How to Prep Store-Bought Exhaust Headers for Track Use | Project Vintage Race Mustang

Tim
Update by Tim Suddard to the Ford Mustang Fastback project car
Mar 29, 2021

Although the folks at Cobra Automotive make their own equal-length headers, shop president Curt Vogt considered our needs and budget and admitted that our Mustang didn't need this rather costly setup.

He suggested that we order a set of Hooker headers—part No. 6901, $498.95 at Summit Racing—but added that any store-bought headers will need some modification to be usable in a serious race car.

Despite how beautiful those new headers may look, Curt said, their coating won’t hold up in a racing environment. His advice: Get the headers recoated by a specialist. We've worked with Swain Tech Coatings for decades and have always received terrific service, so that was our obvious choice for the job.

Curt explained that rust inside the header tubes can cost power—based on his experience, anywhere from 5 to 15 on an engine like ours—so he recommended coating the insides as well as the outsides.

Next, he told us that we could cut off the heat riser tube that was wrapped around one of the header pipes. We won’t be using it, so it would have just gotten in the way and added weight.

He also warned that mass-produced headers aren't always flat on the flange face, so we would need to test this with a straightedge. Sure enough, while one side was perfect, the other was a little off. A minute or two on our large shop belt sander solved this problem.

Since our engine uses World Products Windsor Sr. iron heads, Curt also urged us to check the spark plug access before sending out the parts for coating.

He was right again. Without modification, our headers’ spark plug angles would have caused the plugs on the left cylinder bank to be blocked.

 

Curt suggested that we mark the offending areas, then heat and dimple them. But don’t hit the headers directly with a hammer, he cautioned; instead, hammer a piece of the correct-diameter pipe (used at the correct angle) to massage the header tubes.

These headers end in 3-inch collectors, and Curt recommended that we cut them off. He told us to design a slip-fit pipe to fit the outside of the header and then take that to an X-pipe, not an H-pipe—also attached via a slip-fit.

His reason for this modification: Collector gaskets always leak with racing use. Plus, the exhaust system should be designed for quick removal to allow for repair and service.

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Comments
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dean1484
dean1484 GRM+ Memberand MegaDork
3/25/21 4:32 p.m.

How much would a set of custom welded headers cost?  How hard would it have been to roll your own with a header kit and a tig.  I was with you until you bent them to access the spark plugs. Yes I know the it has a minimal if any effect on performance but it just looks bad to me. Call it header OCD on my part. And besides I would have liked to read your impressions of trying to build your own from one of those header kits I see used in builds.  That would have been an interesting read. 
 

There has to be a manufacturer out there that makes a header that you don't have to bend to fit. To me that is poor design on the manufacturers part. Even if it cost another couple hundred bucks to get a properly engineered set to me it would have been my choice as every time you open the hood people will see the deformed pipes. (That OCD thing I have again). 

DjGreggieP
DjGreggieP HalfDork
3/25/21 5:04 p.m.

I think once they get back from coating, they'll look like the were built to be like that.

I think the biggest thing is with the advancements in spark plug longevity, most street driven vehicles with headers probably won't see a plug change during the original installers ownership, so ease of accessibility for maintenance probably rates low priority during the designing phase.  

FMB42
FMB42 Reader
3/25/21 5:21 p.m.

Store-bought headers are both great and not so great in my limited header experience ('65 GTO and '67 SBC powered Skylark). But, as Djg above says, greatly extended spark plug life makes a big diff in some ways. Note: store-bought headers were a life saver on many RVs of the 70s, 80s, and 90s,etc (cracked OEM cast iron exh manifolds were a very common RV problem back then).

L5wolvesf
L5wolvesf HalfDork
3/25/21 7:37 p.m.

If rust inside the header tubes can cost power anywhere from 5 to 15 how much would large dents in the tubes cost?

NOT A TA
NOT A TA SuperDork
3/25/21 7:53 p.m.

In reply to L5wolvesf :

https://www.bing.com/videos/search?q=youtube++dented+header+test&docid=607988612658657263&mid=8550742B373685B9D5618550742B373685B9D561&view=detail&FORM=VIRE

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/25/21 10:10 p.m.

"Collector gaskets always leak in racing use" is three words too many smiley

 

I've had headers with the little rings on the head side "for extra sealing" turn out to have the rings miss common header gaskets at the corners.  Need to grind the weld ring down a little for a nice V-notch, weld it larger, then file it flat again.

dean1484
dean1484 GRM+ Memberand MegaDork
3/26/21 7:51 a.m.

