royston

Can anyone shed some light on this problem. The maximum egt 2" from the exhaust ports has never exceeded 950 degree centigrade, yet the tips on the turbine wheel have started to melt. The turbo is a garrett gt42/51r with a .91 rear housing. Any ideas would be great, thanks.

Carl Byck

How rich are you? Maybe you are getting raw fuel on the turbine(very unlikely, but I think possible), and it is igniting there.. I know that some WRC cars have that happen when using fuel injected into the turbine for antilag. Seems very strange, that's 1742 *F right? Are you positive it is melting, as opposed to physical damage? WERD...

SPOautos

yea thats what I was wondering....maybe something went thru it and damaged it as opposed to melting. Was the turbo new when you bought it???

EFINI_RX-7_RZ

950 degree centigrade, isn´t that too hot? That´s, I believe, the turbo´s heat limit, if not over by 50 to 100 degrees. What octane fuel you running? A/F ratios? Timing?

fdracer

first of all your egt's are way too hot for a properly tuned car. however, a true gt turbo w/ an inconnel wheel still should not melt at that temp. if you have one of those cheap garrett type turbos, e.g. an e-bay turbo, it might not have an inconnel wheel.

BLUE TII

iTrader: (9)

From what I have read 950 is too hot for a turbo car under load- tune for 700 C.

Remeber, the EGT probe in the runner may be 950 C, but the tip of the turbine could be much hotter! The frictional forces alone of pushing that kind of volume of exhaust through the turbine will raise the teps at the surface.

Do a compression test to make sure the engine is still healthy. At elevated EGTs and with the backpressure of the turbo on the engine it is possible to warp apex seals as they can sag and flatside passing over the exhaust ports, it will sack out your springs, and can break cornerseals and sideseals as they expand too much.

The NA motors that regularly run that high EGT under load don't pose quite such a problem as there is little backpressure and no turbine to reflect the heat back at the engine.

Carl Byck

I agree that is too hot, but I've seen hotter on stock TII turbos, and no melted turbine. That said, a motor wil not last at those temps IMHO. Carl

royston

I'm running 1.5bar on uk 98octane fuel and aquamist 0.6mm nozzle water injection. Leading timing is 10 degree's with a 12 degree split at 1.5bar with a/f of 11.3-11.6. The turbine looks to me like it is slowly melting at the tips, can't see any evidence of any foreign objects hitting it. Thanks for the help so far.

RETed

950C is way too high, especially with the water injection in there?


-Ted

87GTR

iTrader: (61)

please post a few pics of the damage if you can.

Maxthe7man

Where did you guys get that 950c is to hot for a moderate boosted rotary?... That info is just plain wrong... If that turbo cant live at 950 its no optimum for a rotary, if you are tuning via egt, 970 is around where you are reaching maximum power output on a good safe tune on high octane pump gas... Anything below 850 is just wasting fuel...Max

Carl Byck

Max, do you and BDC agree on this? Just curious. 1600-1800 degrees optimum, yes?

BLUE TII

iTrader: (9)

Max, would you run Hearly seals at 970 C? Would you run "zero clearance" sideseals at 970 C? Would you run 970 C on a small-ish turbo w/ higher backpressure?

There are lots of variables, but you can't deny you will get a lot more life out of the system at 700 C than 970 C.

Carl Byck

What are stock EGTs on a TII at WOT?

TonyTurboII

Err, with a series 5 turbo on a Comso motor I was seeing roughly 750 degrees at WOT.

Maxthe7man

Yeah I can deny that, at 700c it would be so pig rich with fuel, you are washing alot of the surface down with fuel and at that point probably diluting the oil in the pan...
I wouldnt run Hurley seals ever either.....
Also no one in their right mind would run Zero clearance side seals.. I run .0015 minimum, if the side seal is to tight it will bow out along its length, and tend to get caught on the top of the port and break regardless if its been angle ported or not..

The optimimum power point is right around 970, I have been pushing my car toward that point and adjusting the a/f's fuel first then adjusting the timing secondly.. At this point I have nearl 14,000 km's on it this summer, with the majority of that boosting in the 17-20 psi region on premixed pump gas, obviously it works..


