CUCV Torque Slip (TH400)

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Buck69

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In the process of repowering a new to me '86 CUCV. It originally had the 6.2 (diesel) with it's current 4.56 axels.
I am going to install a 5.7 and it is my understanding that the torque converters are different between the two. Lower stall speed with the diesel?
Was looking at going with larger tires, but thinking the best option for body clearance will be 35's without getting carried away with more than a 6" lift. While waiting for the stock 4 core radiator to have a custom core built for it, I have been going through the axels, fuel system, wiring and body trim. Most the goodies are a week or two away up here.
So my question is, should I be doing something with this torque converter? I am expecting she will be spinning some rpm's on the highway. The highway is not what I am putting together this truck for though and am sure the 5.7 won't mind it on occasion. Is there better options for torque converters that will help reduce the amount of slip at the higher speeds? Lock up would be nice but not really an avenue I would like to head at this point in the game.
Thanks in advance for any suggestions.
 

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I'm in for an answer because I'm curious. With the steep gearing as a crutch, my guess is that the low stall converter will work ok.
 

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Get a remanufactured converter for your truck with the gas engine. The stall speed will be all wrong for the engine, especially if the engine has some go fast parts.

The diesel engines have a low rpm torque curve, the factory converter is tailored to that. The gas engine will definitely not like the tight diesel converter. As for cruising, once your above stall speed (probably 2000-2400) there will be very little difference in the way the truck drives with either converter.
 

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Get a remanufactured converter for your truck with the gas engine. The stall speed will be all wrong for the engine, especially if the engine has some go fast parts.

The diesel engines have a low rpm torque curve, the factory converter is tailored to that. The gas engine will definitely not like the tight diesel converter. As for cruising, once your above stall speed (probably 2000-2400) there will be very little difference in the way the truck drives with either converter.
I am open to trying a different t/c if there will be gains up in the higher rpms.
There is nothing really go fast in this motor. It is just a marine built vortec with a mild cam.
The truck is light with really low gearing. With no slip at 1:1, it would be 24-2600 on the highway.
I am just concerned the current one will be much above 3000 with a light load.
More rpm, less mpg?
 

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Gas vs diesel=not even close if they actually physically interchange.
 

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The converter will bolt up. I had the factory 6 bolt cucv diesel converter bolted to my 327 before I changed everything. It wasn’t terrible, but a properly matched converter can be had for cheap, so worth doing when swapping the engine.

You’ll also need to change governor parts. Full throttle, the diesel governor will have it shifting in the 3300 rpm range. You’ll want it to shift much later than that.
 

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Not to get too far off your topic, but you can probably get by with a 4" lift with 35's as long as they are not too wide. I have a 3" lift on my K30 with 33's (305/70R16) with 16x10 wheels (4.5" BS). My K30 with a 3" lift is an inch taller than my old '79 K15 with a 4" lift due to the taller 1 ton frame. Both had 33's.

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Gas vs diesel=not even close if they actually physically interchange.
They will physically interchange, it’s the internal pump/turbine/stator combination that is the problem. The torque curve between a gas and diesel engine is completely different, a really tight diesel converter won’t be fun behind a gas engine.
 

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The converter will bolt up. I had the factory 6 bolt cucv diesel converter bolted to my 327 before I changed everything. It wasn’t terrible, but a properly matched converter can be had for cheap, so worth doing when swapping the engine.

You’ll also need to change governor parts. Full throttle, the diesel governor will have it shifting in the 3300 rpm range. You’ll want it to shift much later than that.


I forgot about the diesel governor!!

When I swapped the 455 Olds in place of the blown up 350 Olds diesel on the first test drive I noticed immediately it shifted way too early. I think the shift points were around 3500-3800, it definitely made for a sluggish WOT. I swapped in a “mystery” gov, I have no clue what it came out of but it was much better.

It still has the diesel converter in it, the big torquey 455 doesn’t mind it too much. If I had known then what I know now I would have swapped it. It’s just difficult to take apart something that isn’t technically broken.
 

Buck69

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The converter will bolt up. I had the factory 6 bolt cucv diesel converter bolted to my 327 before I changed everything. It wasn’t terrible, but a properly matched converter can be had for cheap, so worth doing when swapping the engine.

