4.0 V8 super sluggish at altitude. - Defender Source
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  #1  
Old July 10th, 2016, 11:53 PM
Tyler Wirken
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Tyler Wirken
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4.0 V8 super sluggish at altitude.

Just got back from a trip to Colorado and the 110 was as sluggish as it used to be at altitude. Wondering what you all do to combat that? Seeing as it is fuel injected I was always under the impression it would adjust to the thin air but not so much. It has been like this for years when up in the mountains but this last trip got me wondering what can be done.

Thing drove great when back down the mountain. So what can be done to improve performance with a 4.0 gems?

Thanks
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  #2  
Old July 11th, 2016, 12:32 AM
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FWIW, according to the internet, someone posted this formula to calculate HP loss for NA engine:
(Elevation(ft) * .03) * hp at sea Level)/ 1000
If that formula is somewhat true, for our 4.0 @ 6k ft, the HP would be ~150hp and not a lot of torque, hauling 4000lb brick.

To solve thin air/low HP problem could either be force induction (turbo/supercharge) or bigger/more powerful NA engine with expandable HP during high altitudes runs.
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  #3  
Old July 11th, 2016, 06:39 AM
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  #4  
Old July 11th, 2016, 06:56 AM
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turbo?
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  #5  
Old July 11th, 2016, 08:39 AM
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Years ago when it was possible to adjust timing, LR centers in Co advanced the timing between 4 and 6 degrees to compensate for altitude.
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  #6  
Old July 11th, 2016, 10:26 AM
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Timing helps because the air is thinner and therefore needs more advance to fully burn the mixture. Rule of thumb is 3%hp loss for every 1000 feet and that assumes that everything else is spot on i.e. timing has already been adjusted. In other words 3% per 1000 ft is in the best of cases. Many times its even more.

Only way to compensate is to increase mass air flow or O2 flow. Your choices are nitruous, supercharger or turbo. Then there is always engine swap...there is no replacement for displacement.

Personally, i am partial to superchargers.
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  #7  
Old July 11th, 2016, 11:37 AM
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Imagine a 2.5NA at that altitude.
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  #8  
Old July 11th, 2016, 12:28 PM
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97 is almost 20 yrs old, have you tested fuel delivery and pressure, that is fuel filter and continuous pressure.
if fuel filter is dirty it will cause fuel starvation when need arises, likewise with a low delivery fuel pump.
then you have all the rest of the mechanicals and environmentals involved.
some are easy to resolve the rest not so much.
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  #9  
Old July 11th, 2016, 02:54 PM
Tyler Wirken
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Can you advance timing on a gems seeing as there is not a distributor?

The fuel filter is a good idea but mine is fairly new so I doubt that but you never know.

I kept dreaming of an LS up there.
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  #10  
Old July 11th, 2016, 03:00 PM
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The timing should advance on its own. That is one of the points of having EDIS.

The normal problem with these engines is the valve train. The timing chain stretches and kills power followed closely by the cams wearing out. If those are original, that would be my first stop.
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  #11  
Old July 11th, 2016, 03:03 PM
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Keith Armstrong
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Hey Tyler,

All my RV8s have been "sluggish" at altitude. I think you're roughly the same "altitude" that we are

I will say that within a few start / stop / heat / cool cycles it gets a bit better, but they're still pigs compared to the little turbocharged car that always thinks it's at sea level.

KAA
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  #12  
Old July 13th, 2016, 08:29 AM
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Reset ecu to factory conditions at altitude?
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