Hey guys! I've been on this site for a few years, this is my first thread, I usually learn from everyone else's! But I need some help.... I have a 455, pretty much stock except for a high performance manifold, edelbrock carb, and MSD ignition. I have a 200r4 OD trans. I'm not even sure what the rear end gears are, probably original, idk. Last thing is my rear tire set up is 275/40/r20 in rear.

I used to have a TH400 and 17 inch wheels and it would GO! (Off the line) I'm not racing or anything, I just like some good pep.

But it when I put this 200r4 in it, it lost its get up and go. I'm not real worried about highway traveling, I mean, I don't wanna be running like 4,000 rpms at 65-70 MPH but I want it to be Hot off the line. my dad is the one that suggested that I put the OD trans in. 🙄 I want some get up and go again!! If somebody could help me, I would GREATLY Appreciate it.

FYI I don't know much about rear end gears....but I know that you guys do!

Thanks - Alex

 

If you have 2.56 gears, with your current 28.6" tires you will run at 1200 rpm at 60 mph! As long as you keep those tall tires, a 4.11 gear will keep you around 2000 rpm at 60 mph. With those tires don't go less than 3.90 for gearing. The acceleration will be night and day over your current 2.56 or 2.78 factory gearing. What stall torque converter do you have?

 

You could run 4.88 or 5.14 and still have moderate highway rpms, based on the above post.

 

im not sure what stall converter I have, how would I find that out? Is there a way to? Thank you for your reply!

 

i may end up going with the 4.88 you mentioned. Thank you for your reply!

 

Also, do you guys know if I can use a chevelle, gto, or Buick third member? Or will only stock work?

 

Any rear from a 68-72 GM A body will fit under your car. You may need a different driveshaft, depending upon which rear is used.

Chevrolet Chevelle, Malibu, El Camino, Monte Carlo
Buick Skylark, GS
Pontiac LeMans, GTO, Tempest, Gran Prix
And of course Oldsmobile F-85, Cutlass, 442

 

It might be simpler to go with a more standard size 14 or 15 inch rims.

 

If the transmission was the only change, it cannot explain the loss of get-up-and-go. In fact, the TH-200 4R has a steeper first gear, so off-the-line performance should have improved. Only your acceleration in overdrive should feel worse.


It's possible (but unlikely) the torque converter in the 200 4R is tighter than the one in the TH-400. It's also possible that in the swap you somehow screwed up the ignition or carburetion (did you swap throttle brackets and maybe the throttle isn't opening all the way?) or created a vacuum leak.

 

I was thinking the same thing about the trans gear ratio then I realized he now has different rear tires as well.
Those are nearly 29" tall according to the internet.

 

This rear end does not use a third member. The gear housing and rear end are all one unit.

 

Mine was my 19 year old girl friends, what ever.....

 

Did I take a wrong turn?

 

I have a complete 12-bolt Chevy type rear from a 67 Chevelle originally that will fit and has the companion flange for the Olds universal joint. It is also set up for performance with tubes welded to the center section, Mark Williams axles, c-clip eliminators, steel bearing cap, Moroso posi, and 4.88 pro gears. It was under my 66 W30 for about 45 years, seldom used (garage potato car). I have both steel and aluminum brake drums for it.

 

 

how much you asking for that?

 

I'm glad someone else thinks like me. Every time I see this thread, I want to post a pic that would get me banned permanently

 

I'm thinking my wheels being nearly 29" tall are a big factor, but I DID change my throttle bracket, I'm gonna check those things out, can't hurt anyways, thank you

 

I like my 20's too much......and I just spent $2400 on the wheels and tires. Haha

 

Those actually look good. The 4.88 gears will put you around 2300 rpm, 2150 rpm with 4.56 gears at 60 mph with the torque converter locked up. That translates to 2500 and 2700 rpm at 70 mph for each gear ratio.

 

Well, you have to understand that the overall effective gear ratio is a combination of the rear gear ratio, the transmission gear ratio, and the tire height. Since you have tall tires and you want to keep that tire size you need to increase the effective ratio by changing the transmission ratio or the rear gear ratio. Bottom line is you need a lower rear gear ratio in order to regain the off the line performance you had with the shorter rear tires.

 

the Tires and maybe the tranny swap are the issues bro... they look cool but the rear end set-up you would need to bring that oomph back would be even more expensive than the 2400 you just spent on those for parts and labor... another issue may have been your TH400 which may have been a switch pitch... not sure what the pitch is on your fixed (?) stator in that 200 4R as I never had one but the switch pitches on the older TH400s were designed to bump up your rear end power under hard acceleration by changing the angle on the stator through a simple throttle switch to change torque converter stator angle for less slip... that may have lost you about 20-35% off the launch plus the big tires losing you effectiveness off rear end ratio... and they usually stamp the ID letters on the axle housing on the passenger side towards the front for olds cars in stamped not cast 3/8 inch letters... if you tell us the letters someone can tell you which gears and whether it is an open or posi rear... you may have to wire brush it to see it... I just did mine the other day and found they were 3.08's after checking the Rear ID chart if you really want to know