New Build: GM 4.2L Atlas into '91 FJ80 (1 Viewer)

[TwoTonic]

Just getting rolling on a new FJ80 build. We got a great deal on a 4.2L I-6 (275HP, low miles) out of a Trailblazer/Envoy and are putting it into our 1991 FJ80.

We got started with the test fit and pan modifications (sump was on the wrong end to clear the front differential. It's on the correct end now.). We'll post some more photos as we go. The 4.2L is nice for a good power bump, but they are so plentiful in the salvage yards that even low miles examples go for not much money.

Picasa Web Albums - TL Care - 4.2L Atlas in...

TT
Too Many Cruisers
FJ40
FJ60
FJ80s, including Hummer H3 driveline in '91

 

[KliersLC]

Are you replacing the I-5 or doing a new swap?

 

[yoopercharged]

I've been waiting to see this done. Nice. Good engine. Thought about putting one in my 60, but it got too rusty.

 

[Jeeper]

Can you comment on how you are connecting the GM ECU into the Toyota? I'm not sure of the 3FE control details from the factory, but I'm wondering about the factory gauges working with the new engine. For me, getting the GM engine installed and running is easy compared to actually integrating it with the factory instruments.

Good luck with this excellent swap!

 

[TwoTonic]

I-6 4.2L Atlas

Are you replacing the I-5 or doing a new swap?

This is a new swap. Coincidentally, both trucks are that tan/light brown color used in the early FJ80 run, but this one is intended more for towing. The extra 40+ HP and additional torque ought to make it more comfortable to pull a car trailer with.
We haven't figured out what to do with the brakes, but they'll need an upgrade too when we get to that point.

With the better torque, still wish there was a way to get to slightly taller gears, for fuel economy, but that's been the open question... Any thoughts on gearing?

Thanks!

TT

 

[TwoTonic]

Swaps and Rust

I've been waiting to see this done. Nice. Good engine. Thought about putting one in my 60, but it got too rusty.

Yeah, second that. Once you get too much rust... it's just hard to justify putting all the time into it. Even the I-5 probably had just a little too much body decay, in retrospect... But I justify that one with the reminder that I'll keep that truck forever and don't really care about the cosmetics for a daily driver and mountain truck.

Fortunately, the truck getting the 4.2L hasn't a spot of rust on it, so other than a few paint scratches to touch up, it should look like a new 300HP truck when we get done.

 

[TwoTonic]

Electronic integration

Can you comment on how you are connecting the GM ECU into the Toyota? I'm not sure of the 3FE control details from the factory, but I'm wondering about the factory gauges working with the new engine. For me, getting the GM engine installed and running is easy compared to actually integrating it with the factory instruments.

Good luck with this excellent swap!

Hey, NashVegas... Oooh, please send me some brisket and ribs from Jack's down on Broadway. Love that place.


We found that the 'easiest' way on the I-5 was to just use the factory senders from the 3FE screwed into the GM-Atlas motor. That way we didn't have to make any changes to the stock cluster-- oil pressure, coolant temp, etc behave just the same. Even the speedo pick-up is back in the adapter for the transfer case so that didn't change.

The tach is a little more involved, but the signal "IN" to the gauge cluster is pretty simple to emulate. I just built an electronic adapter for tach signal. I did build extra hardware for the tach adapter so if anybody else is putting GM drivelines into FJ series, just PM me.

Other than that, the GM PCM thinks it's running in a Colorado/TB still. We have used the E-Pedal from the GM trucks. There was some debate about that when we started, but feel at the end of the day it was far superior. The pedal was easy to mount and, in return, you get instant throttle response and the automatic is always in the right gear. Right away. So there's no more cable throttle.

So, it's a mix of things, but in the FJ series it's pretty straightforward blend of the old and new. Fortunately, in that vintage there was no CAN Bus to deal with.

The tune was really easy since we were using stock GM MAF, PCM, throttle, O2 sensors, etc. Most of the work there was just using HP Tuners to 'turn off' un-needed stuff like VATS and sensors that don't exist in an FJ.

As we go through this one, we'll document all the electronic changes if anyone's interested.

TT

 

[KliersLC]

Have you tried running taller tires? 33s would make your freeway RPM a bit lower and are a lot easier/cheaper than trying to find higher gears or different axles...

