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  #1  
Old 11-26-2005, 04:39 PM
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Default Turbo 101

Quote:
Originally Posted by rv6ejguy
Longevity of the turbo is related to basically five things rotational speed, proper lubrication, proper air filtration, not operating in the surge zone and limiting maximum turbine inlet temperature. If you can accomplish all five, the turbo should outlast the engine.

It is critical with Wankels to avoid TITs in excess of 1600-1650F when using Inconel wheels and standard nickel/ iron turbine housings. They just won't last long above these temps.

Higher temp $$$ solutions are available. Ni-resist, 321 stainless or inconel turbine housings are available for some brands and MAR-M247 turbine wheels are available also extending the max TIT to about 1800-2000F.

Turbine rear bearing and C ring seal failures are usually caused by lubrication, overtemp and/or overspeed conditions.

As a general rule, people who don't understand turbos fear them, both in the dyno room and on the track. Turbos are far more reliable than superchargers when properly engineered in my view. How many diesels are fitted with superchargers today?
next is the turbo install. the best materials are inconel and hastiloy, not sure which is better, but they are both very expensive. after that is 321 Stainless.

If 321 or for that matter, other Stainless steel is used

1 - the turbo must not be supported by it - it must be supported from brackets hung from the engine.

2 - slip fittings must be used between the engine and the turbo. the ss has a large expansion rate with heat and if the amount of expansion is not allowed for with slip fittings - the welds or maybe even the tubing will crack.

other materials will work, but they will not last as long or will be quite heavy. i am not sure if slip fittings must be used on cast iron manifolds
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  #2  
Old 11-27-2005, 12:04 PM
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Quote:
slip fittings must be used between the engine and the turbo
I asked rv6ejguy about this. If I'm paraphrasing his PM correctly, slip joints are only needed (or possible) if you have long manifold pipes, as Dust does. (25 inches, or so I'm told )

For those of us with short (manifold) pipes, the expansion isnt enough to warrant using slip joints, and there isnt room to put them in anyway.
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Old 11-28-2005, 10:37 AM
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Slip joint - takes NO room. it is just a male into female fit between two pipes with the male fitting on the side that the exhaust is coming from and the other pipe is expanded to take the feeding pipe into. No clamp is used and the male pipe in not completely inserted - room is left for expansion. no exhaust gasses or noise will escape as the pipes seal themselves when heated

SS has a large expansion with temp, the extra pipe must have somewhere to go or it will have to bend or bend the mounting bracket of the turbo. This repeated expansion and contraction can cause welds, bolts or brackets to break, with time. I imagine that rv6jguy said it may not be needed or something similar.

8 inches will still expand, altho about 1/3 less than my 21 inches will. My original factory exhaust was slip fitted between each cylinder - 6.25 inches.

on the engine side of things - with a cast mount expansion must also be considered - the center bolt holes can have a tight fit, but the bolt holes to the right and left of them must be elongated or overly large to allow for the cast manifold to expand with temp - otherwise the studs or bolts can be sheared off.

the temps that we are dealing with in turbo applications are very high - i'm looking at 1400 F continuous - i think you may be looking at 1600 F or more with the rotary

I'll let the engineers among us calculate how much say a 8 inch 321 SS 2" diameter 16 gauge pipe will elongate, if any feel so inclined
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Old 11-30-2005, 09:48 PM
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ok - looks like johns exhaust will be 4 or so inches - you are right - no room for slip joint.

on the main failure mode you are now looking at and so will everyone who chooses to turbo a rotary - HEAT.

The exhaust gasses in a rotary are a higher temp than a piston engine and the turbo can only take so much heat. From what i have been told - about 1700 F or so continuous. this means that the EGT's will have to be closely watched and the engine tuned to run rich enough to keep egt's to around 1650 F or below.

the temps in a piston are lower, i think if you let them get that high - you wouldn't have to worry about the turbo blowing up - there would not be an engine running to blow the engine.

This is all adding up - if you do not know to keep the rotary egt temps in line then you are going to blow it up and from what i have read - this was not covered in any of the few books and many articles i have read as for the normal ground based turbo application, those temps would never be reached.

thanks rv6jguy for the education.
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Old 11-30-2005, 11:48 PM
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Quote:
you are right - no room for slip joint.
Just leave Dust alone and he argues with himself. This is much easier.

I'll be adding a TIT (turbo intake temp) thermocouple. Might even add 2 - one for each rotor.

I called agp today and added ceramic coating of the turbine housing to my order. Another $75 seemed well worth it. This will help keep the radiated heat down inside the cowl.

