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| [GMCnet] Warm air for the Q-Jet... [message #89258] |
Sat, 19 June 2010 19:26  |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
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I heard an interesting theory from my QuadraJet-tuning friend today.
He was commenting on the fresh air duct to my carburator. He liked it
but said that I might see better mileage by NOT using cool air. He said
that power should be better with fresh air but the fuel would atomize
better with hot air.
Not sure that I really believe this. He certainly made my carb work
better but it just sounds ... odd.
Keep in mind this guy knows his Q-Jets because of building lots of hot
GM cars. He's all about Power.
Why wouldn't GMC have ducted fresh air to the Q-Jet? They had to know it
got darned hot on top of that motor.
Kelvin
'73 23' in Eugene, OR
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89268 is a reply to message #89258] |
Sat, 19 June 2010 21:00  |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
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| Kelvin Dietz wrote on Sat, 19 June 2010 17:26 |
I heard an interesting theory from my QuadraJet-tuning friend today.
He was commenting on the fresh air duct to my carburator. He liked it
but said that I might see better mileage by NOT using cool air. He said
that power should be better with fresh air but the fuel would atomize
better with hot air.
Not sure that I really believe this. He certainly made my carb work
better but it just sounds ... odd.
Why wouldn't GMC have ducted fresh air to the Q-Jet? They had to know it
got darned hot on top of that motor.
Kelvin
'73 23' in Eugene, OR
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I am going to jump in here and probably get rocks thrown at me. Blocking the Crossover:
My crossover is not blocked off, my intake manifold is probably cracked, my turkey pan it probably caked with fried gunk and the outside of the manifold looks terrible in the middle; its a mess.
However, the guys who designed heated intakes didn't do it because they wanted the above to happen. I know that there is a theory that this was all smog stuff, but oddly enough, my 50 Chevy's intake was bolted to the exhaust, with that goofy heat riser thingy with bimetal spring that opened it when it warmed up. Some manifolds have corrugations to give more heating surface.
My theory is that one of the biggest problems with using gasoline to run an internal combustion engine is getting the gas to vaporize. Of course, the jets help spray gas, but that makes droplets, and left to their own devices, carbs will ice up. Simple solution, heat the intake. Droplets fly down the Q-Jet and slam against a heated bottom of the intake and vaporize. More gas to burn.
As far as getting more air in, most of the time we are running vacuum. This means that the effective compression ratio is lower. You may have 8.n:1 compression ratio, but only when it is at Wide Open Throttle, and then there are restrictions. (Hence the difference between gas and diesel, which take in full air each stroke.) This is why our engines don't ping at 1/4 throttle... not much air to compress so 8n:1 is moot at that point.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89271 is a reply to message #89268] |
Sat, 19 June 2010 21:25 |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
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On Sat, Jun 19, 2010 at 7:00 PM, George Beckman <gbeckman@pggp.com> wrote:
>
>
> Kelvin Dietz wrote on Sat, 19 June 2010 17:26
> > I heard an interesting theory from my QuadraJet-tuning friend today.
> >
> > He was commenting on the fresh air duct to my carburator. He liked it
> > but said that I might see better mileage by NOT using cool air. He said
> > that power should be better with fresh air but the fuel would atomize
> > better with hot air.
> >
> > Not sure that I really believe this. He certainly made my carb work
> > better but it just sounds ... odd.
> >
> > Why wouldn't GMC have ducted fresh air to the Q-Jet? They had to know it
> > got darned hot on top of that motor.
> >
> > Kelvin
> > '73 23' in Eugene, OR
>
>
> I am going to jump in here and probably get rocks thrown at me. Blocking
> the Crossover:
>
> My crossover is not blocked off, my intake manifold is probably cracked, my
> turkey pan it probably caked with fried gunk and the outside of the manifold
> looks terrible in the middle; its a mess.
>
> However, the guys who designed heated intakes didn't do it because they
> wanted the above to happen. I know that there is a theory that this was all
> smog stuff, but oddly enough, my 50 Chevy's intake was bolted to the
> exhaust, with that goofy heat riser thingy with bimetal spring that opened
> it when it warmed up. Some manifolds have corrugations to give more heating
> surface.
>
I'm willing to accept the logic of this but you also have to figure that GM
needed to make a vehicle that would work in ANY weather. You fire up that
motorhome in Detroit or Denver in the December and it's going to take hours
for it to warm enough to drive it.