You’ll also need to change governor parts. Full throttle, the diesel governor will have it shifting in the 3300 rpm range. You’ll want it to shift much later than that.
This is great! Thanks. Pretty much what I need to hear.
I by no means give disregard to what everyone has offered. I appreciate it all. This is a bit out of my wheelhouse and am hoping to nail it off the get go. I am not looking for street performance with this truck and have no interest of doing so down the road. Just hoping to keep the engine from spooling up as little as possible when I am on the highway. Shift points will for sure be important though.
I haven't addressed anything with the transmission yet. Shift points is not something I had even thought about.
I would like to get everything for parts coming ahead of time though to avoid further delays down the road.
I am really interested with what all you did to yours. It sounds like I am kind of walking in your steps.
I assume your 327 has a 2 pc rear seal? Not even sure if there is a difference, but I did bring in a TCI flexplate. https://www.summitracing.com/parts/TCI-399773
My Vortec is externally balanced. This one is similar to the lighter OE version that would have been behind it originally when salvaged out of a '97 suburban. Since rebuilt and itching to make fire.
What did you go with for a torque converter and would you change that if you were in my shoes?
With the governor, what am I looking at? Springs or the whole assembly? Am sure it is the same as yours. Here is the tag on it.
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Thanks all for your contributions this far.
 

Buck69

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Not to get too far off your topic, but you can probably get by with a 4" lift with 35's as long as they are not too wide. I have a 3" lift on my K30 with 33's (305/70R16) with 16x10 wheels (4.5" BS). My K30 with a 3" lift is an inch taller than my old '79 K15 with a 4" lift due to the taller 1 ton frame. Both had 33's.

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Your truck looks great and thanks for sharing. My original plan was 37/38's to help control rpm's on the highway, but am worried about tearing up the fenders when things start flexing in the trails. I am planning on a 6" lift at the moment and don't really want to go any higher with the suspension. I figured the 35's would be a good safe start on the original wheels. I can measure up clearances in the field and bump up tires and wheels later if I find there is lots of clearance.
 

Frankenchevy

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This is great! Thanks. Pretty much what I need to hear.
I by no means give disregard to what everyone has offered. I appreciate it all. This is a bit out of my wheelhouse and am hoping to nail it off the get go. I am not looking for street performance with this truck and have no interest of doing so down the road. Just hoping to keep the engine from spooling up as little as possible when I am on the highway. Shift points will for sure be important though.
I haven't addressed anything with the transmission yet. Shift points is not something I had even thought about.
I would like to get everything for parts coming ahead of time though to avoid further delays down the road.
I am really interested with what all you did to yours. It sounds like I am kind of walking in your steps.
I assume your 327 has a 2 pc rear seal? Not even sure if there is a difference, but I did bring in a TCI flexplate. https://www.summitracing.com/parts/TCI-399773
My Vortec is externally balanced. This one is similar to the lighter OE version that would have been behind it originally when salvaged out of a '97 suburban. Since rebuilt and itching to make fire.
What did you go with for a torque converter and would you change that if you were in my shoes?
With the governor, what am I looking at? Springs or the whole assembly? Am sure it is the same as yours. Here is the tag on it.
You must be registered for see images attach

Thanks all for your contributions this far.
Same th400 you have. I swapped in an L31-r (4-bolt vortec era 350) and now have an nv4500. As far as a TC, reach out to the local shops and see what they can build you. Hughes performance is what I went with initially. I got the tightest option they had. Good for the freeway, but not very much stall. Especially with a very mild 350. I’d get something a little looser. Get a governor kit as well. I typically order parts from summit that I don’t get locally. You can see if there are any speed shops in your area and ask them what they have.
 

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Thanks @Frankenchevy. We don't have any speed or transmission shops anymore for that matter. Smaller town in the north. Not a big enough market to compete with the reman industry. Will have to reach out a ways.
Switching to a manual trans is also not an avenue that will work for me in this application but had crossed my mind.
What are you referring to with tighter and looser? Torque stall?
Will reach out to Hughes and maybe TCI support departments. Will be relying on the online markets if anyone has other brand recommendations.
Thanks again.
 

Frankenchevy

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Tight, loose, stall, etc. Put a tight converter between an average small block and the somewhat tall first gear of the 400, it won’t be real peppy off the line. I would only go this route if highway miles or trans oil temps were a concern when towing.
 

Matt69olds

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Most factory converters will have a stall speed of around 1600-2200. I know the place I buy remanufactured converters won’t sell a TH350/400 converter without a core. There is no core charge, either you have a core or they won’t sell one. Who would have thought the day would come when stock 12 inch converter are valuable??

Look at summit or JEGS converters, you don’t need anything fancy. The mail order places have free shipping, and no need to mess with a core.
 

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