Header wrap

[rwolcott23]

What exactly is the function of header insulation wrap? I explained to one of our younger team members that it keeps the heat in the exhaust gases, which in turn keeps the velocity up and improves scavenging. He was skeptical pointing out that significant amounts of heat could not possibly escape in that short distance.

Anyways, does anyone have hard numbers as to how much this increases performance? Is it worth the added weight if the thermal insulation is not required to protect components in close proximity?

Thanks,
Bob

[rwolcott23]

What exactly is the function of header insulation wrap? I explained to one of our younger team members that it keeps the heat in the exhaust gases, which in turn keeps the velocity up and improves scavenging. He was skeptical pointing out that significant amounts of heat could not possibly escape in that short distance.

Anyways, does anyone have hard numbers as to how much this increases performance? Is it worth the added weight if the thermal insulation is not required to protect components in close proximity?

Thanks,
Bob

[kozak]

exaust wrap actully comes from drag racing. Drag motors are usually big and produce alot of heat more than a normal motor because they are forcing as much air and fuel through the motor as possible. exaust wrap helps keep the under the hood temp of the drag car gown to allow the motor to run cooler and suck in cooler air.

[james17]

Bob, I've never heard of header wrap being used to keep heat in the headers but rather to keep the heat in the headers from transeferring to other things. The main purpose of header wrap is the protection of things which must live around header wrap. If one was looking to slow down heat transfer from the headers a ceramic coating would be a much better method. As far as how big a difference it makes, good ceramic coatings can cool down external header temps by hundreds of degrees and make the air inside the header and thereby the engine that much hotter greatly effecting exhaust flow and power production.

[Akos]

Header wrap is dangarous. Stay away from it. If you want header insulation to keep heat away from your gas tank and such, get the header coated.

Header wrap will soak up even the smallest qantity of oil and hold it nice and close to the exhaust tubes. It is almost impossible to clean it out, and usually results in oil fires.

I'm speaking from personal experience about this. This stuff should be outlawed.

Cheers,

Akos

[Jon Huddleston]

That is, if you have oil leaks.

UTA has been using header wrap for most cars over the years. We have used ceramic coatings w/ wrap the past few years, but will probably go with just the wrap this year. The ceramic coatings were not changing the car's performance from what we could tell but tend to look bad after running the car for a while.

We use the wrap for a few reasons, but the lower temperatures near the gas tank and electrical components are definitely worth the added weight.

[Underthefloor]

Too bad someone dropped our header wrap in oil. We tested it on the dyno and it didn't catch on fire but it did smoke alot and turn brown. http://fsae.com/groupee_common/emoticons/icon_frown.gif

[John Bucknell]

To answer the original question, header wrap is a negative in terms of ultimate performance. The reason is that friction losses in the headers are a velocity squared term, and for a given mass flow rate the hottest/lowest density gas will have the highest backpressure (causing greatest pumping work). However, keeping your components cool is more than worth the penalty in most cases. An effective heat sheild on the component needing to be kept cool would be even better...

[Z]

Keeping the heat in the headers is especially important for turbos.

Firstly, the exhaust header gases are hotter with a turbo because they can't expand/cool as much, so the headers glow red/yellow... and can cook surrounding components. (The after turbo gases are cooler than normal.)

Secondly, any heat lost out of the headers is energy (pressure) lost and unavailable to drive the turbo.

For N/A the main advantages of wrap/ceramics is a cooler engine bay, hence possibly cooler intake air, and maybe good looks?

Z

[John Bucknell]

Turbos are an interesting case. Usually the exhaust gases are so friggin hot, you're spending huge quantities of fuel to keep the EGTs down so you don't burn exhaust valves, melt exhaust manifolds, etc. (unless you're driving a purpose-built turbo race motor and somehow you've got unobtanium exhaust parts - and even the endurance race four-cylinders I've dealt with have dumb high-nickel cast iron manifolds). Which is why most non-drag race turbo headers running any significant boost are stubby and/or just a cast manifold to hope to last any real length of time (ie not crack after more than two hours due to thermal strain).

Although it's true you want to keep the heat in to get the turbo spooled, once you've opened the wastegate - doesn't really matter how much heat you're rejecting due to surface area because you've already got too much exhaust energy. On the other hand, if you don't have a wastegate - you're all about the top end power anyway and most likely have staged nitrous and/or nitromethane to get the MONSTROUS turbo you've got to spool.

