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Insulating turbo pipes?

 
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lordam  



Joined: 31 Dec 2002
Posts: 45
Location: Perth, Western Australia

PostPosted: Thu Oct 07, 2004 1:09 am    Post subject: Insulating turbo pipes? Reply with quote

In an attempt to keep temperatures under the 931 bonnet reasonable, I have insulated the exhaust manifold, wrapped the J pipe and the exhaust pipe from the turbo.

Then I read the comment by iidi9xx .....
"Many people think of a turbo as a wind blown turbine, but only about 25% of its energy is from it being propelled by exhaust gasses, the other 75% is gained from a thermodynamic effect of high pressure hot gasses entering the exhaust turbine, which cool and contract as they exit the turbine into a lower pressure environment (the turbine outlet and exhaust system). "

Does that mean that this insulation will reduce the power output of the engine?

Conversey, does it mean that we should put a strong draft of cold air from the front of the car past the turbo to cool the exhaust pipes?

Guess I am just confused!

John
931 (on stands)
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Smoothie  



Joined: 01 Jan 2003
Posts: 8030
Location: DE (the one near MD, PA, NJ)

PostPosted: Thu Oct 07, 2004 7:17 am    Post subject: Reply with quote

From what I've read, exhaust and turbo wrapping give a useful performance advantage in racing. In street use it causes too many problems in exchange for the performace improvement. Parts oxidize much quicker and also expand more which causes problems if the expanded parts don't have enough room to expand. -So it shouldn't give you a performance problem. Air doesn't have to be cooled by the turbo on its' way out for the turbo to operate efficiently - apparently they are somewhat more efficient when insulated. -Ok for racing where engines are worked on all the time, but not good for street use where you want everything to last as long as possible.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox
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Paul  



Joined: 02 Nov 2002
Posts: 9414
Location: Southeast Wisconsin

PostPosted: Thu Oct 07, 2004 9:23 am    Post subject: Reply with quote

Insulating the J pipe and the pipes after the turbo will not effect power in any way.

Insulating the manifold and turbo hot section will increase the power available to spin the compressor.

Basically a turbo converts heat into mechanical energy which is used to run the compressor side of the turbo. The more heat in, the more power available to spin the compressor (until it melts!!!)

That said, it will only make boost come up sooner and make it hit the wastegate release quicker.

Since the wastegate determines the maximum amount of boost, no additional power will be made by the motor.
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numbbers  



Joined: 05 Nov 2002
Posts: 1910
Location: Highlands Ranch, Colorado

PostPosted: Thu Oct 07, 2004 10:37 am    Post subject: Reply with quote

I agree that wraping the manifold, and the turbo will help spin-up slightly, but it has been posted on this forum before, that the extra heat retention will also cause cracking in the manifold and turbo. Since this is already a problem with these cars, I have been reluctant to try it. Keep us posted on your experience.
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goturbo  



Joined: 15 Jun 2004
Posts: 87
Location: Massillon Ohio, USA

PostPosted: Thu Oct 07, 2004 2:21 pm    Post subject: Reply with quote

I'm with these guys. Everyone that I have known (myself included) that has wrapped headers/exhaust manifolds has had problems with cracking and decomposition. It is a forgone conclusion in the racing community that the wrapped pipes will last a short time but in that world people are willing to sacrifice those parts for extra power. Since the run is so short to the turbo on these cars the net effect will be negligible-and like numbbers said these manifolds have a history of cracking on their own. Unless you're really pushing the envelope it might not be worth having to replace the manifold every year...
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Kenodog  



Joined: 25 Jun 2003
Posts: 2580
Location: Vancouver,B.C.

PostPosted: Thu Oct 07, 2004 3:18 pm    Post subject: Reply with quote

When I rebuilt my engine I had a friend weld all cracks in the mani and then I Magnafluxed it to make sure it had no cracks.He then sprayed it with a tungsten ceramic coating to protect it against corrosion.I then wrapped it and the turbo hot-side in insulating tape.So far as far as I can tell it hasn't re-cracked.Some bolts came loose but I think that is normal.The actual pipes coming off of the turbo and the J pipe are made from stainless steel as is the rest of the exhaust so corrosion will not be an issue for them no matter how much heat the engine puts off.The manifold and hot-side however are prone to cracking in a normal driving routine so I imagine that insulating them will somewhat shorten their life spans but how many times have people posted the BIG "?" of how to get more muscle from these cars without spending 1000s of dollars?I think the trade off is well worth any possible future replacing of the hot-side or having the ex mani welded again.JMHO,but with the boost to 10 she goes baby,proof positive?Oh,and if you wanted cheap,you shoulda' bought a Kia.
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1981 931, Sabine
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2016 DR650
2019 KTM 790 Adventure
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goturbo  



