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Torque Converters... I'm lost!

THRILLBILLY

THRILLBILLY

1/2 ton status
Joined
Sep 21, 2011
Posts
340
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Location
Melissa, Texas
Hey guys, it's been awhile since I posted anything but I'm back to working on the Blazer and have come to a crossroads on what to do and how to do it.. I searched some but couldn't really find a similar back story so here it goes:

We put the new motor in which sounds awesome. Runs perfect at idle and throttle response is on point. But we seemed to overlook a key component of a high performance motor, the torque converter... Obviously a 11:7:1 compression race fuel 355 is going to fall on its face with a stock converter in place (which it does) so my question for you guys is, with the motor setup I have in the truck setup I have, what exactly am I looking for in a converter?
stall speed, overall size, lockup vs. non-lockup? There is so many factors that come into play when choosing one like vehicle weight, cam specs, gearing, etc. that have kept me up at night reading so much I don't even know where to go from here.

So if you guys wouldnt mind, here is a quick overview of everything I got in the motor/drivetrain to help you guys help me out! :waytogo:

355 sbc
timing set at 34*
.125 dome top pistons
200cc 2.02/1.60 aluminum heads with .600 lift springs
1.5 full roller rockers
single profile hyd. flat tappet cam 301/301 adv. - 247/[email protected] - .525 lift - 110* lobe 106* center
750 vacuum sec. Quick Fuel carb
hurricane high rise single plane intake
built 700R4 with 208
44" tires
4.56 gears.

Thanks guys and let me know if something seems out of wack or doesn't look like it will work. I want to get power to the ground fast for the mud bogs and who better to ask than CK5!
 
I suggest calling B&M with your list of specs and asking for their recommendation.
 
3MAX said:
I suggest calling B&M with your list of specs and asking for their recommendation.
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I called B&M and TCI. They both told me they would give the specs to one of their techs and give me a call back and I haven't heard anything. That was over 2 weeks ago too. I thought about calling back but at the same time I'm too nice to try and be mean over the phone to talk to someone right then... Torque converters are completely foreign to me so I don't know who else I could call?:dunno:
 
I'm assuming this doesn't see much street use?

Get a converter with a stall at or slightly above the RPM range of your cam. For example, if the cam is 3000-6500 then get a converter around 3000-3500. Never let the motor get out of its power band.

Have a converter built for your truck, no off the shelf generic stuff. Your truck is a lot heavier than a car, be sure it's built to handle your trucks demands (weight, motor, etc).

If you're using nitrous be sure the converter is built for nitrous.

Don't worry about the physical size, let the builder work that out.
 
nvrenuf said:
I'm assuming this doesn't see much street use?

Get a converter with a stall at or slightly above the RPM range of your cam. For example, if the cam is 3000-6500 then get a converter around 3000-3500. Never let the motor get out of its power band.

Have a converter built for your truck, no off the shelf generic stuff. Your truck is a lot heavier than a car, be sure it's built to handle your trucks demands (weight, motor, etc).

If you're using nitrous be sure the converter is built for nitrous.

Don't worry about the physical size, let the builder work that out.
Click to expand...

No the only street use the truck sees is loading and unloading it on the trailer haha. The power band of the cam is rated 3200-7200 rpm. So a 3500 would be an ideal choice? No nitrous and probably won't until The Rockwell, coil over, and tractor tire stage. When you say physical size your talking about the converter size correct? Like 9" 10" 12" etc?
 
I would recommend a 3200-3400 stall speed for this application, I would also recommend a lockup style to minimize heat when you are in overdrive and no longer require the stall speed. You will be looking at a converter diameter of 10 inches or less so additional trans cooler will be a necessity, if you have a cooler provision in the radiator I would run through that first then through a large stacked plate design cooler and back to the trans. Do not buy an off the shelf converter for this, you will need to talk to the builder and share your specs so they can build to your requirements. A converter that stalls 3200rpm in a 3400Lb Camaro will stall at 3800-4000 in a 6000Lb rig with tire/wheel that weigh more than the driver. I would choose a billet cover converter as well as most of the plate style converters will not hold up to this kind of extreme without breaking the mounting.
 
Melissa isn't that far from Weatherford, maybe you could take your blazer to Greg and let him help you out :waytogo:
 
I'd call the cam manufacturer and ask them what converter they recommend.
 
Greg Ducato said:
I would recommend a 3200-3400 stall speed for this application, I would also recommend a lockup style to minimize heat when you are in overdrive and no longer require the stall speed. You will be looking at a converter diameter of 10 inches or less so additional trans cooler will be a necessity, if you have a cooler provision in the radiator I would run through that first then through a large stacked plate design cooler and back to the trans. Do not buy an off the shelf converter for this, you will need to talk to the builder and share your specs so they can build to your requirements. A converter that stalls 3200rpm in a 3400Lb Camaro will stall at 3800-4000 in a 6000Lb rig with tire/wheel that weigh more than the driver. I would choose a billet cover converter as well as most of the plate style converters will not hold up to this kind of extreme without breaking the mounting.
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Forgive my ignorance but when you say a converter that stalls at 3200 in a 3400lb. camaro, what makes the same converter stall higher (3800-4000) in a heavier vehicle? Or is it just that simple that a heavier truck will make the converter "change" its stall speed to compensate and I'm just way overthinking this?