I think we all tend to warm out coaches up pretty well before hitting the
roads now. I can't imagine life without that crossover blocked off. And if
you're not going to block it you should probably pull the manifold and
remove the hockey-puck-sized chunks of coke from where they're resting on
the cam/pushrods.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=10758&cat=3954
I also took quite a pile of carbon granola out of the oil pickup.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=10860&cat=3954
Oil pressure on the motor went from 40psi to 48psi. Yes, carbon filtering
is good - but not in this case.
Just my 2¢
Kelvin
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89283 is a reply to message #89258] |
Sun, 20 June 2010 00:13 |
Rick Denney
Messages: 430
Registered: January 2004
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| Kelvin Dietz wrote on Sat, 19 June 2010 20:26 |
He said that power should be better with fresh air but the fuel would atomize better with hot air.
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Dick Balsley said something similar to me several years ago.
Rick "who has done it both ways" Denney
'73 Glacier 230 "Jaws"
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89284 is a reply to message #89283] |
Sun, 20 June 2010 00:43 |
John Sharpe
Messages: 489
Registered: February 2006
Location: Texas
Karma: 1
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| Quote: |
....fuel would atomize better with hot air.
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We've had all these threads about 'vapor lock'. Which is fuel atomizing before it even gets to the carburetor. Down here in Texas, cooler is always better in the summertime. With the new fuel blends in these parts you have to be concerned if the fuel vaporizes too soon.
John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com
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| [GMCnet] Low oil pressure switch guestion [message #89285 is a reply to message #89284] |
Sun, 20 June 2010 04:32 |
Charles
Messages: 455
Registered: January 2004
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If you put a low oil pressure switch in line with you electric fuel pump
how can the pump work when you first crank your engine? Presently
when I turn the key on (without a pressure switch) the pump primes the
system and I can then start the vehicle without a lot of cranking. It appears
to me, I will loose this priming capability if I put a low oil pressure switch
in the system. If I do how do you over come this problem. I do not want
to go back to the five minutes of cranking just to get fuel to my carburetor.Charles Wersal
Duncanville, Texas
1975/26 Glenbrook
Pandora's Box
1973/23 Canyon Lands ???
----- Original Message ----
From: John Sharpe <johnasharpe@earthlink.net>
To: gmclist@temp.gmcnet.org
Sent: Sun, June 20, 2010 12:43:23 AM
Subject: Re: [GMCnet] Warm air for the Q-Jet...
Quote:
> ....fuel would atomize better with hot air.
We've had all these threads about 'vapor lock'. Which is fuel atomizing before it even gets to the carburetor. Down here in Texas, cooler is always better in the summertime. With the new fuel blends in these parts you have to be concerned if the fuel vaporizes too soon.
--
John Sharpe
Humble,TX
'40 Ford Deluxe TBI
'78 Eleganza TBI
'78 Royale TBI
mailto:johnasharpe@earthlink.net
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Charles Wersal
Duncanville, Texas
26 foot 1975 Glenbrook
Pandora's Box
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| [GMCnet] oil in A/C compressor [message #89286 is a reply to message #89284] |
Sun, 20 June 2010 04:38 |
Charles
Messages: 455
Registered: January 2004
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How much oil should be put back in an A/C compressor if the
compressor is removed to replace the front seal if nothing
else is going to be done to the system? I he decides to flush
the rest of bthe system and replace the dryer How much oil
should be added?
Charles Wersal
Duncanville, Texas
1975/26 Glenbrook
Pandora's Box
1973/23 Canyon Lands ???
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Charles Wersal
Duncanville, Texas
26 foot 1975 Glenbrook
Pandora's Box
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| Re: [GMCnet] Low oil pressure switch guestion'/ Oil in AC/ Warm air to Q-Jet [message #89289 is a reply to message #89287] |
Sun, 20 June 2010 07:04 |
John Sharpe
Messages: 489
Registered: February 2006
Location: Texas
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Charles, Somehow you are replying to the wrong threads. Anyway, the purpose of the oil pressure switch is as a safety. You can use a relay and have the pump run anytime the engine is cranking and that would eliminate extended cranking at dry start-up.
As for the refrigerant oil, you should only add the amount that leaked out. Normally, from a seal replacement you would only loose a couple of drops so I would not worry about it.
