Exhaust port matching
Thread Starter
Launching!
Joined: Sep 2008
Posts: 224
Likes: 47
From: Dayton, OH
Exhaust port matching Noob question. Please help me reframe the question if there is a better or different way to ask it.
How important, useful, _____________?, is it to match the mouth of the exhaust port to the header?
What are the benefit(s)?
Thanks!
How important, useful, _____________?, is it to match the mouth of the exhaust port to the header?
What are the benefit(s)?
Thanks!
Thread Starter
Launching!
Joined: Sep 2008
Posts: 224
Likes: 47
From: Dayton, OH
Steve, I don’t alter the exhaust ports. The header tube will be larger than the port. Just make CERTAIN that the MLS exhaust gasket isn’t SMALLER than the header primary tube. Set the gaskets on the headers to ensure they are not restricting flow.
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The "cone exhaust" was called Anti-reversion headers, they did and still work a treat. The reason why they are not economical to make is because few people are willing to pay the premium above a normal header to gain ärea under the curve", they just want advertised power. A/R headers won't make any more peak power, and they'll cost several $100 more perhaps over $1k more due to the intricate labour intensive individual cones that create in effect a port matched extension of equal size and shape, over the top of which a larger primary pipe is flared to create a space all the way around.
If money is no object they are the best you can get for a broad power band with a bigger cam, but reality is you can get 80% of the benefit just by sticking a header flange size significantly bigger than the head port all the way around - esp the top. That helps reduce reversion as mentioned above. Not as good, but a lot cheaper as most decent headers come larger at the flange anyway.
If money is no object they are the best you can get for a broad power band with a bigger cam, but reality is you can get 80% of the benefit just by sticking a header flange size significantly bigger than the head port all the way around - esp the top. That helps reduce reversion as mentioned above. Not as good, but a lot cheaper as most decent headers come larger at the flange anyway.
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As mentioned, for off the shelf headers, having a bigger tube than the port works well enough. It’s needed to get the flow required for higher rpm hp.
Pretty much any production vehicle will have to have a semi-tight bend radius off the head to clear other parts. (Suspension, body, fenders, etc.) A larger tube will obviously flow more thru the bends. I have noticed that a lot of designs have far tighter bends than needed, and suspect this is due to materials/manufacturing commonality. Its easier to make a shitload of headers if there is only small changes made from one version to the next.
However, if we are talking about the best header design… yes an exact match, with the least bend radius, stepped after 7-8”, and a tri-y construction has been proven to make the most power under 8k rpm.
some really good reading on this regarding “blowdown” length:
https://www.speed-talk.com/forum/vie...df1233ffffa53e
Pretty much any production vehicle will have to have a semi-tight bend radius off the head to clear other parts. (Suspension, body, fenders, etc.) A larger tube will obviously flow more thru the bends. I have noticed that a lot of designs have far tighter bends than needed, and suspect this is due to materials/manufacturing commonality. Its easier to make a shitload of headers if there is only small changes made from one version to the next.
However, if we are talking about the best header design… yes an exact match, with the least bend radius, stepped after 7-8”, and a tri-y construction has been proven to make the most power under 8k rpm.
some really good reading on this regarding “blowdown” length:
https://www.speed-talk.com/forum/vie...df1233ffffa53e
Launching!
Joined: Feb 2018
Posts: 225
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From: Bismarck, ND
Tri-y headers As mentioned, for off the shelf headers, having a bigger tube than the port works well enough. It’s needed to get the flow required for higher rpm hp.
Pretty much any production vehicle will have to have a semi-tight bend radius off the head to clear other parts. (Suspension, body, fenders, etc.) A larger tube will obviously flow more thru the bends. I have noticed that a lot of designs have far tighter bends than needed, and suspect this is due to materials/manufacturing commonality. Its easier to make a shitload of headers if there is only small changes made from one version to the next.
