wrap for exhast misleading?

[6bangerwanab]

exaust wrap- and turbo heat wraps seem to me to be misleading, i understand that these wraps help lower underhood temps, but seems as is it would direct more heat to the turbo (in a turbo application of course) which is exactly where we dont want the heat do you think that the header wrap is a good idea for turbos, or is it all just hot air?

 

[xctasy]

It varies between application.

On non-cross flow MG B-series engines, it appears to reduce power, and cause problems with exhast valve failure.

On turbo's it seams to help.

The heat is dispensed by vibrating molecules (convection). You've got to ask where the heat goes when the exhast manifold is wrapped. If it doesn't soak back into the exhast valves or combustion chambers, then its all good. In non-cross flow engines, it may just releflect it back to the intake (by convection through iron and/or alloy) even if the air temperature is less in the engine bay.

Each exhast gas temperature (EGT's) needs to be tested with a pyrometer/ platinum resistance thermometer or temperature bridge linked to a gage, Fluke meter, volt meter or data logger. Then the engine needs to be tunned to suit. Adding thermal rap may help or hinder EGT's. When they go up beyond a certian level, they cause power to drop, and engines to pop!

 

[jwhoss76]

Well as I understand it header wrap helps keep the heat in the pipes which keeps the velocity of air high. If the exhaust cools then it slows down. On a turbo I'd have to say header wrap on the exhaust side would be a good idea since it'll keep the air moving fast. In theory at least LOL

 

[Anonymous]

Well, it's a great advertising gimmick if nothing else. It sounds so "scientific"! On turbo charged cars we avoid putting any thermal wrap on the turbo or exhaust manifold/header. It causes the manifold to warp--and that's a cast iron manifold. When EGTs are around 1500 degrees, how much hotter does the exhaust really need to be?

 

[StrangeRanger]

but seems as is it would direct more heat to the turbo (in a turbo application of course) which is exactly where we dont want the heat

Bad original assumption. Turbos thrive on heat. Heat is energy and the more eenergy you pour to the turbo the more boost it makes. You have oil and water cooling available to prevent damage to the bearings and seals.

Ceramic coatings are the answer to manifold heat. they insulate the manifold from the inside so they reduce warpage and keep the heat energy directed to the turbo where it will do the most good.

 

[Anonymous]

Strange Ranger has it right:
when I worked on industrial engines (the 2000+ HP type), we used up to 4 turbos on the bigger ones. When wrapped, the turbos created almost 11% more power than when they were open. The main problem we suffered was that the engine cleaning process sometimes damaged the wrapping, causing loss of turbo efficiency. In one particular (and very expensive) incident, one engine went out to the field with 2 adjacent turbos unwrapped (on the front of the engine). The engine broke the crankshaft in 2, almost mid-point. It was a V16 engine. The operator sat over the top of the engine in a little booth: he reported that is vibrated very severely prior to the breakdown which indicated quite positively how imbalanced the engine had become with the unequal turbos.

 

[6bangerwanab]

so basically it would be best to use good wrap on the exaust to keep heat to the turbos, but use oil coolers to keep the bearings and such in check, and use an intercooler on the outlet side so that hot air doesn't reach the engine, and use the ceramic coatings. but while going with that, wouldn't it be better to set the turbo as close to the engine as possible?

 

[jwhoss76]

That won't make any difference really, you see hot air moves faster that's why you want to keep the exhaust from cooling inside the pipe. Header wrap traps the heat in the pipe which helps keep the air flowing nice and fast Header wrap paint helps even more. Other than that you seem to have got a good grasp of it. Good luck-Hoss

 

[StrangeRanger]

Forget the header wrap. Just go with the ceramic; much cleaner and works better. You want the turbine inlet mounted as close as possible to the exhaust ports and the compressor outlet mounted as close as podible to the carb or T/B

 

[Lazy JW]

So after the exhaust has done its work and left the turbo, would it be desireable to lose heat or is it better to try to keep it contained in the pipe? It would seem that as it cools down on its way to the atmosphere that it will occupy less space and create less back pressure. It will also slow down, so I'm just curious as to what the dyno jockeys have found.
Joe

 

[Anonymous]

I was going to use some until I heard it corrodes your headers very quickly??? Anyone?