For FSAE (and any road race application), you've hopefully got a small enough turbo to be responsive and make some torque to get off the corner - ie you've probably got a wastegate. So in summary - header wrapping your turbo header for better performance is of negligible benefit in most cases. And if you've mounted your turbo behind the rear axle in your Camaro - I can't help you.

Anyhow, au revoir - I'm off to Phillip Island WSB round and then to NZ WRC. Whoo hoo! Monash, I might stop by if the surf isn't any good....

[strong_auto_concepts]

http://web.engr.oregonstate.edu/~strong/SAE/images/IMG_1665.jpg

So that's not good?

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">To answer the original question, header wrap is a negative in terms of ultimate performance. The reason is that friction losses in the headers are a velocity squared term, and for a given mass flow rate the hottest/lowest density gas will have the highest backpressure (causing greatest pumping work). </div></BLOCKQUOTE>

I had to bring this one up. I understand your'e reasoning, but I think it may be flawed. Who knows, maybe all the ceramic coating / wrap manufacturers are lying to sell their product, but keeping more heat in the exhaust gasses is supposed to produce more power according to everything I've ever heard. The reasoning for this point of view is that keeping the velocity of the exhaust gasses higher increases the scavenging effect a properly built exhaust system produces. Do you have any proof to back up your assertion, because I know this is the claim made by header wrap and ceramic coating companies. I'm not about waste my time searching for test results here, because I think its common knowledge this is the assertion made by these industries. If you have any proof they are lying to the public to push their products, I'd be interested to know about it.

Anyway, I did quickly look up some info, (so as not to look like an idiot):

ThermoTec's Website:

"Q: How does wrapping headers increase horsepower?
A: Wrapping the headers maintains exhaust gas heat within the header. This translates into more exhaust flow due to maintaining exhaust temperatures as it flows out of the engine. By improving the scavenging of spent gases, the engine breathes more efficiently. This reduces contamination of gases, thus allowing the engine to develop more power."

And A Link to dyno tests:

http://www.thermotec.com/technology/dynamometer/dynamometer.html

And heres where Jet-Hot claims horsepower gains:

http://www.jet-hot.com/pages/techinfo.html

I am totally open to hearing other evidence about these products, I'm not trying to argue, I'd just like to know the facts. Thanks for your time.

[DaveC]

Also, as far as the pic 2 posts up, one hint is to soak the wrap in water and gently wring it out before installing. It conforms to whatever your wrapping a lot better that way, and cuts down on the hazardous fibers that get airborne during installation. They also sell SS zip ties to secure it. Hose clamps work too, but are bulkier.

[Frank]

header wrap is stupid, dont use it

eventually, you will burn a car to the ground

use ceramic coatings, and / or non-absorptive shielding

[Lukin]

I use Ansell for header wrap if it's required.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">header wrap is stupid, dont use it </div></BLOCKQUOTE>

C'mon now, lots of people use it without burning their vehicles up. But yes, soaking it in oil/gas then firing up the car may not be too bright an idea. The wrap manufacturers sell a paint for the wrap designed to repell fluids if its a concern. I have one truck with ceramic coated headers, one with ceramic AND wrap, the one with both emits MUCH less heat from the headers.

Ansell must not be available easily in the US, at least I've never seen it for sale, is it much different from Thermotec and DEI stuff commonly available here?

[John Bucknell]

DaveC,

How exactly am I supposed to provide proof on the internet other than saying "F1 cars don't have header wrap"?

See my prior posts regarding my professional opinion on the subject. I think any 'thermal barrier' coating used on a race motor needs some deep thinking before you use it.

I saw an ad on tv with an interview with a 'race engineer' for roundy-round cars saying how great the 'vortex' air swirler was on his race car. I have no association with ceramic-coating stripping services for race headers and therefore no conflict of interest.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">How exactly am I supposed to provide proof on the internet other than saying "F1 cars don't have header wrap"? </div></BLOCKQUOTE>

I'd like to see some research, dyno tests, anything really that shows power losses due to a thermal barrier being applied to headers/exhaust systems. Most car guys, myself included, have been exposed to claims made by numerous mfgs of these products saying they build hp. Their reasoning seems somewhat sane, and they have dyno tests to back up their claims. As I said, I'm open to different thinking, but I'd like to see something, any research that contradicts the claims made by tbc mfgs.

