DeTomaso Mailing List: May 1997, Message #142
     



From: MikeLDrew@aol.com

Subject: Re: DIYS Headers & More on Header Coatings (long & technical)

Date: Tue, 6 May 1997 12:25:59 -0400 (EDT)



Hello all,



This GREAT info just came across the Nor-Cal Shelby Club e-mail net.  Since

both the DeTomaso and Cobra folks have asked questions about these issues in

the past few days, I thought I'd forward this info from Don Wollesen.



BTW, I've went top-shelf and Jet-Hot coated the exhaust on my Pantera (street

coating, 1300 degrees); it looks beautiful.  I kept my headers silver, had

the tailpipes/mufflers done in black (they do it in silver first, then

re-coat it in black).  My exhaust tips were supposed to be masked, but they

coated them in silver.  When polished up, it's virtually as bright as chrome

and MUCH more durable.



My Cobra's system is also Jet-hot coated in Black, has been holding up great

since 1993.



Mike

---------------------



Do It Your Self Headers:



I have just finished the equal length header construction on my Brand

L (Lotus 2 Litre) engine. Not a lot of decent headers available for this

thing, so I had to modify my S&S headers which were well constructed (the

only ones I found that really were), but ... alas ... different primary

tube lengths (32" for #1 and 22" for #4). That translates to about 6000+

RPM on the long one, and ~8400 RPM on the short one. This will makes

carburetor

tuning with Webers a nightmare.



If you ever do succumb to making your own set of headers, plan on awhile

doing it. It really helps to have a spare cylinder head(s) and block with

engine mounts installed (along with anything else that can get in the

way of routing) for a working buck. It is not a project for the faint

of heart, 'cuz even the pros have problems with installation fit from

time to time. If you want to do this, first, go to the hardware store

and buy enough 1/4" aluminum of copper tubing to cover the total of all

of your header lengths. In my case, 4X 32" worth of tubing. Then cut the

tubing into equal lengths of the tube lengths you want for the engine.

Make up a temporary plate for the cylinder head, drill it for the exhaust

manifold bolt holes and a hole in the middle of the port for the 1/4"

tubing (for the head plate, I used plastic, but sheet aluminum of wood

would do). and make up one or more plate to represent the collector (4

holes in a 4" square piece of aluminum in my case).  Make up cardboard

discs the diameter of your header tubes, punch a 1/4" hole in the center

of these discs and put one on each piece of tubing. Then you can slide

these things back and forth to check for clearance. They should not touch

anything on the car ... or each other. I used two short pieces of rubber

tubing to hold the skinny tubes to the temporary header plate and the

"collector" plate. Then bend and route away to your heart's content with

the equal length 1/4" tubing pieces to verify the bends, routing and

clearance.

Make sure the bend radii are the same as the bend radius of your final

header tubes. I bought a bunch of U tubes from Stahl Headers back in

Pensylvania.

I bought a cut-off saw to saw the exhaust tubing with (a tool I should

have bought years ago, now that I have one). Then you get to cut the U

tubes at the right places so the pieces all fit together with smooth

transistions

from one piece to the next.  If you own a mandrel bend tool, you won't

need any U tubes and you don't need any of this advice; I'll listen to

yours.  You wi



ll also need an air compressor and a die grinder to get the cut tubing

ends to fit close enough for welding (about 1/16" max clearance). To hold

the exhaust tubing pieces together, I used band clamps (hose clamps),

which will hold the mess together to verify chassis fit, as well as allow

your welder guy to spot weld the pieces together before the final weld

seams. Gas welding will leave boogers inside the header pipes which will

disrupt air flow of the exhaust gases, so I had them TIG welded. You can

buy inserts to hold the tubing together and then gas weld them without

boogers, but Stahl says the inserts disrupt gas flow and they not only

don't use them, they don't even stock them. I started this header building

process during Christmas Vacation, took 2 days to route 4 tubes "just

so." Time well spent! It took about 30 hours more to cut the U Bends and

get the headers ready to weld. Welding took about 4 hours total. The welder

needs to get access all the way around each seam, so I did each tube one

at a time, with #1 and #4 permanently welded (the last welding to be done)

from head flanges to the 4 into 1 collector. #2 and #3 are slip fit into

the collector. I had 4 head flanges, not a single plate flange to the

cylinder head. This for a 4 banger. OK, it's the first time I've done

this and you speed up at it after awhile. But it does explain why somebody

wants to charge you $1K or so for a custom set of headers.



Well, with all this invested, Joe Wytman sez ... "now that you have this

real expensive set of headers, you want 'em to last awhile doncha?"  "

Yep," sez I, so I was interested in the postings on header coatings a

few weeks ago and made several postings myself. Since then, I called three

outfits:



1)-Swain Tech Coatings in New Yawk-716-889-2786 (note, the phone number

in the SCCA Sports Car Magazine awhile back is wrong)

2)-Sermatech in Compton CA--310-604-0018

3)-Jet Hot (3 places in USA)--1800-432-3379 for the Order Line



Here's what they said:



Swain:-3 layer coating, one bond layer, two different ceramic layers,

15 mils thick. $100 to $150 for my 4 cyl header, coating OUTSIDE ONLY,

good for 3000 deg. F.