 

[Anonymous]

Header wrap is used more to protect the rest of the underhood parts from the heat that non-factory headers radiate. This is most notable with small block chevys and starter failure. However, in theory at least, the more heat (read energy) that stays in the pipes, the more power your turbo will put out.

 

[Anonymous]

I can't say that I've talked to them personally, but I've heard that Thermo-Tec recommends that you *do not* wrap headers with their product. As somebody already said, thermal wrap is mainly to protect other parts from exhaust heat, not to heat the exhaust.

Really, I think this is like trying to pick the fly crap out of the pepper shaker. If your exhaust is the proper size you aren't going to have any problems with gas flow.

 

[StrangeRanger]

It's not about gas flow, it's about getting maximum energy to the turbine so it spins the compressor up quicker and faster. Heat is energy. Any heat lost will degrade turbo performance. Exhaust gasses still approximately follow the the Ideal Gas Law P*V = N*R*T; lose T (temperature) and you must lose either pressure or volume.

Header wrap is often reported to increase corrosion of headers as well as causing warpage. In a properly built turbo header (i.e. sch 40 pipe) the corrosion issue is going to be less important than with normal 18 ga. headers simply because the greater wall thickness will take a lot longer to rust through. Header wrap is a messy solution, somewhat ineffective since it allows the header to absorb heat from the exhaust and it is far from zero maintenance. If you're going to sink a couple thousand dollars into a turbo project, why wouldn't you spend a couple of hundred more and pursue a more effective, more durable and more aesthetically pleasing solution? Ceramic coating is a far better way to go.

 

[Anonymous]

It's not about gas flow, it's about getting maximum energy to the turbine so it spins the compressor up quicker and faster. Heat is energy. Any heat lost will degrade turbo performance. Exhaust gasses still approximately follow the the Ideal Gas Law P*V = N*R*T; lose T (temperature) and you must lose either pressure or volume.

I see. I certainly wouldn't disagree with that, but depending on the turbo charged application, there are other factors that could change things. So far, we've only been considering the exhaust side of the turbo. As the turbo heats up the compressor becomes less efficient as it puts out hotter air. In a street/race vehicle application this is not good. Intercoolers help keep the charge temp down, but it will still be better if it starts out cooler, i.e., an uninsulated turbo. Isn't that why forced induction engines perform better in *colder* temps?

This is just for fun and interesting discussion. Obviously, we both agree that wrapping the turbo or manifold isn't the best way to handle things. I'm no engineer by any stretch of the imagination. I have a couple of turbo cars though!

 

[StrangeRanger]

The turbine (exhaust side of the turbo) does not share an airstream with the compressor (inlet side.) They are separated by a bearing block that is oil and usually water cooled. Running a hotter turbine does not necessarily mean running a hotter compressor. The compressor will however necessarily heat the air. When turbo manufacturers talk about adaibatic efficiency they are referring to that percentage of the work done by the turbo that adds flow/pressure. The inefficiency is heat. For a variety of reasons, an efficiency which even approaches 100% is not possible. Some percentage of that heat can be removed by intercooling, but that process is not related to exhaust heat. The down side of intercooling is that it increases the volume and mass of air caught between the compressor outlet and the throttle body/carb; this directly increases turbo lag. For low levels of boost intercooling really doesn't add much power and may not be worth the tradeoff in response; at higher boost levels it becomes more necessary and more beneficial.

 

[Anonymous]

I just finished porting my exhaust manifold and cleaning up the casting flash for a neater appearance. The exhaust manifold, J-pipe between the manifold and turbine, turbine housing and down-pipe will all be coated with a thermal barrier ceramic coating. Keeps the energy in the system and the heat out of the engine compartment.

Thermal wraps appear to be losers, unless they're the only way to reduce heat transfer to other components in an individual application. Although I've not experienced it, I've talked with folks who've had bad experiences--usually with headers. Besides, they look bad.

 

[Anonymous]

I would put it this way, the turbo has been engineered to withstand most of the temps and RPM's that a hi-output engine can put out. So putting header wrap on it isn't very likely to make much of an effect on the lifespan or durability as long as you have everything set up properly so that the oil doesn't coke on the turbo bearing surfaces.
and yes, what strangereanger said about heat, heat is wasted energy, so the more heat you keep in the manifold, the more energy you can direct at the turbine blades