Gen III Hemi Swap into TJ—Reference Guide & Swap Info

[Mike_H]

If I were doing something like a motorhome, I would certainly be looking at a 6.0LS or 6.4 BTE (big truck engine) Hemi with any of the modern 8-speed transmissions (the 8HP90 is damn near perfect IMO).

My first LS was an 02 Avalanche. Underwhelming to say the least. You're right though. A tune really does wake them up. My colorado is tuned with the HF 3.6L engine. It made a huge different, but its still lacks for torque. the 8 speed transmission puts my RPM so low that it lugs all over (I'm sure this sounds familiar to the 42RLE guys). It really needs some gears, and I think it would be a pretty good powerplant.

The motor home is kind of a unique duck. Its a '78 GMC transmode (think Stripes). FWD and use the Hydramatic 425 3 speed.. The Engine is lengthwise in the chassis, and the transmission runs parallel and beside it. It has three reverse gears, and one forward gear, if you were to put it where it should live normally. Same drivetrain as a late 70's Toronado or Caddy Eldo. Packaging constraints dictate that I stay with that platform.

 

[pc1p]

My first LS was an 02 Avalanche. Underwhelming to say the least. You're right though. A tune really does wake them up. My colorado is tuned with the HF 3.6L engine. It made a huge different, but its still lacks for torque. the 8 speed transmission puts my RPM so low that it lugs all over (I'm sure this sounds familiar to the 42RLE guys). It really needs some gears, and I think it would be a pretty good powerplant.

The motor home is kind of a unique duck. Its a '78 GMC transmode (think Stripes). FWD and use the Hydramatic 425 3 speed.. The Engine is lengthwise in the chassis, and the transmission runs parallel and beside it. It has three reverse gears, and one forward gear, if you were to put it where it should live normally. Same drivetrain as a late 70's Toronado or Caddy Eldo. Packaging constraints dictate that I stay with that platform.

I was curious so I Googled what the Transmode was, since I have very little experience with motorhomes (my mother had one for a short while and my friend has an older Winnie that I've helped with but that was all Dodge stuff). That sounds like an interesting setup from a packaging standpoint, but certainly limits options. I'd love to restore an old one - maybe once I get my shop

 

[Wildman]

I was curious so I Googled what the Transmode was, since I have very little experience with motorhomes (my mother had one for a short while and my friend has an older Winnie that I've helped with but that was all Dodge stuff). That sounds like an interesting setup from a packaging standpoint, but certainly limits options. I'd love to restore an old one - maybe once I get my shop

They are a PITA to work on...

 

[Mike_H]

They are a PITA to work on...

GMC motorhomes or just motorhomes in general? Curious if you've worked on the GMC's before, cuz I'll pick your brain if you have!

I was curious so I Googled what the Transmode was, since I have very little experience with motorhomes (my mother had one for a short while and my friend has an older Winnie that I've helped with but that was all Dodge stuff). That sounds like an interesting setup from a packaging standpoint, but certainly limits options. I'd love to restore an old one - maybe once I get my shop

Yeah, ours was finished out by Coachman. Its a 1978 and its in pretty good shape. Less than 100,000 Original miles. I went through the top end and cooling system last winter. This year, I'm working on the generator, and my wife wants to re-do the headliner...which is the worst of the interior. I have to rebuild the suspension (front and rear) for peace of mind, but it doesn't keep us from using it. I have a thread in the off-topic section here, if you'd like to read a bit more about it.

Ok, enough disruption from the Good Stuff in this thread!

 

[Wildman]

GMC motorhomes or just motorhomes in general? Curious if you've worked on the GMC's before, cuz I'll pick your brain if you have!

I was a heavy line mechanic for 3 years at a Ford/RV dealership.
I worked on 2 of those GMC motorhomes while there.

 

[pc1p]

Got the motor set in the mounts...

It's tight, so I definitely want to get the trans bolted up today or tomorrow to see how it fits. As you can see below, there is a good bit of space in front of the firewall to reach down from above to get to the bellhousing bolts.

You can see that the firewall is clearly meant for a narrow motor, so it's deep in the center but the sides (in front of the driver/passenger footboards) do get close to the valve covers).

The A/C compressor outlets are close to the frame - hopefully I can make something work there!

This motor came with a 45º oil filter adapter. I think it has to go as it is already close to the upper control arm mount on the front axle. I wonder if a standard straight-down filter would work. If not, I'll look at a remote filter kit...

You can clearly see above why the Ram manifolds won't work for a Jeep swap...

 

[NashvilleTJ]

That intake configuration is going to look great under there. Mine...not so much. I’m running the older ram setup with the throttle body on top, and the A/C compressor front and center. Ugly.

 

[Wildman]

Man that LOOKS great. Really looking good. And just like with the Magnum only some exhaust manifolds will work where the others dump right where those do.

 

[pc1p]

Man that LOOKS great. Really looking good. And just like with the Magnum only some exhaust manifolds will work where the others dump right where those do.

I ordered these - it's a set of the factory newer 6.4L SRT Jeep manifolds that are also sold under Mopar Performance Kit #77072462 - these are supposedly damn near perfect and will match my Eagle-headed D-shaped exhaust ports. These handle 707hp in factory form, so I suspect they'll be just fine for my 400hp NA motor.

That intake configuration is going to look great under there. Mine...not so much. I’m running the older ram setup with the throttle body on top, and the A/C compressor front and center. Ugly.