Do F1 cars use any sort of thermal barrier on their exhaust, or any coatings in their motors, such as coated piston domes/skirts, chambers and exhaust ports?

Thanks Again, I'm not trying to be an a$$, I'd really like to know.

[VFR750R]

I think in some cases, the header wrap might speed up the velocity in an non optimum exhaust and provide a hp gain.
The most hp available may be with wrap or without, but i think the header design must take in account of weather you are using it.
Not one car in Nascar uses it, even on restrictor plate where 1hp is HUGE.

[drivetrainUW-Platt]

We had our headers coated along with our piston tops and maybe valves? We also put header wrap on the headers, when its new it looks ok, the guy spent a few hours wrapping it so it turned out really nice, but once we got some oil on it and ran the car it started smoking and lookin like a cheap excuse for a performance upgrade.

What kind of coatings are you guys doing to engine components/exhaust?

[Kurt Bilinski]

My understanding is that as the hot gases move down the exhaust tubes, the portion near the wall of the tube cool and slow down. This in effect causes the header tube to become "smaller" because the cooler, more dense, gases along the walls effectively make the cross-sectional area smaller. So, like VFR750R said above, yes, if the header is designed for use with or without wrap it "should" perform thes same.

FWIW, Smokey Yunick (engine guy from the 60s) had many good things to say about wrapping the tubes and though it was wonderful.

Do NASCAR rules even allow wrap?

[BryanH]

I've always been very dubious of additives,coating etc promising free HP.
Re header wrap, practical consideration comes first, wrapped tube carbonizes and falls to bits. Other peoples exp. indicates that ceramic coating stops the falling to bits.
IMHO you want the exhaust gas to cool as fast as possible, it takes up less space.
I have never seen wrap on a succesful race car.

Internal ceramic coating really is a good thing, I've seen suprising HP gains with this stuff, The only car we have truly back to backed was Mark Buiks Porsche 928 S4, no other changes but ceramic/teflon on pistons,chambers and inlet manifold and RWkw went from 175 to 199. (we dynoed it 3 times to make sure)

[rjwoods77]

You are are missing one important factor. It looks really stupid. Something a redneck would do. "Shoooooo-wwweeee boy. I got me some header wrap. My 350 gunna make me some sick ol' power boy. My 75' Nova gunna be the fastest thing this side of the Mason-Dixon line." Joe Dirt syndrome. Gotta go get my autotrader now. http://fsae.com/groupee_common/emoticons/icon_smile.gif

P.S. Before anyone takes offense I think the worst rednecks in the world are the ones that live in Upstate NY where I am.

[Frank]

i would guess most teams want wrap or ceramic coating to insulate the driver's back...

nothing to do with horsepower, smoky yunick, or rednecks

[John Bucknell]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kb58:
My understanding is that as the hot gases move down the exhaust tubes, the portion near the wall of the tube cool and slow down. This in effect causes the header tube to become "smaller" because the cooler, more dense, gases along the walls effectively make the cross-sectional area smaller. </div></BLOCKQUOTE>

You are getting the heat transfer thing, but not the impact. The boundary layer by definition is created by the fact that gasses must be at zero relative velocity immediately adjacent to a wall. The differential velocity between the bulk flow and the wall generally determines the thickness of the boundary layer, along with the viscosity of the fluid. Therefore a hot exhaust gas (which has HUGE viscosity compared to a low temp gas) will have a thick boundary layer, and a smaller hydraulic diameter and more friction - ie backpressure. On a short race header, this isn't so bad - ultimately the backpressure impact is small (but measurable). So this is why you may be able to make the same power with a more complicated and expensive insulated header designed for the higher gas temps, but never more. The other downside of thermal insulation on your headers is you will break them (much) sooner - which is a big deal, and ultimately why no-one (not F1, not NASCAR, not CHAMP, no-one) runs their header hotter than they have to.

