When we started on Thundercat the goals were fairly simple and benign, but one thing led to another... and pretty soon things had gotten well out of hand (emphasis on "well”). In every project I’ve ever done there are "woulda, shoulda, couldas”, essentially things that in retrospect you wish you’d done differently. (A prime example is painting CHUGSzilla green. That’s one I’ll regret until the day I die.)
Some of those decisions can't be revisited, but sometimes one can go back and make changes, and that’s what project dual is all about. Back when we started the project I had a lot more regard for Tucker’s way of doing things, and I wanted to keep some of the “vibe”, so I was okay with a single exhaust running up the passenger front door post.
One of the signature upgrades on Thundercat is all the custom bent rigid steel lines for the front blade, the steering system, the engine oil cooler, transmission fluid cooler and the hydraulic fluid cooler. Then you add fuel supply and return-to-tank lines, and let's not forget the rear hydraulic winch. There are a lot of lines, and they take up a fair amount of space.
Not much room for a dual exhaust system to run out the back.
But this wasn’t a problem so much with the single exhaust system. However, under hood heat was a big problem and we tried to mitigate that by ceramic coating the exhaust manifolds, exhaust pipes and muffler, and we wrapped the exhaust system under the hood with a thermal exhaust wrap. Those measures might have helped a little, but not nearly what their manufacturers claim.
This is an example of under hood heat. Look at the green plastic of the hydraulic clamp. Yeah, that thermal wrap on the exhaust pipe is really helping…NOT!
The biggest issue though is the poor engine can’t breathe very well, and that causes more heat, and less performance from the engine.
Anyone who has experienced a Tucker with that exhaust layout knows that with the front passenger window open at all, you get an earful of exhaust noise. And with an engine of almost 500 cubic inches, there is a significant volume of exhaust gasses. After SV 2022 Scott and I talked about modifying the system, but Scott wasn’t in favor and:
A.) It’s a bunch of work.
B.) Lot’s of changes to rigid steel lines
c.) You’re going backward, not forward.
D.) More money.
E.) We have to finish CHUGSzilla and the 1544.
So nothing happened…. Fast forward to SV 2024 and we had the formidable tag team of Travler and PP on our case about the single exhaust. CHUGSzilla and the 1544 are gone and that expensive ceramic coating is flaking off the exhaust… after maybe 30 hours of use (talk about disappointing). So we had motivation….
Ceramic coating...
It was time to revisit the exhaust system. The present configuration uses 2 1/2” diameter pipe from both cylinder heads that merge into a single 3” exhaust pipe. Thinking back to high school geometry, a 2 1/2” diameter circle has an area of 4.91 square inches. But there are two, so it’s 9.82 square inches. Then we cram that into a 3” diameter tube which has an area of 7.07 square inches. Those exhaust gasses are fighting for space, and choking the poor engine in the process. The plan is to create a true dual exhaust system with 3” diameter tubing. Exiting the exhaust manifolds at 3” instead of 2 1/2” is a 44% improvement in surface area, and as there is no merge, the improvement is 100% in comparison to the existing setup. There is potential for heat reduction and increased performance as well.
To GM’s credit, the exhaust manifold bolt pattern on the Big Block Chevy never changed. Any BBC exhaust manifold will bolt up to the 8.1’s cylinder heads. While that gives us lots of options, none that I have found meet the parameters of our application needs. PP and Travler were strongly in favor of custom stainless steel headers, but those can be accurately described as Spendy. (Capital S!) One of the things we’re proud of is we did the vast majority of the work on Thundercat ourselves. It’s a “built, not bought machine” and a set of custom stainless steel headers gets away from that.
The vast majority of exhaust manifolds are made of heavy cast iron. The stock manifolds on the 8.1 are stainless steel castings and we decided to do some cutting, piecing and welding to create a set of custom manifolds that meet our needs. I’ll also mention that over the years I’ve bought many sets of headers and every single one leaked after a while. Every one. Maybe custom stainless ones would be better, but so far aftermarket headers are batting .000 with me. I swear at them, not by them, and in my experience any performance gains are more than offset negatively by the ass-pain they bring. Finding used 8.1 manifolds on ebay is not difficult, and they aren’t terribly expensive, either. We’re only looking to harvest some pieces anyway, so they don’t need to be perfect.
A set of stock 8.1 Vortec exhaust manifolds.
Scott and I talked about different options for where to cut, where to join, where do we want the exhaust to dump out... and eventually it was time to start cutting. He was concerned about making a mistake and I was like “If we do, I’ll get another manifold… no big deal”. So out came the angle grinder and cutoff wheel.
You might think that the general manifold layout would be very similar from side to side. That the manifolds protrude the same distance from the cylinder heads and the shape and size of the runners would be nearly identical. But, you’d be wrong. We cut the front cylinder portion off the left exhaust manifold and chopped off the rear cylinder of the right manifold and positioned the components alongside each other. They didn’t match up well at all. We knew it wouldn’t be easy, but still the differences were surprising. So, Scott cut that left front section apart and cut a small pie shaped piece out to better align the respective components. Then he first tack welded them together, and then filled in the considerable gaps to join them.
The next step will be to figure out exactly where, how long, and at what angle do we want the exit flange to be, and then how best to cut the respective parts to achieve our objectives. It’s kind of fun and challenging, but there is considerable difficulty, too.
