Beefing up a Sporto to handle a 2.5SS?

[teenchy]

I recently had a 2.5SS motor built with the intention of running it with a stock 905/20 Sportomatic gearbox. Upon assembly and testing, the builder found that at peak torque between 5500-5700 rpm, the box couldn't handle the torque. He tried replacing the stock 905 pressure plate with a Kennedy performance plate but experienced the same issues. Upon disassembly he saw no harm done to the plate, so he's speculating that the torque converter might be the weak link.

We're now trying to figure out next steps. One option might be to use a 925/xx box in place of the 905/20; another might be to use just the torque converter from a 925/xx. A manual swap is out of the question because reasons, so please don't suggest it.

I'm aware there have been Sporto equipped cars out there that handled 2.7RS and 3.0SC levels of power, so I have to think that a properly prepared Sporto could handle the ~200ish hp from this short stroke motor. What I don't know is how to ensure the box is strong enough to handle that power. I know it's a long shot, but if anyone has any experience in this area (I've already cross-posted at the bird) I'm all ears. Thanks.

[edmayo]

I've never put a sporto behind a modified engine, but like you I'm sure it could be done. Like you I feel the problem is the torque converter. Drag racers are putting several thousand H.P. thru converters, I'd start with talking to the folks that build their converters.

[cwrm4]

At least from the parts diagrams the 925 for the 72-73 T/E used the same torque converter as the 905. The 72-73 S and 74-82 cars used a different torque converter with a 925 part number (but my understanding it just had a 400 rpm higher stall speed). And I agree that are a number of examples of Sportos being used succesfully in 200+ hp cars.

I wonder if you are getting a cavitation issue with the Sporto oil pump at higher rpms (possibly there is a partial blockage in the torque converter oil circuit)?

Following with interest as (one day) I'd like to build up my 70 Sporto T motor to give a "few" extra hp...

[Chuck Miller]

I assume this 'R' did not have a stock Sportomatic ...

(out of the Boschen/Barth book)

Think I also remember the '4 cam injected R' also tested with a Sporto...

[teenchy]

I assume this 'R' did not have a stock Sportomatic ...

(out of the Boschen/Barth book)

Think I also remember the '4 cam injected R' also tested with a Sporto...

Chuck, IIRC the car pictured was running a 901/22 motor which put out ~210-220 hp. I've got to believe the box can be made to handle that kind of power.

[aturboman]

There is an old article of a Sporto modded for a turbo engine in Up Fixin (I believe), unfortunately I don't know the volume.

I recall the factory provided parts and technical assistance. Also recall it being very detailed with some part numbers.

May be worth searching, turbos = torque.

[teenchy]

Have been combing Up Fixin' but have yet to find the article.

In the interim we may have a solution, albeit not the most elegant one. We managed to find a low-mileage 3-speed 925/12 from a middie that we'll convert to a 4-speed while keeping the rest of the guts. Here's a gear chart for the proposed custom gearing.



The T 4th may get swapped for a U, not 100% sold on that yet.

Kind of a shame to put the rebuilt, numbers-matching 905/20 on a pallet but it's there if ever needed.