Old School 4.3 Drivetrain Swap

[Walt Jaquith]

Ok, the engine and transmission are ready, the shop is cleared out and the Jeep is staged. Tonight after work I'll begin pulling the fuel injected 4.0/auto and prep to drop in a rebuilt 4.3 V6 from a 91 S10 Blazer. I'm using the 700R4 tranny (also rebuilt) and the NP241C transfer case from the Blazer as well. I'll be using a Painless wiring harness for the engine. Engine mounts will be Advanced Adaptors 713001-S.

The engine has 93-5 heads, which were the better flowing "Vortec" heads before they were branded that way, and a Astrovan camshaft.

By the way, this means I'll soon have a complete , working 4.0/auto drivetrain for sale with the fuel injection harness and ECM just south of Portland Oregon. I'll post in the classified section when it's ready to go.

I'll keep y'all updated as progress happens. Cheers!

 

[Chris]

How much do you think this engine swap will cost you once it's all said and done?

I keep hearing good things about some of the V6 swaps, but part of me is tempted to go V8. Is there a reason you're going with a V6 over a V8? I'm genuinely curious.

 

[Walt Jaquith]

How much do you think this engine swap will cost you once it's all said and done?

I keep hearing good things about some of the V6 swaps, but part of me is tempted to go V8. Is there a reason you're going with a V6 over a V8? I'm genuinely curious.

It was a tough decision. On the downside, the 4.3s are all really long in the tooth these days (but then, so am I <g>). That drives the cost/effort up if you're trying to make it nice. All the rubber parts are rotten. All the metal parts are corroded, worn, rusty, caked with 30 years of grime, or all of the above. The replaceable items (sensors, etc.) all need replacing...and you can get cheap knock-offs or pay 3X the money for the AC-Delco version. To say this thing has nickle and dimed me doesn't quite do it justice. A newer engine is more expensive to start with, of course, but it's components still have life in them, and you can just slap it in and go.

Here are the factors that steered me to the 4.3 V6...

• I've got a lot of experience with these engines, and GM engines of that era in general.
• I don't need the extra power (or weight), and didn't want to change my rear axle and radiator.
• The 91 S10 Blazer I got for a doner rig has a NP241C transfer case that's nearly identical to the NP231J in my yj. I transferred the vacuum switch and shifter lever, and as long as I position it in the same place as the old one, the drivelines and shifter linkage should work without much tweaking.
• I like the simplicity of the 700R4 transmission. At least 50% of the motivation for this swap was to get the 4 speed tranny for more comfortable highway cruising. The newer ones are all computer controlled, and while I can handle that, it adds complexity. My rig's theme is kind of rat-roddy; I wanted to keep it simple.
• Folks dropping in the newer LS engines are having all kinds of challenges getting stuff like the gauges (all computer controlled), the drive-by-wire throttle, and the baked in anti-theft stuff working right. It's all solvable, but again, I wanted simplicity.

As for overall cost... I don't want to think about it <g>. Not including the transmission rebuild, I'll easily be into this for $3500 by the time I'm done. But I did a complete rebuild on the engine. It will get a new exhaust system, etc; my goal was to create a reliable, old school rig that I could road trip with confidence. Ultimately I want to be able to drive it to Northern California with my wife, run the Rubicon trail, and drive it home.

But yeah, you never think about all the hidden expenses. The special zinc-added break-in oil that I'm going to run for just 500 miles and then change out? $80.

A lot of folks will disagree with my choices on this project, and that's fine. This rig and I will be a perfect match when it's done, and I plan to drive it until I can't drive anymore. it will be more than worth it to me.

Cheers,
Walt

 

[Chris]

I see what you're saying completely.

I'm very tempted to do a small block 350 swap just for the simplicity of carbs (I like simplicity a lot). Of course that brings about the need to change so many other things such as radiator, figuring out the gauges, and likely the transfer case as well. I'd ideally put an older 700R4 behind it as well, because like you, I really like that transmission (had one in my 69 Camaro and really enjoyed it).

I haven't added up the cost, time, or looked to see what else I would need, but I would hope that have carbs would minimize the amount of work required, since there wouldn't be nearly as much electronics or wiring.

