Home » Public Forums » GMCnet » GMCs, Mountains, Fuel Injection, Electric Blowers, Gears (Any valid tests vs theories and guesses)
| GMCs, Mountains, Fuel Injection, Electric Blowers, Gears [message #179865] |
Sat, 11 August 2012 14:30  |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
Karma: 3
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I've been reading the net too much recently. Many different but related topics.
"PS - The lack of performance out of this engine at altitude has made me decide that the Paterson engine I have in Houston will be
fitted with EFI" Rob Mueller
"Anyone out there who has any input on how a GMC runs at 12,000+ feet? " Mark Hickey
"Your last post on EFI reminded my of my conversation with James. He said it made the most incredible difference traveling over Eagle Mountain or Mount Eagle. He fooled with his carburetor and finally threw in the towel.
I suspect the carb in his coach was never exactly right, but others have said that the EFI really makes a difference in higher altitudes." Stick Miller
" 13% grades both up and down, lots of 6 to 11% stuff, some 20 to 40 km long. The coaches are holding up well for the most part. It is a real testament to Manny trans, Manny one ton from ends, alum radiators and the large cooling lines from trans to radiator. Lots of smelly brakes from the coaches without the larger one ton from rotors and calipers. A few with over heating issues on stock radiators, but for the most part every one is making it." Jerry Work
The quotes above all relate to Gmc's performance in the mountains.
I live in the mountains @ 4500' and have to climb to 6000' before getting down to 300' on the Sacramento River at Red Bluff.
Seventy miles of up and down grades with many slow (15 to 25 mph) curves.
About once a month I go to So Cal over the Grapevine @4144'. every 2 to 3 months I go north to Oregon over the Siskiyou Summit @4310'.
I have driven 5 different GMC's over various mountain passes including Deadman Pass 8047", Conway Summit 8143' Tioga Pass 9943' all in California and Monarch Summit in Colorado 11312'
Coaches were:
23' 455 3:07
26' 403 3:07
26' 455 3:07
26' 455 3;07
26' 455 3:07 and 3:70
All had carbs- none had Mark's electric blower. All made it up the grades; slowly and in 2nd gear.
I suspect that neither fuel injection nor electric blowers will make a "significant" difference in power/performance when coaxing a 12,000 pound brick up a 7 mile 6% grade.
Long steep grades and or slow switchback curves seem to have more effect on performance than thin air at higher elevations.
Last week I traveled to Florence, Oregon to see the newly completed shrine to Mr.ERF at Mickey D.'s He's honored as their most regular customer.
Coach, 1976 Palm Beach has 455 w/carb and 3:70. coach weighs~11,000 lbs.
Northbound on I-5 between the Oregon border and Canyonville (about 100 miles) you encounter Siskiyou Summit 4310' (highest point on I-5) 7 miles of 6% grade on both sides, Sexton Pass (named for GMCer Dennis Sexton?) 1960', Smith Hill Summit 1730', Stage Road Pass 1830', Canyon Creek Pass 2020'
All of these hills except Canyon Creek Pass required downshifting to second for part of the climb. Plenty of air volume available at these elevations.
When speed drops below 50 mph and rpm drops below 2500 and vacuum is 5" or less I manually shift to 2nd.
Any of you Great North West Netters travel this route? With FI or carb? What is your experience?
We are all hoping/trying to improve performance but it seems that many "upgrades" don't actually improve performance (headers come to mind) and some have unexpected issues.
The 76 Kingsley that I drove from Boston to San Francisco last Sept. had OEM exaust. It generated substantially less heat and noise in the cockpit than my daily driver 76 Palm Beach with headers.
Enough rambling.
Hope to hear more from the Cross Canada Ramblers on their experience in the mountains. Good opportunity to compare a variety of coaches over the same terrain at the same time.
Comments please.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: GMCs, Mountains, Fuel Injection, Electric Blowers, Gears [message #179919 is a reply to message #179865] |
Sun, 12 August 2012 04:46  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I do not know if there is a question buried in there but basically what it being said is performance is reduced in any normally aspirated engine as you go up in altitude. It is a fact of life FI or not. Any pilot can tell you this as we need to know the exact performance hit to make sure there is enough runway to get off of the ground.
Performance is also reduced as the Intake Air Temperature goes up. Even the current barometric pressure affects performance.
The worse one I ever had with this was coming out of Anaconda, Montana (5000 ft. elevation) at almost 100 degrees with a full load of fuel. I almost did not clear some electric wires about 1/2 mile off the end of the runway.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: GMCs, Mountains, Fuel Injection, Electric Blowers, Gears [message #179924 is a reply to message #179865] |
Sun, 12 August 2012 07:53 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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Senior Member |
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I think that only a turbocharger or supercharger that forces air into the combustion chambers will really help at high altitudes. EFI does help in keeping the air/fuel ratio optimized, but with less oxygen, you can't make the same power as on low altitudes.
Who wants to add nitrous oxide to their coach for an experiment?
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: GMCs, Mountains, Fuel Injection, Electric Blowers, Gears [message #179933 is a reply to message #179919] |
Sun, 12 August 2012 08:56 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Ken Burton wrote on Sun, 12 August 2012 05:46 |
I do not know if there is a question buried in there but basically what it being said is performance is reduced in any normally aspirated engine as you go up in altitude. It is a fact of life FI or not. Any pilot can tell you this as we need to know the exact performance hit to make sure there is enough runway to get off of the ground.
Performance is also reduced as the Intake Air Temperature goes up. Even the current barometric pressure affects performance.
The worse one I ever had with this was coming out of Anaconda, Montana (5000 ft. elevation) at almost 100 degrees with a full load of fuel. I almost did not clear some electric wires about 1/2 mile off the end of the runway.
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Ken,
Aircraft specifications are always published "to clear a 50' obstacle" at the end of the runway......
Why do so many places feel it an obligation to have said obstacle??
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] GMCs, Mountains, Fuel Injection, Electric Blowers, Gears [message #179958 is a reply to message #179924] |
Sun, 12 August 2012 13:12 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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George,
Agree on the supercharger / turbocharger.
As far as nitrous goes - maybe the guys that are going after the LSR will try it! ;-)
Regards,
Rob M.
-----Original Message-----
From: George Rudawsky
I think that only a turbocharger or supercharger that forces air into the combustion chambers will really help at high altitudes.
EFI does help in keeping the air/fuel ratio optimized, but with less oxygen, you can't make the same power as on low altitudes.
Who wants to add nitrous oxide to their coach for an experiment?
--
George
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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