Heat wrapping downpipe,yes or no

[loxxrider]

viscous forces on a gas are negligible and do not change an appreciable amount with changes in temperature

[driftin jo]

why do 3 inch exhausts work well on are cars ?? do you know what happens after the turbo when the gas enters a 3 inch exhaust as opposed to a 2.5 inch ??

what happens is the gas expands and as it does so it cools and slows down and the pressure drops and it flows more freely as it is less active , end of ****in story , feel free to carry on believing whatever you like , I really don't care any more .

[AndyP]

I can't remember enough from my thermofluid dynamics lectures to argue with any of you so I'm going to take the p**s!!

[driftin jo]

I can't remember enough from my thermofluid dynamics lectures to argue with any of you so I'm going to take the p**s!!

very funny

If I put a 5 inch exhaust on my car will it have a higher or lower gas speed than a 3 inch would have ? The answer is obviously lower , but this is a better exhaust as it flows more , not at a higher speed but a lower speed . Simple !

[Thuppu]

If you have big enough DP and exhaust it doesn't matter if you wrap it or not. Simple.

[driftin jo]

If you have big enough DP and exhaust it doesn't matter if you wrap it or not. Simple.

Correct,
getting back to the thread, if you have a 3” downpipe wrapping it will not cause any issues but wrapping the headers and turbo will raise your EGT , so if this is high anyway that would be the only caveat.

[QuattroFever]

very funny

If I put a 5 inch exhaust on my car will it have a higher or lower gas speed than a 3 inch would have ? The answer is obviously lower , but this is a better exhaust as it flows more , not at a higher speed but a lower speed . Simple !

Where are you going with this. The guy asked a question for his application and i gave a correct and no nonsense answer.
You turned it into some kind of pissing contest going into eventualities and theory, why?

Wrapping a 3" dp is not a problem and IS beneficial. How beneficial is negligable but its not a rubbished idea and certainly worthwhile if you cant fit a bigger exhaust.

You obviously didnt look into laminar flow either from your various responses otherwise you would know bigger is not always better, but whatever, im at a bbq and cant be arsed to hypothesize!

[[RPM]]

I tought that a heated metal would offer less resistance in terms of flow
so if i wraped would offer even less

[driftin jo]

Where are you going with this. The guy asked a question for his application and i gave a correct and no nonsense answer.
You turned it into some kind of pissing contest going into eventualities and theory, why?

Wrapping a 3" dp is not a problem and IS beneficial. How beneficial is negligable but its not a rubbished idea and certainly worthwhile if you cant fit a bigger exhaust.

You obviously didnt look into laminar flow either from your various responses otherwise you would know bigger is not always better, but whatever, im at a bbq and cant be arsed to hypothesize!

The bigger isn't always better only applies to NA engines as keeping sufficient gas velocity assists with the scavenging effect . This does not apply to turbo charged engines.

I have read many things from people claiming you can go too big even on a turbo engine and so on .

I have been in various engineering jobs over the last 25 years one of which was working for a company that made all the bearings, a lot of comp wheels, shafts and turbines for Garrett.
I have spent many hours talking to Garrett engineers and as a keen petrol head I have picked there brains on many things that were not related to what I was doing for them .
To quote a Garrett engineer
“There is obviously a point of diminishing returns in an exhaust system size but post turbine you want the least restriction possible. A turbine works on pressure ratios, pre turbine and post turbine, as you lower the post turbine pressure the ratio is greater so the faster the turbine will spool up , the lower the EGT and the more power achieved .
The absolute optimum from the back of a turbo would just be a open to atmosphere or a big megaphone about 1 foot long strait to atmosphere if you really want ".

Also, as you would see if you read my last post , I did not say that wrapping the exhaust wasn't worth wile just not for the reasons of gas flow.

[UUUdirs2newcastle]

Did I mention that I now have a AAS Full 3" Stainless and System now? Oh it's lovely! :-)

[5banger]

hot pipe walls def keep the exhaust efficient. colder air on inside walls is not good. thermal wrap is worth it.

[5banger]

I tought that a heated metal would offer less resistance in terms of flow
so if i wraped would offer even less

http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

[QuattroFever]

This is wandering from the original subject and title and the whole point in what I said in the first place.

The absolute optimum from the back of a turbo would just be a open to atmosphere or a big megaphone about 1 foot long strait to atmosphere if you really want ".

I agree. I never said earlier that a 1" pipe with a high velocity would be better than a 3" low velocity. Thats just madness and way off the title of this thread. He said he had a 3" pipe and thats what I based my answer on.

Also, as you would see if you read my last post , I did not say that wrapping the exhaust wasn't worth wile just not for the reasons of gas flow.

so are you saying to this guy that wrapping his exhaust will not affect his gas flow and therefore not give him any gains?

[s2_wot]

If the reason for wrapping the DP is to lower the temperature in the engine bay and if wrapping the pipe is going to reduce the effectiveness of the exhaust system, would the solution not be to have some fins welded onto the downpipe. By doing so the surface area would be massively increased and thus help in transferring the heat to the air in the surrounding areas. Better heat transfer would mean you could ger rid of more of the heat rather than allowing it to dwell.

And sorry for the off topic but which DP material has the highest specific heat capacity?

[driftin jo]

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

You think the numpty that rote this article knows more about turbos than an engineer form Garrett ?
If so you keep thinking that