As long as we are on the subject, I want to relate a side-bar. If you were following engine development in the early to mid-nineties (when I was in school), the hot topics were plastic/carbon-carbon composite engines and adiabatic/ceramic engines (along with alternative fuels and two-strokes) due to their promised cost/weight savings and improved fuel efficiency, respectively. The same reason I talked about above effectively killed both the plastic and adiabatic engines - they couldn't make good power. This is due to the fact that the heat transfer coefficients of the combustion chamber, piston top and bore walls all were terrible compared to aluminum alloy - and the heat transfer from the hot cylinder walls to the incoming air during the induction stroke reduced volumetric efficiency by 20% or more and made them more knock-sensitive which took about another 10% out of the power compared to similar metal engines. There are some studies to attempt to implement adiabatic concepts on diesel engines using high degree of supercharge, but no-one has gotten far enough along to try it on a large scale.

[Marshall Grice]

If heat in the header pipes is a huge concern for part life wouldn't an internal ceramic coating then increase the life? is the surface smoothness of the internal coating so ruff that the increase of frictional loss out weighs any longevity increase?

[John Bucknell]

Yep, if you coated with ceramic internally you will increase the life of your header - at the expense of your engine. The cermamic doesn't really stick to the metal very well (or itself, being of low fracture toughness) - and the particles get back up into the cylinder and very effectively abrades the bore wall and valve seats until your motor is toast. Ceramic inserts into the exhaust port are one of the methods proposed to reduce heat transfer into the head - until somebody ran one and found out the engine started burning oil almost immediately.

The friction losses with an internal friction coating will be just as bad as an external coating due to the lack of heat transfer, don't think surface roughness should be too much different than bare metal.

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Yep, if you coated with ceramic internally you will increase the life of your header - at the expense of your engine. The cermamic doesn't really stick to the metal very well (or itself, being of low fracture toughness) - and the particles get back up into the cylinder and very effectively abrades the bore wall and valve seats until your motor is toast. Ceramic inserts into the exhaust port are one of the methods proposed to reduce heat transfer into the head - until somebody ran one and found out the engine started burning oil almost immediately. </div></BLOCKQUOTE>

So... many coating companies sell a ceramic coating that is applied to combustion chambers, piston domes, valve faces and exhaust ports to reduce heat transfer into the piston and head. And I'm not sure how many headers have been ceramic coated (this is almost always done inside and out, unless its for a turbo) but I do know Jet-Hot and many others have made a business out of it, so I'd bet theres LOTS of coated headers in use. I just havent heard ANY horror stories about a naturally aspirated motor being trashed by coatings that have flaked off. Turbo vehicles are a different story, and a special case, the inside of the manifolds/headers are never coated in case particles go through the turbo. I dont know, I just think I would have heard people complaining about this if it was a reality. I have known a lot of drag racers, and even with their high output motors, I've still never heard anything about this. As far as a ceramic insert, I think thats a different issue than a coating. Also, I had to slightly "modify" a couple of coated headers, done by heating with an O/A torch until red hot, then shaping the tube. Even after this outright abuse, the coating looked shiny and new after I was done, never fractured or flaked. Seems like its some tough stuff to me...

[DaveC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">You are are missing one important factor. It looks really stupid. </div></BLOCKQUOTE>

Who cares how it looks.

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Bucknell:
Yep, if you coated with ceramic internally you will increase the life of your header - at the expense of your engine. The cermamic doesn't really stick to the metal very well (or itself, being of low fracture toughness) - and the particles get back up into the cylinder and very effectively abrades the bore wall and valve seats until your motor is toast. </div></BLOCKQUOTE>

John I disagree. Surely what you're talking has happened at one time or another. But you can't disregard all ceramic coatings because one or two (or maybe all the early tries) were not up to snuff. Ceramic coatings are used on all kinds of important stuff. Including pistons (and the space shuttle!) You can't tell me it's impossible to make them stick.

We used ceramic coatings on our exhaust for 3 years (until we went to Ti). We ran the crap out of those things. We had them glowing on the dyno (and unfortunatley, several times in the car). We ran engines for several years, and have had the exhausts off many, many times (for various reasons http://fsae.com/groupee_common/emoticons/icon_wink.gif ), the coating has never shown any sign of flaking. In fact we have had lots of trouble even grinding the stuff off, so we can weld something else on.

On top of that we've never had any engine problems related to debris in the cylinder, and we've been into a few of these engines running this coating for a couple years, with no ill effects.

