Technical Another Torque Converter Stall Speed?

I know this question has been asked a million times before, but I gotta ask again. Sorry.
My '26 T coupe has a 355 SBC. 10.3:1 CR. Good aluminum heads, 2.02/1.60 valves. Custom cam- 215/224@.050, .470/4.90 lift. 650 QFT, headers. Idles pretty smooth at 900-1000 rpm. Runs real good! Makes about 350 hp.
It has a 700r4 with stock converter. Rearend is 9" Ford with 3.89:1 Trutrac. Rear tire is 235/75-15 @ 28" diameter. Car weight is 2475# with me in it. (2558# with my black Lab, Barney too)
Current TC bumps hard into gear. And I gotta stand on the brake at lights. Needs more stall.
I've talked to 2 different well respected TC guys and received recommendations from 2500 to 3000.
This is not a racecar. It does run well and once in a while I have been known to leave a little rubber and smoke and maybe exceed the speed limit a little, but 98% of the time it gets driven like the Grandpa I am. The TC I was leaning toward is the guy that recommended 3000 rpm TC, but I'm not sure that 3000 isn't a bit too high. This car will smoke the tires through 3 gears if I lay into it, without a hard-hitting torque converter.
What are you guy's experiences? Do I need a 3000 rpm TC? I just want it to stop pulling at stop lights and quit banging into gear. I cringe for the u-joints every time it does it. Tell me some stories.

 

2000-2500 is my guess. And lower the idle speed.

 

Thinking out loud, your u-joints will be just fine.... Have you tried lowering your idle speed just a bit maybe 800?... From your posting it seems like you are fairly satisfied with the performance.... Apparently with the lower stall TC converter you are now running You've got no problem with getting the power to the wheels in a good portion of your torque range.. I realize it's a personal preference but I don't particularly like revving up to 3,000 RPM with a slippery torque converter. I'm running a 2400 RPM with a 2.88 rear end in about a 3800 lb 49 Ford with a 383 and I think it's just about perfect..

Not to mention how much trouble it is to change a torque converter. Yeeks!

 

If it were me, I'd shoot for 2000 to 2400.

Then I'd call a torque converter company like TCI etc and see what they recommend and go from there.

I always hated it when a light car with a decent motor would come into the shop and no stall, fighting the brakes at stop lights and signs. I'd just shake my head and wonder why with all the other stuff they worried about and spent money on but didn't want to spend the money on a converter.

Even had a few guys tell me, "it's not bad once you get used to it", shouldn't have to get "used" to a car trying to push itself thru a stop light...


...

 

GM added an accumulator at some point that I think I recall was specifically designed into the system to correct the symptom you described. Perhaps someone can chime in. What year is yours?

 

At what rpm does your engine spend the most time at while cruising? Any Rpm below stall speed will be slippage and will generate heat which is what shortens transmission life. Unless running a lockup converter a 3000 stall is going to feel loose, I don’t like that feeling when cruising, yes good launches will be had but what’s the trade off.

 

I haven't heard of that. But there are accumulators in automatic transmissions, which act to soften shifts...it's like a spring loaded hydraulic cushion.

Not really...different converters have different behavior at part load. Some are slippery, some hook up partly. And even if they are above stall speed, they still slip a little, unless it's a lockup converter.

 

If you were closer, I'd make you a deal on a B&M Holeshot 2500 stall with lockup for a 700 R 4. I won't ship it.

Gary

 

Just a couple of questions to start off. How much manifold vacuum are you pulling when idling in gear? Is the trans stock or has it been modified for racing or towing?

I'm no expert on these transmissions. But I'm wondering if the harsh engagement when placed in drive could be something as simple as too much throttle pressure at idle. Could the t/v cable be re-routed or mis-adjusted in such a way that it's not retracted at idle? The idea of of having an accumulator to dampen the engagement sounds plausible. Maybe a broken or missing spring.

As far as the car wanting to creep at idle; could this possibly be a brake issue? Perhaps to much brake bias to the front wheels and not enough to the rears.

Also, the 700R4 has a lower 1st gear than most older trans like a TH350. This might magnify the creeping problem. If you start off with the trans in 2 instead of D, doesn't it start off in 2nd gear instead of 1st? I'd be curious to know if this had any effect on the creeping. Should cause no harm to the transmission and the 700R4 tends to make the 1-2 upshift before you even get thru the intersection at light throttle when driven normally in Drive.

 

Following this one. Jaw22w please follow this one all the way through to your implemented final solution since there seem to be numerous potential root cause issues and thus potential solutions. Help us all learn.

 

Our Anglia weighs the same as your T. With a 3.08 nine incher and a C4 a 3000 RPM 10 inch converter is a perfect match.

 

I spent the majority of my life going round and round on dirt circles, so I don't have much experience with TCs. I still tend to use go-faster stuff on my hot rods. The TC I have been looking at is a billet cover 9.5" TC from Freakshow Converters. They are drag race oriented, and they get great reviews. The price is a little stiff at $800, but not too bad for a quality custom piece. He's the one that recommended the 3000 rpm TC. I'm sure he could make it 2500. I think 2500 is more reasonable for this application. But I hate to spend $800 for a 2500 TC and find out it is not enough.

 

I know that predicting the stall speed of a particular TC when installed on a particular engine is kind of a black art, realizing that a TC will stall at different speeds on different engines.

 

Dad's 4200lb wagon has a Continental tight 3000 converter. Its hits hard enough to pull the front tire when at the drag strip. Driving around town you really don't notice the converter slipping, it drives like any other car. The only time you will notice it is different is when you hit it hard and the motor winds up before locking up the converter. Not all converters are the same.