Bob's generously donated stock turbo arrived today. I'll try to get it installed tomorrow and at least do an oil flow test.
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Old 12-01-2005, 02:24 AM
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John Slade
Quote:
snipped ...
I called agp today and added ceramic coating of the turbine housing to my order. Another $75 seemed well worth it. This will help keep the radiated heat down inside the cowl.
snipped ...
John, I'm afraid that wasn't a very good idea. Common sense would dictate shedding heat not containing it, as a ceramic coating would do. Your turbo may work 24/7 in a Cummins DIESEL with its relatively cool EGTs and survive a couple of hours in a rotary. Please consider my idea of placing the turbo farther away from the engine to reduce TITs.
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Old 12-01-2005, 07:24 AM
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Hmmm. Good point. This may also be a reason for the big heavy cast iron manifold. Then again - the ceramic coating may cause heat to be expelled in the exhaust rather than retained in the turbine housing.

Anyone else have thoughts or experience on this?
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Old 12-01-2005, 08:13 AM
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Seen turbos on dynos and race cars for a long time. Not seen ceramic coated. Mostly seen turbos tucked somewhat away from block with LOTS of intercooler pipe.
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  #9  
Old 12-01-2005, 08:45 AM
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We often ceramic coat the turbine housing to reduce radiated heat and keep it looking nice. This does not reduce TIT. We have found that the high temp ceramic coatings seem to stay on the housings fine but peel off 321 stainless well below their "guaranteed" temperature ratings. May have something to do with SSs high thermal expansion coefficient. You don't need anything on ss headers. Never wrap pimary turbo tubes with blanket type materials, the pipes will fail in short order. Bad news when a red hot turbo falls off into the bottom of your cowling.

I think for longevity on the Wankel or piston engine for that matter, you must keep TIT below 1650F period, somehow, either with longer tubing runs, richer mixtures or ignition timing alterations. It should be noted that dropping the charge temps through effective intercooling does drop the EGT/TITs as well. Don't skimp here as this can create a vicious circle of increasing oil temps, coolant temps, CHTs and reduced pre-ignition limits.
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Old 12-01-2005, 09:35 AM
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Quote:
This does not reduce TIT
But does it increase it?
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Old 12-01-2005, 10:12 AM
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Quote:
Originally Posted by John Slade
Just leave Dust alone and he argues with himself. This is much easier.
heh heh heh - you said 8 inches - found out it is more like 4 inches. on the temps, thought i remembered 1650 F - you said 1750 F

mmmmm - no wrapping primary turbo tubes - how do i stop the three methods of heat transfer from destroying my cowling innards, they will be red hot and that red hot will radiate, convect and ??(always forget the third one) and harm everything.

I can handle the convection, but the radiation - if it can be seen by something - that something will be destroyed. Dam - what is the third one. Oh year - conduction, i can handle that also with out wrap, its the radiation that i thought i needed the wrap for.
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Old 12-01-2005, 10:24 AM
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Quote:
you said 8 inches - found out it is more like 4 inches
Now.... where have I heard that before???
Quote:
its the radiation that i thought i needed the wrap for.
How about the "distance wrap" approach? My turbo and exhaust are surrounded by a 6 - 8 inch diameter stainless shield with an air gap between. This gives you two things - much reduced radiation in the cowl and, as a bonus, you can use it for exhaust augmentation. (ie sucking cool air through the heat exchangers). Finally the cooler air mixes with the hot exhaust and helps protect the prop.
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Old 12-01-2005, 10:33 AM
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Equal length headers - just wait till you see em - i am almost able to picture them in my mind. waiting for 2.5 radius mandrel bent mile steel tubes to figure it out with.

I am planning on augmentation, just don't wee a way to ALSO squeeze stand off SS shield on them
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Old 12-01-2005, 12:09 PM
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Ceramic coating the turbine housing ( inside and out) likely reduces actual temperatures that the rear bearing sees by reducing conduction rates to the rear end of the bearing housing and slightly increases the temps that the turbine wheel sees so some good and some bad. The typical Inconel wheels used are safe up to 1800F. I think coating the turbine housing is worthwhile.

A SS heat shield stood off from the hot parts 1/2 to 1.5 inches is highly effective in reducing IR radiation and doesn't harm the pipe like direct wrapping.

Heat shields are very important. If you have ever done dyno runs on turbos engines at WOT, you will appreciate the amount of IR coming off the piping and T housing. You can feel it feet away on your face.

We ran an L16 Nissan engine with an external wastegate one day, everything was cherry red and we had shock diamonds coming out of the WG pipe under boost. Way
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Old 12-01-2005, 12:31 PM
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dam dam dam - heat shield it is then
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