 4.56, One with 4.88's and Mike always had 5.13's in his Camaro, drove it on the street everywhere.

I love gears.

[i82much]

Originally Posted by Formulajones

Friend of mine used to say, "put a gear in it and be somebody" LOL Most of the guys I grew up around with cars wouldn't run less than a 4.56, One with 4.88's and Mike always had 5.13's in his Camaro, drove it on the street everywhere.

I love gears.

Many years ago I went from 3.23's to 3.90's behind a wide ratio muncie and a 350 Chevy, man that was fun! But really, you get the best of both worlds with the TKO, steep first and a nice cruise.

There's no reason for us to drive around at 3000 RPM anymore. But I still kind of feel like a real hot rod should buzz your nads off on the highway ...

[Formulajones]

Originally Posted by i82much

Many years ago I went from 3.23's to 3.90's behind a wide ratio muncie and a 350 Chevy, man that was fun! But really, you get the best of both worlds with the TKO, steep first and a nice cruise.

There's no reason for us to drive around at 3000 RPM anymore. But I still kind of feel like a real hot rod should buzz your nads off on the highway ...

Agree 100% I'm still that way to some degree. I like gear and that's really what a hot rod is to me.

I guess just getting older has me wanting to cruise more, and longer distances.

I still have one car holding out with 4.10's left....lol. Been that way since 87 but I don't know how much longer I'll keep it that way. May leave it and just put an overdrive in it.