NTXOlds

I am closing in on a purchase of a 1968 Cutlass with the 250hp 2bbl 350 and a Jetaway transmission. I am starting to plan out what I intend to do to it, but one of my biggest questions is whether to keep the Jetaway or ditch it for a TH350. I have read numerous posts here and have yet to find any love for the Jetaway.

I am not planning to race the Cutlass, but I certainly want it to be fun to drive. Back in high school, I bought a '66 4-4-2 with a '68 310 HP Olds 350 (the original engine was gone) mated to the original '66 Jetaway and a 3.23 Posi read end. Now this was mid-'80s, and I did not drive it with the 350 more than a few months before installing a '66 425 out of a Starfire, but I do not remember that the combo of the 350 with the Jetaway was anything but fun to drive. Certainly when I swapped the engine for the 425, it was a blast and a great transmission for street racing.

My questions for you are:
1) Is the '68 Jetaway without the switch pitch torque converter really that bad or that much worse than the '66-'67 with the switch pitch?
2) Does anyone here actually like the Jetaway, or is the TH350 simply a much better transmission?

Thanks!

BangScreech4-4-2

1) No worse than a Chevy with a Powerglide. They're fairly trouble-free but not very exciting, is all.
2) Probably somebody here likes the Jetaway, but I haven't met him. For all practical purposes the TH-350 is a better transmission.

I am one of those guys who firmly believe that if the factory didn't offer it, it shouldn't be there.Yet, years ago, when I got a '64 Cutlass equipped with 330/290 and Jetaway, one of the first things I did was swap in a TH-350. Never regretted it for a second -- that deeper first gear plus the extra forward speed increased the fun factor tenfold.

joe_padavano

First gear in the Jetaway is 1.76:1. First gear in a TH350 is 2.52:1. That means that off the line a 3.23 rear axle with TH350 will feel like the Jetaway with 4.66s, yet in top gear it's still the same 1:1 ratio. THIS is why the TH350 is a better trans.

NTXOlds

Thanks to both of you.

Joe, the numbers don't lie. That is a very compelling argument.

I guess my experience street racing with the mildly upgraded '66 425 (which was 375hp from the factory) made me ignore the shortcomings of the Jetaway. Rolling start races were usually over before I even had to shift to 2nd gear. In races from a dead stop, some cars would gain maybe a car length off the line, but by the time I shifted at 60-65 mph, I was usually well ahead. That setup accelerated very linearly from 0 to 100.

I am not expecting a mildly upgraded 350 to perform like that, but it certainly sounds like a TH350 would make it more lively.

JohnnyBs68S

The Jetaway is great if you want to get good highway MPGs. My '68 (w/ 2.78 rear) had no problem getting 20 MPG on the highway, although that tall 1st gear meant you burned a lot of gas in town heating up the torque converter. That, and the fact that nobody makes performance parts for it like a Powerglide means it is NOT (even potentially) a performance trans by any means. Always a dog off the line, but get behind a slow-poke on a 2-lane at 45 MPH with a gap to pass, and SEE YA. "Passing gear" is its only glimmer of hope.

IMO, a TH350 is a great upgrade from the Jetaway, but if you're "upgrading" why stop at 3 forward gears?

joe_padavano

The Jetaway has the same 1:1 high gear as the TH350. Highway RPMs will be exactly the same for either one.

Keep in mind that drag racing is a very limited subset of the street driving environment, with very tightly prescribed and repeatable performance needs. You aren't accelerating when you shift (dual clutch transmissions aside), so the fewer shifts you have to make in a quarter mile, the better. This is why drag racers use the PG. Of course, if you have a dedicated drag car, you pick the rear end ratio to match the torque curve of the engine so that you can maximize performance with a two speed trans. Just don't try to drive that car in traffic...

More gears means more flexibility when actual performance needs are uncertain. And yes, a trans with four gears and a much wider ratio from low to high will be even more fun to drive on the street. There is a limit, however. I had a 2019 Camaro SS rental car with the ten speed AT. I tried using the paddle shifters, but the gears are so closely spaced that I spent my entire time watching the tach and shifting, which sucked all the fun out of it. The first two gear changes happen before you cross the intersection.

lshlsh2

Had a jetaway in my 68. Never raced it, but was a fine transmission for a cruiser. Depends how you are going to drive, if you are going to just cruise around it will be fine. You can change at your leisure or not.

NTXOlds

This is very solid advice, but it is good to know that the swap is not that complicated if that time ever comes.

NTXOlds

What transmission do you recommend?

Fun71

I agree, with those it's just better to put in in D and select the sport mode. I went to a performance driving school and the instructors said they don't even attempt to shift themselves; the transmission programming is so good that even professional drivers can't do better. I took that advice to my next performance driving school and opted for the Hellcat with the automatic over the manual transmission, and I ended up first in the class in the competitive driving sections.

matt69olds

If all you want is a comfortable cruiser, and have no intention of modifying the engine or swapping in a big block, skip the 350 trans and look for a 2004r. You get the best of both, even lower 1st gear than a 350 (more get up and go) and a overdrive (even lower cruise rpm than you have now).

the trans basically bolts in. It uses the same driveshaft, you need to slide the crossmember back to the position used for a th400 trans (which requires some parking brake cable modifications) and you need to modify the carb for the TV cable.

