Torque converter

[jauringer]

Hey guys, wanted to discuss torque converters for the new engine.

My spare 73 torqueflite is currently torn down and I'm in the process of cleaning and collection parts for the rebuild. It will be mildly upgraded over my stock 72 unit. Part throttle kickdown being the big one along with a bolt in sprag, billet servos, hd retainer, hd strut, tf-2 kit, etc.

It's going behind a 304 60 over, isky split duration cam, roller tip rockers, gasket matched in/ex ports, bowl work on the exhaust side .....all that. Needless to say, I've pushed my power band up a bit. It's hard to say how much but my guess is 400-600 rpm

the most difficult decision I've had with tranny rebuild by far is the torque converter. After a few days of reading, performing specific tests on my current 727, and talking to dacco transmission, I feel like I know where I need to be. Certainly not sure though.

My current worn out tranny stalls 1500 rpm which has been fine with my old worn out stock 304 but I don't think it's ideal with the new setup. A couple things I've noticed.

1st. The truck seems to take more brake pressure to hold still at a light. I can get up to ~7-8 mph just by letting off the gas.

2nd. 1st gear takes longer to build up. It's still strong right off the line but I'm still a ways away from my ideal rpm range and I can feel it slowly building up after that first jump. This one isn't huge but I think it could do better.

3rd and most noticeable is the 1st to 2nd gear shift @ above average throttle. It's a steep drop from 2.45 to 1.45 ratios and when I really get on it my 2nd gear shift drops too low in the rpm range and it slowly builds back up to peak power. I think raising the rpm @ the 1-2 drop just a few hundred would a big difference.

No, this is not a racing Scout but I love to drive.

the dacco guy recommended a performance 2300-2500 stall. That high of a number scared me a bit and I'd certainly rather be too low than high. I hit 70 @ 3000rpm so @ 2500, the converter would be slipping most of the time.

I'm thinking 1800-2000 rpm stall would be ideal. That give me a solid 300-500 rpm bump which I think would be beneficial. What do you guys think? Anybody run a similar setup with a higher stall tc?

Thanks!

Jason

 

[Scoutboy74]

Jason, I'm stepping out of my 727 comfort zone a bit in discussing tc's, so bearing that in mind I'll offer the following which you can take or leave at your discretion. According to the stall speed chart found in the fsm, the range for a stock 304 falls between 1675 - 1825, for a 345 its 1800 - 2000, and for a 392 its 1950 to 2250. Based on those numbers, my limited gut hunch for your warmed up 304 would be to not exceed the 392 range, which falls pretty well in line with your way of thinking.

 

[jauringer]

Hey scoutboy! Thanks for the info, I wasn't aware of the changes between engines. It's very interesting to see the 392 being in the range it's in. I agree that I shouldn't exceed the 392 but it certainly makes me a little more comfortable knowing it had that stall range from the factory.

Jason

 

[Scoutboy74]

Sure. A search on stall speed in this section will net you some more info on the matter. According to posts by mayben and kenney, unless you've increased your top end rpm range by a dramatic margin, the substantial expense of having a custom stall speed converter built amounts to a tremendous waste of cash. From what I gathered, most of the aftermarket converters available for reasonable purchase fall within the 1500 to 1800 stall range, which is certainly not a deal-breaker for even a stock 392. When I swapped the relatively fresh 392 into my Scout to replace the 345, I cinched it up to the existing tc, which was itself a fairly new unit, but certainly nothing special. I imagine its one of the typical 1500-1800 deals. The 392 likes it just fine.