 

[Walt Jaquith]

Heh. I'm not simple enough to ever want to tune another carburetor. With the Fuel injection, the 'simple' comes after, when you get it running and it just works. Last time I did one of these I took a 70s era 350 and retrofitted early 90s throttle body injection on it. It worked great. I used an old stock harness, and that was by far the biggest pain of the project. Painless had a sale last December, and I knew this project was coming so I sprung for the all new harness. it should be a lot easier, and the stock Jeep fuel pump ought to be adequite... another plus for the old V6. The 4.3 has plenty of places to thread in a temp sender, so I'll use a YJ sender for the gauge in addition to the GM unit for the fuel injection. The two engines used the same general type of oil pressure sender, so the Jeep unit just screwed right in.

One thing I haven't figured out is how to adapt the speedometer. The 700R4 has a speed sensor that fed the S10s speedometer, and is also used by the FI/emissions. It puts out a pulse, and the speedometer on the jeep accepts a ulse, but research indicates they're not the same. There will have to be a conversion of some sort. It might be easier to retrofit the S10 speedometer into the Jeep.

Just keep in mind that all the little stuff adds up in a hurry.

 

[Chris]

That's right, with those wiring harnesses, it takes a lot of the guess work out of the swap and allows things to go much smoother. Doing all the wiring by hand would probably be a nightmare.

You have me rethinking that 350 swap all of a sudden. The appeal of carbs is that they are simple, but I remember on my Camaro I was always, always messing with them. So yeah, I could see why even just a basic form of fuel injection would be better, and still probably not that complicated.

Oh yes, it all adds up. I've done a number of engine swaps in the past, and you always end up spending way more time and money than you think you will, that's for sure.

 

[Squatch]

Just wanted to throw this out there. I never had any interest in a 4.3, as I'm not really a GM man. However, I picked up a one owner 2000 S10 Blazer 2wd 2-door with 70,000 original miles on it last December. The 94 year old owner had passed away, and I was offered the ultra clean rig for $300 (which I just couldn't do without feeling guilty, so I gave them $1,000 and still slept well that night). Anyways, I drove it on a 450 mile road trip, and got just under 23 mpg (at 70 mph). Not wicked powerful, but enough so that I will say that I'm impressed with the little engines. There's a kajillion of these things out there, and they can still be found at decent prices, which is the point of my long-winded post. I think your choice of drivetrains is a solid one.

 

[Walt Jaquith]

Progress! The drivetrain is out, and I'm starting to sort the wiring to turn this thing into a...Jeevy? Cheveep? Whatever. It's a mess now, but it'll be nice and clean when I'm done; I promise.

 

[Walt Jaquith]

Point of no return: The 4.0 motor mounts are history. Had to remove the front brake lines and the steering shaft to get enough room to take the left mount clean. Since the brake lines are opened up, I'm thinking about doing the master cylinder/booster upgrade while I'm at it. Decisions...

Also, test fit on the transmission. There's lots of room. I've got the thing positioned exactly where the original T-case sat, the plan being to not have to mod the drivelines. But I could come forward with the whole package and improve my rear driveline angle. Not sure it's worth it; the old one had a little more angle on it than I like, but was working fine. Decisions...

I'd like to make a real rear cross member instead of bolting the tranny to the skid plate like cheap...I mean Jeep did it. The 4x4 version of the stock 700R4 rear transmission mount hangs down too far for that, so if I do it I'm going to have to go completely rogue and scratch-build something with a completely different mount. That's a lot of work, but I want the job done right. Decisions...

 

[Squatch]

I'd think the brake upgrade would be a good idea, though I'm unsure of what upgrade you're considering. As for moving the drivetrain forward, would that mess with the weight bias much, or do you think it'd be negligible? And I like the idea of a dedicated "proper" cross member.

Btw, that's a clever way to hold the torque converter in place. Simple and effective. Love it!

 

[Walt Jaquith]

I'd think the brake upgrade would be a good idea, though I'm unsure of what upgrade you're considering. As for moving the drivetrain forward, would that mess with the weight bias much, or do you think it'd be negligible? And I like the idea of a dedicated "proper" cross member.

Btw, that's a clever way to hold the torque converter in place. Simple and effective. Love it!

There's several different paths to upgrade the yj's notoriously spongy brakes. You can go with a dual diaphragm booster from a '95 yj, or there are a couple others that folks have modded in. The most popular master cylinder swaps seem to be either from a 85 Ford E350 or a Dodge Ram 2500. I'm going to pull the whole setup from my 91 S10 Blazer doner, and just hold it up there to see if it would fit and what it would take to mod it in. If it's not a lot of trouble, it would be worth it to have all the 'new' stuff coming from just one rig. Easier to keep track for maintenance.

