GMT800 Engine Change ['03 Tahoe]
 

After running my '67/'72 GM trucks for over 50 years, I have now crashed the Twenty-First Century time barrier. Since my 2003 Tahoe C/1500 has 297 thousand on the clock with a 4.8L Vortec engine, I am exploring the possibility of replacing the engine -- when its time is up -- with a 5.3L.
Are dealer crate engines available?
What about junkyard [excuse me, Auto Recycler] GMT800 Engines?
Since there's an ECM computer [or more] involved, what do I have to do to get a bigger mill?

Re: GMT800 Engine Change ['03 Tahoe]
 

I"m wanting to do the same thing but it scares me to tackle it

Re: GMT800 Engine Change ['03 Tahoe]
 

Yeah, it's not as simple as swapping out a 307 for a 350 SBC in a '71 K/10.

Re: GMT800 Engine Change ['03 Tahoe]
 

Let’s put some things into perspective.

1. You have a 4.8 but want to go to a 5.3, why? Are you going to feel a gain in performance, yes, but probably not what you’re thinking. It’s not going to be an oh my gosh moment. To compare old school, it’s like swapping a 283 to a 327. People did it, but not popular because the juice wasn’t worth the squeeze. Now a 283 to a 350 swap, meaning an equivalent of a 4.8 to 6.0, then you’re making a big leap and noticeable gains are to be had.

2. If you stay with a 4.8, then your computer stuff stays the same and it’s literally a plug and play with the wiring harness. Yes, 4.8, 5.3, 6.0 use the same computers, it’s just the program is slightly tweaked for each engine.

3. If you go with a 5.3, you may need some tuning to change fuel maps. I say may because I’ve changed some maps and some I have not changed. Best to plug in and go and then see how the engine performs.

4. Junkyard motors are plentiful depending on where you are. Dealer crates are available, but not worth going this route. Plenty of reputable reman companies when it comes to LS motors.

5. My suggestion would be to stay with the 4.8. If you want performance, then you can add bolt-ons but then you have to get a tune done or you’ll miss out on the performance gains with the aftermarket parts.

6. Staying with the 4.8 replacement, mark your wires, unclip the connectors, remove the engine, replace the engine, plug your wiring harness in, fire it up. That’s its, easy. No computer reprogramming required, so long as you stay within the same year group.

7. Now, until you get a better understanding of what’s going on, I will not talk about the different year 4.8s and what will work with your current computer and wiring harness. Don’t want to overwhelm you, just start with understanding the basics first.

That should be enough to get you thinking and ask more questions.

Of course, this is just my opinion based on experience and common sense thinking.

Re: GMT800 Engine Change ['03 Tahoe]
 

Excellent advice!

Re: GMT800 Engine Change ['03 Tahoe]
 

Thanks, EVRLET. That was the kind of advice I was looking for.
To look at it in Old School terms, I like to translate displacements into cubic inches.
So a 4.8 they call a 294 -- probably to differentiate from the L25 292 L6, which was also metricized as 4.8L.
Is a 5.3L a 327?
And 6.0L, 366?

I don't know if it's a gripe, or the way it is, but my '03 Tahoe gets about 13.5 MPG. In fact the PO complained about mileage. While those numbers I would be happy with in a 50 year old truck, they do seem low for this vintage.

Also I just went from 265/70/R17s to 235/75/16LT tires/rims and my speedometer is reading higher than my GPS groundspeed. I know it's reprogrammable but the discrepency is only 2 - 5 MPH off.
So 40 indicated reads as 37 MPH Groundspeed.

I saw a You Tube video on it, but it involves a black box I don't have.
:chevy:

Re: GMT800 Engine Change ['03 Tahoe]
 

The FWD LS4 5.3 is a 325cid engine
3.780 inch bore
3.622 inch stroke

The iron block RWD motors are likely the same.