LLY Turbo Mechanics?

[jsmiracle]

I noticed towing the TT ~1300 mi. (roundtrip) that the turbo boost pressure would seem to double (~15# to 30#) without the RPM's changing accordingly. Initially, I thought the turbo was linked closely with the exhaust pressure solely. Now I think there is something in addition to the exhaust pressure, like variable nozzles and/or vane position.....

Can someone please enlighten me on the operation of the turbo? Thanks.

Jim M.

P.S. I first searched the forum for the info., but didn't find much.

[Kennedy]

Load is what dictates boost primarily.

[killerbee]

I noticed towing the TT ~1300 mi. (roundtrip) that the turbo boost pressure would seem to double (~15# to 30#) without the RPM's changing accordingly. Initially, I thought the turbo was linked closely with the exhaust pressure solely. Now I think there is something in addition to the exhaust pressure, like variable nozzles and/or vane position.....

Can someone please enlighten me on the operation of the turbo? Thanks.

Jim M.

P.S. I first searched the forum for the info., but didn't find much.

was this your gauge indication, Jim? 30 is way out there, stock is 20 psi near sea level.

[Duramaster]

On the GM TECH 2, the data at sea level the turbo PSI at idle (or key on engine off0 is 14 and on a test drive at WOT I heve seen as high as 35! :cool:

[killerbee]

On the GM TECH 2, the data at sea level the turbo PSI at idle (or key on engine off0 is 14 and on a test drive at WOT I heve seen as high as 35! :cool:

You are viewing MAP (absolute), not boost (gauge). 14.0 is atmospheric pressure (BARO) at around 1000 ft elevation. 14.7 psi at sea level. To get boost, subtract BARO from MAP.

A gauge that shows 30 psi, that is not using the factory MAP sensor for its reading, will show 20 psi max factory boost (gauge) if running correctly.

I have seen 30 psi boost, but the truck had a problem I won't go into. It was also a problem GM could not figure out, so i was proud of myself. :)

[jsmiracle]

was this your gauge indication, Jim? 30 is way out there, stock is 20 psi near sea level.

Killerbee,

Yes, it was guage. I have the KD Turbo Boost Stick installed. I don't know how much it effects boost pressures, but at lower pressures it seems to increase it about 50%. At idle, the guage reads zero. I saw 30# (max. gauge reading) when the truck dropped out of OD, going up a mountain, when towing the 9.5k lb. TT. It didn't seem the guage was pegged because it read fluctuated as low as 28# periodically.

It normally reads about 5-6# at about 2K RPM's in OD, unloaded. Is 30# harmful when seen only a few times a year? 15-20# is more common when towing up a mountain.

Thanks,

Jim M.

[Duramaster]

Not to argue Killerbee, but It actually is "BOOST" pressure on the "scan tool." I don't know why GM didn't correct for this. As I recall, the 6.5 diesel showed actual boost. 2001 - 2005 scan data shows boost. 14 psi key on engine off and at idle and then upto 35 psi at WOT at approx. sea level.

[killerbee]

.

It normally reads about 5-6# at about 2K RPM's in OD, unloaded. Is 30# harmful when seen only a few times a year? 15-20# is more common when towing up a mountain.

Thanks,

Jim M.

if you see 30 at the intake, your compressor discharge pressure is between 34 and 37 (51 PSI MAP), depending on IAT and altitude. This is very abusive to the turbo IMO. Your tuner may be adding to the total.

What tune/boost configuration do you use when towing? That is where the lions share of concern should be.

[jsmiracle]

What tune/boost configuration do you use when towing?

I use the Superchips setting called "Tow Safe" (I watch EGT and Boost guages closely) and keep the turbo boost stick installed. Maybe I should remove the boost stick the next time I tow.

I didn't perceive 30# boost pressure to be abusive for short periods of time and on an infrequent basis, especially if stock pressures go as high as 20#. I will check more into it, though.

Do you know how the turbo changes boost pressure? (vane RPM speed, vane position/pitch, etc?):confused:

Thanks,
Jim M.

[killerbee]

I use the Superchips setting called "Tow Safe" (I watch EGT and Boost guages closely) and keep the turbo boost stick installed. Maybe I should remove the boost stick the next time I tow.

I didn't perceive 30# boost pressure to be abusive for short periods of time and on an infrequent basis, especially if stock pressures go as high as 20#. I will check more into it, though.

