GM replacement engine set up for towing

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Macs Garage

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First time posting, but following for a long time. I have a 1999 GMC K2500 "classic" with a 5.7 vortec. The speedometer was broken when I bought 2 years ago reading 161,000 miles, so actual mileage unknown (speedometer and odometer working now). The engine went out this summer. I didn't have time to mess with it so took to a local shop with ASE mechanic. They were going to put a remanufactured engine for me and put a towing cam in for me ( I wanted more power full pulling my fifth wheel). After a week of searching they couldn't find any from a vendor they trusted and said nobody even had cores to rebuild. Finally they found one at a GM dealership in California which they bought through a local GM dealership they buy through. I was told it was an engine built to go into RVs 340hp and 350#tq. The only paper work that came with it was a pretty generic installation guide calling it a GM Performance L31 HD. When I look go to the GM Performance web site it doesn't state any specs for HP or torque. I questioned them about it and they said the 340HP 350#tq engine is what GM told them it was and it was built for RVs. Has anybody heard of such an engine?
 

stutaeng

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I'm guessing it's the 4 bolt main version of the 2 options available? I believe there were other changes, but I'm not an expert on engines...roller cam, etc.?

I'm certain the 4 bolt main was installed on the 8 lug trucks, so it should be the same as what you had before. I don't know about those numbers you quoted though. It it was rated 255 HP/330 TQ... that's with all the accessories, installed as in the trucks.

Unless they are using flywheel numbers?
 

Curt

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I can't speak of any knowledge on that engine BUT I can recommend an alternative. GM sells a HT383 replacement engines for our trucks that is a direct replacement for our trucks. Has the capability of running on our stock tune and stock parts (intake, injector, etc). I've heard people having a lot of good experiences with these as they come straight from GM and are not a reman engine.
 

HotWheelsBurban

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That HT383 is what @SUBURBAN5 used in his Burb, I think. I know it was a 383 stroker from GM. He's been pretty happy with it once he got it in the truck! I'd love to put one in my Burb, but I don't have the bux to get one...and the L31 5.7 is still chugging along with 200K.
 

SUBURBAN5

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The ht383e is plug in play for 1/2 tons according to gm. The 3/4 and higher I believe need a tune or some parts changes like the flexplate.. not sure the technical reasons but on gm website you'll see that is specifically says for 1/2 tons only lol. As for the l31hd I know that was more of a power beast for 3/4 and higher. I'm surprised it doesnt have the technical specs but I'm sure horsepower is around stock and torqued is higher then the standard 330ftibs
 

Schurkey

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1. 340 HP is not gonna happen with an L31 HD. Either you don't have a 12691672 L31 HD, or they're lying to you. The genuine L31 HD is not a "rebuilt", it's "new".

2. The "HD" has nothing to do with power production; it has to do with durability improvements.

3. The lack of those durability improvements is one reason they don't recommend the 383 in anything but 1500s. That, and the lack of fuel delivery needed by an engine working hard in a 2500 or 3500 truck. (Computer and injectors tuned for 350 cubes, actually feeding 383 cubes based on the computer's capacity for adaptive fueling.)

4. OTOH, installing an L31 HD in a 1500 erases most of the warranty. GM gives you 3 years, 50K miles (or something like that) if the engine is a direct replacement. Since the 1500s didn't get the HD version, it's not a direct replacement, so the warranty is 12/12 instead of 36/50.

5. ALL SAE horsepower ratings are "at the flywheel", but net vs. gross HP involves reducing the horsepower based on more-realistic ignition timing and air-intake temperatures among other differences.
 
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