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So what IYHO changed to cause the LLY to exceed the LB7's cooling system?

  • Head redesign

    Votes: 23 18.4%
  • Increased Piston Cooling

    Votes: 5 4.0%
  • Turbo

    Votes: 31 24.8%
  • Emissions (to comply with EPA stipulations)

    Votes: 82 65.6%
  • Allison (fluid mapping changes

    Votes: 1 0.8%
  • Body Design (overall frontal cd)

    Votes: 10 8.0%

  • Total voters
    125
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Discussion Starter #1
So what IYHO changed to cause the LLY to exceed the LB7's cooling system?
 

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I vote cylinder head redesign. IMHO, I believe some of the heads are either core shifted, or the thickness is simply to thin to contain the combustion temps where they belong.
 

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Discussion Starter #3
75% EPA fuel mapping
10% EGR
5% CAT
10% Keeping up with the Jones' = HP
 

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Higher EGT to support the EGR. Designed on purpose using the back pressure of the turbo redesign.

Opinions :ro)
 

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Turbo. Pound for Pound, the VVT generates twice the backpressure (or more) as the LB7 turbos. Those that replace the turbo with an aftermarket do not overheat.
 

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Turbo. Pound for Pound, the VVT generates twice the backpressure (or more) as the LB7 turbos. Those that replace the turbo with an aftermarket do not overheat.
Somebody send me a big honkin' turbo, and I'll gladly test this theory!!):h
 

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Turbo. Pound for Pound, the VVT generates twice the backpressure (or more) as the LB7 turbos. Those that replace the turbo with an aftermarket do not overheat.
So is that the reason for the LBZ turbo change? Do all VVT's create excess backpressure or is it a LLY VVT problem?
 

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turbo!
 

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Turbo. Pound for Pound, the VVT generates twice the backpressure (or more) as the LB7 turbos. Those that replace the turbo with an aftermarket do not overheat.
I agree with Fingers.:)

He explained this to me in detail at Merchant's and it makes complete sense...
 

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Somebody send me a big honkin' turbo, and I'll gladly test this theory!!):h
Rick have you tried doing a Turbo Relearn Procedure?? (with a Tech 2)
 

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I don't know that the LBZ's turbo is much better. McRat might be able to chime in there. He is the only one that I know that has placed one on an LLY. However, there are several with twins and aftermarkets. They can speak for themselves.
 

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So does the added backpressure put more heat soak and load on the cooling system??
 

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I don't know that the LBZ's turbo is much better. McRat might be able to chime in there. He is the only one that I know that has placed one on an LLY. However, there are several with twins and aftermarkets. They can speak for themselves.
The LBZ charger does not run any cooler than the LLY chargers.

If anything, a bit hotter.
 

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I still think it is the heads. You guys know more than me and are probably right, but I don't see how the different turbo can make it overheat like it has been described here. I agree with Rick but add that the water doesn't go straight through the head and creates hot spots.-IMHO
 

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I still think it is the heads. You guys know more than me and are probably right, but I don't see how the different turbo can make it overheat like it has been described here. I agree with Rick but add that the water doesn't go straight through the head and creates hot spots.-IMHO
this doesnt explain why SOME overheat and SOME dont.

As Fingers explained it to me, not all of the VVT's are exactly the same. Some have the vanes "keyd" or "Indexed" slightly differently, meaning 65% commanded vane position on one LLY may be a bit different than 65% commanded vane position on another LLY. GM doesnt tailor each ECM tune to each truck (turbo) obviously, so, if truck X has the vanes slightly more closed than truck Y at B amount of fueling, truck X is going to ahve more backpressure than truck Y. They are both getting the same amount of fueling at that specific time, APP, rail press etc.... B amount of fueling is going to create C* EGT in any LLY because as far as burning the fuel combusting it, all LLY's are the same. So that common C* EGT is going to have a much different effect on truck X as it does on truck Y. Truck X has slighty different turbo vane position even tho the ECM doesnt know it....truck X has more back pressure, Truck X forces the engine to work harder to expell that exhaust, Truck X loads up the engine more in the same given situation than truck Y, therefor truck X overheats.

Why do you guys think GM has this "turbo learn procedure"?? because they know all VVT's are slightly different for whatever reason. The theory/intent of the turbo learn procedure is to cycle the vanes to the extremes, then measure the voltage returned by the vane position sensor. Im guessing that while this works to some extent, its not exact/specific/accurate enough to match EACH different turbo to each LLY engine.

Rick do you know for sure if the turbo learn procedure was performed when your turbo was replaced? Did your truck overheat ANY differently (ie, did it take longer or shorter to overheat, did ECT rise faster or slower) than before the turbo was swapped? Has anyone taken an overheater LLY, done NOTHING to it, except a turbo relearn procedure and documented the results/differences????

Fingers is what im saying/thinking making sense? Is that similar reasoning to yours? Or am I also missing something else key?

ben


Rick do you have EFILive?? I think it would be interesting to play with commanded vane position tables and see if it has any effect on overheating. IMHO, NO ONE has a fix for overheating. There...I said it...people have devised viable "alternatives" that serve as "bandaids" to overheating. Meaning, the truck is still actually overheating/root cause of the problem is still there, they have just INCREASED the capacity/capability of the cooling system to a point where the root cause is not able to show its ugly face. Again, I mean no offence to those dedicated to LLY overheating, thats JMHO. Do those fixes prevent overheating in the first place? Not really. Do they help the cooling system cope with and overcome the root cause?? Yes.....but there is a difference between the above two sentences. :)
 

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Not sure. I have had the turbo replaced on my truck by the dealer. Can I do it with EFI Live? Can you explain?
It can only be done with a Tech 2. Its in the SPECIAL FUNCTIONS menu of the engine/ECM section.
 

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Well using my limited EFILive experience I will have to say there is not a commanded vane position per say. There is a targeted and min/max but the boost is what is going to control the vane position. If a turbo is indexed different then another the needed vane position value to give the resulting boost will be different but the boost will be the same.

Just my opinion....
 

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boost will be the same as well as drive pressure....
 
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