Swap 5.3L for 3.7L

What would be involved in a swap from a 3.7 to a 5.3L other than motor, maybe some adapter motor mounts, ECU, and exhaust?

H32NV said:

What would be involved in a swap from a 3.7 to a 5.3L other than motor, maybe some adapter motor mounts, ECU, and exhaust?

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I have to ask - why would you want to do this?

Probably for power....supposedly the V8 alphas had the firewall pushed back a bit from the factory but some 06s have gotten 6.2s so I doubt there should be issues fitting it in there. Just electronics

I don't think there's much to it. As 06H3, the 08s and up had work done at the firewall or transmission tunnel for extra clearance, which is a bit ironic as I think the I5 is a longer engine. But maybe the 5.3 sits back a bit further, or the trans sits a bit higher.

Some of the other changes for the 5.3 included the newer airbox with a flat instead of conical filter. 16 mm tie rods, but I'm guessing you've got that covered already. I assume the radiator hoses could be different but that's of course small. I don't recall any difference with steering rack lines.

I think the engine cradle was also re-engineered to accept the 5.3L.

Pretty sure none of your wiring is going to be plug and play. More than likley going to have to find someone wire it up. If you were to go through all the trouble with a v8 swap i would be looking at vette motor. Might as well look into upgrading your tranny since your there. Love to see it done! Have a friend doing a 5.3 swap with tranny in a Jeep yj and for a complete swap with everything is 10k.

I dont think wiring will be much of a problem. I'm not home now or I could go look at the ecm plugs and get the ecm numbers and look it up. But i have done several newer motor swaps. GM usually makes the wiring very straight forward. If the ECM needs changed the plugs most likely will swap. A lot of the ECM's are enterchangable but you will have to do a platform swap. At most you would have to repin it and add extra wires for the additional coils, injectors, and O2 sensors. You could look at swaping the harness and ECM out of a newer alpha.

I'm with silvrzuki. Given all the b.s. involved...wouldn't it be easier (and cheaper) to sell the 5-cyl. and buy an Alpha? Sounds like a lot of work! IMO, if you take-on a motor swap like this you should make it really pay...6.0L, 7.4L, maybe even an 8100 big-block?, maybe a diesel? Headaches are headaches and it would suck to go thru all that frustration...only to achieve a stock Alpha (which are readily available). If it were as simple as "plug-&-play", I might feel differently.

I wish there was a company that would make a complete wiring harness that would re-config the entire H3 to a typical old-school wiring system. I would keep all the accessories...but have them wired back to a standard fuse block. Dump the Onstar. Dump the crazy anti-theft coded key thing, Dump the ECM, BCM, and whatever else lurks down there. Dump all the goofy mall-crawler options. Just give me a HOT and a GROUND under the hood so I could run whatever 3rd party engine management system I want. Same with the tranny...aftermarket stand alone module. Install an old-school 2H-4H-4L t-case. You see where this is going...Basically the Bully Dog H3.

Or just flop an H3 body down on 1979 GM short-bed chassis. Done.

:huh:

...:emb:

It's been done with a H3T and no word about the 5.3L not fitting due to the fire wall. This bloke had a shop take care of it the day after he got the T, nice clean job and there's a video of them doing a burn out with it when they still had the from drive shaft out. Also I've always wanted to use the word "bloke". One more thing!!! I think they had to put the body lift on it for the trany but I'm not a 100% on that, maybe he just wanted it or there was more reason to it.


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I cant imagine it being too complicated on a 2008+ since the 5.3 was available those years.

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For your vehicle, you would need to alter the firewall (don't believe it was as much of a depth problem as a width problem at the firewall), change the engine/trans wiring harness, adapt the front cradle to accept the V8 mounts. You will also have to pull the PCM and replace it with two separate controllers (ECM and TCM). I guess you could do some very creative wiring on the existing PCM wiring for the feeds into the module, but you still need to get some more injector harnesses out to the engine as well as some wires may require added length for different locations.

Most likely a 5.3L cal won't load on a PCM; but I could be wrong; honestly never tried it. (The mention of the H3T swap was a lot easier since the T's came out after the firewall re-design and the swap from using a single controller to two separate controllers (PCM to ECM and TCM).

I would also suggest you get a either a new trans, rebuilt trans or go for the sky and get a raptor built trans. With the hard miles you have on your current trans; slapping in some more torque would probably kill it.

But with all that said, it can be done, if you got the money. But if I was doing it, I would just look high and low for a decent alpha, sell the current vehicle and get the alpha.

f5moab said:

Most likely a 5.3L cal won't load on a PCM; but I could be wrong; honestly never tried it. (The mention of the H3T swap was a lot easier since the T's came out after the firewall re-design and the swap from using a single controller to two separate controllers (PCM to ECM and TCM).

