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Turbo Glowing with no Boost at steady State Cruise

Title pretty much says it all. When I take the car out for an extended cruise of 25 miles with no boost, holding rpm in the 2300-3000 range in 4th gear (70mph) the hot side housing is glowing red orange. I mean really glowing, from the inlet flange, to several inches down the exhaust exit pipe towards the muffler. The headers were not glowing at all, and had surface temps near the head of around 550-600F. To contrast this, when I just go out on shorter trips, boosting many times (8-10 pulls) when I return from the garage there is only what I would consider to be a normal dull red glow in the center of the inlet flange.

After I let it idle for 3-4 minutes, the housing has cooled back down. So idle temps are under control, its just the extend low load cruising that is the issue.

Here are the facts:
Timing: 8 BTD at idle, 25 at 4000 no vacuum retard, still has boost retard
Boost: 0.9 bar comes in around 3000-3200
AFR: 12.5 at idle, upper 14ís at steady cruise, low 10ís to low 11ís during boost depending on rpm
Engine temps never exceed 230 at the gauge or 220 at the engine case, or thermostat housing measured with a pyrometer.

I am stumped; I have swapped out a new O2 to confirm that itís not the sensor. What do I go after next? Sticky mechanical advance (seems to advance fine when revving the engine)? Poor oil supply to turbo (I checked flow when I installed the engine 500 miles ago and it was fine)? Plugged muffler (doubt it). Could my timing marks be off on the pulley (donít know if itís a stock one)? I am planning on trying to fatten up the cruise AFRís to the low 14/upper 13 range and see if that helps.

Sorry for the poor pics, the build is still in progress, with brakes, body, interior, and suspension on the list for the long upcoming Minnesota winter.

Cheers and thanks


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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 06:09 AM
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Good info/troubleshooting. Boosting puts a lot of fuel in the engine which will cool the exhaust. Cruising is of course on the lean side. Is it possible your timing marks are not correct? How is the performance?
An occlusion in the turbo oiling would cause a failure quickly if bad enough to make the housing glow.
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Old 10-30-2011, 07:00 AM
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Its probably a good idea to confirm where my timing marks are in relation to true mechanical TDC, so Ill add that to the list.

the tubine appears to spin freely, build boost at relatively low rpm and spins for 10-20 seconds after shutdown, so I think that it oiling to some degree. it also does not smoke, so I dont think its plugged or it would be blowing past the seals.

Do you think my cruise AFR's are to lean?

when should full mehcanical timing be in?
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 07:25 AM
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As far as general drivablity, the car runs great, idles nice, decent off boost throttle response (about on par with the N/A that it replaced) , great on boost acceleration. no stumbles, bogs or smoke. overall, I would say that its runs excellent.
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 07:32 AM
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Around 26į should be in by 4000rpm.
Sounds like the turbo is OK.
Cruise AFR should be ~14.5; what happens if you drop it to 13.5 AFR?
Which distributor is being used? Is the vac retard line plugged?
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 10-30-2011, 10:44 AM
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Quote:
Originally Posted by RarlyL8 View Post
Around 26į should be in by 4000rpm.
Sounds like the turbo is OK.
Cruise AFR should be ~14.5; what happens if you drop it to 13.5 AFR?
Which distributor is being used? Is the vac retard line plugged?
My cruise AFR is a little north of that, averaging around 14.8

Dont know the P/N of the distributor but it is a US model, non california unit with the single pot with 2 connections/ports. I have the rear port plumbed into the intercooler, the other front port is open to atmosphere (was plumbed to just below the throttle blade). I unplugged the vacuum signal becuase I was getting to high EGT's with the retared timing (5 ATDC). the port at the throttle is plugged.