Do you know how the turbo changes boost pressure? (vane RPM speed, vane position/pitch, etc?):confused:

Thanks,
Jim M.


higher boost is produced by spinning the turbo faster. The things required to do that on your VVT, is vanes closing toward 100%, which nozzle down the exhaust stream to spin the turbine faster, OR higher exhaust flow rate. The turbine is shaft connected to the compressor, so they spin at the same rpm. If you have more exhaust gas flow rate (greater throttle and rpm) then the vanes have to close less to achieve the same turbo rpm.

If you have a way to monitor your IAT, this parameter is also very important to how hard the turbo is working to produce a given mass air flow rate (weight of oxygen). Higher IAT=less oxygen content. Higher elevation=more work for the turbo and less oxygen content. Combining these 2 environmental factors can add up to much more stress, and operation further off the approved compressor map. Overspeed of the turbo, over 120,000 rpm, occurs at around 24-26 psi.

I personally would not tow with any boost enhancement that I can't adjust on the fly, and then only with a good CAI (verified IAT). I would not ever tow with 30 psi because it is likely not momentary. Anything that exposed the compressor to more than 26 psi for more than 20 seconds is bad IMO. More than 30 psi for more than 3 secs also, but these are opinions. I believe you exponentially decrease turbo life, if exceeding 26 psi for significant periods, especially when using the stock intake, which completely lacks temperature control, I have seen 220 F IAT. I also monitor compressor discharge temperature. Using a stack similar to what you are describing, I have logged 590 degree temperatures out of the compressor. That gets worse at altitude and shows how badly a cold air intake is needed. at 30 psi, every increase in IAT of 1 degree, increases compressor discharge temps 1.6 to 1.8 degrees.

I might suggest you do a google search on the topic, thermal feedback loops in the duramax.

Another question for you. When you tow with this configuration, what kind of fan activity have you observed?

[jsmiracle]

Another question for you. When you tow with this configuration, what kind of fan activity have you observed?

Short and infrequent cooling fan activity (approx. 2 or 3 occurrences per 1200 mi. trip for about 20-30 sec. duration each). ECT is steady at approx. 208F by OEM guage.

Thanks,
Jim M.

[killerbee]

Short and infrequent cooling fan activity (approx. 2 or 3 occurrences per 1200 mi. trip for about 20-30 sec. duration each). ECT is steady at approx. 208F by OEM guage.

Thanks,
Jim M.

do you ever get on any grades that require the foot to go to the floor for a few minutes at a time, in weather over 90 degrees?

[jsmiracle]

do you ever get on any grades that require the foot to go to the floor for a few minutes at a time, in weather over 90 degrees?

No. I don't think my acceleration foot ever goes to the floor. It usually drops out of OD because the speed decreases to about 53-55 mph.

Jim M.

[jharden1]

If you have a way to monitor your IAT, this parameter is also very important to how hard the turbo is working to produce a given mass air flow rate (weight of oxygen). Higher IAT=less oxygen content. Higher elevation=more work for the turbo and less oxygen content. Combining these 2 environmental factors can add up to much more stress, and operation further off the approved compressor map. Overspeed of the turbo, over 120,000 rpm, occurs at around 24-26 psi.



Do you have a copy of the compressor map? If you have it the turbine map, too. Surging can be a problem as you get to the edge of the map. The map would also show how non-linear temp and pressure are to turbo/compressor RPM.

[killerbee]

Do you have a copy of the compressor map? If you have it the turbine map, too. Surging can be a problem as you get to the edge of the map. The map would also show how non-linear temp and pressure are to turbo/compressor RPM.


yes I do. But the 39KB file size limit prevents uploading a readable version of it.

[DmaxMaverick]

yes I do. But the 39KB file size limit prevents uploading a readable version of it.

If it's an image (it should be), upload it to the Photo Album (http://www.thedieselpageforums.com/photopost), and link it. The file size limitations are much more liberal. If it's a document, you can zip or pdf it to reduce the file size. Or, just reduce the file size (first grade Photoshop job). If you have a worthy document or image, we can post it for you outside of the attachment limitations. If it's the document you've previously referrenced, I don't think it will qualify. Too much fuzzy logic and speculation for this discussion, IMO. I would like to see a turbo map and dyno report, though.

[killerbee]

Thanks for the tip.

http://www.thedieselpageforums.com/photopost/uploads/18997/Compressor_Map_Boost_augmentation_plus_altitude_co py.jpg

the black line on this map is a special condition, with boost up in mid/upper 30's, at altitude. 48-52% efficiency, hand calculated.

It is accepted that the VGT compressor is behaving the same as this GT37. Garrett is tight lipped, so far no actual VVT compressor map release, so this will have to do.

[jharden1]

Thanks for doing this!