I hope to make it as stock looking as possible - I'll see if I can manage something. I put a hole in my cowl for the Aerostar filters - was wondering if I could take advantage of that and run a cowl intake. It's getting really crammed underhood

 

[Wildman]

View attachment 228670

I ordered these - it's a set of the factory newer 6.4L SRT Jeep manifolds that are also sold under Mopar Performance Kit #77072462 - these are supposedly damn near perfect and will match my Eagle-headed D-shaped exhaust ports. These handle 707hp in factory form, so I suspect they'll be just fine for my 400hp NA motor.

I'd like to try some headers like this instead of the block huggers that I have but no one that I can find has ever tried to use any of these. My thought is that if it works on a Ram truck or Jeep Grand Cherokee they "SHOULD" work in the TJ but as you know it doesn't work that way.

https://www.amazon.com/dp/B001CI62MY/?tag=wranglerorg-20

 

[NashvilleTJ]

View attachment 228670

I ordered these - it's a set of the factory newer 6.4L SRT Jeep manifolds that are also sold under Mopar Performance Kit #77072462 - these are supposedly damn near perfect and will match my Eagle-headed D-shaped exhaust ports. These handle 707hp in factory form, so I suspect they'll be just fine for my 400hp NA motor.


I hope to make it as stock looking as possible - I'll see if I can manage something. I put a hole in my cowl for the Aerostar filters - was wondering if I could take advantage of that and run a cowl intake. It's getting really crammed underhood

I run a cowl intake on mine as well. That stroked Hemi puts out a crazy amount of heat, and it was roasting my IAT’s.

 

[pc1p]

I'd like to try some headers like this instead of the block huggers that I have but no one that I can find has ever tried to use any of these. My thought is that if it works on a Ram truck or Jeep Grand Cherokee they "SHOULD" work in the TJ but as you know it doesn't work that way.

https://www.amazon.com/dp/B001CI62MY/?tag=wranglerorg-20

I run of set of these exact headers (but with the EGR tube) on my RamCharger with the 408. I can't speak for the TJ, but I know they clear the YJ firewall just fine...

 

[pc1p]

I run a cowl intake on mine as well. That stroked Hemi puts out a crazy amount of heat, and it was roasting my IAT’s.

You ever share a photo of yours? Now that I got to thinking about it, I don't think I've seen one... I need to go dig through your build thread

EDIT: I just took a look, OMG I love the attention to detail!! That's a wicked build if I've ever seen one and love how you do it all "in house". I couldn't imagine paying someone to build my rigs (not that there's anything wrong with it, I just get a lot of satisfaction from building stuff, messing up a lot, and learning along the way).

 

[Wildman]

I run of set of these exact headers (but with the EGR tube) on my RamCharger with the 408. I can't speak for the TJ, but I know they clear the YJ firewall just fine...

That is good to know. I'm thinking I might order a set thru Amazon so if they don't work I can at least return them.

You ever share a photo of yours? Now that I got to thinking about it, I don't think I've seen one... I need to go dig through your build thread

EDIT: I just took a look, OMG I love the attention to detail!! That's a wicked build if I've ever seen one and love how you do it all "in house". I couldn't imagine paying someone to build my rigs (not that there's anything wrong with it, I just get a lot of satisfaction from building stuff, messing up a lot, and learning along the way).

Yes he has done an awesome job on his Jeep and makes me look at my work and know I need to up the game if I want it to be anywhere near as good.

I really like how that Hemi looks in your TJ.

 

[NashvilleTJ]

You ever share a photo of yours? Now that I got to thinking about it, I don't think I've seen one... I need to go dig through your build thread

EDIT: I just took a look, OMG I love the attention to detail!! That's a wicked build if I've ever seen one and love how you do it all "in house". I couldn't imagine paying someone to build my rigs (not that there's anything wrong with it, I just get a lot of satisfaction from building stuff, messing up a lot, and learning along the way).

Thanks for the kind words.

 

[Ephry73]

Pictures help

 

[pc1p]

I run a cowl intake on mine as well. That stroked Hemi puts out a crazy amount of heat, and it was roasting my IAT’s.

Hey @NashvilleTJ - by chance can you take a pic of your firewall clearance??

 

[Chris]

You really aren't messing around!

When people say they are going to have a V8 swap done in a short amount of time, I usually roll my eyes, because I know that as men we tend to procrastinate. However, it looks like you really will have it done in a decent amount of time. Very cool!

 

[NashvilleTJ]

Hey @NashvilleTJ - by chance can you take a pic of your firewall clearance??

Tough to see with everything surrounding the mill, but I have about a finger‘s worth of clearance at the heads. I positioned the engine as far back as I could for fan clearance. I thought I’d have all kinds of clearance given the length of the I6 vs the V8, but as you also found out the firewall is not flat and recessed in the center so the 6 can sit much farther back than the 8.

What are you looking for in a picture? I might be able to dig up one from when I did the swap, but give me a better idea what you need to narrow it down.

 

[pc1p]

Tough to see with everything surrounding the mill, but I have about a finger‘s worth of clearance at the heads. I positioned the engine as far back as I could for fan clearance. I thought I’d have all kinds of clearance given the length of the I6 vs the V8, but as you also found out the firewall is not flat and recessed in the center so the 6 can sit much farther back than the 8.

What are you looking for in a picture? I might be able to dig up one from when I did the swap, but give me a better idea what you need to narrow it down.

You touched on it - the space between the heads and firewall mainly, as well as the general orientation. I was hoping to see how these Holley mounts placed the engine compared to others. Based on Holley’s statement that it retains factory driveshaft length with a 545/65RFE (which is 3” longer), I was expecting more room back there. I’m at the point where I may file off one of the harness slots on my valve cover...