Collector gaskets work fine if you get quality gaskets and quality clamping ring on both the header/collector and the pipe. The problem is cheep headers are cheep and this is just one more area where you get what you pay for. 
 

With all the mods they made to those headers better quality ones may have actually been cheeper/better. 

dean1484
dean1484 GRM+ Memberand MegaDork
3/26/21 7:57 a.m.
L5wolvesf said:

If rust inside the header tubes can cost power anywhere from 5 to 15 how much would large dents in the tubes cost?

I have never heard of that before but it has me thinking that it would have been cheeper to just get a decent set of stainless steal headers and do the WD40 trick to get that cool gold bronz finish. Versus what ever it will cost to have cheap headers ceramic coated. Both inside and outside. 
 

How do the ceramic coating people know that they get a good coating inside a header?  Run an endoscope down it?  It would be interesting to see how that process is done. 

Sonic
Sonic UltraDork
3/26/21 8:28 a.m.

If you can't dip them then how about pouring the coating in the tubes then covering all the openings and rolling the headers around to all possible angles in your hands so that it spreads around, then uncover the openings and drain (into the other header)

noddaz
noddaz GRM+ Memberand UltraDork
3/26/21 12:02 p.m.

I must be out of touch, but nearly $500 for a set of headers isn't cheap.    But I am probably out of touch.  

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/26/21 12:06 p.m.
noddaz said:

I must be out of touch, but nearly $500 for a set of headers isn't cheap.    But I am probably out of touch.  

Most headers I installed for rare, esoteric vehicles like '69 Camaros and late 60s GM A-bodies were $750, ten or so years ago.  This was for coated headers.

 

And the Camaro, at least, needed the collector mooshed for clearance.

docwyte
docwyte PowerDork
3/26/21 2:03 p.m.

I think on Engine Masters they dented the living snot out of a set of headers and then ran them on the dyno.  Much to my surprise, the dents made almost NO difference in power output.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/26/21 2:07 p.m.

In reply to docwyte :

I wonder if the difference is that rust is all through the pipe, interfering with the flow everywhere, while a clearance dent just looks like another bend as far as flow is concerned.

GCrites80s
GCrites80s HalfDork
3/26/21 2:47 p.m.
dean1484 said:

How much would a set of custom welded headers cost?  How hard would it have been to roll your own with a header kit and a tig.  I was with you until you bent them to access the spark plugs. Yes I know the it has a minimal if any effect on performance but it just looks bad to me. Call it header OCD on my part. And besides I would have liked to read your impressions of trying to build your own from one of those header kits I see used in builds.  That would have been an interesting read. 
 

There has to be a manufacturer out there that makes a header that you don't have to bend to fit. To me that is poor design on the manufacturers part. Even if it cost another couple hundred bucks to get a properly engineered set to me it would have been my choice as every time you open the hood people will see the deformed pipes. (That OCD thing I have again). 

Thing is, they can't design headers for every possible set of heads out there. The heads on this engine are a different casting than stock. All kinds of things can move around including the spark plug hole, the spark plug angle, exhaust port height etc.

84FSP
84FSP UltraDork
3/26/21 3:23 p.m.
L5wolvesf said:

If rust inside the header tubes can cost power anywhere from 5 to 15 how much would large dents in the tubes cost?

A number of independent tests showed the dents cost no hp as long as they are reasonable smooth.

wspohn
wspohn SuperDork
3/27/21 12:46 p.m.

One has to watch for finish quality. I've seen aftermarket headers tack welded in four places on the outside and then a more continuous weld on the inside, but incompletely ground to gasket size.  I've even seen headers with rectangular ports that had the rectangle skewed from the angle they had to be.

By all means have the finished product coated as it protects them, but never use header wrap on uncoated steel, or you'll soon be buying another set.

dean1484
dean1484 GRM+ Memberand MegaDork
3/27/21 1:17 p.m.
GCrites80s said:
dean1484 said:

How much would a set of custom welded headers cost?  How hard would it have been to roll your own with a header kit and a tig.  I was with you until you bent them to access the spark plugs. Yes I know the it has a minimal if any effect on performance but it just looks bad to me. Call it header OCD on my part. And besides I would have liked to read your impressions of trying to build your own from one of those header kits I see used in builds.  That would have been an interesting read. 
 

There has to be a manufacturer out there that makes a header that you don't have to bend to fit. To me that is poor design on the manufacturers part. Even if it cost another couple hundred bucks to get a properly engineered set to me it would have been my choice as every time you open the hood people will see the deformed pipes. (That OCD thing I have again). 

