Turbos & intercooling

[ak diesel driver]

Now were getting some input.:thumbsup: So other than the brief mention from TD I'm getting the impression that most are more concerned about the benefits of the increased volume that the turbo puts out than a reduction in back pressure. In my mind I would think that the back pressure reduction is equally important because it effects almost every aspect of the system. It lets the turbo spool easier hence quicker response and more volume like it was designed to. It lets the exhaust out of the engine more quickly so you don't get the egr effect. and lastly it reduces the energy consumed by the engine in its effort to expel exhaust. So if that really is the case then the ideal turbo would be one that does the best job of balancing output and backpressure. And that's not the GMx. I really appreciate everyones input I like to hear other ideas it makes me stop and think and reevaluate my own ideas. So if anyone has something to add please do.

 

[schiker]

Not really any different explanation than what several others wrote just don't recall the connection or description of velocity of the flow of air and thought that might connect a dot for someone.

I meant actually trying to describe the difference in velocity at the valve seat and how it relates to through put. Man I communicate poorly sometimes.

 

[schiker]

What about the differential pressure or pressure gradient from inlet to outlet of the system say from just inside the air filter to say 2 ft down the down pipe.

Several posts have been talking about it and I believe its best described as "effeciency" in general.

Yep, the "positive displacement pump volume" of the engine is the same.
Its just the turbo pump thats different.

How about this.....

Given the same size piping and same pressure differential you should get the same flowrate. At least you do under choked flow conditions. But not necessarily true when flow is not choked. I don't believe the flow is choked due to valve size or any other cross sectional area along the path.

Its limited by the volume filling, frictional loss (not choked), and pressure differential across valve seat area during the cylcle and valve duration. If I remember right you can have velocity differences to flow but the same pressure and hence different CFM or flowrate in lbs mass per unit time at the same psi.

Because the exhaust stroke "expels" more air because the turbine is bigger and has less back pressure it allows more air to come into the cylinder when the intake opens. The rush of air is at higher velocity because there is more room to rush into. Or in other words with less back pressure of the new turbo once the intake valve opens more air goes into the cylinder faster because the pressure differential across the valve is higher (due to less pressure in cylinder not higher pressure in intake).

So if you measured along the path with super cool unobtainium gauges at equal lenghts along the flow path and compare the GMX to Ateam the ATeam turbo has a lower pressure gradient through both the compressor and turbine along with smoother flow through intake. Probably would be a more level graph of pressure and higher velocity than the GM X which would have larger peaks and valleys of both pressure and velocity.

The biggest thing that would jump out is you would see higher velocity at the valves seats for the A team turbo if you could measure it but the same psi at midpoints of path ie at the plenum due to the compressibility of gas. Might even measure the same pressure at the valve seat area but again the velocity is higher.

You won't measure any differences of this with a boost gauge mounted at the plenum area. But I believe the lbs mass of air going through the engine is different with the same boost pressure. Which I believe we all agree must be happening due to improved performance.

 

[Slim Shady]

Now were getting some input.:thumbsup: So other than the brief mention from TD I'm getting the impression that most are more concerned about the benefits of the increased volume that the turbo puts out than a reduction in back pressure. In my mind I would think that the back pressure reduction is equally important because it effects almost every aspect of the system. It lets the turbo spool easier hence quicker response and more volume like it was designed to. It lets the exhaust out of the engine more quickly so you don't get the egr effect. and lastly it reduces the energy consumed by the engine in its effort to expel exhaust. So if that really is the case then the ideal turbo would be one that does the best job of balancing output and backpressure. And that's not the GMx. I really appreciate everyones input I like to hear other ideas it makes me stop and think and reevaluate my own ideas. So if anyone has something to add please do.

Sometimes I can't get out in words what my mind is thinking, like I said before, always think total picture and how it all relates, then you get a complete idea of how it may work. Kind of like missing a formula for an equation it never will be right without the missing piece of the answer.