Comments:-The inside layer is more important than the outside layer (sez

Joe Wytman of Race Tech Engineering in Campbell) ... cuz it's just hotter

inside along with a bunch of corrosive stuff in the exhaust, itself. 3000

deg. F. is awfully hot and may be true for the Ceramic, itself, but I

doubt if you could actually get the headers that hot (even in a furnace),

and besides, I think iron melts at less than that; I'll have to look it

up out of curiousity. MAX MAX Exhaust Gas Temps can get to about 1550

deg F without doing bodily harm to exhaust valves and seats (assuming

you got the right and best materials, less if you don't); 1350 is probably

more realistic for a non-turbocharged car, so anything beyond that is

gravy. The outside of the header should be just fine, keep it looking

nice, keep it from rusting. The inside of the header will now be hotter

(because the heat won't dissipate through the outside coating as fast),

the steel header material will be hotter and cracking (from the inside)

will likely be worse, instead of better. 15 mils is the thickest material

of the three claims, so any slip fit areas need to be considered, (like

allowing for another 30 mils of tubing size growth on the outside) or

telling Swain to mask this area off.



Sermatech:-Aluminum/Ceramic ~3mil thick, shiny coating, Inside and Out.

Good for ~1000 deg. F and will dissipate at temperatures above that. They

sand blast your headers, spray the stuff on, then bake it at 650 F. Then

they glass bead polish. Takes about 6 working days. $175 minimum charge

for each job, they estimated my 4 cyl (3 piece) headers would cost ~$180

(with my verbal description).



Comments:-Although coating is both inside and out, I'm not sure that a

spray process would get good coverage on long tubes all the way inside,

although it is certainly possible that it could with the right spray

equipment

and process control.  Probably a nice cosmetic appearance, and just fine

for a street machine. 1000 deg F probably not so good for a track car

or even a serious open track car. Probably because the aluminum coating

will diffuse into the steel header, leaving only the alumina outside coating

(a ceramic) ... which is probably still protective from oxidation (rust),

but heat radiation will go up on the part that isn't shiny any more and

appearance will go down. Coating is thin enough so that slip fit probably

isn't much of an issue, and they said that you could use emory cloth or

wet/dry sandpaper to remove the material if you wanted to. They could

also mask it for you if you wanted.



Jet Hot:-A choice of two coatings, one an Aluminum/Ceramic coating good

for 1300 deg F with a 2 mil thick smooth "silver" appearance for $200

bucks minimum charge. The other a proprietary coating (no aluminum) good

for 2000  deg F. with a matte finish with 2 to 3 mil thick "silver," "gray,"

(similar to cast iron in color) "blue," or "black" colors for $300 bucks

minimum charge. They claim most NASCAR racers use the 2000 deg. coating.

They claim the coatings are compatible with steel, stainless steel, aluminum

and cast iron. They strip the headers down to bare metal. The coating

is done with a slurry, inside and out, and then a bake process. Both coatings

are then baked. They claim 1% to 3% gain in HP plus >30 deg. F lower engine

compartment temperatures. They claim the coating is flexible enough to

be used for springs (for corrosion resistance, not temperature in this

case). Won't chip crack or peel either. If you have any header slip fits,

you need to say so so they can mask the slip fit area from the coating

if that's how you want it done..



Comments:-Jet Hot has a Web Page for those interested (www.jet-hot.com).

The slurry process will clearly coat the inside as well as the outside.

They claim that the 1300 degree coating is fine for anything short of

a race car which runs at full throttle a lot. They said this includes

SCCA track cars. For track cars or turbocharged cars, they recommend the

2000 degree coating. For open trackers, I would guess it would depend

on how stock your engine is as to whether you could get by with the 1300

degree coating. It should certainly be just fine for the street. The film

is thin enough that slip fits should not normally be a problem. If you

want to minimize heat radiation, pick the "silver" color and forget the

dark colors entirely. I would consider the dark colors for show, but not

for go. Heat radiation is a "fourth power law" of the absolute temperature

(from zero degree Kelvin), so this is a BIG DEAL on exhaust headers, trust

me. The gray would be nice for cast iron exhaust manifolds. The black

and blue might be pretty, but they would be a bruiser for heat radiation.



If you like to wrap your headers with header wrap tape, I would go with

the 2000 degree coating. The tape will contain heat, but not air (an

oxidant);

yeah, I know, it doesn't blow directly on the header ... it just diffuses

through the tape ... which is enough oxygen over time to cause rust with

no header coating. My concern with ceramic films with my ealier postings

were their mechanical flexibility, but if I believe the Jet Hot claim,

then that is not an issue with these films.



So, there ya go. Pick yer poison!



Don Wollesen