Hey guys! So, just a few questions I have on my mind that I’d like to run past you guys. I have a 68 Cutlass S with a 350, original ST300 transmission. I’m not 100% sure of my gear ratio, but they’re highway gears (open) for sure. I would like to get a little more pep out of it on the street, but not sure if I should start with say an TH350/400 or 200-4R, or go for the gearing and posi first. I know the best route would be for me to do both at once, but it’s not so much in the budget at the moment. Engine had a total overhaul this winter. But, like I was saying.. What would you guys recommend I go for first? I have 275/60-15 tires in the rear, and I can chirp them if I really get on it from dead stop turning either left or right.. but scared to try a burnout lol. I’d like a set up that could squeal them around town, but maintain a decent highway rpm. With that being said though I do very little highway with this car, but would like to be able to if need be. If anyone could point me in the right direction of where to go with all of this, any advice would be greatly appreciated!

-Pat

 

Do you know what rear is under your car? If it's an O-Type, the replacement gear choices are very limited and posi carriers are a bit expensive. Sometimes it's easier and cheaper to replace the entire rearend instead if doing a gear swap.

I think the simplest bang for the buck would be the transmission swap. Your car will launch a lot better due to the lower first gear ratio in either one.

 

Pat, I can tell you what I experienced with my 75 Cutlass Supreme, 350 / Th350 tranny with highway gears. I had 3:42 gears installed with posi. Woke up the car huge. Big difference with original 350 engine and th350 tranny. It felt like I was stuck in 2nd gear at 60 mph though, but was fun around town. I had a complete engine job done 2 years ago and installed a 200-4R, I love it, Lots of torque and can cruise with low revs. Best of both worlds for my driving style.

 

I would go for the trans first. The lower first gear, combined with overdrive, will make a world of difference in performance.

My brother had a 63 Impala with 283 engine and a Powerglide. When the Powerglide started pouring fluid from every seal, we swapped it with a 350. With no engine changes, you would swear the car had 50 more hp. With the lower first gear of the 200r4, plan on thinking it has 75 more!

 

I do believe it’s the O type. Anything 68-72 A body would work under it, right? I’ve seen a couple Chevelle rear ends listed here locally

 

I’m wide open for any setup at the moment honestly haha. I’ve heard the 200-4R with 3.42 gears is the dream setup!

 

I had the trans sealed about a year ago and here we are now and it’s started to leak again. Just a better reason to dump it I guess haha. BOP Th350s are pretty ample around me used, but man I’d really like to do the 200r4.

 

Yes, you are correct.

 

What kind of RPM do you think I’d have at say 60, with my current trans and say a 3.42 rear end for example? Would probably be through the roof, huh?

 

Not unreasonable at all.

One of the online RPM calculators shows around 2500 RPM at 60 MPH with your 28" tall rear tires and 3.42 rear gears.
https://www.randysworldwide.com/calculators/rpm/

 

interesting! Thanks for the link, I’ll have to do some playing around with it

 

I started my drive-train upgrade on my '68 S w/ swapping the rear gear (2.78 open) to a 3.90 posi. Rebuilt the Type-O myself. This gave me alot of pep off the line w/ my Jetaway (ST300), but pretty high RPMs on the highway (didn't really care, I'm working on wearing out my stock 2-bbl 350 so I can rebuild it too). Next step was a 200-4R swap, which adequately addressed the highway RPMs (now w/ a lockup torque converter, my RPMs in 4th gear are a tad lower than they were w/ the stock trans and rear). Now if I stomp it off the line, it'll burn rubber until the car catches up w/ the tires..........the tired 2-bbl 350 doesn't quite have enough umph to bang into 2nd to keep the smoke show going in 2nd gear before the car catches up w/ the tires. When I did my rear, I also upgraded the UCAs w/ Edlebrock adjustable UCAs, and the LCAs were replaced w/ SSM Lift bars, which help plant the rear tires for improved traction. I also added aftermarket no-hop bars that tie the UCA frame mounts to the LCA frame mounts. So if I'm more careful when launching and roll into it and avoid spinning the tires, the car takes off from the line really quickly and turns that HP into forward thrust rather than shredded rubber. I eventually plan on running more rubber in the rear (245-60-14s all around now) and decided to take advantage of that by going w/ more thrust (3.90 gear), vs. lower highway RPMs in 4th (3.42 gear). I figure if my ultimate setup results in lower highway RPMs than stock (which is does), I've sacrificed nothing in that department.

 

Awesome. I think I’d be okay sacrificing some rpm for some pep off the line. I plan on doing both like you’ve done anyways, so it’s great to hear that even with the 3.90s and a Jetaway you can still drive the car haha. Sweet man! I’ll definitely keep that in mind!