Who knows, we may be turning perfectly good manifolds into piles of scrap and end up with those custom stainless headers after all. But we’re going to try our way first. One thing I’ve learned through years of working with Scott is: Never Underestimate The Gorilla!
Some of those decisions can't be revisited, but sometimes one can go back and make changes, and that’s what project dual is all about. Back when we started the project I had a lot more regard for Tucker’s way of doing things, and I wanted to keep some of the “vibe”, so I was okay with a single exhaust running up the passenger front door post.
One of the signature upgrades on Thundercat is all the custom bent rigid steel lines for the front blade, the steering system, the engine oil cooler, transmission fluid cooler and the hydraulic fluid cooler. Then you add fuel supply and return-to-tank lines, and let's not forget the rear hydraulic winch. There are a lot of lines, and they take up a fair amount of space.
Not much room for a dual exhaust system to run out the back.
But this wasn’t a problem so much with the single exhaust system. However, under hood heat was a big problem and we tried to mitigate that by ceramic coating the exhaust manifolds, exhaust pipes and muffler, and we wrapped the exhaust system under the hood with a thermal exhaust wrap. Those measures might have helped a little, but not nearly what their manufacturers claim.
This is an example of under hood heat. Look at the green plastic of the hydraulic clamp. Yeah, that thermal wrap on the exhaust pipe is really helping…NOT!
The biggest issue though is the poor engine can’t breathe very well, and that causes more heat, and less performance from the engine.
Anyone who has experienced a Tucker with that exhaust layout knows that with the front passenger window open at all, you get an earful of exhaust noise. And with an engine of almost 500 cubic inches, there is a significant volume of exhaust gasses. After SV 2022 Scott and I talked about modifying the system, but Scott wasn’t in favor and:
A.) It’s a bunch of work.
B.) Lot’s of changes to rigid steel lines
c.) You’re going backward, not forward.
D.) More money.
E.) We have to finish CHUGSzilla and the 1544.
So nothing happened…. Fast forward to SV 2024 and we had the formidable tag team of Travler and PP on our case about the single exhaust. CHUGSzilla and the 1544 are gone and that expensive ceramic coating is flaking off the exhaust… after maybe 30 hours of use (talk about disappointing). So we had motivation….
Ceramic coating...
It was time to revisit the exhaust system. The present configuration uses 2 1/2” diameter pipe from both cylinder heads that merge into a single 3” exhaust pipe. Thinking back to high school geometry, a 2 1/2” diameter circle has an area of 4.91 square inches. But there are two, so it’s 9.82 square inches. Then we cram that into a 3” diameter tube which has an area of 7.07 square inches. Those exhaust gasses are fighting for space, and choking the poor engine in the process. The plan is to create a true dual exhaust system with 3” diameter tubing. Exiting the exhaust manifolds at 3” instead of 2 1/2” is a 44% improvement in surface area, and as there is no merge, the improvement is 100% in comparison to the existing setup. There is potential for heat reduction and increased performance as well.
To GM’s credit, the exhaust manifold bolt pattern on the Big Block Chevy never changed. Any BBC exhaust manifold will bolt up to the 8.1’s cylinder heads. While that gives us lots of options, none that I have found meet the parameters of our application needs. PP and Travler were strongly in favor of custom stainless steel headers, but those can be accurately described as Spendy. (Capital S!) One of the things we’re proud of is we did the vast majority of the work on Thundercat ourselves. It’s a “built, not bought machine” and a set of custom stainless steel headers gets away from that.
The vast majority of exhaust manifolds are made of heavy cast iron. The stock manifolds on the 8.1 are stainless steel castings and we decided to do some cutting, piecing and welding to create a set of custom manifolds that meet our needs. I’ll also mention that over the years I’ve bought many sets of headers and every single one leaked after a while. Every one. Maybe custom stainless ones would be better, but so far aftermarket headers are batting .000 with me. I swear at them, not by them, and in my experience any performance gains are more than offset negatively by the ass-pain they bring. Finding used 8.1 manifolds on ebay is not difficult, and they aren’t terribly expensive, either. We’re only looking to harvest some pieces anyway, so they don’t need to be perfect.
A set of stock 8.1 Vortec exhaust manifolds.
Scott and I talked about different options for where to cut, where to join, where do we want the exhaust to dump out... and eventually it was time to start cutting. He was concerned about making a mistake and I was like “If we do, I’ll get another manifold… no big deal”. So out came the angle grinder and cutoff wheel.
You might think that the general manifold layout would be very similar from side to side. That the manifolds protrude the same distance from the cylinder heads and the shape and size of the runners would be nearly identical. But, you’d be wrong. We cut the front cylinder portion off the left exhaust manifold and chopped off the rear cylinder of the right manifold and positioned the components alongside each other. They didn’t match up well at all. We knew it wouldn’t be easy, but still the differences were surprising. So, Scott cut that left front section apart and cut a small pie shaped piece out to better align the respective components. Then he first tack welded them together, and then filled in the considerable gaps to join them.
The next step will be to figure out exactly where, how long, and at what angle do we want the exit flange to be, and then how best to cut the respective parts to achieve our objectives. It’s kind of fun and challenging, but there is considerable difficulty, too.
Who knows, we may be turning perfectly good manifolds into piles of scrap and end up with those custom stainless headers after all. But we’re going to try our way first. One thing I’ve learned through years of working with Scott is: Never Underestimate The Gorilla!