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Depends on the year. In the 08+ the I5's and V8's use the same PCM and TCM, so you could certainly reuse what you've got. We can handle stuff like that here as well, we have all of the GM software for reflashing new VIN/operating system, and then of course tuning.

Kelly@PCMofNC said:

Depends on the year. In the 08+ the I5's and V8's use the same PCM and TCM, so you could certainly reuse what you've got. We can handle stuff like that here as well, we have all of the GM software for reflashing new VIN/operating system, and then of course tuning.

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Yes it does, He has an 07.


However, the problem is easy to solve. He needs new engine and trans harnesses and two new modules; ECM and the TCM. Harness for the three more injector/coil outputs, ECM for that particular circuitry to match the new outputs, and there might be more and then the trans module to match the new trans harness. Those are just very obvious changes in the controlling circuitry of the engine/trans.

However, I'm sure you could supply the ECM (and maybe a TCM) if he decides to leap into this swap.

So, Robb, are you going to swap?

I can probably understand the want for the V8. I drove in flagstaff for a day (rob, you still live in flagstaff right?) and it sucked. Elevation and steep freeway climbs just maybe the I5 unbearable...if only we could regear it would help us with our issues.

Simple physics...

Smaller tires.
More power.
Less weight.

That's pretty much it for the easy fixes. Like you say...re-gearing is not a cheap or simple mod (for the 5-cyl anyway). I'm most intrigued by that last one...I wonder how light you could get an H3 if you just kept the shell and dumped a bunch of fluffy features (and the roof). I have a buddy with a 74 Trans-Am (455-SD)...and he cut hundreds of pounds out of it, with no obvious change in appearance. He cut the crash bars out of the doors, used a glass hood, removed a bunch of steel reinforcement from around the nose, etc. It made a dramatic improvement at the drag strip. Obviously, an H3 will never be a hot rod but, the principal is the same.

Maybe someday I can pick-up a used high-milage H3 for $2500 with a bunch of check-engine lights and some dents. After a day with the plasma, it would be cool to back out of the garage under 4000lbs. I might suddenly find out that the 5-cyl. is plenty enough motor!

I think it is a crazy idea, like making a silk purse out of sow's ear..It would probably be cheaper and less problematic if you just hunted around for a low miles ALPHA H3...

Interesting thread - I do think the others are right - that it's cheaper to simply buy an Alpha; however, the Alpha has 4:10 gears rather than the better 4:56 gears. Transmission is the same, though you may have to change the bellhousing.

But if you're going to go to all that work for more power - have you considered a 4BT Cummins diesel? 200 hp and 420 lb of torque (stock) and you can turn them up a lot. Put that monster in front of your 4:56 geared I-5 chassis and you'll eat Alphas and about everything else for lunch in the stoplight wars and in running off-road - and you'll get 20 mpg rather than 12. Or wait a year or so and I'll sell you my 5.3 when I do that swap.

Yeah the 4BT is without doubt the "go to" motor for a vehicle the size of the H3. The only downside is that the 4BT is a true "mans" diesel. They are loud, rattly, shakey, and all of those things that make people hate (or love) diesels...they're downright obnoxious! 4.10s might even be too low for it (unless you run 37"s). He was shooting for 23mpg.

Whatever the case...I got a buddy that has a 4BT, an NV-4500, and twin-stick gear-driven NP205 sitting in his TJ frame. I think he's burned-out on the project and I keep waiting for him to bail and sell me the drivetrain on the cheap. He's also got a D60 front axle and a trussed, disc-braked, 14-bolt FF rear to go with it....3.70-geared. I'm waiting for the bank to come after his house...then we'll talk! -HA.

4speedfunk said:

Yeah the 4BT is without doubt the "go to" motor for a vehicle the size of the H3. The only downside is that the 4BT is a true "mans" diesel. They are loud, rattly, shakey, and all of those things that make people hate (or love) diesels...they're downright obnoxious! 4.10s might even be too low for it (unless you run 37"s). He was shooting for 23mpg.

Whatever the case...I got a buddy that has a 4BT, an NV-4500, and twin-stick gear-driven NP205 sitting in his TJ frame. I think he's burned-out on the project and I keep waiting for him to bail and sell me the drivetrain on the cheap. He's also got a D60 front axle and a trussed, disc-braked, 14-bolt FF rear to go with it....3.70-geared. I'm waiting for the bank to come after his house...then we'll talk! -HA.

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I hear that, literally - but I love the clatter of diesels; they just sound like work is gonna get done and you best just get out of the way to let it get done.... as for smell, it bothers me occasionally because I get migraines, but then everything bothers me when I get migraines so it is just one noise.... plus, diesels cure tailgaters - especially if you've turned up the wick