The 100 mpg carb - Does it really exist?

[BMac]

Hi David,
I'll try this reply again but I'll keep it short since it ate my last one!
I've got two of your books, Horsepower Vol. I & II.
I've tried several ECU fooling devices but I'm dealing with a computer that is smarter than me!
My belief always was that the major part of fuel efficiency and hp and torque was in the intake design. One of my ideas was to take a constant pressure carb like the SU or a motorcycle carb and adapt it to a V8. That way you should have a torquey engine that gets better mpg than stock by a good margin. But just what size and how many would one require. I would be planning to adapt this to a dual plane intake.
I have tried the EFI way but and scared I might fry the engine. I have a MegaSquirt programmable computer. I am thinking of switching to a carb/carbs again. I've played with the Carter series for some years now but still intrigued by the constant vacuum/pressure design.

What are your thoughts on that? How big and how many?

Blaine

[DavidVizard-GFN]

Dear Blain,
I think I have answered some of your questions else where but to give rundown usefull to as many as possible I have some broad recomendations.

First a constant vacuum (pressure) cab such as an SU is good in as much as it is almost impossible to over curburate the engine. Remember they ony open up as much as needed not as much as the driver thinks they need be.

The SU Stromberg and all similar carbs have the potential to be super high milage carbs in as much as they will deliver a well atomized mixture to the engine. They can also deliver an extreamly wide range of air/fuel ratios accurately. The problem is that giving what is needed boils down almost entirely on how acurrately th carb needles are profiled. As a do it at home deal you will need as a minimum an O2 sensor in each exhaust bank and I would recomend in each ex. pipe as optimal.

The idea of putting this type of carb on a dual plane intake is a sound one. I would say that a pair of 2 inch SU's would support about 300 hp on a well set up engine. Our milage testing with this type of carb on a Mini engine indicated the water heating the intake gave better results than exhaust heat (which appeared too much) or no heat.
I suggest you convert the heat cross over passage of a good smaller port two plane to water heating.

Hope all this helps,
DV

[erantanen]

I have been experimenting with an older 600 cfm 4010 Holley (with annular boosters) while trying to maximize fuel economy. This is partly due to your writings on atomization, party due to Ford's application of the technology on the 4180's, and partly due to a good experience I had with a 4010 circa 1990.

This carburetor has a very linear fuel delivery once you are on the mains. I have tuned it to cruise at stoichiometric with a conventional O2 sensor and it is good for a hair over 17mpg in my truck at 70-75 mph cruise on the flat roads we have here in Florida. I wonder how much more is to be had with more work, as I have no idea what is actually going on in the engine. Any thoughts to where the limits are? My latest tuning focused on running the engine at stoich as I knew my O2 sensor would give me good readings there, but my understanding is that there is generally a bit to be gained running slightly lean at cruise.

The vehicle is a mild 350 powered 2wd GMC C10, about 4040# unloaded, SM465 4spd, 3.07 (3.08?) rear, 235/75R15 tires. I have definitely noticed the impact of temperatures on performance. For example, with my particular combination I found that a 190 degree thermostat vs. a 180 eliminated a very small hesitation at light throttle. As I have no heat crossover in the heads I concluded the small increase in water temperature was providing enough extra heat to keep fuel vaporized, in suspension or something similar. I suspect keeping the vacuum up also serves the same purpose; cruise is about 17 " Hg at speed.

I am working out the details for a high mileage project with a different vehicle using the old Honda CRX hf's 50+ mpg for inspiration. Again, I wonder what the limits are with a slightly smaller displacement engine and less weight.

Eric

[mlilja]

Hi David,

My interest has always leaned towards the efficiency aspect of engine building and figured long ago the 100 mpg carburetor never existed for precisely the reasons you give. It is the thermodynamic efficiency of the engine that is lacking. I have been reading and re-reading your books and articles for years. Your writings have attracted me because you have a penchant to include a little reality as well (gas mileage, driveability and a little cleanliness.) I started my collection with a copy of "How to Rebuild Your Small-Block Chevy" (the original version now quite well thumbed) and have enjoyed your writings since.

I always thought there was lot to be garnered from the smallest details and have also gleaned a number of ideas from your tech articles, "Performance with Economy" and "How to Build Max Performance Chevy Small Blocks" One last thought, I know you said you are planning on giving this information away with enough readers, but just to let you know, I would be happy to pay for it as well. Please, keep up the great work. Thanks.

Mike

[seattle smitty]

Mr. Vizard, in the course or classes you teach at UNC, do you have a track for students who want to specialize in fuel efficiency and economy in street cars and trucks (bikes, boats, planes)?

I am hoping that this subject, which is very interesting to a lot of us old guys who used to race and who now want to apply their skills to building daily-drivers with enhanced efficiency, will be given it's own section on this site . . . or if that seems inappropriate to GoFastNews, you will address the subject on one of the sites devoted to improving fuel-efficiency.

[DavidVizard-GFN]

Originally Posted by mlilja

Hi David,

I always thought there was lot to be garnered from the smallest details and have also gleaned a number of ideas from your tech articles, "Performance with Economy" and "How to Build Max Performance Chevy Small Blocks" One last thought, I know you said you are planning on giving this information away with enough readers, but just to let you know, I would be happy to pay for it as well. Please, keep up the great work. Thanks.

Mike

Thanks for you kind words and confidence. I will send you an address to ship checks too!

Serieously though the economy stuff will start soon.
DV

[DavidVizard-GFN]

Originally Posted by seattle smitty

Mr. Vizard, in the course or classes you teach at UNC, do you have a track for students who want to specialize in fuel efficiency and economy in street cars and trucks (bikes, boats, planes)?
.

I left UNCC Jan 1st last year (2006) but kept teaching some of the more enthusiastic students untill they graduated. I am now down to one.

Originally Posted by seattle smitty

I am hoping that this subject, which is very interesting to a lot of us old guys who used to race and who now want to apply their skills to building daily-drivers with enhanced efficiency, will be given it's own section on this site . . . or if that seems inappropriate to GoFastNews, you will address the subject on one of the sites devoted to improving fuel-efficiency.

I think having a section devoted to minimum consumption of fuel and, for that matter, cash to build said gas mizer is a great idea. While we are at it we will also look at the impact anything we do has on the ecology. I'l figure out how we will go about presenting this section at the next GFN commitee meeting which should be right after PRI.

DV

[Jesse Lackman]

Does anyone know what Smokey's hot vapor engine got for gas mileage?

That design has always been interesting to me as his intake manifold temp was 440F. The end point of vaporization for pump gas is/was 437F. What this means is the fuel was 100% vaporized before it got to the chamber. He remembered liquid fuel does not burn.

What Smokey improved was vaporization efficiency by using waste heat. He maintained mixture density with a turbo. The engine did not ping even though many tried.

What is the percentage of vaporization in today's fuel injected engines? 100%? What is the percentage of vaporization in a carbureted engine? 100%?

[Pinhead]

BTT...

Does anyone know what is wrong with lean burn with current technology?

[BMac]

Yea, they still don't atomize the fuel enough to be able to do it without burning up an engine. It takes time to do that. Time = distance. The fuel discharge must be a good distance away from the intake valve.

Remember David's article, the CV side draft carb atomizes fuel better than a fuel injector unless that injector has more than 100psi behind it.