Boosting the efficiency of a tubocharger
 

Has any one with a turbocharged tried wraping the exhaust to make sure more heat gets to the turbo?
Since a turbocharger is a heat engine just like all the other thermodynamic cycles it needs heat, wraping the exhaust will keep the heat in.
Mainly I would like to know if any one has tried this on a turbo diesel.

It would work a little, but the gains would be small as heat rejection through the manifold is small compared to the total energy of the exhaust gas.

Also it would be risky if maximum pre-turbine temperatures exceeded the maximum limits (typically atound 720°C for non-water cooled small passenger car turbos) when towing or driving hard for example.
But if you never drive hard or tow up mountains etc then you should be safe.

It all adds up, and with a modern VNT turbo the small gains in energy driving the turbine wheel may well result in lower pre-turbine pressure as the vanes would be open more for the same boost. This would have a knock on effect with lower pumping losses.

I am going to be running a Holest HE351VE VGT (aka VNT) out of a 2007+ cummins diesel in my 6.5L chevy diesel truck. EGT will be limited to apeak of 1250'F. Normal operational temperature is under 900'F.
In an IDI diesel if you hit 720'C you will need a new engine.
That holset unit has water cooling and I will be using it.
I will also be running an intercool and water mist injection.
On a lot of V8 diesels you have a cross over pipe, it makes a big "U" turn that goes from one exhaust manifold to the other. I think that is where there will be a lot of heat loss.
I was considering exhaust wrap for 3 reason really.
1 to spool the turbo faster in the cold and hopefully make it over all more efficient.
2 keep the exhaust hot to keep soot and gunk from building up on the vanes in the turbine housing.
3 keep the added piping from cooking items under the hood.

Its mostly all right here:
http://ecomodder.com/forum/showthrea...uck-18187.html

#3 is the reason why most people do it... you do get a slight boost in efficiency from getting more heat to the turbine side of the turbo- but you're probably not going to notice the difference.

If you want to maintain boost while light load cruising, then something like this could be effective. But if you got a VGT, then why?

Wrapping a steel exhaust pipe will usually cause it to rust much faster and can induce heat cracks.

I am going to pick up a 304 stainless cross over pipe from Heath diesel for $100 ($20 over the cost of a regular steel pipe). So rust and cracking wont be a problem.
The rest of the system is cast iron exhaust manifolds and the turbo charger.
I am adding a turbo to an originally non turbo vehicle so I get to decide the charistics of every nut, bolt and pipe going into it.
Plus I have an oil and water proof exhaust pipe cover. The only way I can discribe it is if some one were to take a 4 foot long fiber glass sock and coated it with high temperature orange RTV. Its not hand made and I don't know who makes this item because I salvaged it out of a scrap metal pile off from a flexable exhaust pipe that had the ends rusted off it.
I got the feeling that I would be able to use it some day as soon as I saw it.
I also have a good size collection of mostly free used exhaust wrap.

I do not see wrapping the pipe before the turbo to be worth the trouble unless you want to keep other things cooler. Hotter exhaust does move faster but it also heats the air entering the engine more and if to hot that can hurt the performance of the engine.

I would not consider a turbo a heat engine but more of a water wheel (air is a fluid). Hot exhaust moves faster than if it was cool but cooler exhaust is more dense allowing for it to have more force. The issue is where the crossover point is between the two. Going back to the water wheel idea think of it like this powering it with a 1/4" hose at 60psi or powering it with a 1/2" hose at 30psi you can get the same amount of work completed. If you can get more pressure or more water out of a setup between the two you will have a gain in performance. (For reference size of hose is in relation to density and psi is to speed.)

I do not have any clue how to calculate the change in density of the exhaust in relation to the change in speed of the gas and its ability to do work.

One thing I will recommend is to keep the exhaust temp up after the turbo so it does not slow causing back pressure.

Actually a turbine is a heat engine to some degree. Power extracted is proportional to the square root of the gas temperature entering it. So increasing the exhaust temp a little going into it isn't going to get you much. Phantom is correct however that power extracted is directly proportional to mass.

...taking a paraphrasing from realestate: "...INTERCOOLER, INTERCOOLER, INTERCOOLER!"

Yes I am stuffing as much over sized intercooler as I can in there, plus water mist injection.
I want to see what happens if I can get the pressurized air very near or below the out side temperature when under load.