Old School 4.3 Drivetrain Swap


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Walt Jaquith

Walt Jaquith

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Started on the first try? That rarely happens!

Heh. Yeah, this last couple weeks I haven't posted much because it's been all boring detail work making sure the wiring was right. I'd tested everything carefully and didn't hit the key until I was sure I had the best chance possible. It was still a very satisfying (and relieving) moment. Lots of planets had to line up.
 
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Chris

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Heh. Yeah, this last couple weeks I haven't posted much because it's been all boring detail work making sure the wiring was right. I'd tested everything carefully and didn't hit the key until I was sure I had the best chance possible. It was still a very satisfying (and relieving) moment. Lots of planets had to line up.

That has to be satisfying as hell. 9 out of 10 times you start it and it won't fire up. Of course if you did what you did and checked everything thoroughly, I could see how it would.

Again, very, very satisfying. Hell, it's satisfying for me just hearing this :LOL:
 
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Walt Jaquith

Walt Jaquith

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Last few pictures. I've got 75 miles on the new drivetrain, and things are starting to settle in. I like it. Not too much power for a short wheelbase and high COG, but enough. Leave it in 3rd gear and it's spunky. Drop it into overdrive and it cruses at 65 comfortably.

The engine compartment. Lots of room...
20200531_175755[1].jpg

I replaced the funky expansion tank; that was just a temp to get running.

Skid plate modded for the 700R4 tranny:

20200604_192107[1].jpg


Needed a new tranny hump cover. Need to figure out what to do about a shifter boot...
20200609_171037[1].jpg


Y'know how you always have a few fasteners left over? This is what that looks like when you start with 3 engines and make one running rig. <voxHanSolo> Don't worry; she'll hold together...
20200606_100808[1].jpg
 
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Chris

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Very nice! That's the trick with these SWB Jeeps. People want to put 400-500 HP engines in them, but have no idea what that's like in a vehicle with such a short wheelbase. It's terrifying!

I would say that 300 HP (or around that number at the very most) is more than enough for one of these things. Sounds like you made a good choice.
 
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Walt Jaquith

Walt Jaquith

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Final addendum to my build thread. My 4.3 was a frankenengine, with an early block, later heads and an Astrovan cam. That meant there was no stock fuel/eprom map that worked well for it. That's not a huge loss; the stock mappings for the 4.3s don't seem to be all that great, and largely account for the V6's reputation for having "4 cylinder power and V8 fuel economy". Fortunately, tuning the early 90s GM engines used to be a big thing, and the know-how is still out there along with the tools needed. I've been scouring forum posts and tutorials, trying to learn 30 year old fuel delivery technology.

You program some settings, burn a eprom chip, and go test it out with the laptop in the passenger seat collecting data. First you get your fuel map so the O2 sensor reports good fuel burn under all conditions. Then you start carefully tweaking the spark advance. There's stuff like "accelerator enrichment", which is the equivalent of a carb's accelerator pump, and dozens of other settings. It's been a long, sometimes frustrating journey. At one point my rig was throwing an error code for the knock sensor. It turned out my spark advance settings were so conservative that when the computer tried to run a routine to test for knock, it couldn't make the rig knock even when it bumped the spark advance considerably under full load, and so it thought the knock sensor wasn't working and put the rig in limp mode to save the engine.

But...

When it finally all works, it's a glorious thing. I've got 3:55 gears, limited slip and 31 inch Goodyear Wrangler tires, and I can chirp the rears if I stomp it off the line. Yesterday I was doing a final datalogging run, climbing a 6.5% grade, and walked past a fancy Dodge pickup that was doing everything it could to keep me from passing. Heh. That was fun.
 
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Flyer58

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Has anyone looked into the MegaSquirt DIY EFI controllers? I've been reading about them and the MegaSpark for ignition for several years now. They're very popular for older classic sports cars, ratrods, custom cars, and have a large following of users who have created custom profiles for each application. Check out the forums for the 4.3 users.

 
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Walt Jaquith

Walt Jaquith

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I never had heard of them. Man, wouldn't it be cool to ditch the distributor? But I have a lot invested in my stock tbi setup at this point. I also like the fact that there's still a gazillion potential parts doners kicking around out there. Maybe on my next project...
 
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Chris

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Has anyone looked into the MegaSquirt DIY EFI controllers? I've been reading about them and the MegaSpark for ignition for several years now. They're very popular for older classic sports cars, ratrods, custom cars, and have a large following of users who have created custom profiles for each application. Check out the forums for the 4.3 users.


Oh yeah, I've heard of them quite a bit when I was much younger and used to be in the import scene. They are a lot of work to get setup and running correctly from what I hear, but you can do just abut anything with them.
 

HoldMyBeer

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I just got done reading through this entire thread and I gotta say, you've done an exceptional job and a very clean install.
The 87 I picked up was intended to get the 4.3 transplant but only got as far as removing the stock drivetrain.
I have multiple different options on putting it back together and the neighbor is a car junker so I have access to do something completely stupid. I think I'll concentrate my upgrades to the underside for now but knowing that the information is available before getting started helps keep me in line with future considerations