EGTs, Internal Wastegate, Small Turbine Housing
 

A while back I had a turbine wheel grenade on me and after some reading I've come to the conclusion that it was most likely sustained boosting that brought about the damage. Specifically from exhaust temps. I've got an EGT gauge, though it only goes to 1600f, the needle will go higher. The gauge always peaked around 1550-1600 and that was on my final tune, around 19* near peak hp @ 15psi.

Just wondering what the thoughts are on my current parts causing the current temps. I'm running a tubular stainless manifold. Turbo is (was) a t3/t4. Compressor 50AR 50trim and the turbine a 48AR Stage 3. The turbine housing is an OE Mercedes stage 1 that was overbored to fit the stage 3 wheel. I'm using the OE Mercedes internal wastegate housing that is about the largest OE IWG housing to come on a car (diesel engine). It's got a 2-1/2" outlet and has a pretty big "mouth" BUT it still sends the bypassed gases from the gate into the wastegate housing and right back at the turbine wheel. 15psi is reached ~4k so the wg is bleeding boost from that point up to 7k. Though it's not tracked I did regularly give it successive boosted runs. Usually full throttle from low rpm to redline in fourth AND running through the gears to redline. Again, EGTs were stabilizing right around 1550-1600f. Thoughts?

Since I'll be bringing over the setup to a new chassis, it won't be a big deal to run an EWG. I've got a 63AR turbine housing and can pick up a t3 flanged v-band adapter for that housing.

How and where were you measuring EGTs??? Every turbine wheel has a max inlet temp (TIT) that you cannot exceed without risking/causing permanent damage to the alloy. The specs I've seen run from 1,650 to 1,750 degrees F (aviation turbos, not automotive). However, EGT readings on individual cylinders are generally lower that the TIT temperature (TIT reading is typically taken as close to the exhaust turbine as practicable). If you are trying to prevent overheating your turbo, you need to be measuring TIT. If TIT is too hot, you need a richer mixture which will lower both individual cylinder EGT and TIT (for the sale of simplicity, I'm omitting the option of lowering EGTs by running lean of peak).

Header/manifold collector- about 1" from the turbine flange. EGTs were essentially the same as rich as 10.5 as they were at the final tune. I've seen TITs of 1600f cited as "OK" in several aeronautical contexts. The prior turbine wheel was believed to be a turbonetics, but that's not positive. And it had excessive tolerance to the housing wall - about 1/8". Not sure how any of that would impact temps either.

1600F is pretty hot. A quick search on honda-tech (they've been there done that to most questions) says they aim for 1400F MAX at full load and wot, but I see alot of guys say they are hitting 1600 after 1-5th pulls.

Sounds a bit high. I always tried to keep it under 1400 on my old car. I would see 1450 while cruising down the highway though until I tipped into the throttle to richen it up going uphill.

I don't have a gauge on this car.. :noes:

I'm sure the temps aren't a result of the tune. I've been all over the ign and fuel map specifically focused on this, all with negligible change. Given that, I suspect that the IWG is the culprit. It's a relic compared to the newer internal designs. It dumps directly into a wall that reflects exhaust gas right back at the turbine.

It depends on the alloy used in the turbine wheel. Some Rajays are rated at 1,650 max, others at 1,750. It may not be safe to assume that an automotive application is rated quite that high. Note that air cooled aircraft engines use fuel for cooling at high power settings (climb & takeoff); full throttle on an aircraft engine enables an extra enrichment circuit. Additionally, unless you've done some testing, you don't know if the TITs you are observing are peak, lean of peak or rich of peak. Peak EGT generates the most cylinder pressure (and highest chance of detonation), so conservative aircraft operators run cylinder EGTs in the 100-125 degree rich of peak EGT range which yields lower TITs. I've always seen the highest TITs on max takeoff power climbouts; throttling back to max continuous power brings TITs down.

I would suspect your running a bit rich a WOT & unburnt fuel builds up in the turbine/WG housing. Where is the EGT located?

Sensor at fault maybe? Ign and fuel trims should show a change in egts

Could have been worded better- I went from 15* to 19* up top and and saw a negligible change- maybe down from 1600f to 1550. More fuel did nothing but lose power. I'm not man enough to run more than that up top on a pump gas street tune at 15psi... not right now w/o a back up engine. ;)

Only if there is an ignition source between the exhaust valves and turbo to afterburn the fuel! :giggle:

Peak EGT = hottest

From peak EGT, you can add fuel to run Rich of Peak (ROP) or subtract fuel to
run Lean of Peak (LOP). Exhaust temps will fall in either case until you attain a mixture that is either so rich (ROP) or so lean (LOP) that it will not combust and the engine dies.

