Hydromatic vs turbo 400/700r4

[eoseitz]

I currently have a stock hydromatic in my 1974 Corvette L88. The motor has been swapped in my car and I'm not really sure if it's an L88 or not any more. I'm still trying to locate the vin on it.

Anyway, lately I've been driving and it shifts hard out of first into second. However, I never feel it pull into third. Since the engine has been swapped the rpm gauge doesn't work. They switched the points distributor over to HEI, so there is no way to hook up the stock tach gauge.

I've had the car up to around 100mph and the engine doesn't sound like its over reving. Could a 3 speed auto even get to 100 mph in second gear if third is out?

My cousin offered to sell me a turbo 400 transmission. Would this be a good upgrade, or should I go with a 700r4 to get over drive. Later up the road I want to add a supercharger. I've been told I can push about 8-9 lbs of boost on stock internals. Which transmission would be best for speed and fuel economy?

 

[damoroso]

Have you tried to manually shift it? What happens? You should be able to hold first, second, and then get it to shift into 3rd. I doubt you have a powerglide in the car. The 400 is a great trans but it's a 3 speed too. The 700r4 is a beast, and it's a tight fit, but it'll go. With a stock engine, I doubt you could hurt it. One of the complaints about the 700 is the reach between 1st and 2nd gear. The 2004r is another choice, it has a closer 1st-2nd gear, it's physically smaller, and it's an OD. The 2004r will take all a stock engine can dish out too.

 

[Hib Halverson]

It's unlikely your 74 has an L88 in it and your information says you own a 74 L82, so I'll assume the engine is an L82 small-block not the L88 427.

The stock trans in your car is a Turbo Hydra-matic 400 three-speed auto.

A 700R4 may fit your car with some changes in mounts and driveshaft and perhaps a little trimming here and there. In fact the 700R4 was stock in the last year of C3 production, 1982, so generally, it will fit the car. It's a good choice for a street-driven Corvette because it's low first gear ratio works well the the tall axle ratio you'll want for better mileage. It will work quite well with a 3.08 rear end.

 

[73shark]

While a good L-82 could probably withstand the rigors of 9 lb of boost, it will for sure find the next weak link in the drive train. Not sure what that will be but you might want to make sure the rest of it is up to the added stress.

 

[eoseitz]

Sorry about that. I don't know why I put L88. My engine is an L82 or some other 350. The engine has been swapped and I still haven't looked up the vin number on the block, mostly because I still haven't found it. I believe it should be on the front drivers side of the block. I know it came out of a 74 Camaro. I have no idea if it's from a z28 or a lower model.

When I look into a 700r4 should I get a newer one? I used to have one off of a 92 camaro. Will that fit?

 

[KANE]

...When I look into a 700r4 should I get a newer one? I used to have one off of a 92 camaro. Will that fit?

Yes- it will fit. Having done the 700R4 swap on a C3, you'll need a modded or specific crossmember, tranny mount, shortened driveshaft, and TV hook-up.

Remember- it is a swap and not a 1:1 bolt in.


As for the year tranny- later 700R4s tend to have more desirable innards. Make sure you have a Z28 transmission when you start. The Z28 has a better servo than the V6 and is appropriate for your V8's application. I'd recommend that you get it rebuilt if it is used.

 

[Rodney Gold]

Go for the strongest box if you gonna go SC..My ideal would be a bullet proof 4l80e and an offboard controller - you can program the box to do what you want..
Heres a site where all the issues are discussed.
http://www.montygwilliams.com/1982corvette/trannyinstall.html

 

[eoseitz]

Is the 200r4 a direct replacement for the turbo 350/400? I'm almost positive when I was doing an oil change my tranny was labeled hydromatic turbo 350.

While I need to cut down driveshafts and get new mounts for a 200r4? I'd like to keep it somewhat close to original in case for some odd reason I ever need to switch back.

 

[6880 Mike]

...I currently have a stock hydromatic in my 1974 Corvette L88. The motor has been swapped in my car and I'm not really sure if it's an L88 or not any more. I'm still trying to locate the vin on it....

Unless they have been machined awaay, you will find two stampings on the pad on the block at the front of the right head. You may have to clean gook off the pad to see the stampings.

The first will identify the engine; the second will be a VIN derivitive for the vehicle the engine was originally installed in.

Post your stampings and we can decode them. If you prefer not to have the information known, purchase a copy of The Corvette Black Book or the NCRS 1968-82 Corvette Specifications Guide and decode them for youself.