Thing is, they can't design headers for every possible set of heads out there. The heads on this engine are a different casting than stock. All kinds of things can move around including the spark plug hole, the spark plug angle, exhaust port height etc.

Why I was wondering if in this case a roll your own option would have been better. 

GCrites80s
GCrites80s HalfDork
3/27/21 3:42 p.m.

I suppose that would be a different article. I don't remember the last time they did a DIY headers article but I do remember them doing at least one.

noddaz
noddaz GRM+ Memberand UltraDork
3/27/21 6:26 p.m.
Pete. (l33t FS) said:
noddaz said:

I must be out of touch, but nearly $500 for a set of headers isn't cheap.    But I am probably out of touch.  

Most headers I installed for rare, esoteric vehicles like '69 Camaros and late 60s GM A-bodies were $750, ten or so years ago.  This was for coated headers.

 

And the Camaro, at least, needed the collector mooshed for clearance.

Ok, I finally had to look.  The expensive (to me) headers are because:

1) They are Hooker Headers

2) The headers are coated

3) I am out of touch with header pricing

I did see headers listed for as cheap as $182.95.  And since I have not bought headers for over 20 years I guess I will go with #3 above.

GCrites80s
GCrites80s HalfDork
3/27/21 7:52 p.m.

I think I got a set of '69 Chevelle headers for $69.99 back in the late '90s from ASAP if anybody remembers them. I'm sure some older users rememberer getting headers for like $35.

philacarguy
philacarguy New Reader
3/28/21 8:37 p.m.

My question is, how do you keep spark plug wires/boots from frying with the headers this close?

Totally agree with the comments about starting with headers that are a better fit.  

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/28/21 8:45 p.m.
philacarguy said:

My question is, how do you keep spark plug wires/boots from frying with the headers this close?

 

Heat sleeves.

Had a regular customer with a street rod that had shorty headers where the plug wires were very close, kept burning them, so we installed heat sleeves.  Never an issue ever again, even though the sleeves themselves were burnt white where they touched the headers.

Had another car with an LT1 where, thanks to the different plug angle on the aftermarket heads, the #7 plug was so close to the header tube that you could not remove the spark plug without removing the header, it bottomed against the tube before it was fully unthreaded.  (But remember, Chevys are easy to work on)  The plug boot was in hard contact with the header tube.  With a heat sleeve, it was never an issue, and this was on a 700hp supercharged engine.

 

I figure the D in "DEI" stands for Dark-arts, the way their products work.

malibuguy
malibuguy GRM+ Memberand HalfDork
3/29/21 7:52 a.m.

Never had a problem with Remflex gaskets in extreme use, but slip fits are easy to work with.

And to touch base with a comment above, custom headers can add up REAL quick especially an in-chassis set, and add on top if you want top quality materials, TIG welding with backpurge (if stainless).  For alot of applications its just more cost effective to take an existing set thats close enough and then make the necesary modifications.

Another note, worrying about equal length headers on a dual-plane v8 is pretty useless as they are very insensitive to header lengths differences to one or another, testing has shown differences up to like 8-10" between runners has showed no real difference in power output.  Your better off chasing smooth bends and better chassis fitment.

Here is a few headers I built just to add some porn

 

Tim Suddard
Tim Suddard Publisher
3/29/21 9:58 a.m.

Custom headers would have been at least twice the price. While these headers took more work than I anticipated, I felt a lot of people might want to learn how to make adjustments to their headers.

The headers are now coated and look beautiful again.

 

z31maniac
z31maniac MegaDork
3/29/21 1:16 p.m.
noddaz said:
Pete. (l33t FS) said:
noddaz said:

I must be out of touch, but nearly $500 for a set of headers isn't cheap.    But I am probably out of touch.  

Most headers I installed for rare, esoteric vehicles like '69 Camaros and late 60s GM A-bodies were $750, ten or so years ago.  This was for coated headers.

 

And the Camaro, at least, needed the collector mooshed for clearance.

Ok, I finally had to look.  The expensive (to me) headers are because:

1) They are Hooker Headers

2) The headers are coated

3) I am out of touch with header pricing

I did see headers listed for as cheap as $182.95.  And since I have not bought headers for over 20 years I guess I will go with #3 above.

You would be shocked to see what the highest quality and most power making header cost for a BRZ. 

https://www.counterspacegarage.com/ace-a350-rhd-gt86

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/29/21 1:27 p.m.