Joined: 15 Jun 2004
Posts: 87
Location: Massillon Ohio, USA

PostPosted: Fri Oct 08, 2004 8:05 am    Post subject: Reply with quote

Kendog you are right, ceramic coating will prolong the life of the manifold but unless you use Electron Deposition Coating ($$$$$$$) the coating will break down and fail if wrapped-even it it is not wrapped for us turbo folks. When the metal is heated and cooled in such a degree as the turbo manifold, the material changes phases and that is the reason for decomposition. In other words rewelding again might not be possible. I have seen wrapped manifolds and headers fall apart when they were removed due to the presence of a 'crack'. The fact is that it is a fractional increase in torque/power that is directly related to the overall level of tuning done to the engine. I am not trying to discredit wraping don't get me wrong I am all about maximum preformance, but for someone who is going to build a 225HP true daily driver the added risks/headaches of wrapping -IMHO- are not worth it . With that said, for an occasional driver go for it! Chances are that if it is an occasional driver you can spend all winter tinkering and fixin, plus the total number of heat cycles that it takes to break down the manifold will be less given occasional use so it will last a couple of years at least.

I think that the 25/75 figures given are a bit misleading I need to dig up some of my old work to check...
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numbbers  



Joined: 05 Nov 2002
Posts: 1910
Location: Highlands Ranch, Colorado

PostPosted: Fri Oct 08, 2004 11:38 am    Post subject: Reply with quote

So Keno, do you feel like you got a noticable change in spin-up time?
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Kenodog  



Joined: 25 Jun 2003
Posts: 2580
Location: Vancouver,B.C.

PostPosted: Mon Oct 11, 2004 3:40 am    Post subject: Reply with quote

It's hard to say because iv'e done other things to it as well.The turbo was rebuilt with a new hot side housing and rotor so i'm sure that helps.Also with the two stage boost controller,best power adding fun tool for the money,it has a ball bearing/spring combo in the control line bleed off fitting so my boost comes on around 2000 rpm instead of 3000.With everything else that's been done ,like most of you the list is damned near endless,like gapless rings,cold air intake,o-ringed head,3 angle valve grind with new valves and springs,and on and on....The wrap does for sure keep the underhood temps alittle lower and it allows the manifold and housing to COOL OFF WAY SLOWER which as you all know is A VERY GOOD THING to help control cracking especially in cast iron.I've put around 7000 miles on the engine since the O/H and was under the car last weekend looking for leaks and tightening exhaust bolts and the coating on the manifold is fine,it should be it's supposed to be used for building up the exhaust flanges on a gas turbine engine.It can for sure take what little heat by comparison my car puts off.
I'm sure the car has more power than when it was new,and it's definitly lighter so yea I like it.I will have it dyno'd but first I want to finish installing the intercooler,LSD and an MSD btm box.Then i'll hold my breath and see if all the effort was worth it.One thing for sure though,when I drive it I love it.Awsome acceleration,awsome handling.
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1979 Euro 931, Olive
1981 931, Sabine
2014 Mazda CX-5 (Kinderwagon)
2008 GS500
2016 DR650
2019 KTM 790 Adventure
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goturbo  



Joined: 15 Jun 2004
Posts: 87
Location: Massillon Ohio, USA

PostPosted: Wed Oct 13, 2004 9:12 am    Post subject: Reply with quote

kenodog has got the goodies!!! Sure sounds to me like it would be a fun ride! Just a couple of Q's if you don't mind... when you say 'replaced the hot side and rotor' do you mean repalced with new stock parts -or- upgraded with some other part that has been sprinkled with some go fast pixie dust-if you know what I mean. The two stage boost controller is a nice touch, who's did you use? Why MSD BTM, just curious.

And if you could entertain just one more...

...its a biggie...


...WHERE YA GONNA PUT THE INTERCOOLER!?!?...

I have decided (after reading probably hundreds of posts on this site regarding the IC location) to go with the more conventional top mounted IC setup. The car goes in the garage this week for the big 'overhaul'
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Kenodog  



Joined: 25 Jun 2003
Posts: 2580
Location: Vancouver,B.C.

PostPosted: Mon Oct 18, 2004 9:11 am    Post subject: Reply with quote

The hot side housing and rotor were new stock parts.The two stage boost controller is by an Australian company called TurboSmart.Great product.The MSD btm because 1)It has the option of adding a knock sensor,2) It has the option of adding a high output coil,3) It has an adjustable rev limiter,4) It has an adjustable in-cockpit timing retard dial so if I use it in conjunction with my adjustable cam gear I can have the timing advanced manually on the gear for better "off the line"power but as RPMs build,and boost with it,the MSD will automatically retard timing up to 3 degrees for each pound of boost for better top end power.In theory this should widen the power band considerably while greatly reducing any chance of detonation.Coupled with the intercooler and LSD and i'll see you later.In theory anyways.
Oh and the intercooler is going in the battery box.I've already moved the batt to the rear of the car and preped the tray for the ic install.I can always buy some bags of ice and fill the tray up around the ic for some serious cooling.....or add an alcohol injection fitting to the cool side of the ic for more cooling or........where will it end,argh....
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1979 Euro 931, Olive
1981 931, Sabine
2014 Mazda CX-5 (Kinderwagon)
2008 GS500
2016 DR650
2019 KTM 790 Adventure
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