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LB7 Turbo on an LLY

17811 Views 60 Replies 11 Participants Last post by  killerbee
Thanks Idahofox and Rick for the info on the LB7 turbo on the LLY.

LB7 on LLY This is the kind of thing we should be talking about.
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What is your estimation then of parasitic HP loss to the VV turbo?
Fingers said:
On the 6.6 Dmax, each PSI of backpressure costs about 2 HP in strictly mechanical terms. So by reducing the VVT's drive pressure to be 1/2 way closer to the IHI you could easily find 30 HP.
I am still fumbling over this statement. It implies that that over 60 HP must be dedicated to the VVT to spin it.

Am I missing or misunderstanding something? I mean, I understand that it is preliminary, and you will test it, I just don't get the remote possibilty of 60 HP. What criteria does this come from? You've peaked my interest.
open mind

Fingers said:
I called it scavanging, but the same thing.

Also, I would like to correct the pure mechanical HP loss at 2800 is 1.4239 HP/PSI of drive pressure. I rounded WAY up. My fault. Still significant.
The turbo, in it's "free lunch" aspect, is driven by exhaust, a waste product (expanding exhaust gases that have left the cylinder), so it is not tapping power from the motor, at least not like a parasitic device, alternator for example.

This is where I am not seeing a benefit, but I am trying.:Thumbup: My limited forced induction knowledge is showing.

Are you saying that excessive turbo backpressure is causing less expansion (thus less work performed) in the cylinder? For that to be the case, drive pressure would have to be significant (vs negligible) compared to cylinder pressures.
Guess I just don't see what you do.

From what I know, most turbine work performed is a result of leftover adiabatic (or near so) expansion of combustion gases, energy that would be wasted if the turbo were not there. Cogeneration, more or less.

The turbos ability to spin with little parasitic loss (producing more than it consumes, via use of a waste product) has always been its main selling point, albeit with a backpressure tradeoff. To suggest there may be a significant gain opportunity, you must be suggesting that is not the case with this VVT.:shrug:

The belt driven supercharger, by contrast, is 100% parasitic, if it is being fully funded by the power stroke, with no backpressure consequence.

Not criticizing, I see what you are after. Hope you have good results.

Perhaps you can post some of those drive P charts from PUSU here, that might be good for discussion.
That is right up Jon's alley. He works with steam turbines in his profession I believe.
For the majority of those looking for improvement, a turbo swap would not likely be a viable alternative. I do commend the effort, in the interest of discovery, invaluable.

I personally would like to gander deeper into the workings of the VVT, to see (as you probably have done, Jon) where some real benefit can be had to overheat resistance.

Can simply opening up the vanes get us back on track?
Is the VVT fighting itself (egt)?

EFI will be helpful in doing this analysis. First, it would be helpful to have an understanding, defintively, of the feedfoward and feedback mechanism, a mystery to some of us.
Jon, is this a fair statement?

"The VVT is much less efficient than it's predecessor."

I am working with a vehicle, and the CAC just cooks the radiator on the driver side. Albeit with 160 degree IAT.
ambient temp after CAC

Did the same test on my truck, this time sampling the driver side (T1) the pass side (T4), and 2 others between them. CAI installed.

Did a little empty stop and go, then loaded it up at 14:51, a 45 second test. Who knows what this would be after 10 minutes.

The avg ambient temp presented to the radiator is about 190, 220 being the hot side, 160 the cold side.

95 out today. You are on the right path Jon, I think.

Anyone in the area with an LB7, I can rerun the test.


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...will poor turbine efficiency, CREATE poor compressor efficiency?

This baby produces heat better than it produces boost.
OH good. Let's plan on that. Thanks Brandon.
Fingers, have you been able to get ahold of compressor maps for these trucks?

Ford uses a version of the VVT I think
Fingers, recall the test charts for drive pressure last year.

On each run, drive pressure increased precipitously early in each run. Looking back at those charts, I find no relationship that would cause that. Did you draw a conclusion, other than boost induced? A downshift? Too bad we weren't logging vane position.

Is there anything I can do to help out with your swap experiment?
BTW, I have done some logging on an overheater here, I looked at the logs and couldn't figure out why vane position was higher than the "target". I looked deeper and saw that vane position is constantly running up against the "turbo vane target position maximum" table B2224.

We were using a pred tun, and he had a BS on also, FWIW.
I would probably not do it just to prove a point, but I do believe the VVT has problems.

Interestingly, the MAP sensor may well be culpable. It's new role in the LLY, is as a feedback sensor. It was never intended for this role, and tolerances may well a real issue for various LLY's.

Can 21 vs 25 psi be the difference between overheating, and not overheating? Yes.

I took one overheating LLY vehicle that was running "too much" boost, and fixed it by removing the boost enhancement, no other changes. Then I started thinking:

What if many vehicles were overboosted?

I have read about a few instances where the guy who had an edge attitude (LB7) was reporting 10 psi on the display. Then found it was actually 21 psi (normal), turns out the MAP sensor was bad, heat damaged. But other than noticing the display was off, on the LB7, there were no consequences, and were it not for the Attitude, he never would have had cause to investigate.

LB7: The MAP sensor is a simple reporting sensor, no induction related ECM decisions are made with it. The boost is designed by turbine gas flow, and merely capped by the wastegate. It's compressor innefficiency is hardware limited.

On the LLY (VVT), by contrast, this is not the case. If there is a MAP sensor anomoly, it appears the VVT will just produce more boost till the desired MAP sensor return volatage is achieved. The reading on the attitude display (or any scanner for that matter) will be no help in identifying the problem, because it will always read 21, even if actual boost is 40 psi. This is unlike the LB7. Plus, there is no software efficiency degradation limit, and certainly no hardare limit, the wastegate is gone. In fact, the VVT has, in my opinion, serious efficiency erroding feedback loops, and nothing to safeguard against them.

If you have a LLY MAP sensor damaged by heat, and it is reporting 10 psi when the plenum is seeing 21, guess what? That 21 psi reported in the attitude display, might actually be 32 or more, which the turbo is glad to produce unchecked. AND THAT IS AN OVERHEAT, the stack cannot handle that much heat, as much as (5) five-bedroom heating and cooling units worth, from the CAC alone. Reports of unusual or constant fan without load is also an indicator, there is heat, but where from? The CAC.

I started thinking more. "isn't there LLY comparator tables that issue a MAF code, if mass air flow doesn't mate with boost, correlated within certain tolerance parameters?" There is. And I adjusted them so that the ECM would expect to see really low MAF numbers when boost was high. For example, I set it to read 20 lb/min of air when boost was 25 psi (in actuality, 25 psi produces around 50-60 lb/min of air, so there is a clear mismatch). To my surprise, I got NO codes, after running around for 20 minutes. Then again, you need 100 occurences of failure to set the code. I can change that to 1 and retry

I started thinking more. "if no code results from overboost conditions due to a bad MAP sensor, then all these LLY's might be overheating, without the telltale cause showing up".

Then from a different angle "what if MAP sensor voltage scaling changed with sensor temp itself?" IOW, what if, as the sensor itself heated up, it's scaling became unreliable with too low a return voltage? We would never find the problem, because it would fix itself every day.

I am still playing with this, but more can be found about this and other real VGT forced induction issues HERE.

I really like the VVT for its other virtues. I have finally gotten Ross to fix the ECT boost issue (thank you again Ross), that allows us to use boost as an artificial load, and I am able to warm up the truck much quicker in the winter, for example, and have that boost disappear at 170 ECT.
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