Alot of misconception on egt's are born from using guages that are sold without rotaries in mind.. Look at the autometer stuff, it maxes out at 1600, so any more than that must be bad... wrong.. Most egt or pyrometer sets were made with diesels in mind and or gas n/a piston engines, where anything above 1500 is bad..
Some people with electronic guages also have the polarity wrong on the thermocouple, it will read cooler as it gets hotter past a certain point, in other words it will climb like it should, then hit a point, then indicate temperature falling as it gets hotter..
Another word on thermocouples is that if the wire is extended with wire that is not the same resistance as the feed wire out of the thermocouple it will be out by alot, sometimes more than 200 deg C.. They sell special wire for thermocouples to maintain the same resistance quantities and it has to be joined in a proper manner as well...Learned that from working on Blast furnaces and incinerators..

Alot of the Japanese guages have rotaries in mind, most go up to 1200C...Although I see Autometer is evolving and now has a 2200 F guage..

If you can or know someone that reads Japanese, buy a subscription to the Japanese "rx-7" magazine, its loaded with tuning info that is reliable and works..

BLUE TII

iTrader: (9)

Yeah I can deny that, at 700c it would be so pig rich with fuel, you are washing alot of the surface down with fuel and at that point probably diluting the oil in the pan...

Nah, if you get it down to ~700C at 10.5:1 AF and advancing timing you should start looking into exhaust restrictions, too high CR, too high intake temps or other causes.

If you tune it for ~700 C it and log your EGT racing I bet you see EGTs quite a bit over 700 C unless you tune by doing back to back runs allowing heatsoak to build; that is one reason to advise someone to tune to lower EGTs instead of "run 970C".

I wouldnt run Hurley seals ever either.....

Right, but you didn't ask what the poster was running; another reason to advise lower EGTs- you don't know his set-up. Neither do I, but I would err on the side of caution.


Also no one in their right mind would run Zero clearance side seals.. I run .0015 minimum, if the side seal is to tight it will bow out along its length, and tend to get caught on the top of the port and break regardless if its been angle ported or not..

"zero clearance" was in quotes as it is not possible to get the sideseals that tight and have them move properly in the groove. Watch Amemiya's GT engine builder seal up a rotor and you won't see a feeler guage as he grinds until both the corner seal and sideseal move easily but the side seal doesn't "cachink cachink" when you wiggle it forward and back in its groove. Your .0015 is .0005 under Mazda minimum so is "zero clearance" but it doesn't matter because if you gently break it in it will gain its larger operating clearance without hurting anything. The difference between your .0015 and "zero clearance" isn't much when comparing the difference in thermal expansion along the length of the seal between running 700 C and 970 C. I bet your sideseals have more clearance than .0015 now- especially if you count the groove it has worn into your corner seal.


The optimimum power point is right around 970, I have been pushing my car toward that point and adjusting the a/f's fuel first then adjusting the timing secondly.. At this point I have nearly 14,000 km's on it this summer, with the majority of that boosting in the 17-20 psi region on premixed pump gas, obviously it works..

Optimum for what set-up for what driving? If you manage to raise the EGTs above that without damage/adverse intake, oil, water temps you will make more power!

Of course you make more power with more exhaust gas expansion and your set-up may work fairly reliably at 970 C in short bursts, though 14,000 KM or even 14,000 miles is no benchmark for reliabiliy so don't boast that. I did 12,000 miles boost creeping 20psi to 24psi on 91 octane and running way to high EGTs until it let go- it wasn't reliability- it was stupidity on my part, but "obviously it works". Examining my engine and long conversations with the builder will keep me on lower EGTs (and I think I got the boost creep licked). He recommended tuning for ~700 C. Its a street car not time attack.

If the turbine is melting and he claims EGT at 950 degrees (when he could take the time to look at the gauge) with the sensor at 2" from the port, you can bet the EGTs are higher than this at the point of exhaust restriction (the turbine).

I still buy RX-7 magazine/Hyper Revs and watch Options, though my Japanese is not as good as it was in school (sucks actually).

Some people with electronic guages also have the polarity wrong on the thermocouple, it will read cooler as it gets hotter past a certain point, in other words it will climb like it should, then hit a point, then indicate temperature falling as it gets hotter..

