Home » Public Forums » GMCnet » [GMCnet] Injection versus Carbs
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| Re: [GMCnet] Injection versus Carbs [message #73731 is a reply to message #73729] |
Sat, 13 February 2010 16:14   |
Ron
Messages: 250
Registered: February 2004
Location: Conifer, Colorado
Karma: 0
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Senior Member |
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Bill..
I am going to Fuel Injection for this very reason.. I live higher than Emory.. I am at 9300 feet in elevation.. Much of the driving here in the Colorado mountains is above 7000 feet.. My tail pipe is always sooty.. But the coach runs well.. Just too rich.. If nothing else I am always into the power valve as intake vacuum gets quite low even at a cruise at this altitude..
And electronically controlled , Map sensor ed EFI is the best way to go..
Have you tried to find an altitude adjusting Q Jet for your coach? I did briefly.. Not a reasonable alternative I think..
Ron JMHO
now a P.O.
Conifer, CO
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| Re: [GMCnet] Injection versus Carbs [message #73767 is a reply to message #73765] |
Sat, 13 February 2010 22:07 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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On Feb 13, 2010, at 8:58 PM, paul array wrote:
>
>
> I have a Howell on mine and it SUCKS, keeps getting rich for no
> reason, changed the injectors, map sensor, exhaust sensor, computer,
> chips and it still SUCKS.
> Howell cant fix it and neither can two GMC places I brought it to.
> I have just ordered a carb
> If you know someone that wants this thing, let me know.
>
;A lot of people had problems with the chip and the injectors that
Howell uses.
It has recently been found that the Howell system is set as shipped to
15 psi.
The injectors that Howell uses on the recent kits are Holley 522-43.
A Holley tech man told me that they are rated at 60 pounds per hour at
13 psi and you would have to run at 21 psi to get 85 PPH flow.
The 454 truck that GM made with TBI had two 85 PPH injectors at 13 psi.;
So, if Howell is shipping the kits set to 15 psi there is no way to
get good performance unless you increase the fuel pressure.
That may be part of your problem
That system at 15 psi was designed for a 350 cu in. engine, not a 455.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Injection versus Carbs [message #73921 is a reply to message #73914] |
Mon, 15 February 2010 14:40 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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| emerystora wrote on Mon, 15 February 2010 13:42 |
On Feb 15, 2010, at 12:33 PM, Bill Freeman wrote:
>
>
> $2175 for "Affordable" fuel injection, plus a lot of work installing
> all that new stuff? It might run perfectly as installed but from
> reading this forum many seem to require a substantial amount of
> additional tuning. Some fuel injection conversions apparently never
> run right.
>
> $15 for a couple of metering rods and 30 labor minutes to put them
> in sounds a lot better to me. If you re-tune a q-jet for 5000 feet
> I expect it would run good enough from sea level to 10,000.
>
>
> --
> Bill Freeman
> 78 Royale 73 Sequoia
> Colerain, North Carolina
> http://tinyurl.com/yx7nra
I think that you would still be too lean near sea level and too rich
above 7500 feet. Of course, than might be "good enough" for you
depending on how much traveling you do away from 5000 feet.
Emery Stora
77 Kingsley
Santa Fe, NM
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IF you tuned it properly for 5000 feet, you WOULD be to lean at sea level and still to rich at 7500 and higher. Tuning a Q-Jet is not as easy as just changing rods or jets. Until I started using a wide band O2 sensor and an LM-1 FA ratio gauge, I had no idea how much altitude plays in FA. I had no idea how much changing rods or jets had on FA. I had no idea that changing the idle screw can change the FA in both primary and secondary circuits. Just as an example, I spent most of October and November trying to tune a Q-jet that has an adjustable part throttle. There are an incredible number of variables when working with a Q-jet. Any minor changes to any of the primary circuits effects performance at WOT...yes even changes to the idle effect WOT. I finally got my carb (a Q-Jet from a 81' chevy PU with 454) set so that I had a highway lean burn of about 15.5/1 going down the road at 60mph, no wind, flat run, 11 to 15 inches of vacuum. That was in Menomonie Wisconsin at an altitude of 970ft. I am now in Texas along the gulf coast at sea level. Just the change of 900+ feet changed my FA from the 15.5/1 to 14.7... under nearly the same driving conditions. Imagine the change that can take place from 5000 to sea level...or 5000 to 10,000 ft.
You could go to a altitude compensating carb, but those are tuned for an automobile and have an extra power valve in them. This adds another whole dimension with several more variables than the standard Q-jet.
After working with a q-jet for several months now, I'm going to MPI for my cad. Instead of pulling the top of the carb for jet changes, changes will be made from my lap-top..maybe even in real time. JMHO
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: [GMCnet] Injection versus Carbs [message #73924 is a reply to message #73921] |
Mon, 15 February 2010 15:31 |
mlincoln
Messages: 107
Registered: August 2006
Location: Salt Lake City
Karma: 0
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Senior Member |
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Does anyone have actual experience with "splitting the difference" in the Quadrajet enrichment to suit a MSL of 4500 to 5000 feet? I was once told that some old Detroit iron came with a "high altitude option" (possibly a re-metered carb?). A shop in Ann Arbor told me that when I was about to use my rusty old Caprice to tow my 912 and other belongings to Utah after finishing my residency. They were right, Loveland pass really hurt going uphill and to the west. Was that supposed option in fact a re-carburetion in order to "split the difference", or was the shop wrong and there was in fact no such option at all? If they were right, what was the Detroit engineers' target altitude for the rejet/meter?
