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  #41  
Old 06-30-2006, 12:44 PM
DA BIG ONE DA BIG ONE is offline
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Default Peak Torque

[QUOTE=TurboDiverArt]If I'm understanding things correctly, I "think" we are all talking the same thing but using different or maybe slightly incorrect semantics. You are definitely correct that the shift point is load and TPS based and not strictly RPM based.

One area I think I'm going to disagree with you on is that the stock shift points are where you want them and that lowering them somewhat is not what you want to do. Yes you hold torque multiplication longer by delaying the shift point higher in the RPM range but torque multiplication is power in multiplied by the gear ratio. So, making the shift point above the max output on the torque curve means less power into the torque multiplication so less power out. Now, you do have to shift higher than the max torque otherwise the bottom of the shift will be below the torque curve and the truck makes no power after the shift. I don
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  #42  
Old 06-30-2006, 12:59 PM
ronniejoe ronniejoe is offline
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The shift points should actually be near the engine's power peak because power is the rate at which work is being done. You want the work to be done at as fast a rate as possible to get down the road as quickly as possible.
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  #43  
Old 06-30-2006, 01:23 PM
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Default Power peak?

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Originally Posted by ronniejoe
The shift points should actually be near the engine's power peak because power is the rate at which work is being done. You want the work to be done at as fast a rate as possible to get down the road as quickly as possible.
Hello RJ, When you mention power peak, is this torque, or hp, or somewhere in between? In my case peak torque is at 2,200 rpm's, peak hp is at 3,500 rpm's, I'm thinking peak torque, right, or?
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  #44  
Old 06-30-2006, 03:02 PM
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Yes I believe you are all correct in that you want the shift at peak torque, in fact you want the engine to always operate at this point. But.... after the shift you don't want to be out of the power range either. If you shift at 2200 RPM
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  #45  
Old 06-30-2006, 03:56 PM
ronniejoe ronniejoe is offline
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I am talking about power as measured in HP. The engine is most efficient at its torque peak, but gets the work done more quickly at its power peak.

Now in the case of these engines in stock form, the real optimum point is around 2700 - 2800 rpm where the rate of increase of power (second derivative...) drops. On my dyno plots, you can see the power curve trail off at about that point. It keeps increasing all the way to 3500 rpm, but not very rapidly. If I were racing, I would want to shift at that roll off point, or around 2800 rpm.

If performance is your goal, you want to operate near the maximum power point, which will be above the maximum torque point. If efficiency is your goal, operate near the maximum torque point.

I should have an experimental turbocharger installed next week that will let this thing breathe up to 3500 rpm. I think big numbers are possible with good airflow at 3500 rpm. Planning to go to Montana in a coupla weeks...
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  #46  
Old 06-30-2006, 04:32 PM
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Default Thank's

I want to thank all of you for the expert input, mine is just so, so but the rest of you make sense of it.
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  #47  
Old 06-30-2006, 04:39 PM
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Will it hurt a high mileage motor (like mine) to run all day in 3rd at 2800 RPM? Mine does seem to pull best like this, but I have avoided it because of fear of blowing it up. BTW, I tow a little less than 9,000 lbs. I am not greatly concerned about gas mileage, but don't want to get stranded on vacation.
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  #48  
Old 06-30-2006, 05:57 PM
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As discussed, the 45mph is the lockup point on the 4L80E with 4.10's and 245's.

I like that lockup point and want to maintain it during the swap to 3.42's and 265's (at the same time).

But, one thing I don't like is that once up to speed at say 65mph and above, I don't get a shift out of OD, so passing is done with boost and fuel.

So, my question...

If you use the vss modifier and I leave my VSSB at the stock 4.10 setting, will I still see a no-shift out of OD at 65+?

Hmm.
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  #49  
Old 06-30-2006, 06:11 PM
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Quote:
Originally Posted by john8662
As discussed, the 45mph is the lockup point on the 4L80E with 4.10's and 245's.

I like that lockup point and want to maintain it during the swap to 3.42's and 265's (at the same time).

But, one thing I don't like is that once up to speed at say 65mph and above, I don't get a shift out of OD, so passing is done with boost and fuel.

So, my question...

If you use the vss modifier and I leave my VSSB at the stock 4.10 setting, will I still see a no-shift out of OD at 65+?

Hmm.
I'm not sure how the 4.10's work. The 3.73:1's lockup the converter at about 47-48, which is pretty close to the 45's you now have. At 65MPH it'll drop out of OD. it'll drop out of OD at 75 if there is enough load like when you have a trailer in tow up a hill.

Art.
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  #50  
Old 07-01-2006, 02:30 PM
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Good Day!

On reflection, I really don't care much about the shift points, I just wish the TC would lockup at a lower speed, & have more hysteresis in that lockup speed.

I sure wish I'd known about these trucks as they were being introduced in '94. I think a guy could have written some killer code to allow changing many different parts of the algorithm to suit the owner. I would REALLY have liked to integrate my Gear Vendors Aux. OD into the PCM.

Blessings!

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  #51  
Old 07-01-2006, 06:05 PM
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Quote:
Originally Posted by ronniejoe
Boost is the reason you feel the lessening acceleration. The problem is the small housing and nozzle on the GM-4 turbine. Above about 2800 rpm, it simply cannot flow enough to keep up with the engine. The backpressure blows the waste gate open (even against full vacuum straight off the pump...as I've been running for a year now) and the turbine rotor holds constant speed. I've plotted data points on the compressor map and the compressor is following a constant speed line above 2800.