What were your AFRs when you were altering the timing? Unless you are using a fast acting aviation style EGT probe (most automotive probes sold are old style Westach or Alcor slow acting probes) you are not going to get accurate EGT readings unless you hold the engine at a constant load long enough for the probe to temp stabilize.

I'd suggest testing the car on a chassis dyno that can hold the engine at a constant load for as long as desired (e.g., not a Dynojet). Get the engine running at a safe load (60-75% power) and RPM that puts the engine in boost but does not cause the wastegate to start dumping. Monitor AFR and EGT at constant load until both stabilize (at least 1 minute) and then start slowly adding/subtracting fuel in small increments and waiting for the EGT gauge to stabilize after each change. You should be able to find peak EGT this way and also see what richening AFR does to EGT/TIT.

Last time on the dynojet I was tuning the top end target boost IGN map and adjusting fuel accordingly for power with regard to knock and EGT. No knock and the usual EGTs during those runs. Final AFR was 11.5 in the newly tuned zones on 93. I was running leaner AFR but with less advance when I rolled in with a rough street tune. There was probably a 50* drop in EGTs by the end.

Agreed - loading dyno is the ideal way to tune (all of it for that matter). So are you saying I should reach peak EGTs at a lower rpm, and boost?

I get up to 1200-1300f pulling 1st-5th wot, my bung is welded in 2-3" before the cat.

Any speculation on what that would translate to at turbine inlet? How far is your cat from the turbine?

Cat is where factory location is, turbo, SG begi DP, then cat. Its all 3" exhaust. I think your temps are normal to be honest because if mine are that hot down there i dont want to imagine the manifold. Heres a video of tuning fuel cells at the dyno i wanted to cry lol, was there for 6 hours still not done tuning...returning this summer to retune

I'm suggesting a safe approach to validate your EGT gauage is working properly. By starting at a lower power setting w/the wastegate completely shut you can safely globally add/subtract fuel (while at constant load) to determine Peak EGT (and corresponding AFR) and then add fuel from there. Your EGT/TIT gauge should show peak and rich of peak values by doing this. You then have the option of upping boost until the wastegate opens and seeing if you get the same results. If you test methodically like this, you have a better chance of determining if your IG is causing elevated TIT temps or if you simply have a malfunctioning EGT probe/gauge.

Post turbine temp is now way to judge your inlet temp. The heat performs a large portion of the work that drive the turbine, and you will see a large temp drop across the turbine as well due to pressure drop.

Turbine inlet temp is critical to longevity, and it sounds like you were pushing it.

Most aluminum alloys start to get pretty wobbly around 1650F, so if you are there a lot your head might have a problem anyway.

Most diesel guys are very worried about EGT because they tend to run under load for much longer time frames than we do when towing, even compred to a road course car.The general rule of thumb there is that if you are sustained over 1300 degrees you are basicaly asking for it. You can have peaks that are higer than that, but not for too long.

WI drops EGTs really well. I would simply run a really basic system with pure water. That will often drop temps by about 200F. If you want to run more timing to take advantage of it, so much the better, but you dont have to. And then you can run a more sensible AFR, as the 10.5 is not doing you any favors or making you safer.

Richening the AFRs themselfs is a bad idea. You get cooler combustion temps but you might end up simply burning fuel in the manifold post-cylinder head and spiking temps that way. The increase in timing is simply burning the fuel more completely in the chamber and using it to make TQ, which avoids this to a degree, which is why it cooled things down.

This. Often you will see a 250 degree diff in pre and post turbine temp with a restrictive housing, sometimes even more. If you have 1600 post-turbine, then I gurantee you that you are in heat-death land by quite a bit.

Without a doubt. I've been trying to find do not exceed TIT specs for auto turbos; so far all I've come across is one Suby WRX DNE of 1,625 TIT. I can't fathom why anyone would waste the time and effort to install an EGT probe in the TOT position, even on a diesel.

Rob, let me preface this by admitting I have no clue about this issue. That said; I've told you before that I have my EGT sensor about 6 inches down on the downpipe. I see average temps of 1250 in my gauge and these drop to around 1100 to 1150 when I use the WI. I've tried it both squirting and without back to back and those are the results I always get.

It seems to me you're on the right track about your IWG. FWIW, I have an external one dumping back to the exhaust further down stream.

If you guys are directed at me- my probe is about an inch from my turbine inlet and that's a long ways away from the cylinder head thanks to the long tube header. My original point was to gain some insight on whether or not my internal wastegate might be contributing to the temps. I know the smaller turbine AR doesn't help with the large compressor.

Whoops, threads tend to get hijacked quickly around here. As I noted above, I think your probe is properly positioned to measure TIT, but you probably need to do some testing to see if your high TITs are IWG induced:

As you already know, retarding timing also raises TIT so there is somewhat of balancing act when tuning a pump gas, turbocharged car at high boost levels; too much boost raises the knock level and retarding timing to stave off knock raises EGT/TIT. Sustained TITs in the 1,600+ F are going to fry most turbos, so you probably want to keep TIT below that figure.

m2cupcar, do you have pics of the carnage?

