68conv455

Is anyone running this combo? I've got a slightly warmed up '71 455, 3.55 rear gears, and 235-15-60 street tires. It's a street car but I want it to withstand any abuse. I'm looking for reasonable highway cruise RPM and gas affordability. Of course it would be a heavy duty unit from someone like bowtie. Please let me know how you like this combo.
Thanks.

Redog

I think you will need some kind of connector to kick the overdrive on at a certain speed, or you could overheat the trans

joe_padavano

You're thinking of the torque converter lockup. The overdrive is automatic.

The real problem is that you need an aftermarket 200-4R with beefed up internal parts to handle the torque. I've snapped the input shaft on a 200-4R with a stock 140 hp 307.

Olds64

Joe is right. A stock 200 4R will not take the torque of a 455. If you want a stout transmission have Brian Hofer build one for you. He builds 200 4Rs for the Buick GN guys, his work is phenomenal.

http://www.turbobuick.com/forums/ven...r-trannys.html

GoldOlds

Isn't the 200-4R the same tranny Chevy put in its RWD minivans (Astro/Safari)? I've always thought the 700-R4 was much stronger (TPI Trans Ams, Camaros, Vettes); I know of someone who put one behind the 454 in his '68 Chevelle conv. and as far as I'm aware, it's still holding up.

- GoldOlds

joe_padavano

Pretty sure that's the 700R4


First, in stock form they both suck. The 4L80E is the only OD trans that will reliably take a big block in stock form - that's because it's based on the TH400. Note that the 700R4 has been continually upgraded in the form of the 4L60, 4L60E, and now the 4L65. Also, a single data point does not guarantee performance in all cased. Finally, the 700R4 doesn't bolt to an Olds motor.

Olds64

Hey Joe, isn't it a 200 4R in your 86 Caprice wagon? I had a 91 Buick Estate Wagon with a 307. It was a pretty decent car except for the fact that it had so many miles on it.

joe_padavano

Yup. That's the one I broke. The replacement has been beefed up in anticipation of the 403 swap.

W30post

To answer the original question, I have a 455 with an almost stock Buick Grand National transmission behind my 72 455 and 3.42 gear.

List of mods:
Billet servo
larger boost valve
larger reverse boost valve
Raybestos blue plate clutches
Kevlar band
Transgo shift improver (valve body only kit)

Pros, 15.5 miles to the gallon in mix driving conditions. Cruise RPMs are below 2000RPM. Bolts right into the stock 400 Turbo locations with a 350 Turbo driveshaft.

Cons, this particular set-up doesn't down shift from 4th until below 30 MPH. The Bowtie Overdrive cable corrector may fix this problem but I just live with it. Also second gear holds on too long with this Transgo kit and big servo. Last, the exhaust note is at drone levels at 60 MPH because of the lower RPM.

I only have about 500 miles on this trans and I haven't given it too much of a beating to see how it will hold up.

Ask yourself what you want. Try to have a ride in someone elses car before you decide. You may decide that a 400 Turbo will do all you need instead of the extra gas mileage. How long can you drive the car before you pay for that 200 4R with the "gas savings"? It may take a while with the limited driving you will probably be doing.


James