Replacing 7.4L (L29) with 5.7L (L31)

[xXxPARAGONxXx]

Hello all, I am looking to buy a 2000 K2500. If I buy a K2500 with a 7.4L, I would like to swap in a 5.7L and keep the 4L80E. Primary reason is that I need the relatively better fuel economy of the 5.7L in case I need to use the truck to commute to work. I might not be set on 4WD, so C2500 might be possible.

What all does the swap entail? I appreciate your insight and advice.

 

[Supercharged111]

It entails cutting off your manhood!

Seriously though, the small block trucks are easier to find. Any reason you can't just wait for the right truck to come around?

The swap would require a fully dressed motor with manifolds and cat pipes, computer, and engine harness for bolt in goodness.

 

[Devon 11]

Better off finding one with a 5.7 already or just swapping a 4l80 into one with the 4l60

 

[618 Syndicate]

You can find a 2500 with a 350/80E, just gotta look.
The difference in fuel economy between the two isn't going to be that great however.

 

[stutaeng]

I doubt you'll get marginally better fuel mileage...

But to answer your question: get the engine, complete wiring harness and ECU for a plug-and-play swap. From an 8 lug gas truck with an automatic transmission of course...

You "can" adapt your harness and change tune in the ECU, but that's going to be a bit more advanced...I don't know your capabilities.

 

[yevgenievich]

From having owned 350 and 454 trucks, not much mpg difference unless a lot of idling.

 

[RichLo]

x3 from above

If you have a well tuned 454 your MPG will be aprox the same as a 350 but with the added capacity when you need it obviously.

Otherwise, why not go 'all-the-way' to a 4.3/4l80e Dually!

 

[someotherguy]

You want a GMT400 but are concerned about MPG? Get a C1500 / 5.7. Just the heavier drivetrain and gearing of a 2500 is going to hurt your MPG. Everything the engine is turning, from the 4L80E to the transfer case to the 14 bolt rear and minimum 3.73 if not 4.10 gears of the K2500 are all MPG-eaters.

Richard

 

[RichLo]

I get the same mileage with my 97 454/4l80/dually that I get with my 93 305/5-speed/k1500 Just saying

 

[xXxPARAGONxXx]

Thank you all for the wisdom.