 

[TwoTonic]

Have you tried running taller tires? 33s would make your freeway RPM a bit lower and are a lot easier/cheaper than trying to find higher gears or different axles...

Yep, that's the conclusion we've come to--- "rubber differential" is the best way to change gearing to taller gears. Consensus seems to be that 33s are about the largest that can be mounted without lifts? Sounded like going to 35s were more likely to encounter interference at the limits, especially off-road.

TT

 

[Jeeper]

I'll have to double check my notes, but I believe going from stock rubber to 285s only shaved about 130 RPMs at 80mph. Still higher revs than the GM engine would like, but a step in the right direction.

 

[e9999]

impressive all around

man, that pan customization looks like a ton of work.

Is this a good solid engine by design, though?

 

[Walking Eagle]

hopefully you didn't get an early 4.2 - I can't remember what the failure mode was, but something was majorly wrong with them, I remember my dad fighting to get them to replace his engine under waranty.

 

[TwoTonic]

2002 LL8 Cylinder liner issues

hopefully you didn't get an early 4.2 - I can't remember what the failure mode was, but something was majorly wrong with them, I remember my dad fighting to get them to replace his engine under waranty.

No, it's one of the later-model ones. Typical GM-- never buy the first year of production! It was the cylinder liners that cracked and failed- and it was ugly. I think they ended up replacing all the 2002 MY run of Bravada/TB/Envoy series 4.2s.

There'd be no reason to use a 2002 or 2003 model year motor-- the nice 2004-on engines are plentiful in the wrecking yards. And, oddly, the 4.2s tend to be a lot less expensive than the 2.9s or 3.7s, since there are so many of them around.

Once the liner problem was resolved, the 4.2 has been a very reliable powerplant. It's extremely smooth and is notable for its light weight and specific power output. It's also got a compression ratio well above 10:1, but runs on 85 octane. We do like the I-5, so are expecting to really like the 4.2 with 40+more HP.

TT

 

[TwoTonic]

LL8 Atlas

impressive all around

man, that pan customization looks like a ton of work.

Is this a good solid engine by design, though?

Good TIG practice! Actually we did look at 'stretching' an I-5 pan, but doing it this way preserves the pan-gasket-sealing edge. It looks like more work than it probably was... cutting it was a pretty straight 'section' below the pan edge. Then, just backfilling the seam. Basically, lots of TIG practice!

The Atlas series was on the C&D "Best Engines" list for years, for whatever that's worth. It is all-alloy, much lighter than the 3FE. (A LOT lighter.) It's big calling card is basically making full-torque from 1400 RPM to 6000-- the heads are amazing and, coupled with VVT and high-compression, it's just a dream for flat torque and smooth power delivery. It's literally got the flattest torque curve I've ever seen, this side of an oil-burner.

 

[Jeeper]

Am I seeing this right? You are going to use the stock Toy tranny this time? The I-5 swap used the GM tranny as well, but it looks like you're using the A440 with this swap. Interesting.

 

[Walking Eagle]

Once the liner problem was resolved, the 4.2 has been a very reliable powerplant. It's extremely smooth and is notable for its light weight and specific power output. It's also got a compression ratio well above 10:1, but runs on 85 octane. We do like the I-5, so are expecting to really like the 4.2 with 40+more HP.

TT

glad it's the later one - the one thing dad's trailblazer did well was go. Drove it once with his camper behind it, just to the car wash, and was impressed with the power.

 

[TwoTonic]

Am I seeing this right? You are going to use the stock Toy tranny this time? The I-5 swap used the GM tranny as well, but it looks like you're using the A440 with this swap. Interesting.

Nope, we didn't mate the GM gearbox yet, but the A440's going away.
We are doing a different take on the T/C adapter this time, but using the Toyota case behind the GM transmission.

I'll post pics when we test-fit the gearbox.

TT

 

[TwoTonic]

glad it's the later one - the one thing dad's trailblazer did well was go. Drove it once with his camper behind it, just to the car wash, and was impressed with the power.

The heads are just amazing, ported kind of performance from as-cast factory heads... the resulting power delivery is really sweet. I always laugh that I can hardly hear the I-5 running when it's idling next to the other 91 with the 3FE in it and the I-6 is a lot smoother still, with the 6's dynamic balance.

 

[lt1fire]

mpg??

 

[alia176]

nice swap. Would it be worth swapping out a 1FZ-FE with an Atlas and a GM transmission? Just curious!