Got the idea when I was building my own turbo master, truck ran better at 1200 to about 2000 rpm then just kind of fell on its face. Felt tight driving it at highway speed and fuel mileage went down. Then thought why the heck is a 6.2 getting 22 24 mpg on the highway and I am at 16 and 17 mpg and turbo charged. Bingo little light goes on in head (lots of time to think on 12 hour road trip alone). I get out and back off home made turbo master run know mileage after fill up truck gets 1 mpg more, hey whats up I think, and so we have it. ):h

Well at least thanks to Turbine Doc and HAnk1948, Turbine doc saw merit in the project and Hank did the machine work to get the turbo to work on our engine. Then with the faith of a few people that purchased them and we have had consistent data from them increased mileage, better petal feel and better towing with less EGT temps. Time will tell, but my but and 12000 miles of running an ATT turbo tells me. yes.

 

[buddy]

Not exactly, there is overlap, where the intake and exhaust valve are open at the same time. This is where I believe the exhaust back pressure makes the most difference.

In a 4-stroke engine there are specific separate air intake and exhaust output strokes, so the valves aren't open at the same time. That is different in 2-stroke engines where they are open at the same time.

So the flow is choked, if it wasnt choked there wouldnt be pressure buildup at all. It is choked/closed completely by the cylinder and there is absolutely no way to push more air at a lower pressure as volume is constant.

However the ATT allows better efficiency because its a much better turbo that is more efficient and doesnt require the engine to work as hard to create backpressure to create boost, which is very welcome on such a high compression ratio engine. The ATT spools easier and has more efficient pitch or balde design (like why the DMAX fan is so much better than our stock fan). Turbo 101 says the greatest pressure differential will create the most boost from a turbo, well the GM-X requires way more pressure differential to create the same amount of boost, which causes the engine to work harder to complete an exhaust stroke (which has to be powered by another cylinders combustion stroke) and increase IATs. Its obvious why the ATT is so awesome.

I was happy to see the new Maxxtorque magazine today, and Heath says his landcruiser gets like 30MPG, must be non wastegated turbos and free flowing headers and that water injection.

 

[Slim Shady]

In a 4-stroke engine there are specific separate air intake and exhaust output strokes, so the valves aren't open at the same time. That is different in 2-stroke engines where they are open at the same time.

There is vale overlap, even if for an instant, MOST all internal combustion engines have a timing overlap. Open as far as completely at the same time, NO, but they do have overlap.

 

[NVW]

In a 4-stroke engine there are specific separate air intake and exhaust output strokes, so the valves aren't open at the same time. That is different in 2-stroke engines where they are open at the same time.

There is vale overlap, even if for an instant, MOST all internal combustion engines have a timing overlap. Open as far as completely at the same time, NO, but they do have overlap.

When I was a lot younger I knew more about this and I believe it was called duration. After market cams had different lifts and duration, I think extended duration helped scavenge the exhaust gases and probably other things. It seems as I have forgotten a lot of things.:nonod:

Leo​

 

[buddy]

A little scavenging efficiency boost isnt going to increase flow of air for the combustion stroke that you could measure in a turbo charged diesel, but add it to the list of reasons the ATT is better. More efficient scavenging to help cool the engine and EGTs, now that I know that it does that, because not all of them do scavenge.

 

[chrisk1500]

Would wiring in a MAF sensor after the turbo show a difference in amount of air (CFM) produced between the two turbos?....

 

[chrisk1500]

Evidence of the need Heath racer with 2 GM-X turbos making 153 mph, if a high psi turbo could flow the air, I think it would be on it.

I may have to give Bill a shout....Diesel Power must have screwed up yet another article....they claim that Bill was running twin turbos from BD Power....S2000?

 

[Turbine Doc]

No you may have that right Chris, actually I sort of recall special built turbos in one of my conversations, (Thanks for reminding me) I talked to Bill yesterday, he has all final pieces & parts for the TD-07 (ATT's twin brother sort of, I did not have an extra ATT laying around) test I want him to run and see if tweaks can be had to HP-4 to work better with ATT. Weather and other shop work precludes the test, so don't go bugging Bill about the test.