The 4.3 is almost 100 lbs lighter than the Jeep 4.0--one of the reasons I wanted to be rid of the thing. It's also considerably shorter being a V6 instead of inline, so I could probably bring it right up to the radiator without adversly effecting weight distribution. As it is, the entire engine block will be behind the front axle; just the bracketry and pulleys will be forward of that. There's going to be a *lot* of room between the engine and the radiator.

The little torque converter tab is how you get them from a rebuilder. This is the second tranny I've had rebuilt, and they both came with them.

 

[Fouledplugs]

The 4x4 version of the stock 700R4 rear transmission mount hangs down too far for that, so if I do it I'm going to have to go completely rogue and scratch-build something with a completely different mount. That's a lot of work, but I want the job done right. Decisions...

Universal Transmission Crossmember Kit

Shop for Jeep Wrangler cross member kits at GenRight.com. American Made Off Road Jeep Parts

genright.com

Would something like this take some of the work out of it for you?

 

[Walt Jaquith]

That's the option I'm leaning towards. I've done something similar on a crawler I built, and it worked well. This rig will spend most of its life on the road, so the urethane bushings you get in kits like that would be too hard. With a pair of bushings so far from the transmission, which will be trying to rock back and forth, I'd want something pretty soft. One alternative would be to get some leaf spring or suspension link bushings from a sedan and press them into a tube.

 

[Fouledplugs]

That's the option I'm leaning towards. I've done something similar on a crawler I built, and it worked well. This rig will spend most of its life on the road, so the urethane bushings you get in kits like that would be too hard. With a pair of bushings so far from the transmission, which will be trying to rock back and forth, I'd want something pretty soft. One alternative would be to get some leaf spring or suspension link bushings from a sedan and press them into a tube.

It might require some research, but surely you could find a softer rubber bushing to press in there. GenRight might actually know of a rubber bushing that could work in this application. Might be worth a call or email.

 

[Walt Jaquith]

Ok, I like some elements of Genright's design, but not others. Here's my first pass at a crossmember design. I still have some refining to do, and none of it's to scale; I'll have to measure everything tonight and plug the numbers in. This one allows me to capture all four mounting holes (the regular 700R4 pair and the pair on the 4x4 extension) on the transmission for extra strength. It's ultra-low profile, and shouldn't hang down much farther than the transmission itself. The bushings are inbound where they can allow the tranny to rock a little if it wants to. They're press-in TJ control arm bushings, $9 each from Quadratec.

Before I finalize the design I'll probably switch from the round tube to square. It won't look as cool, but it will make some stuff a lot easier, and it all gets hid by the skid plate anyway.

 

[Chris]

What don't you like about GenRight's design?

 

[Walt Jaquith]

I don't like that the bushings are outboard and hard. That's perfect for offroad rigs, but transfers too much vibration and restricts movement more than I want for a Jeep intended for pavement and light trails. I'm not needing a universal kit; I can fit mine without the extra joints and holes. Finally, having spent more money than my wife likes to think about on fabrication tools, spending another $200 when I have a pile of steel hanging around and could make it for under $25 seems counterproductive.

 

[Chris]

Makes perfect sense. Do they use poly bushings in their mounts?

I assume you'd use rubber or something a bit more forgiving for the road?

 

[Walt Jaquith]

Yeah, the mounts in that kit are polyurethane. Most all the aftermarket stuff uses poly bushings unless they're trying to match OEM. It's cheap and easy, and there are advantages to it, but a harsh ride and more vibration are the downsides. Poly also lasts a lot longer and stand up to abuse better. If performance is your top priority, poly's the way to go because it *doesnt* flex like rubber does, so it gives you better feel and stiffer support.

 

[Walt Jaquith]

Rumors about the yj steering columns being a Chevy S10 column from the same era are true. I need a park/neutral switch for the GM fuel injection, and the Jeep has nothing like that. I also need to do something for a backup light switch, which on the Jeep was on the transmission, but the GM tranny doesn't have provision for one. For the column shift automatic S10s, GM put a switch on top of the steering column that does both. My YJ's automatic column has the same slot, so the GM switch will snap right in. Both problems solved.