BTW an EGT probe in the collector is the right approach, since the bulk temperature is higher there than at one of the exhaust ports.

Side note: acceptable turbine inlet temps vary. It depends on the turbo. Virtually any OEM gasoline turbo car made in the past ~ 8 years or so will support 950 C, with some that do 1050 C. 1050 C is becoming the norm.

950 C = 1742 F
1050 C = 1922 F

However, a diesel turbine housing like the one you're running was not intended to live at the (higher) EGTs of a gasoline engine. It will creep and distort, oxidize, crack and generally turn grumpy. But I'm curious about what your wheel looks like.

i have run maybe 30 trackday events since i purchsed my turbo na from my buddy. many of them were high-speed tracks with alot of wot time. all the while my egt's were 1550-1600deg.f

while i don't doubt your turbo could have been damaged by those egt's. i do think there's other possible causes. sounds like you had a mix of parts and work done to that turbo. i've seen turbos come apart from not being balanced, or small turbine/big compressor puts alot of stress on the shaft and wheels. one thing i do know, punching it on the street, even consecutively, is nothing like 20mins. on a road course. basically it shouldn't have happened unless your turbo was already sick.

Pic of wheel below. When I first saw it I was sure something went through it - blades looked bent at the tears. But then I found some pics recently that had similar damage claiming to be from extreme EGTs.

I used this turbo in my original "Mercedes" turbine housing for simplicity since the downpipe was built around it. What I didn't do was measure the turbine wheel - which was a stage2. My turbine housing was a stage3 - well almost. As near as I can tell the housing was overbored to fit a turbine wheel that had some wear on the blades. I figured this all out when I got the new Garrett only to find that the stage3 turbine wheel wouldn't quite fit into the housing. So I was running a stage2 turbine wheel in an almost stage3 turbine housing (bore) when it failed. That's about the entire history of that turbo. ;)

Never saw over 1600f. I can't verify the exact origins of the turbine housing. I thought I had the typical ford 5 bolt until I bought a ford flange and it didn't fit. I asked around and somebody said they had the exact same housing and it was an OE Garrett housing from a diesel Mercedes. It hasn't shown any signs of failing. There were no obvious signs that it interfered with the wheel (understandable given the smaller wheel in the larger bore). I couldn't find anything in the exhaust (from the cat to the head) that looked like it went through/by/into the wheel. At that point the cause was left unanswered. I got a new Garrett t3/t4 (using the same turbine housing) and have put as many hours on this one without issue.

http://i158.photobucket.com/albums/t...lades1_640.jpg

Here's shot showing the extra tolerance of the stage2 wheel in the larger bore:
http://i158.photobucket.com/albums/t.../stage2in3.jpg

That's foreign object damage.

An over-temped wheel looks like the blade tips were pulled and stretched like taffy, and little bits of the wheel turn molten and fly off radially. The bent-backward blade tips indicate ingestion of something heavier and slower than the blade tips.

That's good to know... I think. Though I gotta say that it's bizarre I never found what it was. I took the entire exhaust apart and never found anything but the little shards of blade... they all collected in the entry of the cat.

Those EGTs you listed- are those temps that Garrett regards as "expected"?

Your comment on the diesel EGTs has got me thinking about all the guys using the Holsets on their cars, but I suppose those turbos are so large on the turbine side that the EGTs wouldn't be too high with reasonable tuning.

Those 1,850-1,922F rated current gen auto turbos may be overkill for your application. The latest OEM turbo motors (GM Ecotech 2.0L, BMW 335i turbo) are designed to run at stoich/peak EGT at light boost (not WOT). They have direct injection into the combustion chamber and combustion chambers that are optimized for this type of operation. You don't have direct injection and can't safely run your motor at stoich/peak EGT with any significant amount of boost. Peak power is always rich/cooler of EGT, so you don't really need the extra temp rating if you have tuned properly. I also suspect that the current generation of budget priced Chinachargers and replacement turbine wheels lack the advanced metallurgy to survive at 1,900F.

Yes. Routine, normal, sustained, etc, and will live for ~150k miles like this. But again those values are for modern gasoline turbos that are on cars that attempt to eke out fuel economy by running as lean as possible.

That and a squirt here and there isn't enough to really saturate things to where the housing feels the pinch. The truth is that most guys drive like candy asses and never expose the turbine to elevated temps for prolonged periods.

A diesel engine may have to run at 1200-1300 degrees for minutes or hours.....

What I always found interesting was that Cummins rated thier EGT's post turbo. I guess since they knew what the entire setup was they had the EGT's post turbo. Most big trucks are this way. Most are rated in the 800-900 F range.