However, if we are talking about the best header design… yes an exact match, with the least bend radius, stepped after 7-8”, and a tri-y construction has been proven to make the most power under 8k rpm.
some really good reading on this regarding “blowdown” length:
https://www.speed-talk.com/forum/vie...df1233ffffa53e
Pretty much any production vehicle will have to have a semi-tight bend radius off the head to clear other parts. (Suspension, body, fenders, etc.) A larger tube will obviously flow more thru the bends. I have noticed that a lot of designs have far tighter bends than needed, and suspect this is due to materials/manufacturing commonality. Its easier to make a shitload of headers if there is only small changes made from one version to the next.
However, if we are talking about the best header design… yes an exact match, with the least bend radius, stepped after 7-8”, and a tri-y construction has been proven to make the most power under 8k rpm.
some really good reading on this regarding “blowdown” length:
https://www.speed-talk.com/forum/vie...df1233ffffa53e
On page 7, they did talk about the Tri-y headers which I run, because they were the longest--- how be it that they are the older Thorly midlength headers, that I could fit on my 4 wheel drive truck that the exhaust pipe would tuck over the cross member so that I would not lose ground clearance.
As you can tell, plenty of ground clearance on my lawn mower also! [ Avatar]
Allways interested in reading about the "Try-y" system.
Last edited by Metalchipper; Oct 13, 2025 at 10:52 AM. Reason: adding more nonsence
Launching!
Joined: Feb 2018
Posts: 225
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From: Bismarck, ND
again Nope Quote:
Originally Posted by Metalchipper
Better to have larger ports on the manifold side. Helps with anti inversion flow. You don’t want the exhaust pluses back flowing into the head.
Quote: SteveJewels
I think the supercharger pretty much takes care of that. Scavenging is not really a thing with air being forced into the cylinder during valve overlap.
How much supercharger pressure do you have at idle? Same as atmospheric, same as a NA engine, right? Unless your supercharger is set up to provide boost at idle.... which.... how would I know that.
Reversion is greater at idle and slower RPMs.
Do you want combustion residue, [carbon residue] to flow back into the intake path? At some point in the exhaust cycle, cylinder pressure approaches atmospheric pressure. Reversion will happen then.
Just trying to help.
Originally Posted by Metalchipper
Better to have larger ports on the manifold side. Helps with anti inversion flow. You don’t want the exhaust pluses back flowing into the head.
Quote: SteveJewels
I think the supercharger pretty much takes care of that. Scavenging is not really a thing with air being forced into the cylinder during valve overlap.
How much supercharger pressure do you have at idle? Same as atmospheric, same as a NA engine, right? Unless your supercharger is set up to provide boost at idle.... which.... how would I know that.
Reversion is greater at idle and slower RPMs.
Do you want combustion residue, [carbon residue] to flow back into the intake path? At some point in the exhaust cycle, cylinder pressure approaches atmospheric pressure. Reversion will happen then.
Just trying to help.
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Reversion in a 2026 engine Hi MC, this is exactly what I wanted to state. You were first; good job.
I want to replace the engine in my 2008 Escalade.
I have a 2026 engine (Escalade engine) that needs some "mods".
Would you like to help ?
Lance
I want to replace the engine in my 2008 Escalade.
I have a 2026 engine (Escalade engine) that needs some "mods".
Would you like to help ?
Lance
Launching!
Joined: Feb 2018
Posts: 225
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From: Bismarck, ND
Honor It would be a honor to try to help. But I do not know how much help I would be. I am pretty much "old School"! Currently working on a 1956 Hudson Hornet 308, 6 cylinder flat head motor to replace my Dad's 1952, 308 that he installed in his 1946 Hudson Super Six Coupe.
I am sure that others here on this forum would have more current knowledge than an old fart like me.
Thread Starter
Launching!
Joined: Sep 2008
Posts: 224
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From: Dayton, OH
[QUOTE=Metalchipper;20627209]Better to have larger ports on the manifold side./QUOTE]
How could it be otherwise? I can't imagine there being enough material in the head to be able to make the exhaust port volume larger then that of the intake ports.
The head are DART Pro1 280's. The intake port volume is 280 cc's.
I dont know the exhaust port volume but the intake valve diameter is 2.165" and the exhaust is 1.6". I would assume the corresponding port volumes to be commensurate.