FYI we ran Jet-Hot 2000, although I doubt this is the only coating that isn't an 'engine destroyer' http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif http://fsae.com/groupee_common/emoticons/icon_wink.gif I've seen racecars with exhaust coatings before.

We ran it for heat reasons, as our exhaust was always close to the fuel tank. I always wanted to do a back-to-back on the dyno, but never was able to fit it in.

[John Bucknell]

You guys. I'm telling you my professional opinion - I'm sorry if I'm calling your baby ugly, but it's true. Use this stuff if you can justify it to powertrain judges (me) - and we would like it if you could demonstrate to us how it is better, especially for performance.

By the way, if your header coating is glowing on the outside(!) - it isn't doing it's job. Space shuttle tiles you can heat to glowing on one side (2000 deg F) and be room temperature an inch away - but you notice that stuff is made in plates not bonded to tubular metal? That may be why your ceramic hasn't flaked off, it isn't very ceramic-like. Read through this page -&gt;Jet-Hot Technical Page (http://www.jet-hot.com/pages/techinfo.html), and make your own judgement - keeping in mind they are putting a highly reflective surface on the INSIDE as well as the outside of an exhaust.

To reiterate: My opinion is a radiation shield with an air gap is far superior in protecting components sensitive to heat. Secondly, you won't see a performance advantage by insulating your header unless you are already getting heat transfer from your exhaust into your induction.

[Nick McNaughton]

We've seen ceramic coated exhausts glow on the dyno, but what we figured was happening is that the steel under the coating was glowing, and the coating itself was thin enough to let some of the light through. Huge difference in extractor surface temp between coated and uncoated too, from memory, but the exact numbers escape me. We've had some trouble with the coating flaking, but only ever in small patches - as if it wasn't properly bonded for a bit, or as if the extractors weren't cleaned properly before the coating was applied. We've had two versions, a really-high-temp and a high-temp, and the really-high-temp was thin and really flaky, while the high-temp was thicker and more durable, but apparently we ran the risk of burning it off if the exhaust got too hot. We tried pretty hard to do exactly that, and couldn't...

[DaveC]

There is a wide range in product quality in the industry. Some are only high temp paints, some are done like powder coating, and are cured in a powdercoating oven. Others, like Jet Hot are only a couple thousandth thick, but dont burn off/flake like the lower quality stuff. There is also stuff much better than Jet Hot, such as Swain Tech's "White Lightning", which is .015 thick, and more effective than Jet Hot. It is also super hard, much harder to grind than the high-nickel EVO III cast manifold I'm using on my Rally Car. Link to info:

http://www.swaintech.com/header.html

I think the higher end stuff (Jet Hot 2000 and better) wont have any flaking issues.

[Charlie]

I'm not arguing it's perfromance benefits- I'm skeptical as well. I never tried to test that.

I also agree that an air gap is more effective of an insualtor - we used that too, for the fuel tank. But the coating was very effective overall, and kept wiring looms and bodywork much cooler.

I just disagree with your comments about coatings being destructive to engines. Hey I can have a professional opinion too! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Frank]

i've never understood why a dyno operator needs to hold an engine at power long enough for the pipes to glow red

UQ... acceleration winners 2004FS / 2004FSAE

[DaveC]

Yeah, no doubt. When I ran my car on the dyno, it seemed like it saw way more load than it would EVER see on the ground. It seems abusive.

[John Bucknell]

You know, there is an exception to every rule - and I just realized it. Snowmobile expansion chambers when it is REALLY cold out would benefit from a thermal insulator to keep the pipe operating in the right frequency band. This is why snowcross engines have a 'launch' feature that retards spark in combination with a rev limiter to heat up the chamber while on the start line.

Charlie,
I have yet to see a ceramic deposition process that is able to stick on the inside of an exhaust and prevent the kind of failures I'm familiar with. The high velocity oxy fuel (HVOF) deposition processes can only get at the outside of a small diameter part, and really that is the only process that I've seen that will stick to metal well enough that I'll use it. It works particularly well on heavily blown two-stroke piston tops to prevent melt-down. We've also used it as an alternative to Nikasil on aluminum bores to good effect. More info here -&gt; Ceramic Coatings (http://www.dynacer.com/coatings.htm).

