H3 Manifolds?

[NorCalAnthony]

Has anyone tried running Hummer H3 exhaust manifolds for LSx swaps in a square body? I believe they're the same ones used in the Colorado's and Canyons with the 5.3 so they should fit in some pretty tight engine bays... I'm collecting parts for my 5.3/4l80e swap on my '89 K5 and was originally going to use the TBSS exhaust manifolds like most people do but I'm having a really hard time finding any and have heard that they may now be discontinued. These look like they may be a good factory alternative but I haven't been able to find anyone who's used them before. What do you guys think?

Here's the left/driver's side (P/N 12598548)



Here's the right/passenger's side (P/N 12600527)

[ls1nova71]

I thought the H3 was built on the Trailblazer platform? The right one in your pic looks exactly like a TBSS manifold.

[NorCalAnthony]

Originally Posted by ls1nova71

I thought the H3 was built on the Trailblazer platform? The right one in your pic looks exactly like a TBSS manifold.

I think you're right about the H3's being built on the Trailblazer platform, I was referring to the engines and exhaust manifolds being the same though. I think the right one even has the same P/N as the TBSS manifold but the left one has a different P/N and looks quite a bit shorter/more compact. That may wind up being a good thing but I'm not sure where that would sit in a 4wd square body's frame...

[aknovaman]

Quick ebay search for h3 exhaust manifold found several available.

[NorCalAnthony]

Originally Posted by aknovaman

Quick ebay search for h3 exhaust manifold found several available.

That's actually how I found out about them, they came up as a similar item when I was searching for the TBSS manifolds lol. I was hoping to find out if anyone had tried them out before I went ahead and ordered them is all...

[LS1Impala]

Have you looked into the LS3 manifolds? Thats what Im using on my 68 C10...they are a 2 bolt flange and Ive purchased several sets used for 100 bucks with flanges and O2 bungs!

[NorCalAnthony]

Originally Posted by LS1Impala

Have you looked into the LS3 manifolds? Thats what Im using on my 68 C10...they are a 2 bolt flange and Ive purchased several sets used for 100 bucks with flanges and O2 bungs!

Thanks those are the other ones I've been looking at and may get if I'm SOL on the TBSS manifolds. Where have you been finding your LS3 manifolds that cheap? I've been looking around for the last couple months and most of the ones I'm finding on ebay and some of the other forum's classifieds are at least twice that much and don't always have the flanges and O2 bungs. The H3 manifolds on the other hand use the 3 bolt flange and should bolt right up to the flanges and y-pipe I already have from the 5.3 donor...

[LS1Impala]

Sent PM

[dayj1]

Originally Posted by NorCalAnthony

Has anyone tried running Hummer H3 exhaust manifolds for LSx swaps in a square body? I believe they're the same ones used in the Colorado's and Canyons with the 5.3 so they should fit in some pretty tight engine bays... I'm collecting parts for my 5.3/4l80e swap on my '89 K5 and was originally going to use the TBSS exhaust manifolds like most people do but I'm having a really hard time finding any and have heard that they may now be discontinued. These look like they may be a good factory alternative but I haven't been able to find anyone who's used them before. What do you guys think?

I used the H3 manifolds on the 5.3 in my '57 BelAir. The fit is very similar to the TBSS manifold, but the H3 is shorter and gives more clearance at the transmission (the TBSS manifold actually wants to occupy the same space as the transmission case if you're running a 4l80). I know it's not a truck, but I can get you some measurements if you let me know what you need.

[NorCalAnthony]

Originally Posted by dayj1

I used the H3 manifolds on the 5.3 in my '57 BelAir. The fit is very similar to the TBSS manifold, but the H3 is shorter and gives more clearance at the transmission (the TBSS manifold actually wants to occupy the same space as the transmission case if you're running a 4l80). I know it's not a truck, but I can get you some measurements if you let me know what you need.

Wow I'm really glad you jumped in here since I'm planning on using the same 5.3/4l80e combo that you are. I don't think I necessarily need measurements but if you have any pictures of the manifolds installed that'd be great. Maybe one from the side looking straight at the engine/manifold and another from the front looking toward the rear so I can see what you mean how you routed the exhaust around the 4l80e?

PS I have a lot of fond childhood memories of my grandma and her '57 Bel Air so your LS swap sounds even cooler to me

[dayj1]

I'll get you some pictures in the morning due to this afternoon being pretty busy. They may not be the best in the world since the engine is installed, but I'll get what I can.

As for the TBSS manifold vs. the 4l80e transmission case, you can get them to fit by trimming off the lifting point just below the dowel pin hole in the bellhousing and also trimming the "ear" on the bellhousing and dust cover.

Here's a picture of the trimming that I stole off the web by googling TBSS 4L80 swap. It doesn't look bad if you're neat about it. In my case, I had to buy manifolds anyway. So, I just bought some that fit with no trimming.

[dayj1]

As promised, I got you a few pictures today. I know they're not the best in the world, but the engine is in the car, so it's tough to get a good shot.

For reference, the frame rails in a '57 BelAir are about 30 inches apart (inside to inside). The H3 driver's manifold extends past the cylinder head by about 2 1/2 inches, so it's very tight to the block. On a '57 the steering box really encroaches on manifold/header space. I have about 1/4 inch between the manifold and steering box.

Here's an overall view. The blower explains the logic behind the 4l80e :



Here's the best shot I could get from the top side:



From the bottom:



Flange to transmission clearance:



I think the H3 manifold will easily fit in the frame rails of a truck, but hopefully the pics will help you make up your mind.

[NorCalAnthony]

Thanks for taking the time to take and post those pics. I'm in the same boat you were where I already have the truck manifolds but they won't fit without trimming the frame (which I don't want to do). Since I need to get a new set anyways I'd rather get some that don't require modifying the trans or anything else if I can help it.