It's time for me to start thinking about a Torque converter for my 496/TH400 combo.
Problem is, I'll never know the actual peak torque RPM of this engine as it will never see a dyno. It's a 10.3:1 496, alum Brodix BBO 270 heads, 229/241@.050 roller on a 109 LCA, RPM air gap, 850 Quick fuel double pumper with 2" primary full length headers. Standard recipe to power really. Est. high 500's in HP and torque. Torque probably will peak at a little higher RPM owing to the cam. The general thought is to pick a stall 500-750 RPM below peak TQ RPM. I googled some dyno charts for similar combo's, and I see the peak falls somewhere between 3600-4500 RPM, but this one should make good torque starting at 3500 and carry through to at least 4800.
It's a 3:55 Posi with a 27.5" tall tire. 60mph cruise is about 2650 RPM. I'd say at least 4500 lbs with me in it with 1/2 a tank of gas.
Not concerned about any type of drag racing whatsoever, not max launch power, just a good street cruiser with killer get up and go, but don't want to be stuck with a dog due to a poor choice of stall. And I don't want it to be too loose on the converter either as to create a ton of heat. I'm willing to spend good money on a quality piece to avoid it melting down and taking the tranny with it. My gut tells me something more conservative around 2500-2700.
Any ballpark thoughts about what might work well in my case here? Or thoughts about converters in general?
Cheers,
Mark
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
I would suggest you speak to a couple (or more) of torque convertor manufacturers. However, by the looks of it you will be making some pretty good hp/tq numbers.
When I was building a BBC a few years ago I too was wondering what convertor would work best for my application. The www was more than helpful and I ended up contacting Pro Torque for their professional assistance and ended up filling out their detailed questionnaire. Even then, they contacted me to work out the 'finer details'...
The folks at Pro Torque were most helpful and I imagine others such as B&M, TCI etc. would be also. Good luck with your research.
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1949 Pro Street Meteor Coupe, 468 BBC, 4L80E, Narrowed 9" 3.50 posi
1966 Biscayne post, 427 L72, M21, 4.11's 16600 original miles
1966 Hemi Satellite 4 gear 59K original miles 1968 Z28 302MO, M21, 3.73's, cowl plenum induction
Seems to me the only reason for a high stall speed is for drag racing launch. You are not going to do that.
Any street tires could not stand up to a full-bore launch anyway. Plus with 500 ft-lbs on tap, you will have plenty of punch from a dead stop (less torque off-idle then will help keep tires from burning) or from any speed, actually.
TH400 has a nice low first gear, which will help get you moving from a stop. And if you run the motor between 3000 and 5000 rpm (which, since your motor is not greatly different than mine, should have similar torque curve) you'll have fat acceleration all the way up to as fast as you want to go.
Higher stall speed means more slippage at all speeds, leading to poor gas mileage (maybe not an issue, because if gas mileage was of concern you would not have built that big motor, eh?) and as you noted, much greater heat generated (detrimental to long transmission life, even with an extra cooler).
Seems to me that 2000 or maybe as much as 2500 would work for how you will be driving.
Better yet, get a 3rd pedal and eliminate a torque converter altogether
Dave
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1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod
You're right, I think the thing will be fat with torque anyway Dave, so it shouldn't have to be buzzed to get the benefit. And who really cares about a launch with a cruiser anyway. My little 9.25" wide tires won't do very well.
I have a 2400 B&M paired with my SB and 400, and it works really well in that combo. But I'm not sure I can trust an off the shelf converter to last. I think I'll have to spend a little more on a custom.
Did you get your 496 running well Dave?
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
Is that 9.25" tread width? That is NOT a "little" tire! All I could stuff in mine (older, so likely smaller wheel well - I did not tub it or change spring perches) is 7.8" (10.2" section width, and I can barely get them on without dropping the rear axle). BFG Radial T/A's.
My 496 final installation (electrical, linkages, plumbing, etc.) is coming a long ... slowly ... had a little medical setback, acute GI bleed, lost 1/2 my blood, 3 units blood brought me back to 2/3 which is what they figured was OK but still have minimal energy. But I'm plugging away, hopefully the old girl will be on the road soon.
Dave
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1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod
I went with an 11" Coan Pro Street series converter. Heard nothing but good about this brand.
PN# 20212-4. 2600-2800 Stall. Although will probably flash quite a bit higher with all the torque (if and when it can ever get traction lol!)
Kind of stayed away from the higher stall converters, as I don't really want it to continually slip and build heat at cruise RPM, which will be around 2750 at 60 with my setup. But I still wanted the stall a little higher than stock.
Bought it through Jegs. First time with them...zero issues just like Summit.
1956 Pontiac Pathfinder 2dr sedan, 496 - dyno'd 545 hp, stick shift, 4.11 posi - Hot Rod