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by John Bucknell:
If you were following engine development in the early to mid-nineties (when I was in school), the hot topics were ... adiabatic/ceramic engines ... due to their promised ... improved fuel efficiency. The same reason I talked about above effectively killed ... adiabatic engines - they couldn't make good power. .... compared to similar metal engines. </div></BLOCKQUOTE> (My emphasis added.)

John, by this do you mean that they couldn't make the same power/litre, or the same energy/kg-of-fuel?

The engine capacity limits of most racing formula are a very artificial design constraint. A more sensible rule would limit maximum fuel flow rate, regardless of engine capacity. In this case would adiabatic engines have an advantage? (Ie. use a larger capacity "adiabatic" engine that generates more power from the maximum allowed fuel flow rate, rather than a smaller, less efficient aluminium engine.)

Z

[TG]

I was just down in the pit at PIR where all of the Daytona Prototypes are. From what it appears like, the richer teams had the gold reflective foil over EVERYTHING, as John suggests, and the not so rich teams used header wrap. I guess that the header wrap was used to try to contain the heat and keep it out of the engine conpartment. I think the heat in the engine compartment might be more critical for these teams because of the limited air flow in there (I think that would make sense?). Just observations.

[John Bucknell]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
John, by this do you mean that they couldn't make the same power/litre, or the same energy/kg-of-fuel?

The engine capacity limits of most racing formula are a very artificial design constraint. A more sensible rule would limit maximum fuel flow rate, regardless of engine capacity. In this case would adiabatic engines have an advantage? (Ie. use a larger capacity "adiabatic" engine that generates more power from the maximum allowed fuel flow rate, rather than a smaller, less efficient aluminium engine.)

Z </div></BLOCKQUOTE>

Hmmm, the answer to that isn't clear to me. The adiabatic engines were more typically diesels as they could tolerate dramatically hotter charge temps due to the aforementioned heat transfer because they depend on it for ignition. Spark ignition engines are knock-sensitive enough that the heat may present further power reduction beyond the reduced volumetric efficiency without octane increases. However, race fuels are phenomenal enough in the octane category that that may not present an issue - methanol comes to mind as a good candidate (also because of it's huge heat of vaporization which would offset the heat transfer). Ultimately, yes I believe the thermal efficiency increases may allow a larger engine to make more power - but you have to offset the volumetric efficiency with thermal efficiency, and that's hard to do. By reducing in-cylinder heat transfer, most of it goes out the exhaust (ie a big jump in EGT) which is best recovered with a turbo charger - ie more weight yet to offset the volumetric efficiency penalty. Therefore you may make more power at the expense of much more weight...

If I was constrained by energy flow rate - I'd be doing what Audi is doing at Le Mans, direct injection turbos. DI allows higher compression ratio because of knock relief, which lowers EGT, which lowers fuel consumption by reducing cooling enrichment. Turbos allow a smaller engine for the same output, and therefore lower friction losses and improved efficiency. So whatever you would do for an endurance engine (or reduced fuel tank capacity as in late turbo-era F1) is what you would do for fixed energy flow rate.

[Sam Lin]

John, Porsche 944 Turbos from back in the mid-80s have ceramic liners in the exhaust ports to reduce exhaust heat transfer into the head, and numerous modern cars use them today.

Sam

[John Bucknell]

Sam,

You're right, Porsche did have an exhaust port liner on their 2.5L turbo (951 engine) in the 944. However, as far as I can tell not one gasoline engine has a ceramic exhaust port liner today (Porsche didn't put a liner in any subsequent engine to the 951 - literature says it was done to improve turbo response, which I believe based upon the distance the turbo was from the port). Several OTR truck diesels do have exhaust port liners, but operate at dramatically lower exhaust gas temperature. The normal solution in those diesel trucks is to cast in a hollow stainless liner so there is an air gap. But those heads are iron - it is the differential thermal expansion rates of ceramic versus aluminum that makes it very difficult to make such a liner live in a gas engine. I'm curious whether Porsche had warranty difficulties due to this...

John

[Dan G]

I just inspected the liners in my 951 head this morning. Almost 20 years old now, 160k miles, and the liners still look great!

http://evilallianceracing.com/ipw-web/gallery/albums/951Head/IMG_0611.thumb.jpg http://evilallianceracing.com/ipw-web/gallery/albums/951Head/IMG_0612.thumb.jpg http://evilallianceracing.com/ipw-web/gallery/albums/951Head/IMG_0613.thumb.jpg (http://evilallianceracing.com/ipw-web/gallery/eVil951)

The "subsequent" engines after the 951... the 3.0L S2 and the later 'S3' in the 968, were both non-turbos. No need for liners.