If rejetting/metering for altitude in a car or MH likely to change altitudes is a bad option, how about buying an additional carburetor and swapping the high for the low altitude unit depending on locale (apart form the obvious expense and bother)?
Mike Lincoln, now in Michigan but usually in Utah
>>
>>
>> I think that you would still be too lean near sea level and too rich
>> above 7500 feet. Of course, than might be "good enough" for you
>> depending on how much traveling you do away from 5000 feet.
>>
>> Emery Stora
>> 77 Kingsley
>> Santa Fe, NM
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> List Information and Subscription Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> IF you tuned it properly for 5000 feet, you WOULD be to lean at sea level and still to rich at 7500 and higher. Tuning a Q-Jet is not as easy as just changing rods or jets. Until I started using a wide band O2 sensor and an LM-1 FA ratio gauge, I had no idea how much altitude plays in FA. I had no idea how much changing rods or jets had on FA. I had no idea that changing the idle screw can change the FA in both primary and secondary circuits. Just as an example, I spent most of October and November trying to tune a Q-jet that has an adjustable part throttle. There are an incredible number of variables when working with a Q-jet. Any minor changes to any of the primary circuits effects performance at WOT...yes even changes to the idle effect WOT. I finally got my carb (a Q-Jet from a 81' chevy PU with 454) set so that I had a highway lean burn of about 15.5/1 going down the road at 60mph, no wind, flat run, 11 to 15 inches of vacuum. That was in Menomonie Wisconsin at a
n
> altitude of 970ft. I am now in Texas along the gulf coast at sea level. Just the change of 900+ feet changed my FA from the 15.5/1 to 14.7... under nearly the same driving conditions. Imagine the change that can take place from 5000 to sea level...or 5000 to 10,000 ft.
>
> You could go to a altitude compensating carb, but those are tuned for an automobile and have an extra power valve in them. This adds another whole dimension with several more variables than the standard Q-jet.
>
> After working with a q-jet for several months now, I'm going to MPI for my cad. Instead of pulling the top of the carb for jet changes, changes will be made from my lap-top..maybe even in real time. JMHO
> --
> Larry :)
> 78 Royale w/500 Caddy
> Menomonie, WI.
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Mike
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| Re: [GMCnet] Injection versus Carbs [message #74042 is a reply to message #74037] |
Tue, 16 February 2010 12:21 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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Re: [GMCnet] Injection versus Carbs Tue, 16 February 2010 11:55
Richard Lister
Hi there. That's good to hear thanks for your advice. I've heard plenty about Howell TBI but not so much about Turbo City and I'm looking at a coach this weekend which has that fitted, so I appreciate your comments.
Richard
DC
Richard,
I have had a Turbo City unit on my 1976 GMC since 1997 and am very happy with it.
The reason I did:
Wife complained about gas smell (perc) after a long run, loss of power @ higher elevations, choke/cold operation, lots of mileage on carb.
Bought Turbo City @ GMCMI convention = $100 off, got $200 for carb on trade in, built with GM parts, uses GM diagnosis. In last ~13 years only repair was to replace TPS.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
[Updated on: Tue, 16 February 2010 12:23] Report message to a moderator |
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| Re: [GMCnet] Injection versus Carbs [message #74176 is a reply to message #73924] |
Wed, 17 February 2010 17:34 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| mlincoln wrote on Mon, 15 February 2010 16:31 |
Does anyone have actual experience with "splitting the difference" in the Quadrajet enrichment to suit a MSL of 4500 to 5000 feet? I was once told that some old Detroit iron came with a "high altitude option" (possibly a re-metered carb?). A shop in Ann Arbor told me that when I was about to use my rusty old Caprice to tow my 912 and other belongings to Utah after finishing my residency. They were right, Loveland pass really hurt going uphill and to the west. Was that supposed option in fact a re-carburetion in order to "split the difference", or was the shop wrong and there was in fact no such option at all? If they were right, what was the Detroit engineers' target altitude for the rejet/meter?
If rejetting/metering for altitude in a car or MH likely to change altitudes is a bad option, how about buying an additional carburetor and swapping the high for the low altitude unit depending on locale (apart form the obvious expense and bother)?
Mike Lincoln, now in Michigan but usually in Utah
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Mike,
Altitude compensated carburetors have been around a very long time. Detroit did not use them on passcar engines except as a special (and extra co$t option) until the EPA forced the issue in the mid 70's. Then they were required based on the elevation of the dealership. Fuel injected vehicles that demonstrated inherent altitude compensation (like Bosch K-jetronic) were exempt. There were all manner of high altitude vehicles assembled. As I have never lived west of the Mississippi, I have seen very few.
Matt
Detroit
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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