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Gasoline Engine Fuel Mixture
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Supporting Member of Barthmobile.com 12/18
Picture of Duane88
posted
Since I removed the AIR and EGR from Nose, my fuel usage decreased, but I feel it could be better. My exhaust pipe is pretty black, I have been under the impression that is a sign of a rich fuel mixture.

It has been stated here many times that converting to a fuel injection is the best answer to helping fuel economy, but I can't get it out of my head that I can tune this Quadra jet better than it now is..

Having read several articles, most indicating that the only way to do this job correctly is to put the engine on a odynometer and keep re-jetting until the best power options are found by adjusting timing, and fuel flow.

Light aircraft use EGT (Exhaust Gas Temperature) to adjust for best economy at altitude by leaning fuel flow, if memory serves me !300F is a good run temperature and should be about a 13 to 1 FAR (fuel air ration). So if I put a thermometer in my exhaust or around the pipe at the manifold outlet and insulate it well with a hot engine under good load say a long incline do you think I could start to swap out the metering rods with any kind of precision. Searching for an EGT of around 1300F.

Just food for thought and debate!


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 6/19
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I'm thinking a 1300 egt is about where pistons start to melt .

The black exhaust could be a faulty choke or just too much foot applied to the go petal under load .

I would guess that if under normal driving and no black smoke , you should be good .


Harold
Cat
Sam is 10 year old Miniature Schnauzer
Currently without a coach

KE5WCW
 
Posts: 212 | Location: Mooringsport,LA | Member Since: 05-30-2019Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 1/19
Picture of Steve VW
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Tuning the Qjet is part science part artform. There are numerous problems, much has to do with the fact that road vehicles seldom run at a specific power setting. Speed, hills, ambient temperature and payload vary a lot more than the airplane example.

The Qjet has choke settings, idle mixture, off idle transitions, midrange cruise and full power variables to contend with. Without good sensor data it would be very difficult to get it right without many trials. Furthermore, changing one setting will often overlap other settings.

Even with the optimum carb settings, the mixture control is still crude at best and would be optimum only under specific conditions.

EGT might work but you would want to have the probe right at the exhaust port, about 1200 is as hot as you will want to go. Better yet, a probe in each port as in high end aircraft setups. I think you would be better off to get an O2 sensor as the fuel injections systems use. This gives you more direct air/fuel mixture data. The theoretical ideal mixture is about 16 to 1 but that is dangerously near detonation. Most fuel injected engines shoot for about 14 to 1.

There are other more difficult variables at play. For optimum fuel efficiency you want the highest compression ratio possible without detonation. (This is one reason diesel engines are more effiecient, high compression and direct injection to prevent preiginition) The 454 in our coaches has a miserable 8 to 1 compression ratio. Modern engines use around 9.5 to 1 for regular octane gasoline. Furtermore, the timing and camshaft specs were a compromise for pre catalytic combustion conditions. Rear axle ratio is another variable to contend with.

Before any carb adjustments are made be sure you are running as much spark advance as possible without knocking. Using an O2 sensor could then verify the best fuel air ratio, if the carb can be adjusted to find it.

My 86 was getting 6-6.5 mpg when I got it. Playing with timing, installing headers and dual exhaust got it to about 6.8. When I installed the fuel injection system, it ran better hot and cold, had better throttle response and mileage improved to around 7.5 mpg. Installed the 454 HO engine with 9.5 to 1 compression, better intake manifold and a better camshaft, horsepower went from 240 to about 400. Mileage went to 8.0 mpg. I don't think it can get much better.

With stock compression, camshaft, manifolds, carburetor and axle ratio I think about 6.5 mpg is about what you get, assuming carb and timing are set right.

Better intake and manifolds are maybe worth about .3 mpg.

Increased compression ratio and better camshaft specifications will get the most improvement.

Fuel injection will further optimize fuel mileage and also improve performance under all throttle settings, temperature and load conditions.

Good luck with your tuning project. Keep careful records and try to change only one variable at a time. A dynomometer is the gold standard.


9708-M0037-37MM-01
"98" Monarch 37
Spartan MM, 6 spd Allison
Cummins 8.3 300 hp
 
Posts: 4160 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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Hey, Harold I had the carb checked at a Hot rod shop, he thought it was running pretty well, of course it is I did the rebuild!! I would never push the speed limit the police set their radar on me.. Ok I joke and send wet air to Minnesnowta!!!

Steve, I like the Idea of putting an O2 sensor in the exhaust. Can I get a readout off a volt meter or is there a meter available? I have a couple of sensors bought for my caddy and did not need. I wonder what numbers would mean the burn is optimized? If we get a system to tune carburetors perhaps it will be a profitable enterprise and we can make enough money for me to buy a fuel injection system. And you can get all kinds of parts for that VW and a first class paint job!!

Now remember who you are dealing with and keep the reply within my threshold. Smiler

It is a cold winter week, this is good for the soul!!!


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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I had another thought when Steve mentioned rear end ratio, Nose has plenty of acceleration power, never seems to bog down when accelerating. so I was thinking about putting a lower ratio in it, hoping also cruise noise in the coach would lessen due to lower cruise RPM. Wonder what this would do to gas mileage. A newer transmission with overdrive would be nice, if we get a carb tuner system to sell maybe I can afford that too.


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 6/19
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It is possible that by changing the gear ratio to lower rpm at cruising speed , will adversely effect fuel mileage .
It will be harder on the drivetrain to get up to speed , therefore using more fuel .
An overdrive transmission would be preferable.