What is the best way to lower cruise AFR's? via the WUR or the mixture screw on the metering arm?
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 01:29 PM
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If I were you, I would pull the muffler off and go run it down the same roads. See if it glows after that. I know you don't think the muffler is plugged, but 14.8 should not make the turbine glow. It's four bolts and it would at least ensure that is not the issue.
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Old 10-30-2011, 02:52 PM
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Shouldnt the boost retard be going to the intake manifold in the engine side of the throttle plate?
Old 10-30-2011, 03:50 PM
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Quote:
Originally Posted by DSPTurtle View Post
If I were you, I would pull the muffler off and go run it down the same roads. See if it glows after that. I know you don't think the muffler is plugged, but 14.8 should not make the turbine glow. It's four bolts and it would at least ensure that is not the issue.
good suggestion, I am in the process of fabbing up a zork tube and will add this to the list. I have all of the materials, just need to find time to hit the welder.

if the muffler had a big constriction, wouldn't it be glowing first? when you set cats that plug, they glow pretty quick.
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 05:16 PM
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Quote:
Originally Posted by pdx930 View Post
Shouldn't the boost retard be going to the intake manifold in the engine side of the throttle plate?

At WOT it shouldn't really matter, save for negligible pressure drop across the throttle plate, etc. being tapped at the intercooler, it will see boost sooner then the cylinders (talking milliseconds here) and would therefore pull timing out sooner then at the intake and in theory a little safer, though in practice it shouldn't really matter.

When you take your foot off of the throttle and the plate closes, which means that you would start to build vacuum/loose boost in the manifold, which means that the the timing would be put back in (advanced). if your bypass valve is working correctly, the intercooler will not see much vacuum, but will loose boost, so the result is still the same. if it were tapped to the intake side, it would put the timing in quicker then the intercooler side, but since you are theoretically not under load or boost it wont really matter at that point, again no practical difference.

now if you were looking at the vacuum side of the distributor dash pot (the side that is meant to be engaged at idle/cruise) it most definitely had to be attached to the intake side throttle plate.

If somebody sees a flaw in my thinking, please correct me
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-30-2011, 05:35 PM
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derek,

have you looked at each [6] of your exhaust ports independently at idle? And, are any of them glowing? Or, have you checked the temperature of each individually [with pyrometer/infared]?

Just curious if you have a single cylinder or maybe two doing something funny at idle...
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Old 10-30-2011, 06:15 PM
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Quote:
Originally Posted by mooney265 View Post
Derek,

have you looked at each [6] of your exhaust ports independently at idle? And, are any of them glowing? Or, have you checked the temperature of each individually [with pyrometer/infared]?

Just curious if you have a single cylinder or maybe two doing something funny at idle...

yep, checked the surface temp of all 6 headers at the port with a pyrometer when I got home and noticed the glow. None of them was glowing, and they ranged from mid 500F to low 600'sF within a minute of pulling into the garage (I keep the pyrometer in the car as I am still in tuning mode).

I haven't had a chance to read the plugs yet, but is it possible that one is not firing and passing raw gas into the exhaust system and it being ignited when it hits the collect and mixes with the other cylinders mixes which are still combusting/have residual O2 which would allow post ignition of the raw gas and overheat the turbo? this is probably a stretch, as the car runs great, idles smooth, and has not miss, but I am reaching at this point.
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Old 10-30-2011, 06:47 PM
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I hope this sheds some light for you , I got other pic's . I'll look for them and post them for you , If you want to call me I believe I can help


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Old 10-30-2011, 07:15 PM
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1986 944 turbo -first car
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1992 964 C2 turbo
SOLD, 911GT ,CIS, 428 fwhp 450 trq, Carrillo rods, 964 cams, TT retainers,7.5 comp 1.1 bar boost 320 ml black fuel head 009 injectors, 044 pumps, 60-1 T4/T3 dual scroll turbo
Old 10-30-2011, 07:38 PM
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I hope the illustrations helped out