John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com
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| Re: [GMCnet] Low oil pressure switch guestion [message #89295 is a reply to message #89287] |
Sun, 20 June 2010 08:20 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Charles,
On the diagram I posted, the diode from the starter solenoid serves the same
function as the NC connection in the diagram Gene posted; either is
satisfactory.
The Prime switch and diode provide another way of being sure there's fuel
available when you hit the starter. I don't consider it necessary, but some
folks like to use one, so there it is. With my EFI arrangement, including a
surge tank, it's potentially useful if that 1 g. reservoir is depleted.
Gene,
"All those relays" are certainly not absolutely necessary, as you well know:
The tank selector switch is probably already a double throw switch even
though it's wired as a single throw, if not, it could be replaced with a
SPDT switch. With that minor change, and a wire run from the NC contact now
available, each of the pumps could be wired directly, with no other wiring
changes except those dictated by safety (LOP/alternator source).
Personally, I think the IGN contacts in our old switches are already
overloaded so I prefer to add load relays for new loads; running 5A or so
through a 30A rated relay doesn't seem to hurt reliability very much.
Adding the selector relay was easier than pulling the dash to
check/change/wire the selector switch to provide the selection function.
Use of a SPST LOP switch was dictated by what I had on hand, not any
objection to the SPDT alternative, even though I do find diodes more
reliable than LOP switches.
Whatever rocks your boat. :-)
Ken H.
On Sun, Jun 20, 2010 at 7:01 AM, Mr.erf ERFisher <mr.erfisher@gmail.com>wrote:
> >
> > If you put a low oil pressure switch in line with you electric fuel pump
> > how can the pump work when you first crank your engine?
>
>
> If you look at the drawing here
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=19123
>
> you see during low oil pressure (engine stopped), the pump is connected to
> the "IGN" line which supplies voltage during cranking. I do not want
>
>
> to go back to the five minutes of cranking just to get fuel to my
> > carburetor.
>
>
> the electric pump is much faster than the mechanical pump was, and
> sometimes, you would like a little cranking time to get the oil to the
> engine before it is started.
>
> works great
>
> gene
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89296 is a reply to message #89271] |
Sun, 20 June 2010 10:00 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| Kelvin Dietz wrote on Sat, 19 June 2010 19:25 |
On Sat, Jun 19, 2010 at 7:00 PM, George Beckman <gbeckman@pggp.com> wrote:
Oil pressure on the motor went from 40psi to 48psi. Yes, carbon filtering
is good - but not in this case.
Just my 2¢
Kelvin
_______________________________________________
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Kelvin,
You got my attention with the oil pressure comment. I had not thought of these things. I am thinking I need one of those pretty aluminum intake manifolds that are blocked off.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Low oil pressure switch guestion [message #89309 is a reply to message #89287] |
Sun, 20 June 2010 12:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Mr ERFisher wrote on Sun, 20 June 2010 06:01 |
>
> If you put a low oil pressure switch in line with you electric fuel pump
> how can the pump work when you first crank your engine?
If you look at the drawing here
http://www.gmcmhphotos.com/photos/showphoto.php?photo=19123
you see during low oil pressure (engine stopped), the pump is connected to the "IGN" line which supplies voltage during cranking. I do not want to go back to the five minutes of cranking just to get fuel to my carburetor.
the electric pump is much faster than the mechanical pump was, and sometimes, you would like a little cranking time to get the oil to the engine before it is started.
works great
gene
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There is one improvement you can make to this circuit if you have an HEI ignition. There is a spare terminal on the stater solenoid that was used to jumper the ignition resistor on the points style ignition during cranking. This unused terminal provides a DIRECT PATH BACK TO THE BATTERY during cranking when the battery voltage is normally lower due to the high current demands of the starter. This terminal is also isolated from the starter solenoid coil circuit.
If you move the LOP wire from the coil terminal to the unused terminal of the solenoid you will have higher voltage to the electric fuel pump during cranking.
The second advantage of using this terminal is you can connect a second wire to this terminal and run it to a momentary or push button switch and use it a a prime switch. This addition requires no diodes or an anything other than a switch, a piece of wire and a 12 volt source to the switch capable of 2 amps.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Low oil pressure switch guestion [message #89315 is a reply to message #89285] |
Sun, 20 June 2010 13:29 |
Rick Denney
Messages: 430
Registered: January 2004
Karma: 0
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| Charles wrote on Sun, 20 June 2010 05:32 |
If you put a low oil pressure switch in line with you electric fuel pump how can the pump work when you first crank your engine?
|
The switches made for this application have a terminal position for the starter circuit, so that the pump will be activated during cranking.
