Is The 700R4 Best For Daily Driving

    *What About Performance Driving?

    MS: I am in the process of buying a Canadian-built '68 Malibu convertible. It was born blue with a black top, a 307 and a Powerglide. It is now lipstick red with a white top, a 350 and a Powerglide. It will be an everyday driver for the season. It has the console shifter. It has a 650 Holley with Edelbrock headers and a baby cam. Can you give me some insight on how the TH350 and the 700R4 compare? I will be driving freeway to work. Will the overdrive benefit gas mileage greatly? How tough is the 700R4 to Powerglide swap?

    JP: My vote is with the 700R4. I bought mine from a transmission shop which guaranteed it for one year (up to 550 hp). I have run mine behind a 500 hp big block torque monster for 1 1/2 years now with no problems. Overdrive is the way to go.

    AF: I have a 700R4 living behind a 450+hp big block. At the time I researched it with my transmission shop, they recommended staying away from low (numerically high) rear-end ratios. I am using a 3.08:1 gear which idles at 70 mph.

    BS: I have a '65 with a 350cid mated to the TH350. Mine is a go-to-work and go-to-car hops car. I freeway drive in L. A. with this combo. I'm running a 3.55 rear end which is kind of low gear causing 3500 rpm at 78mph. I have a mild cam and 600 cfm carburetor and I'm getting around 13 MPG even with my heavy foot. Because I've heard to many times that the 700R4 transmission is weak in comparison to the TH350 I've decided not to go with the 700R4 which runs about $1,300.00 built with the electrical parts. Instead I have my Chevelle in my buddy's transmission shop getting the TH350-C which is the Th350 with a lock up torque converter. The lock-up converter will drop rpm's about 400-500 less at same speeds on the freeway. Yet the transmission is as strong as any TH350 especially when it is beefed up. The lock-up works with a electrical switch which, when turned on, puts fluid pressure to the converter clutch, locking it up. This transmission was most in late GM TH350 applications just before GM went to it's 200r4/700r4 transmissions.

    The only catch with this deal is the TH350C electrical switch was operated off a throttle sensor, speed sensor and computer. The switch at the transmission is nothing more then an positive-negative switch. So I'm just going to throw in an on/off style switch where it's easy to reach and I'll use it freeway only. My transmission guy said it will only engage while in 3rd gear so letting off on the gas suddenly is no big deal. The only thing he suggested was not to punch it down to passing gear when lock-up is on because you'll get a shift bang which is not real good for the transmission.

    MS: The early model 700R4's were weak. However, any current model and any after-market model you buy today is every bit as tough, if not tougher, than a 350, 400, etc. I have a 700R4 in my '71 Chevelle, mated to a warmed-over 350 with an Edelbrock 600 cfm, Heddman headers, 9.8:1 compression, and a respectable cam (268/276 adv. dur; .489/.501 lift). Rear gears are 3.31's. I had a stout TH350 in it before. The difference is almost night and day. The first gear is better (700R4 has a 3.06; th350 only has a 2.52), and the overdrive makes the car purr on the highway, and it saves on unnecessary rpm's. If I want the high rpm performance, I just put it into 3rd. Depending upon your cam, you may want to go with numerically greater gears. If you want the kick of 3.73's, you can do them much more easily with a 700R4 than with a TH350.

    Gas mileage did not increase dramatically in town - I still get about 14 mpg. However, on the highway I get 18-22 mpg, and I can still beat most anything off the line, thanks to that great first gear. The torque converter is a little looser than stock, set at about 2100 rpm. And it locks up automatically upon 4th gear, so I don't have a switch hanging off the dashboard. I have the transmission set to engage 4th gear @ about 45 mph, which for me is the 2000-2200 rpm range while in 3rd, and 1400 rpm range in 4th. I think the toughness issue is put to rest.

    I also have the console shifter. No problems in hook up; it is a direct bolt-on. My package included the transmission, torque converter, transmission cooler, brackets, TV cable - everything needed to install. Cost was $1300 - a bit more than a hyped-up 350, but considering the first gear jump off the line and the smooth rpm's on the highway, it was worth every penny! I had a mechanic friend install it. If you've got a lift to get the car off the ground, and stuff to pull the transmission down, it's not hard. The crossmember may need to be moved back just a bit and the drive shaft may need to be cut.

    Archivist: Tom Wilson

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