986 is a non-turbo, the 993/996/997 and Cayenne S are the only turbos that have been designed since the 951. But you're right, I don't think these cars have ceramic exhaust liners.

Another cool piece of 951 trivia. Sodium filled exhaust valves. The phase change of the liqui-gasified sodium helps keep the valves from over cooking. 951s are cool!

[DaveC]

In a production car, the gain in power vs. production costs may not be worthwhile. Especially in a street-driven sports car youre not (usually http://fsae.com/groupee_common/emoticons/icon_biggrin.gif) at WOT for very long at all. Then, as John mentioned, there are durability concerns, as warrantying motors will get expensive. However, on a race car durability isnt much of an issue as it isnt meant to last 100,000 mi. On a restricted race car, youre fighting for every hp, so I think TBC coated chambers, piston domes, exhaust ports and valves could be an advantage, especially after seeing Bryan's observations:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Internal ceramic coating really is a good thing, I've seen suprising HP gains with this stuff, The only car we have truly back to backed was Mark Buiks Porsche 928 S4, no other changes but ceramic/teflon on pistons,chambers and inlet manifold and RWkw went from 175 to 199. (we dynoed it 3 times to make sure) </div></BLOCKQUOTE>

I also dont believe that the coatings will flake off and destroy our motor, or do any harm. They have been tested and improved upon for decades at this point, at the very least, they are an insurance policy against thermal failure of pistons and exhaust valves.

I'm giving up on talking about whether its a good idea to coat/wrap exhaust piping. I have been shown NO evidence, actual testing, NOTHING to back up the claim that keeping heat in the exhaust gasses causes a decrease in power. I asked a couple of times previously for some basis in real world testing to back this up, and its not here... And, yes, we can provide proof on the internet in terms of links to test results or analysis done. Most are done in written form so others can read them.

[TG]

John,

I'm curious... what happens if you can warm the cats up fast enough? Or is this not an issue? I know a lot of cars sold in the US have their cats close up to the manifold, but some european cars have them well down stream.

Dan,

the new Z06 has sodium filled exhaust valves, too. So did some of the old Porsche 356 engines as well.

[John Bucknell]

Tim,

Getting catalysts warmed up is the name of the emissions game these days. In the last ten years, emissions tests have become dramatically more difficult to pass (like over 90% less tailpipe emissions) - and yet the engines themselves have no yet become much more clean. This is due to the ability of the engines to warm up the catalyst to functioning temperature quicker and quicker, from minutes ten years ago to mere seconds on today's cleanest vehicles. A modern catalyst fed a proper feedgas can operate at 99.9% conversion efficiency, and that is a huge stick to reduce tailpipe emissions.

Many European cars rely on a system of injecting air into a rich mixture to provide an oxidation reaction in the exhaust to heat the catalyst. Such a system is expensive and relatively high warranty - most north american vehicles make due with reducing heat transfer between the exhaust port and the catalyst, which is essentially free.

[Dan G]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">the new Z06 has sodium filled exhaust valves, too. So did some of the old Porsche 356 engines as well. </div></BLOCKQUOTE>
I don't think the practice is unique, they might not have been the first to do it either (obviously not, if they were on the 356s as well). Just not very common and kindof cool. Still, if you want bigger valves on a 951 head you just go to stainless like the rest of the world.

Another interesting bit of 944 trivia...
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The totally new engine was a 2.5 litre inline four-cylinder developed at Porsche. This engine has been called half of a 928 engine, in that they do share the same cylinder head, valves, and bore & stroke (the 944 4 valve, 959, and 928S4 all have the same valves, valve guides, valve angles, and combustion chamber). The new engine utilized contra rotating balance shafts to cancel out vibration in the relatively large four-cylinder engine. Optional sport package available that added Koni/Boge sport shocks, front/rear sway bars. The forthcoming turbocharged version was originally intended to replace the aging 911. </div></BLOCKQUOTE>http://www.connact.com/~kgross/FAQ/944faq04.html

That 959 commonality is a good one to toss out when airheads try to make the VW/audi "insult".