 

I'd start by working on the idle speed. It must sound like the engine is racing when you are stopped. More timing less throttle. Are you running a vacuum advance using manifold vacuum?
To soften the shifts, I'd try to loosen the cable slightly, maybe 1/2 a turn.
I don't think the torque converter swap is the place to start to solve the issues you described.
Have you calculated your cruise rpm at 70 mph?

 

Stall speed isn't constant but varies with the square root of the torque the converter sees. If cruising speed is close to the engine's peak torque rpm, you might be able to work from the advertised stall speed. If the engine is far below its peak torque rpm, the converter might be stalled at way below its advertised stall speed.

 

Jim's 2nd suggestion.

Ben

 

Call converter manufacturers and you'll get exactly what you want. I've always called and received great service and excellent products. Off the shelf converters aren't always the best choice, but many people don't know what's available outside of products listed in a catalog, and that converter manufacturers can customize your converter to your exact specs.

Just Monday & Tuesday of this week I've called Coan, FTI, Neal Chance, Circle D, TSI, Hughes, & TCI. I ended up buying the Circle D converter due to price, availability, and to support a fantastic Texas based manufacturer.

 

this is the spec that matters most...and is what I based my 2000-2500 suggestion on.

but also, you didn't mention whether or not you are using lockup, and if the converter you are looking to buy is a lockup converter. That will make a significant difference.

You didn't mention what you've done to attempt to make the idle speed of the engine compatible with the torque converter you have. If you can get it to idle at 600-700 rpm, your main complaints will probably go away. But then you'd also gain some off the line performance by increasing stall speed a bit. And if you have the lock up functioning, you should not have any concerns about converter slippage while driving in high gear(s).

 

I had a T.C. built by a guy who is probably the most well known in the Treasure Valley near Boise. I asked him at what R.P.M. my converter will lock up. His answer, I dunno... t all depends upon the engine build. Torque and RPM. And it will vary from build to build. By the way, it works perfectly !!

 

Yes, I know that the cam is probably the single most important piece of the TC puzzle. I had this cam custom ground on a 112 lobe center. It is a fairly mild hydraulic roller cam.
I do use the 4th gear lockup in the 700, so yeah, slippage shouldn't be a problem. I think that is key here. I'm thinking that is why Freakshow is recommending a 3000 stall.
One of the things I really like doing is messing with carbs (Holley carbs). I use my AFR and vacuum gauges and plug reading to tune with. I just can't get it to idle any lower and still keep the afr from going to 11.5 at idle. 900 rpm is about as low as I can get it. I've played with main jets, IFR jets, idle air screws, air bleeds, power valves and anything else I could think of. Where it's at now, it has no stumbles off idle and idles smoothly. AFR runs in the 14-15 range at cruise. 13.5 at idle, WFO goes to 12.5. It's tuned pretty close. Gets pretty good mpg's. This bump into gear has been present throughout all my experimentations, up and down with idle speeds. I don't really think I need to change the carb to fix this problem. I think it is strictly stall speed.

 

uh...why do you care what the AFR number is at idle? disconnect the stupid gauge once you get the thing running right. The numbers don't mean anything at idle...you just need it to not stall or hesitate.

 

Are you using manifold vacuum advance? It will help you lower the idle rpm.

Your cam is mild enough that you don't need to idle at 1000 rpm to keep it from stalling.

 

They can always re-stall it if you decide you need more.

 

My 32 roadster has the engine and trans from an '89 vette (350 w o/d trans). Completely stock. Although it ran great I had the same problem with trying to control it in gear at idle, entertaining with the choke operational, maneuvering on a gravel driveway, front wheels locked and rears powering the car forwards!!!! Swapped the TC with a compatible 'Saturday Night Special' (forget brand, specs, but it came from Summit). Transformed the driving experience with no downsides that I can find. Docile when you want it, as angry as it can be with what it is / has when you want that. No reving it up to get it moving, slight touch on brake to hold it at lights etc etc. Very happy.

Chris

 

2500-3000 "stall" wont actually be 3000 hard hitting RPM in that car. You'll get the slip you need at the light and then she will go. It's not going to flash straight to 3grand just by applying the throttle normally at a light.

Stalls are very HP dependent. A monster engine in a heavy car will stall a TON more than that same converter in a Tbucket with a smaller engine- there's just no resistance in that set up. Also, when you are at light throttle 70mph in a t bucket, you're probably only producing 30-40hp to keep it at that speed. and 30hp isn't going to blow through a stall converter with mega slippage.

You just need to trust a converter company's suggestions using your setup info.

-rick

 

Idling anything at 900-1000 rpm will require a heavy foot to hold it at a light. Your compression and the cam should be able to idle at 600 in drive.
My son’s car was difficult to idle under 900 until I rebushed the carb throttle shafts and went to ported vacuum from intake manifold vacuum to the ignition. It idles now at 650 with the same CR and close to the same cam you have.

 

I suggest manifold vacuum advance because it will raise idle speed, which allows backing off the carburetor slow idle screw, to get idle down to lower rpm.

The additional idle ignition advance will also allow the engine to run cooler at long idle stop lights.

 

Exactly, people seem to have the misconception that a 2500 rpm stall is just like dropping the clutch at 2500 rpm, the car will move way before 2500 rpm.
I took the 1800-2000 rpm stall from a friend's 427/425 hp 56 chevy and put it in my 350 ci t-bucket, it doesn't stall at all in my car, I just throw it in neutral at the traffic lights.

 

Regardless of the discussion of manifold or ported vacuum, the issue here is; can we get the idle rpm lowered by 200 or more rpm while maintaining drivability?
The easy first step is to work with ignition advance and idle speed adjustment to lower the idle rpm.

The first step is not to change torque converters.

Does anyone agree?