This means that boost falls off even as total flow increases. Power falls as well.
I thought my turbo was a GM-8? I thought the GM-8 came on the newer trucks. Mine being a 1999 I assumed mine came with it. Maybe the GM-8's only came on the Hummers?

Thanks,
Art.
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  #52  
Old 07-01-2006, 06:34 PM
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Art,

RJ's only had experience with the GM4 turbo which was used from 94-95. Being that you have a '99 you should have the GM8. I do personally believe there is a little better flow with the GM8, but the internals of the turbo are almost identical, the change is in the exhaust side. GM5 and GM8 are almost the same turbo too, except for a better wastegate bushing on the '8.
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  #53  
Old 07-01-2006, 07:42 PM
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Quote:
Originally Posted by john8662
Art,

RJ's only had experience with the GM4 turbo which was used from 94-95. Being that you have a '99 you should have the GM8. I do personally believe there is a little better flow with the GM8, but the internals of the turbo are almost identical, the change is in the exhaust side. GM5 and GM8 are almost the same turbo too, except for a better wastegate bushing on the '8.
So, has anyone seen a compressors map of a GM-8? In our motors where does the turbo run out of steam? On mine it appears that at high RPM's it
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  #54  
Old 07-02-2006, 04:37 AM
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Default Yep, It's a GM-8, however

[QUOTE=TurboDiverArt]So, has anyone seen a compressors map of a GM-8? In our motors where does the turbo run out of steam? On mine it appears that at high RPM's it
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  #55  
Old 07-02-2006, 05:35 AM
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Quote:
Originally Posted by DA BIG ONE
Art, The GM-8 exhaust turbine "exhaust outlet" is some of the limiting factor needing some porting. How much porting? It's more a matter of how much risk one is willing to take making walls too thin.

Some say the elbow after the gate is an issue, then some smoothing out of its inside surfaces are in order.

I really thing wee need those bigger Holset 35, 40 turbo's providing we stay out of the surge line, and keep boost at a level of 15+- psi @ intake.
If the GM-8 seems to run out of steam at 2800, were does a GM-8 run out with a free flowing exhaust? Mine definitely seems to lose it by 3100, maybe 3000.

Art.
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  #56  
Old 07-02-2006, 08:52 AM
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The rotors on a GM-4 and GM-8 are identical. The only difference is a slightly better compressor housing and a slightly better exhaust elbow. The waste gate was moved out of the exhaust housing into the elbow on the 8's and I've been told that the elbow is more efficient. With that said, I don't think you'll see significant performance differences between the two. The wastegate move was to improve reliability of the bushing (mine failed) and had nothing to do with performance.

I have an outline map of a the GM series compressors...it has no detail and IHI will not even respond to my inquiries. The other manufacturers have been very responsive to my questions.

It is fair to take my comments as being applied to the GM-X series in most cases.

My main comment here was to clarify the relationship between peak torque and peak power and to give you some of the rationale behind choosing shift points. The turbo talk was simply to help explain some of your observations.
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  #57  
Old 07-02-2006, 06:13 PM
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Quote:
Originally Posted by ronniejoe
The rotors on a GM-4 and GM-8 are identical. The only difference is a slightly better compressor housing and a slightly better exhaust elbow. The waste gate was moved out of the exhaust housing into the elbow on the 8's and I've been told that the elbow is more efficient. With that said, I don't think you'll see significant performance differences between the two. The wastegate move was to improve reliability of the bushing (mine failed) and had nothing to do with performance.

I have an outline map of a the GM series compressors...it has no detail and IHI will not even respond to my inquiries. The other manufacturers have been very responsive to my questions.

It is fair to take my comments as being applied to the GM-X series in most cases.

My main comment here was to clarify the relationship between peak torque and peak power and to give you some of the rationale behind choosing shift points. The turbo talk was simply to help explain some of your observations.
Thanks for the info, it's good information! It definitely seems that the stock turbo putters out in the 3000 range. This is why I thought the shift point should be at about that point. It just seems to take forever to get from 3000 to 3500. Now if you had a turbo that would pull all the way up to 3500 RPM
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1992 Tube Chassis Camaro, 468 BBC, 8.54@157MPH (SOLD)
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  #58  
Old 07-02-2006, 07:59 PM
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[quote=TurboDiverArt]Now if you had a turbo that would pull all the way up to 3500 RPM
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  #59  
Old 07-02-2006, 11:29 PM
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Quote:
Originally Posted by ronniejoe
Hold that thought...
You just couldn't resist could you!
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  #60  
Old 07-04-2006, 12:16 PM
ronniejoe ronniejoe is offline
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Quote:
Originally Posted by jspringator
Will it hurt a high mileage motor (like mine) to run all day in 3rd at 2800 RPM? Mine does seem to pull best like this, but I have avoided it because of fear of blowing it up. BTW, I tow a little less than 9,000 lbs. I am not greatly concerned about gas mileage, but don't want to get stranded on vacation.
My experience has shown that egt's run high under those conditions. I prefer to run in OD at higher boost levels where things stay cooler.
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