Dry Headers on a Bravo setup.
 

Anybody ever try running dry headers w/ thermal barrier coating w/ an enclosed engine compartment. My experience w/ HPC coated headers on race cars is that they keep engine room temps down quite a bit. I know it's apples and oranges but lots of race cars front fenders & hoods are made of fibreglass too.
I'm thinking of trying to fabricate some dry stepped headers and HPC coat them. My engine compartment will have a lot of ventilation and I'll probably run a Harwood Scoop as well.
Anybody think (or knows) whether it would be safe to do this and would there would be any power advantage (on a normally aspirated 509 cid)? Also, does anybody make dry headers for the Merc. Bravo 1 setup?
I can only imagine that if this could work, it would make the cost of construction of boat headers substantially cheaper (especially when it comes to large displacement engines which need large tubes w/ stepped primaries).

It will be a very well ventilated compartment once the hatch bursts into flames. I dont think it's even legal to run non-water jacketed exhausts in enclosed compartments.
Gary

you need eth jackets. I ran non jacketed tailpipes once. Mind you they were attached to fully jacketed and colled CMI and the damn things still started glowing. You 100% need some cooling water.

if yu want dry just get dry tailpipe and dumop the h2o totally seperately from the exhuast gas through thru hulls dumps.

I say try it! Let me know how it works. I think it is possible, if your are careful.
Dennis Moore

If you wrap them you can keep the heat in the pipe pretty well. Problem I see is getting them out through the transom. They will run HOT and remember your boat motor runs under a load for long periods of time compared to a car. Be very carefull if you try this!!!!!!!!!!

I assume your looking at cost compared to jacketed headers that run dry. :)

Hardcore,I agree with PUDER ,get wet headers and dump the water before the pipes.Race cars have an open(bottom)engine bay,boats are completely enclosed(until the hatch bursts into flames like GARY said)You'll probably come out ahead(time vs money)just buying rather that building your own.BOB

Hate to be so negative , but....






fugettaboutit... hope you have an automatic halon system too:rolleyes:

Dry headers in an open ski boat , yeah ok , but enclosed I'd say too much heat:(

when i ran eth tailes it was dusk when i took it out for spin. IN 5 minutes of idling and maybe 3 minutes at 1/2 to 3/4 throllt i had them glowing. For the cost of making your own headers and tails and coating your better of buyign apari fo cmi and pipes. I happen to have a pair od lighlty used CMIs (fullpolish) and dry pipes. The water mixxes right at the very end of the pipes so they aren't FULLY dry. buts its enough. Reversion is't and issue. Th eabsolutle fully dry is way to damn loud. I like loud and it gave me a headache.

but if you wanted fully dry you coudl easily weld up eth wate rdump wher eth two walls meet and put a bung in for en external water dump. 0-mail me if your interested. I'll make ya a deal. I am running stellings (with CMI pipes i modified) cus they fit better.

Thanks for the responses guys - even the negative ones! However, what I'm trying to find out is, has anyone actually tried HPC (or other Thermal barrier coated) headers. I know the coating works. I would say it works as good as wrapping the header. I take the point about exiting the transom though. I was thinking of injecting a small amount of water - say through a AN-8 fitting, to cool the tailpipes. Loud is good. Louder is better. As far as legality goes, I live in the Cayman Islands (like Cayfomula) and we have very little in the nature of Coast Gaurd type certification of boat hardware down here. (Still wouldn't want to turn my newly painted and rigged A/O 2600 into a funeral pyre though!)
I am looking at the water-restricted Lightning Headers and for the cost of those it will probabaly be worth my while to buy those instead of piecing together a dry header and sending it away to get it coated.
BTW: there's a company called GGB that's advertising some really good looking headers in Powerboat. anybody know anything about those? They appear to have an inverted cone like collector (like what the Nascar boys use) and look like they might make power. Of course, looks don't necessarily win races...

can't run lightenings in salt. the inner tubes rust out super quick as they aren't stainless.

I am sure you can get the lightings with stainless inner tubes now.

Yep. I definitely need at least stainless inner tubes (or good coating) since all we have down here is salt water. You can get the Lightnings with S/S inner tubes for about $1600.00 or fully Stainless (platinum finish) for about $2500.00.
Teague also has the new CMI Sport Tube Lights (long tube primaries and no tailpipes) for about $2600. These are what I will probably go with if I decide to buy a fully S/S water-jacketed header. They are rated for up to about 750 HP, but I recall reading somewhere that the inner tubes are 1-7/8" I.D.
That provokes a thought - why is it that most race cars (drag and other) as well as dynos seem to need to use larger primary tubes (like 2 1/4" +) to make maximum power on a 1hp+ per cubic inch B.B. Chev. but boats tend to use something smaller with a similar engine? Is it that the cooling effect of the water-jacketed header makes the exhaust gas denser and therefore will not need the larger pipe? (Or is it just that no one except the most serious racer can afford to spend six Grand on a pair of CMI Big tubes or Stellings?)

Inner tubes are stainless on all Lightnings. The outer tubes are the ones you have a choice on.

There is a definite performance benefit to keeping the outflowing gases as hot as possible. For this reason, it would be worth the trouble and expense on a race boat to have a set of dry longtube CMI tubetops or Stellings thermal coated on the insides of the headers and tailpipes. They would still run water jackets but the outflowing gases would exit the tailpipes MUCH hotter than normal. This will improve exhaust scavenging.

Aside from that, I honestly see no lure in using the thermal coating as a means for ensuring engine bay safety on an inexpensive set of jetboat headers. It will never be legal, if you care about that.

Try a set on a dyno motor. If the external wall of the pipes stays below 300 degrees after extended WOT operation under full load, then I say you're onto something. Over 300 degrees, and you'll never get my blessing.

Cool. That's the kind of answer I was expecting. I don't have access to a dyno and I'm very anxious to get this boat in the water so I think I'll probably just go with the Lightnings with the restricted water injection. This option apparently reduces the amount of cooling water going into the exhaust by dumping most of the water through a couple of 3/4" dumps and only enough water is allowed into the exhaust stream to cool the tail pipes and hoses. Sounds like the best of both worlds to me.
Thanks again for all your input guys.

The tailpipes are already cool cause they are fully waterjacketed. The water reduction is where the water is introduced at the rearmost portion of the water jacketed tailpipes. As you said, this is to cool the gases so they don't catch your hoses (that go from the taipipes to the tips) on fire. I'd run the blue silicone hoses with reduced water just for longevity (and while the blue hose is expensive, the 4 6"-long pieces don't really cost that much since you only gotta have 2 feet of it ($60 versus $15).

Restricted water only adds $60 to a pair of headers if you order them that way. You do gotta add a dump fitting thru the hull for the excess bypass water though.

ahhh rubebr hoses!!! (you can run tailpips that go through the transom as well. no rubebr to melt (i've done that )

Re: Dry Headers on a Bravo setup.
 

When you are running the pipes will red hot. This will be worse with the wrap as it will keep the heat in. I've heard of people thermally cooking their headers until they blow out from the fatigue. That's why they run stainless in the race cars.

Mc-I thought the inner tubes on the Lightnings were mild steel, but with a barrier coating.

BTW-the coast guard (and insurance company) would frown on not having a jacketed or injected exhaust.

Re: Dry Headers on a Bravo setup.
 

I have a set of CMI straight tails if your interested. They can be run dry or wet and have the mercruiser style flange.