Big Leche

My th-350 is going out....should I rebuild it and install 3:42 gears and torque convertor...or install a 700-r4?...they cost about the same...I was just wondering which way will give me more "performance" in my situation. I have a stock 350/350 combo with 10 bolt posi.....I figure rebuilding 350 is 300, gears 200, and torque convertor 175. 700 would be 650 to rebuild, then 100 for drive shaft, 100 for misc cables and brackets...any thoughts are definitely appreciated. Thanks in advance.

lshlsh2

I would consider a 200-r4 also. Same length as a 350, better first gear than a 700 and won't need an adapater plate to hook-up to your engine. It will have to be built up to survive behind your engine. This is the way I'm going to go when the funds and time come. my.02
There are a bunch of threads on this conversion on this site.

Larry

hookem horns

What are your plans for the car and what gears are in it now? Since you already have a TH350, a rebuild and 3:42 gears will work well for most streed use and be most cost effective. Especially if keeping the 350 engine. An OD tranny like the 200-R mentioned above would be nice if you do a lot of highway driving or the car is your daily driver.

Professur

The 4th gear of the 700 is only useful if you can get into it. Otherwise you're dragging around useless weight. If most of your driving is city, that's wasted gas. I thought I was being clever when the 200c under my Parisienne started bleeding and found myself a 200-4r to rebuild. But when I later sat and did the math, unless I changed out the rear end, I'd need to be doing 80+mph to get into 4th. Even if I was doing mostly highway, it still wasn't going to work.

The 700-r4 is one of the heaviest rotational mass transmissions. It will cost you a few ponies at the rear wheels. The 200-4r is much lighter. The 200-4r can be built to handle as much power as a stock 700 ... but the same effort applied to the 700 makes it even stronger still. Since you're already open to swapping out the rear end ... take the time to do all the math; don't rely on opinion. Work out just what ratios you'd have at the rear wheels for the various combinations ... work out just what use, if any, the 4th gear would give you.

joe_padavano

For starters, what gears do you have now, and how do you plan to use the car? I'll also suggest a properly built 200-4R. The 0.68 OD in that trans means that 3.91 gears are effectively reduced to 2.66 in fourth. That's a great blend of performance and economy. By the way, if you do have gears in the 3.91-up range, you WILL engage OD around town.

I'll also point out that your prices are optimistic for properly built parts. Expect to pay over $1000 for a good quality 200-4R or 700R4. The 200-4R doesn't need an adapter plate and is ultimately easier to install in a non-Chevy.

tmaleck

I have a 700R4 in my 67. It has a 4.10 rear gear. The trans has been built with a 2500 stall, recurved shift governor, shift kit, hydraulic lock up conversion and other durability upgrades. The tires are about 27 inches in diameter.

I get into fourth gear around 35 mph @1400 rpm. O.D. kicks in about 45 mph and 70 MPH on the highway is abouth 2500 RPM. The engine is always in the power band and the car has great city manners now.

I would highly recommend on O.D. swap, 700 or 200 based is your call. I got my car with the 700 already swapped in, so I just made it work right. For sure get a lower rear gear and you'll be very happy. I posted a simple RPM calculator a while back, it may help you decide what you want to go with.

Tim

joe_padavano

Um, fourth gear is OD. Perhaps you mean the converter locks up at 45 mph?

Professur

4th at 35 .. incredible. With the 2.41 I've got, I'm lucky to stay in 3rd.

tmaleck

Doh, you're right, I meant lockup.

cutlassjoe

I did a 200R4 in my 72' with 3.08 gears. Hits fourth gear around 40 and converter lock up around 45 mph. I can cruise comfortably at 70 at around 2200 rpm. This has to be one of the best upgrades I have ever done.

BlackGold

For what it's worth, both of the G-body 442s I've owned -- which have a 3.73 rear end -- shifted into 4th at about 35 mph under light-throttle city driving. Torque converter locks up just over 40 mph and will stay engaged while cruising at 40 mph (unless I lift or brake).

Less relevant is my Ford Crown Vic police interceptor with 3.55 rear end. It, too, shifts into 4th at about 35 mph and will cruise with the converter locked up at 40 mph.

So my point is that a 4th gear and lock-up converter really is "useful" in city driving (seeing as how 80% of my city driving is at 45 mph). Whether it actually saves any gas in the city is debateable.

That said, I'd prefer a TH350 for both reliability and shift characteristics, unless the car spends a lot of time on the highway.

Koda

For what it's worth, my 2.73 geared with a th-350 with a 350 small block (72 Monte) will sit at 2500 at 70 mph, 3500 at 100, and 1500 at 40 in drive. Punch on that car is solidly in the "fun" range, but not awesome. I can image what it could do with lower gearing and an overdrive, though it's too original to mess with.

Big Leche

I pulled the trans this weekend and actually just decided to rebuild it myself...I purchased a b&m 2000 stall, shift kit, and will be installing 3:42 gears next weekend. Hopefully this will liven the car up a bit compared to a slipping trans and 2:56 gears...ill take some pics and post soon.