Any 2004R in good condition will live a reasonable life behind a mild 350.

69CSHC

Here are the hard facts.

A) 1965 442 Jetaway Switch Pitch 3.23 rear. 15.5 @ 89 MPH in the 1/4 0-60 7.8 seconds. Car Life, May 1965 ( 400 CID 345 HP 440 LB FT)
B) 1967 442 THM 400 with 3.08 rear--------. 15.8 @ 91 MPH in the 1/4 0-60 7.8 seconds. Car and Driver, Dec 1966 ( 400 CID 350 HP 440 LB FT)
C) 1967 442 THM 400 with 3.08 rear---------. 15.5 @ 91 MPH in the 1/4 0-60 7.1 seconds. Motor Trend, Feb 1967 ( 400 CID 350 HP 440 LB FT)

So as you can see the numbers at first glance look close, thanks to all that torque. But the MPH is significantly different. The 67 is absolutely a quicker car, even if the traction limited tires couldn't post better ETs. The 67s, are also much heavier. 3 speeds allow you to tap into more power.

A) 1965 442 test weight was 3890 , performance MPH shows 214 NET FLYWHEEL HP
B) 1967 442 test weight was 4284 , performance MPH shows 251 NET FLYWHEEL HP
C) 1967 442 curb weight was 3850 + 2 on board.

As you can see missing "1st gear" on the Jetaway is devastating. Imagine if the 65 had the same test weight as the 67...


All that extra torque made the car much more agreeable.


I also owned a 1966 442 A2 all original in the mid 2000s, engine was on the tired side but car still moved well and the Jetaway was great.

Regardless to me unless originality is a sticking point the upgrade is a no brainer.

Swapping a THM 350 in place of a Jetaway all else the same is like adding 50 HP . Launching with a Jetaway, switch pitch or not is like taking off in 2nd gear no matter what.

NTXOlds

Thanks for the suggestion!

NTXOlds

Very compelling numbers. You are correct about my Starfire engine in my 4-4-2; it was a torque monster that I specifically built for the street.

You have all convinced me to put a transmission on the list.

Thanks!

JohnnyBs68S

True, but I suspect that there is less frictional losses inside the Jetaway. I also had a '70 C/S 'vert w/ the same 350-2bbl and TH350, same rear gear (2.78) and it never broke 20 MPG on the highway.

200-4R is what I used, it has a better gear ratio spread than the 700-R4, which has a big ratio jump from 1-2.

joe_padavano

At 1:1 in high gear, the input shaft is locked to the output shaft. Frictional losses are equivalent. It's not like the power path runs through a planetary gearset to get there.

This actually brings up a related topic that's bothered me for a while. If efficiency is what you want, an OD gear set introduces frictional losses due to the added planetary gears. You'll get higher efficiency by using a direct drive high gear and just adding underdrive gears in the lower ranges. Change the rear end ratio so the effective final drives are the same.

danktx

I have a BOP Turbo 350 and 3.08 open rearend out of a 69 Cutlass if your interested and I'm in your neighborhood.

NTXOlds

Thanks, danktx. I will keep that in mind. I am looking for a 200-4R and a 3.23 or 3.42 posi, but if I have trouble finding these, your combo is a good alternative.

BackInTheGame

I have a NIB OEM 588 carrier, but not the OEM gears, for a 3.42:1 anti-spin rear end, if you need it.

NTXOlds

Thanks, BackInTheGame. I will keep that in mind.

Lonnies Performance

My friends Camaro with the 10 speed, drag radials & only exhaust/tune runs 11.7's, pulling 60ft times in the 1.6's all while letting it shift on its own.... Hard to criticize that kind of performance.
Yes,.. GM paddle shifters are just a glorified toys... the shift delay along with the factory torque limiting on shifts is annoying enough that I hate using them.

My 442 with Jetaway & 4.33 gears is still not impressive on the launch. The high gear pull is nice as well as full throttle downshifts but It would be a different car with a 200-4R trans. I've never liked 2 speed transmissions unless coupled with a high stall & a lot of gear.

JohnnyBs68S

I was thinking more along the lines of parasitic loses due to the Jetaway having one less planetary gear set (and other moving parts?) than the TH350, that continues to slosh though the trans fluid even in high (1:1) gear even though it's not involved with transferring torque from the input shaft to the output shaft. While probably not significant at lower speeds, at highway speeds these parasitic losses will grow. All other things being equal, this would seem to tilt the efficiency factor towards the Jetaway, but not enough to overcome the efficiency impact of a gear ratio change.

I agree with your synopsis of OD gears increasing parasitic loses because a gear set under load will experience more frictional losses than if it were not under load and just coasting through the fluid. I am surprised that auto designers and manufacturers don't opt to make the high gear in the trans a 1:1 ratio and just use a tall (numerically low) rear gear to minimize drivetrain losses for improved highway MPG. Maybe there is some constraint or negative tradeoff when making a final drive ratio in the 1.xx range? That would be a gearset with a (relatively) large pinion and small ring. This would also improve NVH by reducing driveshaft speed at a give road speed.