I'll let ya'll know when testing is finished at Heath's shop and if any program changes deemed worthwhile or necessary, no need to bug him about it, as several have called, and he really has not had opportunity to run it yet, he's not hiding test results from anybody, it really has not been put on his truck yet.

He'll pass data to me, and I'll pass to you, I've have not hidden anything from anybody, I made Slim a deal I would go down this path with him & if I thought it to be a turd I'd say so, all he asked for was a fair evaluation, he even went so far as to offer to buy mine if I didn't like it, wasn't the case, liked it and bought one from Slim to replace the TD07 I sent to Bill.

Those of you new to this thread following it has been almost 2 years in the making, intent here by Slim was not to get rich but to find a viable replacement to the GM-X which are getting harder to come by, as it turned out TD07 & ATT not only were viable replacements, but do indeed surpass GM-X in most respects.

It's hard to not sound like a salesman for ATT and not sing it's praises, but I'm not the only one running it now and as of yet no one has said it's a turd so something positive in the 6.5 world must be happening with this turbo.

 

[Chicago TDP]

Hey Chicago TDP: How many miles do you have now on that 22-28psi motor?
Did you put cometic head gaskets in it?
Are you happy with that Holset?

Just turned 60k on the motor, over 205K on the truck.

Boost is still peaking at 26 psi and maintain 15 psi while driving 65 MPH.
I have stock head gaskets from Fel-Pro, with TTY bolts, no studs and I have had no problems. One day, I hit 31 psi of boost up a hill with an enclosed car trailer behind me.

I am most happy with the Holset because I can maintain 18 MPG empty and 16 mpg with the bed full of camping gear or shooting gear.

 

[Goldsburg]

Just turned 60k on the motor, over 205K on the truck.

Boost is still peaking at 26 psi and maintain 15 psi while driving 65 MPH.
I have stock head gaskets from Fel-Pro, with TTY bolts, no studs and I have had no problems. One day, I hit 31 psi of boost up a hill with an enclosed car trailer behind me.

I am most happy with the Holset because I can maintain 18 MPG empty and 16 mpg with the bed full of camping gear or shooting gear.

Chicago -

Have you ever thought about a turbine housing with a slightly larger A/R? Those boost numbers sound unnecessarily high to me for 15 PSI running empty at 65MPH, even with the additional exhaust heat from your 18:1 engine taken into account.

A larger A/R would likely increase your mileage and increase mid-range and top-end performance.

Regards,

 

[Goldsburg]

... But I believe the lbs mass of air going through the engine is different with the same boost pressure...

This is the concept that many people (not necessarily here) often fail to grasp. To "get the concept" all you have to do is remember that boost is a product of "restriction to flow". That restriction can be a product of pipe flow and/or backpressure (ala a lower differential pressure). Since changing the turbo can't change the pipe flow characteristics of an engine, the improved flow must come from reduced backpressure and therefore improved differential pressure (across the valves)...

Regards,

 

[chrisk1500]

so don't go bugging Bill about the test.

Who said anything about bugging him about his test?

 

[Turbine Doc]

Now were getting some input.:thumbsup: So other than the brief mention from TD I'm getting the impression that most are more concerned about the benefits of the increased volume that the turbo puts out than a reduction in back pressure.

I backed away from the discussion as I know what I'm wanting to say but can't get the message out all are talking the same thing but from different angles. Airflow dynamics do play a role here, we arent filling a static chamber, P over V laws do not change, if one goes up the other has to go down, a larger more efficent wheel will net more flow. Since my air compressor analogy fell flat (no pun intended) lets try this, 2 jet engines, something I've spent 28 years previous to this one working on,

2 turbines; 1 small, & 1 large both capable of making say 1500 shp, but the bigger one is capable of 3000 shp, you might eek out more hp from the small one and get say 1750 shp out of it, but putting signifcant stress on it to make that and no safety margin left in it, or go with safety margin of the bigger one but underload it and run inefficiently fuel wise and run it also at 1750. The larger the turbine the slower it spins yet both are making same shp.