In reply to z31maniac :

I assume that header is for non OE management.  Combining left and right banks like that could throw the computer all into a tizzy when it tries to adjust fuel trim based off of the wrong sensor's reading.  (assuming Subaru is doing left/right bank control, and not just combining all four cylinders into one "bank".  I have zero practical Frisbee experience here)

 

i also assume that the header will crack, stainless is an awful material for headers.

 

Looks awesome!

jfryjfry (FS)
jfryjfry (FS) Dork
3/29/21 7:12 p.m.

By slip-fit is that where one literally slips over the other and you use a ln exhaust clamp to crush the outside pipe down?   Can't imagine anyone would ever describe them as easy to disassemble!

 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
3/29/21 7:34 p.m.

In reply to jfryjfry (FS) :

Designed properly, you do not use a clamp.  The fit is close enough that the inner pipe expands into the outer with exhaust heat.  There is surprisingly little leakage.

One of the cars I did had three piece headers because Ford.  The front two tubes on each side were attached to the collector, the rear two tubes were individual pieces that you had to slip into the collector as you offered everything up.  Extremely fiddly but it worked well.

 

In the post-collector part of the exhaust, what you do is install a couple tabs that bolt together to hold the pipes in the proper orientation.

malibuguy
malibuguy GRM+ Memberand HalfDork
3/29/21 8:01 p.m.
jfryjfry (FS) said:

By slip-fit is that where one literally slips over the other and you use a ln exhaust clamp to crush the outside pipe down?   Can't imagine anyone would ever describe them as easy to disassemble!

 

You dont use a typical muffler clamp in this situation, its a proper fit and use either a formed bandclamp or a accuseal clamp.

You can also do springs or bolts.

Also I like to use double slips when I can when set up right no clamp is needed and they don't leak or at most very minor until some carbon builds up.  I typically use them when routing wastegate exhaust back into the downpipe

jfryjfry (FS)
jfryjfry (FS) Dork
3/29/21 10:51 p.m.

Very helpful.  Learned a little bit today 

frenchyd
frenchyd UltimaDork
3/30/21 2:34 a.m.
dean1484 said:

How much would a set of custom welded headers cost?  How hard would it have been to roll your own with a header kit and a tig.  I was with you until you bent them to access the spark plugs. Yes I know the it has a minimal if any effect on performance but it just looks bad to me. Call it header OCD on my part. And besides I would have liked to read your impressions of trying to build your own from one of those header kits I see used in builds.  That would have been an interesting read. 
 

There has to be a manufacturer out there that makes a header that you don't have to bend to fit. To me that is poor design on the manufacturers part. Even if it cost another couple hundred bucks to get a properly engineered set to me it would have been my choice as every time you open the hood people will see the deformed pipes. (That OCD thing I have again). 

I hope everyone understands that most prebuilt "headers" are just tubular exhaust systems.  
 Real headers have equal length ( and volume )  primary pipes length based on  the camshaft ( s) used. Contrary to the sales literature  the goal is not to make. Peak power. That's just bragging rights. The goal is to gain the most under the curve.  Or the RPM used  on the race track. If you race between 4500-6500 that's you goal.  You may use a smaller diameter primary pipe of longer diameter to achieve that. If you honestly race between 7,000-9,000 rpm then that's your design goal. There are plenty of free sources to figure out length and diameter. 
     One final point. The real goal of a racing header is to assist the intake to fill each cylinder with as much fuel and air as possible. Measure each intake port carefully.  A single 4 barrel intake manifold will often have a pretty serious difference.  

fearlesfil
fearlesfil New Reader
3/30/21 1:04 p.m.

In reply to docwyte :

Suggests to me that perhaps the tubes were too big to begin with for the combination, or that they are purposely made a bit large because they too-often need customer custom dimpling in order to fit!  If only the shape is being changed, e.g. from round to oval while not affecting the cross sectional area, I can see there would be little impact (pun).

z31maniac
z31maniac MegaDork
3/30/21 2:14 p.m.
Pete. (l33t FS) said:

In reply to z31maniac :

I assume that header is for non OE management.  Combining left and right banks like that could throw the computer all into a tizzy when it tries to adjust fuel trim based off of the wrong sensor's reading.  (assuming Subaru is doing left/right bank control, and not just combining all four cylinders into one "bank".  I have zero practical Frisbee experience here)

 

i also assume that the header will crack, stainless is an awful material for headers.

 

Looks awesome!

Yes, you don't put on a header like that without a tune smiley

Of course I wouldn't put any header on without a tune. 

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