I have MADE industrial blast funnaces and incinerator controls for companies that do things like low level nuclear waste incineration I know how a thermocouple works, but perhaps this would have been a good first post in his thread from you since he was claiming melty exhaust wheel and you say raise the EGTs for more power...

If you run anti-lag you may appreciate a 1200 C gauge, but your engine/ turbo would still appreciate cooler EGTs. Auto meter makes 11,000rpm tachs and boost gauges over 100psi, but I am not going to try to max those on my car either.

EFINI_RX-7_RZ

I agree with you Max, but you have to mind the limits of the turbo in question, which in itself was designed as a high performance turbo for the diesel crowd. I remember reading somewhere that 850 degrees centigrade was the maximum heat the GT42 family of turbines will take. Makes them unsuitable for our rotaries, right? Maybe Sean, of A-Spec, might shed some light on this matter for us. But, anyways, and regarding the Garrett "Ballistic" line, even those turbos designed for use on gas engines (apart from the GT38R and the GT42, I think pretty much all other GT turbos were designed for gas engines) are limited to 950 degrees, bar an Inconel wheel or other heady, unobtanium stuff like that.

On the matter of high octane fuel, well, you have to also mind the thermal limits of the parts going onto the engine. You might push timing to the limits and lean to 13s and still not get pinging with high octane fuels, but that does not mean that the engine won´t melt, it will just the same, just without the pig-screaming to let you know it is melting away. And as for Carl, he is using water injection, so instead of pinging his engine to dead (which, with the pump gas he is using, he should have had at 950c), he is just melting stuff away, like his GT42R, for example, and god knows what else (I´ll mind the corner seal rubber plugs and, maybe, just maybe, the oil seal O rings). To be able to run a rotary at 950c plus efficiently, you have to prepare your engine for it, like using solid corner seals, Viton oil seal O rings, an Inconel wheel if it is a turbo engine and so forth and so on.

One more thing, I´m not an expert on rotary timing, but Carl´s seem to be too retarded, which might lead to heady exhaust temps. Can someone in the know take a look at Carl´s timing?

EFINI_RX-7_RZ

Sorry, on my previous post, when I was mentioning Carl, I actually meant royston, sorry for the confusion. BTW, here is some reading on the state-of-the-way-too-hot-turbine-art from the very source:

http://www.honeywell.com/sites/ts/tt...2155816136.htm

Maxthe7man

700 c is way to cold, when I first tuned I was seeing that egt with the wideband reading 10.2:1 with 4x1600. The truth it was i t was in the 9's and the lowest reading of the wideband was 10.2, it was running 700 c because it was pig rich, and thats the only reason it was running at that temp..
970 is the optimum, if you tune to that egt you will most likely find your maximum power there, tuning with egt and g-tech I found this to be so... If your tune is right and your maps smooth and not knotchy jumping all over the places with the air fules, you will find your egt will find its peak, and its tunable to a given egt..



If the Hurleys cant handle 970, they simply dont belong in a rotary period...



The point of the side seal being in at zero, if you cant fit a feeler guage in there its msot likely sprung between the two corner seals... I have met RE's engine builder, and he does not "zero clearnace", Zero and .0015 are not the same..And gently breaking it In? whats with that, if its bowed at all it will have a broken side seal from the first day its started...What are you going to do? Keep pulling the motor apart to see if its self clearanced itself?... Start at .0015 and work from there, not zero..


The optimimum power point is right around 970, I have been pushing my car toward that point and adjusting the a/f's fuel first then adjusting the timing secondly.. At this point I have nearly 14,000 km's on it this summer, with the majority of that boosting in the 17-20 psi region on premixed pump gas, obviously it works..

Optimum for what set-up for what driving? If you manage to raise the EGTs above that without damage/adverse intake, oil, water temps you will make more power!

