TH325-4L Upgrades?

I've been looking into doing something to my '83 Toronado, and one idea that came up was swapping out the 307 for a 455. As far as I know, the mounting points and transmission patterns are the same, but I know my stock trans would never take the torque of a big block. I've been told that the internals of the 325-4L are basically the same as the RWD transmission that was used it Cutlasses and Regals of the era (TH350?), and that performance parts for those can be used. Is this true? Are there any other transmissions that might fit (like one from a big block toro)?

A good performance trans shop can build a 325 to take quite a lot of power.

The stock 325 will hold up under mild use. If the 455 is to be stock, I would suggest just swap it in and do a transmission filter and fluid change. A shift kit would help, especially one which boosts line pressure somewhat.

I would highly recommend you change the Hy-Vo chain that sits behind the converter. It is IMO the weakest part of the 325 trans. This chain will almost certainly be stretched. The extra power of the 455 will almost certainly make a worn chain slip or skip its sprocket teeth. Even a stock Olds 350 will do this in a Toro.

If you are going to lean on the 455 somewhat, consider rebuilding the 325. Have the trans shop pay attention to the clutch packs. Light duty THM 350's have 5 plate clutches. Heavier duty versions have 6 plate clutches. I do not know what the 325 has.

If there is any saving grace, unlike a RWD car, a Toro will not hugely overload a transmission because of the somewhat limited off-the-line traction afforded by the FWD layout.

I don't intend to make a drag car or anything, but I would like to perk up the 455 a bit if I can. Hell, if I could get the car to run in the 14's I'd be more than happy with it.

Do you have any suggestions for a shop in the northeastern Ohio area? Or at least a place where I could find parts? If I do the swap, I'd like to do the work myself so I can learn.

Well, there is now a '76 455 in my garage. I'm planning a mild performance rebuild (intake, cam, heads if I can find the cash.). Nothing fancy, just a bit more kick for the Boatmobile.

As far as the tranny is concerned, it was the th 700r4 that is supposedly the same as the 325-4l. Can anymone confirm this? If not, there is a 455 toro tranny a few miles from here for under 200 bucks that I was thinking about swapping in if its about the same size.

I've replaced an Olds 350 diesel in my 1981 Eldorado about 5 years ago with a 350hp stock Olds 455 from a 1976 Toronado. I have rebuilt the original THM325 with a shift kit and added an additional oil cooler and that's all.
I never had a problem with the transmission in 5 years so far. I use stock tires (same as on the '83 Toronado), and try not to accelerate too agressivelly from a dead stop. (I was told the wheels will spin before any real overload will hit the transmission anyway as long as I use stock tires) As for the top speed I regularly cruise above 85mph...

One thing though...the 455 is very heavy in either 79-85 Eldorado or Toronado. To keep the weight down I've replaced the stock manifold with aluminum, bought, aluminum water pump, aluminum Edelbrock carb., alum. radiator,...

That's good news. Where did you find a shift kit? I can't seem to locate one (I've googled and checked summit racing). Did you just have the trans rebuilt to stock specs, or was it beefed up in any way?

The added weight does worry me. The car already brakes very poorly. Are there any know brake upgrades that I could use (or adapt from a cutlass application)?

I found and bought the Transgo shift kit from at www.txchange.com/sk.htm (http://www.txchange.com/sk.htm)

No other changes have been made with the exception of the additional in line oil cooler (mounted before the radiator temp. exchanger).

Even though the 455 is suppose to be as heavy as the original diesel I am convinced it is even heavier. I have replaced the cast iron intake manifold with the aluminum (on older Edelbrock model due to the carb lip height which became critical as the 455 seats about 2in higher over the 350), replaced the water pump with the aluminum one, alum radiator,aluminum anything I could find...and now the weight is down for about 90lbs or more which is OK. I think the diesel engined cars have stiffer suspention too but am not sure.
No problems with brakes due to the Hydroboost brakes used on diesels. The brakes are hydraulic not vacuum operated. The power steering pump drives the power brake booster...highly recomended! "Feather Touch Brakes!"
You can also replace the discs with drilled replacement and ceramic pads (Ebay). May reduce early disc fade...