How could it be otherwise? I can't imagine there being enough material in the head to be able to make the exhaust port volume larger then that of the intake ports.
The head are DART Pro1 280's. The intake port volume is 280 cc's.
I dont know the exhaust port volume but the intake valve diameter is 2.165" and the exhaust is 1.6". I would assume the corresponding port volumes to be commensurate.
Last edited by SteveJewels; Dec 13, 2025 at 08:18 PM.
Launching!
Joined: Feb 2018
Posts: 225
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From: Bismarck, ND
Ok [QUOTE=Steve]
"How could it be otherwise? I can't imagine there being enough material in the head to be able to make the exhaust port volume larger then that of the intake ports.
The head are DART Pro1 280's. The intake port volume is 280 cc's.
I dont know the exhaust port volume but the intake valve diameter is 2.165" and the exhaust is 1.6". I would assime the corresponding port volumes to be commensurate."
OK, who said anything about matching the intake ports with the exhaust ports?
Your question was "is it to match the mouth of the exhaust port to the header?"
OK, I used the words " manifold side" maybe I should of used "header" or "exhaust manifold" or " exhaust header manifold" or "the part that bolts on the exhaust ports".
Hope that clears things up.
The exhaust port on the LS7 head ranges from like 85-87 cc for the OEM head to say 95-100 cc to most of the after market / ported heads. Some exhaust ports like All Pro are bigger at 110 cc.
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From: Mefis
Hello Lance,
It would be a honor to try to help. But I do not know how much help I would be. I am pretty much "old School"! Currently working on a 1956 Hudson Hornet 308, 6 cylinder flat head motor to replace my Dad's 1952, 308 that he installed in his 1946 Hudson Super Six Coupe.
I am sure that others here on this forum would have more current knowledge than an old fart like me.
It would be a honor to try to help. But I do not know how much help I would be. I am pretty much "old School"! Currently working on a 1956 Hudson Hornet 308, 6 cylinder flat head motor to replace my Dad's 1952, 308 that he installed in his 1946 Hudson Super Six Coupe.
I am sure that others here on this forum would have more current knowledge than an old fart like me.
Launching!
Joined: Feb 2018
Posts: 225
Likes: 31
From: Bismarck, ND
Yes it is Yes it has hydraulic lifters. We are goining to take a chance that they will work. The 308 is what we pulled out of a donner Hornet, was a replacement motor with few miles on it, just sludged up. I think they used the oil pan to collect the contaminates that would drop out of the oil!
It is the two carb intake [ H ], my brother and I want to get it running first, as there is some body work and the interior is shot.........they we can upgrade the engine later if needed. Our Dad used it to haul his race car to the track. But has not ran for 65 years? Also it has the smaller 1946 9" clutch so we do not want to push it too hard. For now it is going to get rings, crank and rod bearings, porting, valve job and OVH accessories. Had to get the 1952 crank ground because the 56 came out of a auto-trany and was 1/2" too short. So, no on the 262 or Clifford head for now.
I wonder what forum here would be the place for "Hudsons"? The car they built too good!
Thanks for asking.
Steve, I see you’re interested in going with the TSP sleeved shortblock. I caution you here. TSP quality has gone downhill by a large margin since they sold the business several years ago. The std sleeved offering by TSP uses PowerBore sleeves, not Darton. Do your homework. Cheap price never means quality. Ever. I see a lot of bad reviews for TSP in the last couple years. Just don’t want to see you get a product that ends up costing you double in the long run.
Thread Starter
Launching!
Joined: Sep 2008
Posts: 224
Likes: 47
From: Dayton, OH
Steve, I see you’re interested in going with the TSP sleeved shortblock. I caution you here. TSP quality has gone downhill by a large margin since they sold the business several years ago. The std sleeved offering by TSP uses PowerBore sleeves, not Darton. Do your homework. Cheap price never means quality. Ever. I see a lot of bad reviews for TSP in the last couple years. Just don’t want to see you get a product that ends up costing you double in the long run.
They are about an hour or so drive so I can pick up the engine and drag it back to Dayton.