It's very important to get the part # on the dizzy , So that you have it set at right timing , you should be able to seethe part # on the side , Porsche made a few different dizzys with dual vac, the first being the early California one which is set up for 31 btdc at 4000 rpms hoses disconnected, then then a 84 thu 89 ROW dizzy with dual vac setup for 29 btdc 4000 rpm hoses disconnected , then came the USA 86 thu 89 dizzy dual vac , set up for 26 btdc 4000 rpm's hoses disconnected , It's very important to have BOTH hoses hooked up to the right places or you will have problems , If you have any Questions please feel free to call me at any time

Helio
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Old 10-30-2011, 07:56 PM
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here's another pic
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1986 944 turbo -first car
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1992 964 C2 turbo
SOLD, 911GT ,CIS, 428 fwhp 450 trq, Carrillo rods, 964 cams, TT retainers,7.5 comp 1.1 bar boost 320 ml black fuel head 009 injectors, 044 pumps, 60-1 T4/T3 dual scroll turbo
Old 10-30-2011, 08:15 PM
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Quote:
Originally Posted by roxanne68 View Post
yep, checked the surface temp of all 6 headers at the port with a pyrometer when I got home and noticed the glow. None of them was glowing, and they ranged from mid 500F to low 600'sF within a minute of pulling into the garage (I keep the pyrometer in the car as I am still in tuning mode).

I haven't had a chance to read the plugs yet, but is it possible that one is not firing and passing raw gas into the exhaust system and it being ignited when it hits the collect and mixes with the other cylinders mixes which are still combusting/have residual O2 which would allow post ignition of the raw gas and overheat the turbo? this is probably a stretch, as the car runs great, idles smooth, and has not miss, but I am reaching at this point.

I don't think any of the plugs are dead as your temps are about equal. I think your distributor timing on cruise is too retarded (sticky or bad distributor). The AFRs seem reasonable. Report what you find on the actual TDC vs. the pulley marks.
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Old 10-30-2011, 10:41 PM
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heliolps2: thanks for digging out the vacuum diagrams, ill follow up with the P/N's for the distributor. generally speaking, I think running w/o the vacuum retard should only help matters, as typically lack of advance and lean are the two main suspects when it come to high ETG's (Or ultra rich, but that would have other symptoms.

I have confirmed what the timing does under vacuum and boost using a hand pump:

1. front port: under vacuum in the front port (the one that I have been running disconnected) it seems to retard about 10 degrees, under positive pressure nothing.

2. rear port: under vacuum nothing, under pressure it retards about 8 degrees. don't know why it would be less, though it tricky to get accurate readings while performing this test at idle.

It may be worth noting that I don't have thermotime vacuum switch in the system. the distributor, when the vacuum side of the distributor pot was hooked up was plumbed directly to the throttle body
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Old 10-31-2011, 02:09 AM
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Quote:
Originally Posted by smurfbus View Post
I don't think any of the plugs are dead as your temps are about equal. I think your distributor timing on cruise is too retarded (sticky or bad distributor). The AFRs seem reasonable. Report what you find on the actual TDC vs. the pulley marks.
Great point. I need to start at the obvious and confirm my base timing is correct before doing much else. I will also try and measure what my timing is at cruise RPM (low to mid 2000's), sort of a poor man's distributor mapping exercise once I have confrimed based timing via TDC.

Does anybody know what the typical timing would be at in the mid 2000 RPM's?

The one thing that I cannot figure out is why just the turbine would be overheated. if its high EGT's due to timing or fuel, why wouldn't the headers be glowing? it is literally just the turbine housing that is effected by whatever is causing this condition
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'81 Euro SC coupe, 79 3.3 930 engine, 930 transaxle, B&B full dual outlet exhaust, 964 intercooler, 964 cams, CIS injection, K27 7006 turbo. '08 Triumph speedtriple. '06 BMW 330xi
Old 10-31-2011, 02:18 AM
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For those interested, my distributor part number is 0237 302009 - that is the bosch part number, which is stock for a '79 930 I believe (which is what the engine is). to reconfirm, it is a single pot, dual port unit
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Old 10-31-2011, 03:37 AM
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