But with my mechanical oil pressure gauge, it's apparent to me that I get oil pressure within the first 5 or 10 seconds of cranking. The pressure switch cuts in at about 5-7 psi oil pressure, which is there nearly as soon as the needle first moves. And cranking long enough to establish oil pressure might not be a bad thing in any case.
Rick "who routinely cranks a cold engine with the pump turned off until the needle moves" Denney
'73 Glacier 230 "Jaws"
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89332 is a reply to message #89308] |
Sun, 20 June 2010 16:56 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| Duce Apocalypse wrote on Sun, 20 June 2010 10:17 |
if you want to atomize the fuel in the absolute best way, use fuel injection, then run a CAI to the throttle body and be done with it...
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My setup, exactly, with Intake Air Temperature sensor thrown in for good measure. Watching the TBI, I am not convinced it does any better at atomization than the quadrajet. I am guessing that the injector spraying fuel is better than it being pulled out atomizer style? Do you have some more info?
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Low oil pressure switch guestion [message #89417 is a reply to message #89285] |
Mon, 21 June 2010 11:33 |
KB
Messages: 1262
Registered: September 2009
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>> If you put a low oil pressure switch in line with you electric fuel pump
>> how can the pump work when you first crank your engine?
The way GM did it in their late 80's - early 90's TBI fuel injected system was
with a "fuel module". This powered the fuel pump for I believe 20 seconds or so, bypassing
the oil pressure switch. I know this because I have said EFI system currently laid out on
my dining room table, and had to figure it all out.
Karen
1973 23' Patience Tester
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1975 26'
San Jose, CA
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89428 is a reply to message #89258] |
Mon, 21 June 2010 13:05 |
WayneB
Messages: 233
Registered: July 2008
Location: Ontario, Canada
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| Kelvin Dietz wrote on Sat, 19 June 2010 20:26 |
Why wouldn't GMC have ducted fresh air to the Q-Jet? They had to know it
got darned hot on top of that motor.
Kelvin
'73 23' in Eugene, OR
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In 1984/85 GM used a small blower fan and plastic ducting that blew cool air to the float chamber on Quadrajet equipped 305 HO Formula Firebirds/Trans Ams and IROC camaros to stop fuel percolation /vapour lock in the float chamber.
If Quadrajet equipped motorhomes are having similar problems it might be a good idea to retrofit this device to the older GMC's.
Wayne
1976 23' GMCII By Explorer
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| Re: [GMCnet] Warm air for the Q-Jet... [message #89465 is a reply to message #89258] |
Mon, 21 June 2010 22:08 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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GOING BACK TO THE ORGINAL THREAD HERE on HOT AIR DUCT
The way I understand it----
As we know engines can tolerate leaner mixtures at higher temperatures (opposite is choke required when cold to richen temporarily). This is largly due to the better vaporiztion of the fuel and the better vaporiztion of the heavier molecules so they too actually vaporize and can better contribute to the burn. Temperatures are always a variable in the real world so there was no good level playing field to tune to and try to be as lean as practical for economy and emissions and not be too lean on cold days with resultant sag and drivability issues. So since they couldn't cool the air, they choose 115 degrees as a standard to preheat to so the carb would think that it was always that 115 temp outside and they could tune to that specific level playing field. The AC AutoThermAC starts with vacuum to the damper to make it reach 115 deg preheated until the internal temp sensor sees it reach that temp and then blends cool/hot to keep it there within a few degrees. Granted on a hot day with high underhood temperatures it will often be wide open anyway. The important thing to remember here is that that this only applies to light throttle conditions (most normal driving) and as you get into the secondaries the vacuum drops and the hot/cold door gets no or weak vac signal and the spring goes to 100% cold anyway for max power and performance. So the way I see it it allows you to run leaner primaries for mileage and emissions and keeps the engine cleaner (lasts longer as less water in oil at warmup, less carbon from a more constant control of mixture, less cold misfire waste fuel in oil)with no downside of power loss when you need it. I guess in about 1968 when GM started putting these in cars they did know what they were doing.
John Lebetski
Woodstock, IL
77 Eleganza II
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