Or design a jet capable of producing power for 1750 shp, maximizing flow for power demand/projected max hp, my point that seems to be getting lost in translation is we have upped power request from the 6.5, yet GM designed the GM-X to meet the demand for 195 shp,

Yes it is backpressure, yes it is flow out of the turbo into the engine, yes it is overlap, yes it is charge air density, yes it is dispacement it is all of those things, we can debate the individual pieces and parts, but that isn't how an engine works, it is all about total flow dynamics and power to ground after it all happens, air flow is the key impediments to that are bad ergo flow loss through an IC, backpressure out the back of the engine, you can do things to make the trade off tolerable but there is a trade to be sure, you have to manage it.

We aren't completely dealing with a fixed compression into a fixed cyl, yes one stroke =X psi & cfm, but increase the number of strokes with rpm, and push from the turbo that range of availble power shifts to occur at different points of operating range from what it once did, ergo n/a 6.2 flywheel more/less peaks at 135 shp, 6.5 n/a a little more 150 IIRC, 6.5 turbo stock 195, peaked & tweaked 6.5 single turbo 300+, 6.5 dual turbo peaked & tweaked estimated 500+ or 153 mph capable all that was done to those same essential blocks is add more fuel & cfm of air, boost psi remains fairly similar with all, with exception of n/a's where physical dispalcement is changed.


I'm not a scientist, nor do I play one on TV, it's been a while since I stayed in a Holiday Inn Express, maybe I need to do that and have a fresh go at explaining how I think it all happens. Just a knuckle dragging field service guy that dabbles in engine repair, turbines once as a profession, Diesel locomotives as profession now, and a plethora of other vehicular contrivances as a hobby over the years, gasoline-Diesel-and even pedal powered.

 

[Chicago TDP]

Chicago -

Have you ever thought about a turbine housing with a slightly larger A/R? Those boost numbers sound unnecessarily high to me for 15 PSI running empty at 65MPH, even with the additional exhaust heat from your 18:1 engine taken into account.

A larger A/R would likely increase your mileage and increase mid-range and top-end performance.

Regards,

I would like to change the A/R and I am going to, as soon as it warms up. The high boost is nice though for me because when I am driving for about 6 hours to my cabin in WI and I want to pass someone, I am so far up into the boost pressure that when I accelerate, the truck speeds up instantaniously. I would like to mearure my 65-100 one day, it is FAST and I like that ):h

But, needless to say, I am looking to swap out to a different turbo in the spring. At one time I did run a T3 housing turbo with a bigger A/R and it killed the low end for me. But, it might have been too much A/R

 

[ercaduceus]

I'm not a scientist, nor do I play one on TV, it's been a while since I stayed in a Holiday Inn Express, maybe I need to do that and have a fresh go at explaining how I think it all happens.

HAHA! that was a great line. Thanks for the explanation.:thankyou2:

 

[Turbine Doc]

Who said anything about bugging him about his test?

Bill did not share names, but did say several folks have asked about it, not sure from which site where the ATT has been discussed, some folks got downrite unpleasant. :nono:

 

[buddy]

OK, yes you can increase RPM to increase air flow, same on any engine, and I whole heartedly agree that it is more efficient and better power with the ATT, but it is the same fixed volume when that exhaust port closes. However now you could reach higher RPMs safely and efficiently, because of the lower pressure differential, boost and backpressure both.

If the scavenge process, or exhaust stroke weren't working correctly before at high RPM due to high backpressure, then that might be a way to slightly increase the volume of fresh air in the cylinder, but its not like youre gettting even a 5% increase there, not like you saying it is capable of twice the CFM at the same PSI.

And yes if you maintain lower IATs the air mass is increased, but not flow, same flow but more dense, which is also a big imporvement. It would be better to just say you get more air mass at lower pressure.