Harold
Cat
Sam is 10 year old Miniature Schnauzer
Currently without a coach

KE5WCW
 
Posts: 212 | Location: Mooringsport,LA | Member Since: 05-30-2019Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/10
Picture of ccctimtation
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Get the belts to stay on! Then it runs, it stays in its lane, its good, its paid for, its yours. Enjoy! He who is obsessed is obsessive, perfection is the enemy of the good, and I'm sure there are other sayings to add.
Mostly get your water out of our river by early May. Wink


If your not Royal don't get Coronated!
 
Posts: 911 | Location: St. Charles, MO, USA | Member Since: 10-09-2003Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 7/17
Picture of Doorman
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If you get 8 mpg and get a 10% increase, at $3.00 a gal. 50.000 miles will save you aprox $1,750.00. If you put 50.000 mile on your coach that $1,750.00 will be priceless.


1986 31' Regal -1976 Class C
454/T400 P30 -350/T400 G30
twin cntr beds - 21' rear bath
 
Posts: 881 | Location: Dayton, Ohio | Member Since: 09-27-2009Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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Tim, right you are, getting the belts to stay on is a must! River water is in control of those in the Great State of Minnesnowta, so throw that ball to Dana, it is in his domain!

Craig, I dream of getting to put 50K miles on nose, having it reliable would be the best thing that could happen.


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 3/11
Picture of Tom  and Julie
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The truck version of the BB has its max torque at 4400 rpm and that is its optimum point of efficiency. Since your coach will spend most of its time on the road you might set the fuel mixture ratio at that point. Because all carbs are compromises it generally will run leaner above that level and richer below. To match your driving style pick the best upper range for comfort in the highest gear and set it there. You probably won’t be happy doing 4400 on the road because it will likely be above the speed limit, but tuning has to be matched for the average optimal rpm. Overdrive always lugs the engine with higher fuel demand at lower rpm, but you can adjust for it. There are different size jets and the primary are the most important. You can also get optimized metering rods that have different “steps” in the rods to manage fuel flow. In short, load up the vehicle and go to a Dyno shop with equipment large enough to accommodate the coach. If you can talk a diesel shop into running your gas engine they can do the work, although they may not be able to get or select jets and metering rods. It’s a difficult job but possible.


1993 32' Regency Wide Body, 4 speed Allison Trans, Front Entry door, Diamond Plate aluminum roof &
1981 Euro 22' w Chevy 350 engine and TH 400 tranny
 
Posts: 1531 | Location: Houston Texas | Member Since: 12-19-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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Tom and Julie, It seems like a dyno is the best way to optimize the engine. I have seen all kinds of jets and rods available for this carburetor. I run 3000 rpm at 60 miles an hour approximately.

Gas mileage is one sure way to save a bit of cash as Doorman says, if one can save 10% it still takes a lot of miles to pay for a fuel injection system or a dyno analyses.

As many of the Super Stars on this forum have said, we do what we do to these old machines not for a financial benefit but out of a desire to have a Barth that adds to our life.

From a logical point of view if one has a Barth that runs well, is reliable, has the creature comforts and fills our travel needs. That is perfect!! Only a few of us put a ton of miles on our units like ED AKA MWRENCH does and reap the awards of costly upgrades.


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 1/19
Picture of Steve VW
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Hey Duane, I believe I have an fuel/air mixture guage. (as you suggest it is really just a voltmeter measuring the voltage of an O2 sensor.) Ed gave it to me and I never got around to using it because I went with the fuel injection system. It would require a bung in the exhaust pipe and an O2 sensor. I can bring it to you in June.


9708-M0037-37MM-01
"98" Monarch 37
Spartan MM, 6 spd Allison
Cummins 8.3 300 hp
 
Posts: 4160 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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Steve we are getting closer to being big time entrepreneurs, I can just feel the bulged wallet. Ok I will bring my O2 sensors. Will we have to bring ED into the fold? Perhaps I can get a bung welded in place before the GTG.

Well went up and got ole Nose from its winter home, had a heck of a time with piled up snow in front of the gate. As usual something went amuck, speedo cable was not engage and the power steering belt was loose. But Nose sits in my driveway!!! Front tires need some air too.

OK the Miata has a Gilmer system driving the cams and I think the oil pump, it went 90k before giving up the ghost this spring when nose was on vacation in Indiana making repair trips back and forth.

This set up is much easier to get at and the belt is cheaper, providing it stays on the engine. It can readily be inspected or changed and if it has to be replaced even every year it is better than a V-belt every 50 to 150 miles! Going to put the system on this weekend. Best test will come in June 3xx miles to Minnesnowta.


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/18
Picture of Duane88
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Well watched a car TV show yesterday, "Hot Rod TV" they had a couple of guys on there that already have a business tuning classic Cars and Trucks carburetors using a system very similar to what Steve has suggested using the O2 and fuel to air ratio. Guess we will not get rich doing this Steve, but at least we are on the correct path. They of course have a dyno!!


25 Ft Glassnose, 2792, 1982
454 Engine
Plain Jane Interior
Original Paint
Picture by Kevin
 
Posts: 1193 | Location: Clinton Iowa | Member Since: 04-02-2017Reply With QuoteReport This Post
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What yeall are referring to hear is a Wide-band. Is basically what your engine computer sees except it uses an o2 sensor with a a"wide" range of output rather the very narrow range around "lamba" that is used normally. They are the cat's nuts for tuning carburetors also. the one have can be observed real time while driving or can data log into your laptop while driving. They are especially valuable with a FI system that will you to adjust the AF map. 2 things to be very careful about 1 do not get too lean during acceleration or heavy load and 2 do not get so rich that you wash the cylinder walls. there are several different makes some quite reasonable. A little research on line or talk to a kid with a hopped up rice rocket. AND remember more gas is cheaper than a burned piston. and Edelbrock has a very good and "simple" manual for their carbs.
 
Posts: 73 | Location: golden valley, az | Member Since: 02-05-2009Reply With QuoteReport This Post
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