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Would you grind on these header tubes? |
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Trader 
AMC Addicted 
Joined: May/15/2018 Location: Ontario Status: Offline Points: 6910 |
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 Posted: Mar/22/2020 at 4:00pm |
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You can taper the sharp edges 2/3 the depth of the header flange and not cause any problems with the welds.
The exhaust gasses are changing direction and therefore increasing turbulence once out of the head. Just removing the problematic sharp edges should make flow significantly better. A cousin made his own headers, but used temperature readings and not tube length to make custom headers - motorbikes and snowmobiles. Gaskets that don't match and sharp edges were killers of flow. He did not loose many races and one of the few people I know that, without sponsors, raced and broke even most years.
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Greyhounds_AMX
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Posted: Mar/22/2020 at 4:16pm |
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I'd go at them with a die grinder, but first build up some material on the outside of the tube with a MIG so you don't break through. It's easier to do before hand, when the tube is backing up your weld. Some preheat would be good too.
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1968 AMX 390 w/T5
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Boris Badanov
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Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4210 |
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Posted: Mar/22/2020 at 6:32pm |
I have done the same, and it is the only way to get an inexpensive AMC header to fit and not leak. IF you have room a for a head plate, it can be added between the head and header and welded on for a far better transition but it starts getting a bit pricey. Issues with head plates are spark plug and frame clearances. I have made a set, but I will not make them to sell. |
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Gremlin Dreams
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rang-a-stang
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Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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Posted: Mar/24/2020 at 1:21pm |
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Copy all, everyone.
I got feedback from Hedman and they said the "header ports should be correct" and are sending me a set of their gaskets. I will lay their gasket over my headers, and over the Remflex gasket I port matched to and see if there is a difference(s). Does anyone have a drawing of how the port should be from the factory? Since I cleaned my head ports up, they may make the argument that since I ground on my heads, it is my fault they do not match...
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79 Cherokee, 401
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: Mar/24/2020 at 1:32pm |
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Top is from vintage FIA SCCA TransAm Homologations Papaers still available in the FIA Archives web site and the bottom image is from an AMA or SAE Paper, has no dimensions.
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rang-a-stang
AMC Nut
Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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Posted: Mar/26/2020 at 5:31pm |
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Hedman gaskets showed up today. Here is what I wrote to their
tech:
Hedman gaskets match the Hedman header ports well (as we both
expected). There are some slight variances here and there, but nothing I would
consider unacceptable. So then I compared the Hedman gaskets to the Remflex
gaskets. The Remflex gaskets port openings are quite a bit bigger than the
Hedman gasket port openings which I believe accounts for the difference between
how I port matched my exhaust ports and the header port opening (in other
words, it is MY fault the header ports do not match my exhaust ports). Also for comparison sake, I grabbed my stock exhaust manifolds to
see where they lie. It looks like the Hedman gaskets are slightly smaller than
the stock manifold ports and the Remflex ports are slightly larger. Since I
matched to the slightly larger than stock opening and the Hedman ports are
slightly smaller, it makes the difference much more obvious. My take aways: a) I super appreciate you sending these gaskets! In my opinion
they showed that you guys are putting out a good product. I appreciate you guys
assuming the cost of this! I will let the folks on my forums know you guys are
awesome! b) I plan to do a little grinding to the flange to bevel the
corners to address the mismatch a little. c) Next time I do this (there will be a next time) I will make a
template of the of the header port, match the exhaust port to the header port,
and then make sure the gaskets matches those two. d) I will probably use the Remflex gasket when I re-install these.
They are SOOOoooo thick. These flanges can be super bent and they still seal. I
also noticed when I went to re-torque them, they never moved. Remflex calls for
20 foot pounds on installation. I checked the torque after one heating cycle
(no change), checked them again after an hour of run time (again, no change),
and then again after about a week of driving and no change. They are pretty
amazing. Spendy but amazing! I am OK with all this. Here are some of the pictures I took. I
have LOTS more if anyone wants to see them. Hedman gasket over header ports:
Hedman gasket over Remflex gasket:
Remflex over Hedman:
Hedman gasket over Manifold:
Remflex gasket over stock manifold: |
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79 Cherokee, 401
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Trader
AMC Addicted
Joined: May/15/2018 Location: Ontario Status: Offline Points: 6910 |
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Posted: Mar/26/2020 at 8:14pm |
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I'd still just take off the sharp edges and call it a day.
Factory castings were that far off or more. Headman is within 90% to 95% of the casting. Take the gasket and mark the sharp edges of the header to be removed and then take the gasket and match the head for material to be removed. The only losses your going to see are 95%+ WOT. Your running at WOT that often? Your head flow losses before the header will be greater then the matched headers unless professionally ported and flow tested. Headers are only providing 30+ HP at top RPM. What else is on the engine to be running top RPM for long periods of time to actually be using this gain? My opinion.
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rang-a-stang
AMC Nut
Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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Posted: Mar/30/2020 at 12:40pm |
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So with all the recommendations you guys gave and an inventory of my "skills"/tools I decided to bevel any edge that is sticking directly in the flow of exhaust gas and generally try to clean up the port with out getting to the point where I would need to put some chewed bubble gum on there (like I said, I am a horrible welder with a horrible welder). I did not want any 90 degree corners in the port at all but this was as good as I could get. One of the ports (I think it was #8?) was sooo far off, I could not grind it enough without rebuilding the entire flange. Here is that port. Notice the carbon mark goes all the way past the sealing lip. I did not have any exhaust leaks so this is a testament to how AWESOME Remflex gaskets are.
 Here are some after pics. Again, they are not perfect but they are better IMHO. None of these are the same port, and I did not take pictures of all the ports. Just a sampling. It looks like I hardly made any changes at all and hardly ground on them at all, but if you go back and look at the original carbon marks, it actually made a pretty significant difference. Looking at the pics, I may spend another hour on them today cleaning a little more.    My 401 is only slightly warmed over. It does spend some time at WOT (My 16yo son daily drives it, I weekend cruise it) but not much. I will admit, this will almost certainly not make a noticeable difference whatsoever but it is one of those things that would bug me forevvveeerrrr if I knew I did not do anything about it when I could have. |
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79 Cherokee, 401
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Greyhounds_AMX
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Posted: Mar/30/2020 at 1:09pm |
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So what I'm getting from this is that the Hedman headers and gaskets have the port roof too low compared to the stock manifolds.
If there's going to be a mismatch, you want the smaller ID on the upstream side, not the downstream side. The Remflex gaskets look great - I'm ordering some of those puppies.
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1968 AMX 390 w/T5
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WesternRed
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Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808 |
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Posted: Apr/02/2020 at 5:42am |
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Looks like the Hedman stuff was traced of some rough factory head casting rather that working with the actual engine blueprints.
I have noticed that the as cast exhaust ports on the heads I've worked with seem to have that low roof at the top, almost like they are trying to turn the gasses into the manifold. If you straighten it out, you would end up with something that matches the Remflex Gaskets. You can see it here:  |
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I've finally given up drinking for good...........now I only drink for evil.
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jcisworthy wrote:
