43 replies to this topic

[red300zx99]

With many different exhaust coatings on the market to heat in the headers to improve gas flow through them and keeping heat out of the engine bay, something strikes me as odd as I have yet to see any of them on an F1 exhaust system. Now this team and that team is having cooling problems, but it seems none are using this technique to help, anyone know anything about this, or what if anything is being used?

[SalutGilles]

Your road car can utilise these materials because it really isn't running all that hot. Bear in mind that F1 engines use compressed water as coolant, and sustain temperatures far hotter than your street-car engine utilising ethelyne glycol and water as a coolant. F1 engines just run too hot for those coatings to be effective.

























- that was just a guess, but it sure sounded good!

[red300zx99]

We offer coatings that protect up to about 1500C, not sure how hot an F1 motor gets, but I doubt it's that high. For a properly tuned gas engine (12.8:1) egts get in the range of 1100-1200F (sorry for the different temp measurements). We coat mainly race engines, drag race, circle track, and such. So the question still remains, why don't we see coatings or what kind of coating are used in F1, again assuming that they dont run over 1500C?

[dosco]

Originally posted by red300zx99
With many different exhaust coatings on the market to heat in the headers to improve gas flow through them and keeping heat out of the engine bay, something strikes me as odd as I have yet to see any of them on an F1 exhaust system. Now this team and that team is having cooling problems, but it seems none are using this technique to help, anyone know anything about this, or what if anything is being used?

Please specify coating types.....or give a link.

[12.9:1]

A good guess - close at any rate. The coatings keep more heat in the ex. tubing - good for low HP engines ? may be, but the F1 exhaust is fabricated from tubing of less than 1mm thickness (though a high temp nickel alloy) it still needs to radiate as much heat as possible, in order to survive the 1000deg C + temps and violent shaking. Just holding together long enough to complete one race distance, - only to be scraped !

[Greg Locock]

That's a good answer, there is an advantage in cooling the exhaust gas down, if you can do so without heating anything else up. In a conventional car you can't do that, in an F1 car you can.

[scdecade]

I had an issue of F1 Racing that said the Williams team use a material called (this is from memory) iconnel for their exhausts. I'm not an engineer so I have no expertise to offer other than that...

[12.9:1]

scdecade,

Good memory

[VAR1016]

Originally posted by scdecade
I had an issue of F1 Racing that said the Williams team use a material called (this is from memory) iconnel for their exhausts.

Yes that's right.

Inconel is one of a range of the so-called "super-alloys". Many of these were developed by Henry Wiggins & Co., in the 1940s to meet the requirements of gas turbine engines. The requirements included withstanding very high temperatures, whilst retaining strength, resisting elongation and also resisting very hostile high-temperature corrosive gases.

"Nimonic" is another well known range, and used quite often for exhaust valves.

Most of the super-alloys are alloys of varying amounts of chromium and nickel - most have no iron - with other alloying elements, e.g. Molybdenum, Vanadium, etc., for various applications. There are also applications in the oil industry for these materials.

PdeRL

[Ben]

Originally posted by red300zx99
With many different exhaust coatings on the market to heat in the headers to improve gas flow through them and keeping heat out of the engine bay, something strikes me as odd as I have yet to see any of them on an F1 exhaust system. Now this team and that team is having cooling problems, but it seems none are using this technique to help, anyone know anything about this, or what if anything is being used?

http://www.zircotec.com/exhaust.html

Ben

[red300zx99]

One of our coatings is very similar Zirocotec's coating, not exactly sure what the specific chemistry is but it's some form of Zirconium Oxide, a ceramic, usually stabilised with something else. Hmmmm, inconel, yes fimilair with that too, know the developer's son, and we've coated that too for some of these drag racers. Except for the engine running to 19k I still don't see what is so extreme in their engines that they don't use some sort of thermal barrier coating, their are improvements to be had with this type of use.

[Greg Locock]

So what's the advantage of using this stuff on a non-turbo car with no need to worry about under-hood heatload from the exhaust?

[skiericski]

Anything that keeps heat in the exhaust system will give HP benefits, whether turbo or NA. The more heat that stays in the exhaust the better. As your exhaust cools off, it contracts, thus losing velocity. Velocity is key to scavenging both because it means more momentum and lower pressure.

My personal conjecture on why F1 doesn't (seem to) use ceramic coatings is that inconel has a thermal conductivity less than a fourth that of mild steel that most street headers are made from. That means that it transfers way less heat, so thermal coatings might not be of any real benefit.

[red300zx99]

Aren't McLaren having cooling problems, this may not be the answer but it would surely help

[Greg Locock]

skiericski - have you any proof of that? the reason I ask is that the momentum near the exhaust valve would be unchanged, and if the velocity near the tailpipe is really important you could reduce the diameter of the pipes as the gas got cooler to keep the velocity up.

[Patrice L'Rodent]

Quote SalutGilles............."Bear in mind that F1 engines use compressed water as coolant,".....


Compressed water? Unlikely =]
Very high vapour pressure in the cooling system to raise the boining point? Far more realistic

Pat D'Rat

[VAR1016]

Originally posted by Patrice L'Rodent
Quote SalutGilles............."Bear in mind that F1 engines use compressed water as coolant,".....


Compressed water? Unlikely =]
Very high vapour pressure in the cooling system to raise the boining point? Far more realistic

Pat D'Rat

Quite early aero engines certainly used steam cooling

PdeRL

[dosco]

Originally posted by Ben


http://www.zircotec.com/exhaust.html

Ben

Aaaahhh, TBC. Know the stuff....used in "turbine inlet" stator sections in gas-turbine engines. Had problems with it coming off in the Allied Signal ATF-3 reverse-flow turbofan engines.....

Inconel.....know that stuff well too. Where I work we make aircraft ducting from Inco 718 (precipitation-hardenable) and Inco 625 (non-hardenable). We do lots of welding of the stuff. A nice high--refractory nickel super-alloy. Good stuff, difficult to machine, easily welded. Work hardens like a sonofabitch.

Inco 625 (from a paper on my desk) - 58 Ni, 20 Cr, 10 Mo, 4 Nb+Ta, 5 max Fe, 0.5 max Mn, 0.5 , max Si, 0.10 max C (all % by weight).

I had heard that the F1 exhausts were fabricated from Inco.....since Inco is refractory, would adding the TBC improve heat retention in the exhaust gas? Plus the mass flow is so high (and the periscope exhausts so short) how much heat transfer is going on in the first place?

[skiericski]

Certainly, Greg.

Any text on exhaust system design will confirm this. The whole idea behind headers is to decrease pressure(thus increasing velocity and therefore momentum) at the exhaust valve especially just before it closes(during valve overlap.) This draws burnt mixture out of the cylinder and pulls in fresh mixture behind it. There are lots of books that explain the theory better than I can, but suffice it to say that the more total energy that remains in the exhaust stream the better. Reducing pipe size would indeed increase velocity, but the penalty would be in the form of increased back pressure. F1 exhausts flare out after the collector to produce a sort of megaphone. The taper of the megaphone is key in spreading the "tuned" rpm band over a wider range.

For details, read "Scientific design of intake and exhaust systems" by Phillip Smith and John Morrison. ISBN 0-8376-0309-9

I'm sure there are more current books out there, but I haven't read any of them. For a simplified explaination, see: http://www.burnsstai...ory/theory.html

[dosco]

Originally posted by skiericski


This draws burnt mixture out of the cylinder and pulls in fresh mixture behind it.

[/URL]

Really. In a 4-stroke engine?

Please elaborate.......

[scarbs]

From my experience no current F1 team uses visible coatings, Ferrari used a white coating on their early 90s V12s.
I also know Toyota use Inconnel 625 for their recent exhausts. With the pipes running so (red) hot anyway, what level of gain is there from a coating? would it withstand the surface temp, the expansion and bending of a F1 system on full song. The teams coat the inner sides of the bodywork to reflect heat, rather than the pipes. plus very little downstream to overheat from them, seeign as they now exit through the top of the sidepod..


BTW - the F1 exhaust on the zircotech is from the Toyota TF101 (2001 test car). The De Cortanze designed early version was unusual in that the collector points forward and then turns 180 degrees to exit rearwards.

[skiericski]

Dosco,

I'm definately not an authority on the subject, but the basic idea is that when an exhaust valve opens, a strong pressure wave is created in the runner. This wave travels at the speed of sound toward the collector. At the change of cross section that the collector presents, the wave is partially reflected (inverted)and travels back down the runner as well as down the other runners attached to the collector. It's hard to explain without a picture, but since the wave is inverted upon reflection, the node at the back of the valve will be low pressure instead of high. If the length of the runner is correct(for a given RPM), that low pressure will arrive at the valve as it is closing (at TDC Intake). This low pressure(hopefully) draws the last little bit of the burnt mixture out of the cylinder (since the piston isn't pumping it) and since the intake valve is opening at this point, fresh mixture is drawn into the chamber by the low pressure.

In addition to all that, the momentum of the exiting charge creates a low pressure area behind it which helps to accomplish the same end.

At any rate, it all comes down to cylinder filling. The end of the secondary pipe also creates a reflection so its length is also critical.

As you hinted, two-strokes rely completely on these effects for exhaust scavenge and cylinder filling.

I'm guessing that the configuration of that toyota pipe is geared toward getting an efficient secondary length and keep the outlet where the aero guys wanted it.


I don't know if anyone makes a coating that would withstand 1700+(F) temps together with that expansion and contraction that scarbs talked about.

[J. Edlund]

I have heard some about coatings used in the exhausts in the head but never seen any coating on a F1 exhaust manifold. If used in the head it should be able to reduce the temperature in the head, not only reducing running temperature (and risk of pre ignition) but also reducing valvetrain friction, which has shown to increase on the exhaust side when the temperatures increase.

Another question is why F1 aren't using directionally solified (DS) or single crystal (SX) superalloys? DS alloys like CM Mar-M 247LC (Ni-10Co-10W-8.5Cr-5.5Al-0.7Mo-3Ta-1.4Hf wt %) can be found in turbine wheels of turbocharged racing cars for example. SX alloys like CMSX 10 (Ni-2Cr-3Co-0.4Mo-5W-8Ta-6Re-0.1Nb-5.7Al-0.2Ti-0.03Hf wt %) are the very latest in the nickel based superalloys but can probably only be found in military turbine engines. Both these alloys do however have better high temperature properties than the much older Inconel.

Thermal barrier coatings are applied in layers with a bonding layer first which protect the metal from oxidization and reduce the difference in thermal expansion between the metal and the ceramic. The thermal barrier is often zirconiumdioxide stabilized with diytteriumoxide. The layers can be applied with several methods, as long as the parts aren't moving the requirements are lower but with moving parts EB-PVD should be used, which is quite costly. These layers ends up with a thickness of about 0.3 mm (if they are too thin they won't help), what will this do with the weight of the exhaust manifolds? Furthermore I don't think it's a good idea to coat just the outside of the pipe, since it can increase the thermal stress on the pipes.

From what I've seen F1 cars seems to use pipes with a quite large diameter, this reduces exhaust temperature and maybe they want this effect. The temperature of the gases will also affect the speed of sound and therefore the tuning of the pipes.

Formula One cars are using a pressurized cooling system much like conventional engines. A couple of years ago I think Renault released the running temperature of their engine which was in the region of 110-115 degC if I remember correctly. Higher engine temperature will be able to improve aerodynamics (smaller radiators, higher temp on air from radiators) and should be able to increase engine efficiency as it reduce the temperature difference between the cylinderwalls and the burning gas trapped inside and therefore the heatloss to the cylinderwalls.

The exhaust temperature isn't much different from conventional engines, most oem turbocharged cars run with temperatures somewhat below 1000 degC (measured before turbocharger inlet) even if some aftermarket tuners have accidentally been up over 1100 degC under shorter periods.

[dosco]

Originally posted by skiericski
Dosco,

...the basic idea is that when an exhaust valve opens, a strong pressure wave is created in the runner....the wave is partially reflected (inverted)and travels back down the runner as well as down the other runners attached to the collector....This low pressure(hopefully) draws the last little bit of the burnt mixture out of the cylinder (since the piston isn't pumping it) and since the intake valve is opening at this point, fresh mixture is drawn into the chamber by the low pressure

As you hinted, two-strokes rely completely on these effects for exhaust scavenge and cylinder filling.

I don't know if anyone makes a coating that would withstand 1700+(F) temps together with that expansion and contraction that scarbs talked about.

I know what your getting at....I was being a bit sarcastic (at your expense....sorry )

Isn't the "scavenging" effect really minimal on a 4-stroke? I suppose if it improves HP by 1% the F1 guys will go for it, but it seems like a stretch to me.

Yes, I understand that the scavenging is critical in "performance" 2-strokes.

More thoughts on hi-temp barriers.....usually if something gets to 1700+F, the designers use "film cooling" where a thin "film" of cooler air is "blown" over the surface of a part....the film prevents heat transfer, yadda yadda. Used in turbine stator blades, rocket engines, etc etc.

Good stuff and interesting discussion.

[skiericski]

Lol...Boy, I feel dumb

Originally posted by dosco


Isn't the "scavenging" effect really minimal on a 4-stroke? I suppose if it improves HP by 1% the F1 guys will go for it, but it seems like a stretch to me.

Good stuff and interesting discussion.

Scavenging in four strokes is critical for making real power! Way more that 1%, anyhow. Think about the low pressure in a poor intake manifold and the back pressure in an inefficient exhaust. When both valves are open just before TDC exhaust, this condition makes it easier for burnt mixture to go out the INTAKE valve than the exhaust. The low pressure area produced by tuning the exhaust and the high pressure on the intake side produced by tuning the intake runner lengths, etc. are very efficient at scavenging and filling the cylinder(with fresh mixture)

[dosco]

Originally posted by skiericski
Lol...Boy, I feel dumb

I hope not......

Originally posted by skiericski

Scavenging in four strokes is critical for making real power! Way more that 1%, anyhow.

Seriously, how much power? We've had some discussions on this BB about the subject. I don't have any books/references at my desk......

[J. Edlund]

Originally posted by dosco
More thoughts on hi-temp barriers.....usually if something gets to 1700+F, the designers use "film cooling" where a thin "film" of cooler air is "blown" over the surface of a part....the film prevents heat transfer, yadda yadda. Used in turbine stator blades, rocket engines, etc etc.

For high temps a mix of air cooling, thermal barrier coatings and the latest superalloys are used. Turbine blades have internal ducts which are fed with air from the compressor, holes allow air to leak out on the surface of the blades. The surface air and coating reduce the heat transfer to the blades and the internal cooling keeps the temperature down. A believe temps of 1500 degC or so is possible with this, much higher than the melting point of the metal.

Air films do also protect the internal parts of a internal combustion chamber, the vibration caused by knocking can "remove" this film and therefore knocking can melt holes in pistons, for example.

[Scoots]

Originally posted by dosco
Seriously, how much power? We've had some discussions on this BB about the subject. I don't have any books/references at my desk......

It's not uncommon to get 2% just by replacing a fine factory cat-back exhaust with a freer flowing one ... replacing rough cast manifolds with tuned headers makes an even bigger difference.

Here's a brief explanation written by an engineer friend who works for Garret.

http://vishnutuning.com/exhaust101.htm

[Greg Locock]

Neat article, but as he points out the requirements for an NA exhaust are the OPPOSITE of those for a turbo exhaust (where, obviously there are advantages in keeping the exhaust hot).

I have seen no evidence that retaining heat in the exhaust for an NA engine gives a power boost, other than by reducing the heat load in the engine bay. That's what I'm looking for, and surely, what this thread is mainly concerned with. I've done a check on the SAE papers using the search terms exhaust and coating, and cannot find anything that talks about power gains in NA engines. 940312 looks vaguely relevant, but the abstract only discusses heat load, so I'm not buying it. 968299 sounds more promising, but the abstract does not say whether it is talking about turbos. I've ordered that one.

I'd even be prepared to argue that heat loss via the exhaust pipe might even be beneficial, since it will not affect the gas' momentum near the valve, but will reduce the volumetric flow rate further downstream, reducing back pressure.

[Scoots]

Originally posted by Greg Locock
Neat article, but as he points out the requirements for an NA exhaust are the OPPOSITE of those for a turbo exhaust (where, obviously there are advantages in keeping the exhaust hot).

I have seen no evidence that retaining heat in the exhaust for an NA engine gives a power boost, other than by reducing the heat load in the engine bay. That's what I'm looking for, and surely, what this thread is mainly concerned with. I've done a check on the SAE papers using the search terms exhaust and coating, and cannot find anything that talks about power gains in NA engines. 940312 looks vaguely relevant, but the abstract only discusses heat load, so I'm not buying it. 968299 sounds more promising, but the abstract does not say whether it is talking about turbos. I've ordered that one.

I'd even be prepared to argue that heat loss via the exhaust pipe might even be beneficial, since it will not affect the gas' momentum near the valve, but will reduce the volumetric flow rate further downstream, reducing back pressure.

I mostly deal with turbos so I know less about NA exhaust, but it seems to me that other that heat in the engine bay, if the exhaust is designed with the heat loss factored in then it would make little or no difference.

My street car had the wastegate dumping about 4 inches away from the turbo ... it sounds really nasty.

[Formulaben]

Originally posted by dosco


Really. In a 4-stroke engine?

Please elaborate.......

I believe the statement assumes valve overlap (race engine.)

[VAR1016]

Originally posted by Formulaben


I believe the statement assumes valve overlap (race engine.)

Not just in race engines; all four-strokes run with some overlap, race engines have more.

PdeRL

[Yelnats]

Originally posted by dosco


I hope not......



Seriously, how much power? We've had some discussions on this BB about the subject. I don't have any books/references at my desk......

It could be argued that exhaust scavenging and it's brethern, intake ram are the two most important tuning elements fo achieving competative power from a racing engine. Not only peak power but the overall power curve is stronly under the influence of these factors and as no racing engine in the last 4 decades has been designed without close attention to these factors, extraction being the most complicated to deal with, I don't see how one could answer your question other than to point out the differences obtained in production engines when tuned for racing which are in the order of 50%. Probably the majority of this gain being contributed to by exhaust extraction tuning.

[dosco]

Originally posted by Yelnats

It could be argued that exhaust scavenging and it's brethern, intake ram are the two most important tuning elements fo achieving competative power from a racing engine.

Hm. We were having a similar discussion on another thread, and I calculated the difference in isentropic stagnation pressure as increasing by 4% from 50 mph to 200 mph. Now I can see in F1 trying to extract that 4% increase in pressure....but it's still quite low, and I can't see that translating to large HP gains.

Now compare the 4% increase in pressure to 100% increase in a turbo application, and you can see that the gains in improvement (in NA application) is pretty low. Important in the long run yes, but really minimal overall.

Originally posted by Yelnats

I don't see how one could answer your question other than to point out the differences obtained in production engines when tuned for racing which are in the order of 50%. Probably the majority of this gain being contributed to by exhaust extraction tuning.

Also interesting....I was under the impression that the most gains to be had in exhaust scavenging were in 2 cycle engines....and that exhaust scavenging in 4 cycles would only yield limited performance improvements.

That's not to say that tuning both the intake and exhaust sides is irrelevant.....but it seems like
that "little bit" that only the F1 guys would have the time and money to optimize.

As far as comparing race engines to production engines.....I'd think that misleading. Are there any "production engines" with similar bore-to-stroke ratios? What about pneumatic valves?

Now, I can see comparing a stock Corvette engine to a Calloway-tuned version - and see the large gains in performance......aren't the HP gains a function of cam shape, compression ratio and spark timing?

[Scoots]

Originally posted by dosco


Hm. We were having a similar discussion on another thread, and I calculated the difference in isentropic stagnation pressure as increasing by 4% from 50 mph to 200 mph. Now I can see in F1 trying to extract that 4% increase in pressure....but it's still quite low, and I can't see that translating to large HP gains.

Now compare the 4% increase in pressure to 100% increase in a turbo application, and you can see that the gains in improvement (in NA application) is pretty low. Important in the long run yes, but really minimal overall.




Also interesting....I was under the impression that the most gains to be had in exhaust scavenging were in 2 cycle engines....and that exhaust scavenging in 4 cycles would only yield limited performance improvements.

That's not to say that tuning both the intake and exhaust sides is irrelevant.....but it seems like
that "little bit" that only the F1 guys would have the time and money to optimize.

As far as comparing race engines to production engines.....I'd think that misleading. Are there any "production engines" with similar bore-to-stroke ratios? What about pneumatic valves?

Now, I can see comparing a stock Corvette engine to a Calloway-tuned version - and see the large gains in performance......aren't the HP gains a function of cam shape, compression ratio and spark timing?

Club racers will work VERY hard to get .1% gain in hp, and tuned intake and exhaust (totally independant of head work and cams) can gain 10% on some engines that are otherwise stock. It really depends on where the restriction is on any particular setup, but add in porting and 20% isn't outragous on some engines. Cam timing is usually a smaller gain, then there is cam grind (lift and duration), injector timing/duration, spark timing, valve size, balancing, lightening components, knife-edging the crank, changing to a dry-sump oil system, going to more exotic materials ... all of those individually will likely yield less performance increase than optimising the intake and exhaust.

Now, do all that, lower the compression, run on 110 octane fuel and add a turbo and we can talk power

[richdubbya]

Getting back to the original question here, i think that header coatings help in two ways. one is that they transfer less heat to the under hood air in production based race cars, thus transfering less heat to their intake systems. the second is that they smooth the surface (especially welds) on the inside of the pipes, even high quality drag type headers have mandrel scratches and rough welds inside. i think these welds can set up wave pulses (even if very weak) that can have some detrimental effect. in f-1 i dont think pipe outside temp is an issue and the amount of money spent on manufacture allows smoother welds and the shortness of the system allow the welds to be further touched up (im just guessing here, but if i were building them they would be honed inside somehow). as far as the exhaust gas temp being lost into the pipes or not has no effect on the power output as long as the pipes are sized right, ie a theoretical system with 100% efficient insulating coating would require slightly larger piping as you got farther from the valve for the slightly larger exaust volume, and maybe a slight length change for the exaust temp change but when both systems were optimized power would remain the same. i think this is also why some are really sold on coatings, if an exhaust system is sized a little large, coating will bring this system closer to being optimized, especially on a long 7k to 9k rpm system that is only ran at temp for 6 or 7 seconds. during an engine development stage, every header change would have to be sent out and coated, plus im not sure how uniform and repeatable the coating process is. you coating guys could answer that. anyways thats my 2 cents.

[dosco]

Originally posted by richdubbya
Getting back to the original question here, i think that header coatings help in two ways.

the second is that they smooth the surface (especially welds) on the inside of the pipes, even high quality drag type headers have mandrel scratches and rough welds inside. i think these welds can set up wave pulses (even if very weak) that can have some detrimental effect. in f-1 i dont think pipe outside temp is an issue and the amount of money spent on manufacture allows smoother welds and the shortness of the system allow the welds to be further touched up (im just guessing here, but if i were building them they would be honed inside somehow).

I thought we were talking about ceramic coatings here? The outside of the pipe is where the TBC is applied, not the inside .

Besides, on a properly welded duct, the weld re-enforcement is maybe .030 inch above the surface of the tube, well inside the boudary layer of the gas flow. The change in direction of the flow causes more drag/turbulence than the weld does (granted, in a properly welded unit......most welds I've seen on products out there are crap, so the drop-through becomes 'higher').

I'll see if I can get my hands on some duct CFD......

[red300zx99]

We coat the inside of pipes for those we like, and the illusion to those we don't

[richdubbya]

The sonic waves travel along the pipe, arent affected by boundry layers or bends like air flow is, i know from years of 2 stroke tuning, poor welds can make a big difference in 2 stroke power, as can too thin wall of pipe that will absorb some of the energy, granted two stroke waves are much stronger and more important. Take a look inside a $500 merged collector and see what it looks like. Seems to me an insulating coating on just the outside would melt the pipes, but thats just speculation.

[red300zx99]

Anyone got a pic of one of those high dollar merge collectors?

[richdubbya]

http://f1.pg.photos....m&.dnm=60f6.jpg






sorry it's not a very good picture red300zx99

The finish inside is polished similar to an exhaust port.


Richard

[dosco]

Originally posted by richdubbya
The sonic waves travel along the pipe, arent affected by boundry layers or bends like air flow is, i know from years of 2 stroke tuning, poor welds can make a big difference in 2 stroke power, as can too thin wall of pipe that will absorb some of the energy, granted two stroke waves are much stronger and more important. Take a look inside a $500 merged collector and see what it looks like. Seems to me an insulating coating on just the outside would melt the pipes, but thats just speculation.

There is substantial gas flow through the exhaust (esp in F1). So there are other considerations besides the "wave tuning" - like mass flow rate, B/L thickness, etc etc.

And I would have to disagree with your assertion that the sonic waves are not affected by the B/L - I suspect that both the sonic wave tuning and the mass flow rates are highly dependent on boundary layer thickness, turbulence, etc. (admittedly a SWAG on my part, though).

Lastly, why would an insulating coating on the outside cause the pipes to melt? The melting point of Inconel 718 (from which I understand F1 exhaust pipes are fabricated from) is roughly 2300 degrees F.....

[richdubbya]

originally posted by dosco: There is substantial gas flow through the exhaust (esp in F1). So there are other considerations besides the "wave tuning" - like mass flow rate, B/L thickness, etc etc


i agree completely, i just said that rough welds protruding into the inside of a pipe could set up weak sonic waves that could cause a small detrimental effect, not that that was the only consideration.


one note on boundry layers, some say that surface finish and small protrusions dont matter because of this "boundry layer". I think you will find that if you use up all or part of the boundry layer with these things that dont matter you will find a boundry layer on top of them. And if you use up that one with things that dont matter...........................................


i dont know what material is used in f-1, or what the exhasust gas temps are (ive seen combustion temps said to be 1800f I would guess the exhaust temp is less) ive seen a picture of an f-1 engine on the dyno with the pipes glowing bright orange with ducted air directed at them, the melting thing was just speculation like i said.


i'm not an engineer, just someone that has been in racing for a long time and during that time ive read many different articles on exhaust wave tuning, and i have had practical experience with it and i believe the waves travel along the surface of the pipe. The whole principal of anti reversion devices is based on this. The wave reverses and returns at the end of the pipe, not somewhere in the atmosphere where the mass flow is diffused. I'm just giving my opinion on coatings not saying that smooth exhaust pipes are the only key to power. I do know that at the highest levels of racing where every possible gain has to be realized for success you will find smooth pipes.

[dosco]

Originally posted by richdubbya

i agree completely, i just said that rough welds protruding into the inside of a pipe could set up weak sonic waves that could cause a small detrimental effect, not that that was the only consideration.

one note on boundry layers, some say that surface finish and small protrusions dont matter because of this "boundry layer". I think you will find that if you use up all or part of the boundry layer with these things that dont matter you will find a boundry layer on top of them. And if you use up that one with things that dont matter...........................................

Yes, bad welds would definitely be problematic. And considering the fact that most of the welded products available on the market that I have seen have marginal welds........

Yes, a B/L will form over a crappy weld, but generally speaking, in a duct application, the boudary layer is generally very thick....only the flow along the centerline of the duct is at maximum velocity.

With that in mind, the B/L varies with flow velocity and temp, so I'm not sure what it would look like in an F1 exhaust.....

Originally posted by richdubbya

...the melting thing was just speculation like i said.

I'm just giving my opinion on coatings not saying that smooth exhaust pipes are the only key to power. I do know that at the highest levels of racing where every possible gain has to be realized for success you will find smooth pipes.

As far as melting, I was only pointing out the fact that generally speaking, the upper echelons of racing use refractory alloys that easily stand up to the heat.

As far as coatings, I could see a small section of the exhaust manifold, right at the cylinder head, having an internal ceramic coating for heat resistance.....of course, I'd question the ability of the TBC to stand up to the acoustic pressure of the exhaust pulses - but that's another consideration altogether.

OTOH, external TBC ont eh exhaust pipes makes sense to preclude bodywork overheating (did Kimi's car meltdown this morning in Bahrain, or was it another engine failure?).