Again thanks for the help! I ain't scared to admit when I don't know about something but be warned, because when I don't know I turn into a child playing 20 questions so I can understand it!:thumb:
 
The reason the stall speed is higher is that the engine will have to work harder to move the greater mass of the heavier truck. Stall speed is the point at which the converter hydraulically couples to turn the transmission input, it can be measured by brake stall speed, or flash stall speed and the variables are almost endless. That is one reason you will never see a converter advertised with an exact stall speed, it is almost always a range. Whenever engine torque, weight or gearing, tire size etc are changed it will change stall speed as well. One more reason to get with a converter builder when you are looking for the right choice in a vehicle that exceeds stock parameters on pretty much every level.
 
Greg Ducato said:
The reason the stall speed is higher is that the engine will have to work harder to move the greater mass of the heavier truck. Stall speed is the point at which the converter hydraulically couples to turn the transmission input, it can be measured by brake stall speed, or flash stall speed and the variables are almost endless. That is one reason you will never see a converter advertised with an exact stall speed, it is almost always a range. Whenever engine torque, weight or gearing, tire size etc are changed it will change stall speed as well. One more reason to get with a converter builder when you are looking for the right choice in a vehicle that exceeds stock parameters on pretty much every level.
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Ok I spoke with a company here in Dallas and they work with FTI. They told me that for my application with the weight of the truck and the setup I have that I would need a 4500 stall converter. I was a little thrown off by that number seeing as everyone else I've talked to said in the range of 3200-3800. Does 4500 sound even remotely right?
 
That seems awfully high unless this is strictly a drag only application being operated for short bursts of acceleration. That converter would be worthless in any other scenario.
 
Greg Ducato said:
That seems awfully high unless this is strictly a drag only application being operated for short bursts of acceleration. That converter would be worthless in any other scenario.
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Definately not a drag race application but it is one of those hammer down in the mud hole till your out or stuck kind of trucks. Getting quick wheel speed is needed for sure but I think telling them a mud bog truck was the wrong term. It's made for crossing deep mud and water holes in off road parks and running a bog at the mud pits around here but in no way a 6,000 lb. race truck.

Something very much like this is what this truck is made for: http://youtu.be/CuuNe60pVcA
 
With that scenario you will need to get engine rpm up for a good launch in the power band but you will want as much power to the wheels as you can get. The higher the stall speed the less power to the wheels, so you will need something that will get you up and going but wont waste the engine rpm at the converter. I think a 3600-3800, possibly a 3800-4000 would be all you would want here. If you will never be cruising down the road in 4th gear then the need for a converter clutch is zero. You will need to modify the pump to run as a non lockup.
 
You definitely don't want to cruise in overdrive with a huge stall speed and no lockup. The tranny will be making more heat than the engine!

I had a Corvette converter in my K5 once, which is supposedly about 2000rpm. It felt about as loose as my DD car does now with about 3000 stall. A 4500rpm "car" stall would make you launch your truck up in the range where an HEI ignition starts falling off, no?

You should just order a converter from Greg!
 
Greg Ducato said:
With that scenario you will need to get engine rpm up for a good launch in the power band but you will want as much power to the wheels as you can get. The higher the stall speed the less power to the wheels, so you will need something that will get you up and going but wont waste the engine rpm at the converter. I think a 3600-3800, possibly a 3800-4000 would be all you would want here. If you will never be cruising down the road in 4th gear then the need for a converter clutch is zero. You will need to modify the pump to run as a non lockup.
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Blue85 said:
You definitely don't want to cruise in overdrive with a huge stall speed and no lockup. The tranny will be making more heat than the engine!

I had a Corvette converter in my K5 once, which is supposedly about 2000rpm. It felt about as loose as my DD car does now with about 3000 stall. A 4500rpm "car" stall would make you launch your truck up in the range where an HEI ignition starts falling off, no?

You should just order a converter from Greg!
Click to expand...


So Change of plans over the past couple of days.. I have made a deal with my uncle to trade him my 700R4 for a either a TH400 or a TH350 he has. He's a mechanic and originally built my 700 for me. Since I don't need an OD tranny in my K5 because it never sees the street, we both think the 700 would be much better in a street car of his or someone he knows and a 350 or the 400 would fit my needs a heck of a lot better. The 400 needs a rebuild but already has a 208 behind it. He offered to help me rebuild it if I wanted to go with it. The 350 is freshly rebuilt out of a strip car but would have to be tore down anyways to change the output shaft to mate up to a transfer case correct?

As far as torque converters go for these 2 transmissions does the same 3800-4000 stall still stand as the most accurate or does this change the stall speed because of the lower gear ratios?
 
I think the 400 is a great idea for the kind of use/abuse this truck will endure. I would still stay with around 3800 stall, the good news is that is a much less expensive converter than a 700R4 uses.
 
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