[Q]Of course you make more power with more exhaust gas expansion and your set-up may work fairly reliably at 970 C in short bursts, though 14,000 KM or even 14,000 miles is no benchmark for reliabiliy so don't boast that. I did 12,000 miles boost creeping 20psi to 24psi on 91 octane and running way to high EGTs until it let go- it wasn't reliability- it was stupidity on my part, but "obviously it works". Examining my engine and long conversations with the builder will keep me on lower EGTs (and I think I got the boost creep licked). He recommended tuning for ~700 C. Its a street car not time attack.[/Q]

Short burst, hardly most of my boosting is long duration highway pulls, I live in the middle of nowhere, a short burst for me is 25 miles.. IF you cant tune to a proper egt without raising your oil/water temps into danger range, you have other problems, like your cooling setup.. Through a 4th gear pull I only raise 2-3 deg on coolant and 10 deg on oil pre cooler...Cooling stability is half the key to running high boost on pump gas...If your tuner recommends 700c, he is no rotary tuner, he's just runing the motor in a overly cautious detuned inefficient state since he has no idea of the engines true bounds...Street car or Time attack, it doesnt matter, tuning the engine for high output and reliable power is important for both, it wouldnt be much of race if the engine blows on the first straightaway would it..


[Q]If the turbine is melting and he claims EGT at 950 degrees (when he could take the time to look at the gauge) with the sensor at 2" from the port, you can bet the EGTs are higher than this at the point of exhaust restriction (the turbine).
[/Q]
The egt will not be higher than it was at the port, restriction or not..

[Q]I still buy RX-7 magazine/Hyper Revs and watch Options, though my Japanese is not as good as it was in school (sucks actually).[/Q]

Obviously, or you would know the maximum recommended egt of stock seals is 1100 C and you wouldnt be arguing against 970c....

[Q]I have MADE industrial blast funnaces and incinerator controls for companies that do things like low level nuclear waste incineration I know how a thermocouple works, but perhaps this would have been a good first post in his thread from you since he was claiming melty exhaust wheel and you say raise the EGTs for more power...[/Q]

Thats not what I said in reference to his turbo melting, what I did say if the wheel cant handle 950, its not the best turbo for a rotary...

I have run antilag and its not that hot...it peaked at just over 1000 c....
The point was to buy guages that match the range the engine is capable of , not guages that are pinned well within the engines realm, or buying big guages to just pin them...

Maxthe7man

Interesting, it states 1050, a bit under what the rotary can handle as an absolute maximum... Could be his turbine wheel isnt a genuine part...

Carl Byck

I was getting worried... BTW, keep it up, I learned a fair bit in the last two exchanges...

EFINI_RX-7_RZ

I just fonud where I read about the GT42's design specs, from "BC Information 00-11", a page from an old Garrett catalog I have in hand, the letter head read: "Garrett GT-Series Ball Bearing Turbochargers", "Update: Ballistics Concepts Performance Products", the paragraph which concerns this post reads:

"LARGE FRAME BALL BEARING CHRAs:

Garrett has released a new production GT42 ball bearing turbocharger to the Aftermarket. This unit, howerver, is a low teperature (diesel application) large frame ball bearing cartridge assembly, which may fit certain niche market applications whithin the Aftermarket diesel sport industry."

Then, further down, the catalog describes this turbo as the GT42/45R, part number 703654-0012. Now, this is NOT the exact turbo we now know as the GT42 sleeve bearing or GT42R ball bearing, but I just wonder if Garrett made the current GT42s suitable for gas engines. I think they should have, as the GT42 is placed in their current catalog and web site with all the other GT turbos, except for the GTP38R (a known diesel turbo), which gets its own catalog and separate web page.

In the end, the 1050c turbine Garrett described on the link I previously gave, is for OEM engines running stoich (A/F: 14.7:1) all the time, cars designed to spew the least contaminants possible while providing good fuel efficiency, thus running at such "lean" (for us, anyways) A/Fs. 950c should be the top temp for a turbo that is not prepared for running at high temperatures.

RETed

I saw 720C in the downpipe (Racing Beat 3"), 14psi of boost, GReddy 52mm EGT gauge.
I saw 760C in the exhaust manifold (S4), 14psi of boost, GReddy 60mm P/H EGT gauge.


-Ted

RETed

I thought water injection is supposed to drop EGT's?
When did Max start messing with water injection?

To claim "shoot for 970C" is just plain ridiculous.
Come on Max, you figure it out why.
EGT gauges don't always read the same.
There's a fine art to tuning with an EGT gauge, and telling anyone to shoot for a certain temp is very wrong.

I had to tune a GT35R that would like 900C EGT's for best power.
At the same time, I tuned an H-trim hybrid that was barely getting over 700C.
Both motors were similarly ported.
Both were using the same brand and type of EGT gauge.


-Ted