The 100 mpg carb - does it exist?

[gregory]

Originally Posted by DavidVizard-GFN

Nothing is ever perfect but a carb can be engineered without much additional R&D to do exactly what the fuel economy minded driver wants. Why am I sure of this - I have taken out carb patents and been a design consultant to several carb manufactures. Addionally I have been called in to engine development projects as a carb speicalist. Bottom line is I am not without skills in this area.

Delivering fuel to an angine in vapor form is not hard to do. Incidently if the fuel droplet size is below about 5 microns it acts as a vapor anyway. Of couse with even the smallest amount of heat droplets that small turn to a vapor.

Hi David...
What carb in your opinion is one of the better carbs for performance on a v8?

[shrinker]

And may i add a further question as to what size droplets exit different carburetor designs please?

[DavidVizard-GFN]

Gregory,

I have not done any serius part throttle work on the dyno of late but back a half dozen years or so I was looking at carbs and fuel consumption for street V8's. I was doing this sort of as a side project so the results ar far from definitive. However, here's what I found with the limited testing I did. Holley's Spread Bore carbs when jetted for ecomomy on the primary did very well. # 1 (remember this is not the be all and end all of tests in this area) of the carbs I tested was a Quadra-jet built by the Carb Shop in California. It had an external part throttle mixture adjusting screw which allowed the leaning of the mixture untill best results were seen. I really liked that carb - maybe I should build an econo motor using one. Last but hardley least, and real close to the Q-jet, was a Carter Thermo-Quad. That's now the Edelbrock carb, and some testing we have done of late indicates this could be a good choice for reasonable performance and good economy. As for regular square bore Holley and BG carbs I have done little in the way of fuel economy testing. That said I do believe that more time spent looking at part throttle stuff instead of fixating on big Tq & hp #'s with these carbs would reveal that they can do a pretty good job in both camps. Then there is the Kendig carb - those guys have somthing there but don't listen to advice (or at least they didn't).

DV

[Cammer]

As ascending engine performance becomes critical carburetor designs such as a Holley or BG may outperform the others.

Most of the other designs reach a point where added performance is difficult or impossible to achieve.

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Maintaining fuel homogeneity is paramount to a good running engine.

You would be surprised at the amount of fuel found on the walls of the intake manifold and intake ports of a running carbureted engine.

Air and fuel like to do their own thing and fuel drops out of the mixture easily in corners and transitions.

I wish the combustion chamber could right all the wrongs with mixture, but in many cases evidence of raw fuel spatter can be found on combustion chamber walls.

Many heads must be modified to recondition raw fuel so it burns properly.

Sometimes just slightly roughing up problem areas will straighten out the situation.

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Intake manifold, heads, cam, CR, exhaust, intended use, etc., must be considered when choosing a carburetor.

An engine builder needs to examine everything as a whole and build to the specific application!

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[gregory]

Hi David,

"It had an external part throttle mixture adjusting screw which allowed the leaning of the mixture untill best results were seen"

When you say until best results were seen,what were you using to see the result?


Hi Cammer,

"As ascending engine performance becomes critical carburetor designs such as a Holley or BG may outperform the others.

Most of the other designs reach a point where added performance is difficult or impossible to achieve."

In what way does the holley outperform other carbs?
Why is the added performance difficult to acheive with other carbs?What is it that holds them back?

[Cammer]

A big plus for the Holley and BG type carburetors is the tremendous amount of parts available for them.

Much carburetor research and development is concentrated on the Holley/BG type of carburetor.

In my younger days I seem to recall running a bevy of Keihin motorcycle carburetors on a straight six Ford with great results!

IMO, modern EFI is vastly superior to any carburetor, both for economy and power!

This last statement should provide for some lively discussion!

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[gregory]

Cammer,

"modern EFI is vastly superior to any carburetor, both for economy and power!"

Please tell more.

[shrinker]

hello; EFI has the ability to vary the fuel flow injected into the engine but thats not impossible to do to a carburetor either so that leaves the difference in atomization and EFI has small drops but you can do that in a carby too so that leaves the short distance of fuel engagement by injector placement designs and that may reduce the wet flow distance but that also is reducing the heat vaporization distance so all that results in is a different tune strategy. So overall i havent found any benefits for EFI that cant be done on a carburetor. For the times i have removed fuel inection and fitted carburetors I have increased power of the engine and decreased heat loss and improved efficiency. That is my practical experiences. I realise there is a lot more compexities than this but I think both systems have very deserved placements in aspects of engine performance and either needs to be considered with open mind as to applicability. I have even setup an engine with a carburetor and fuel injection in dual operation. That worked very well.

[DavidVizard-GFN]

OK this topic is hotting up.

Some very valid points are being aired here.

First the part throttle adjustment screw on the Q-Jet. I used this to adjust until the best freeway milage was seen. This was a 468 inch BB Chevy which, on this very same Q-Jet, pumped out 530 hp and 545 lbs-ft. It was in a 71 (or so) Monte Carlo with a TH 400 tranny (not the worlds most fuel effcient unit). At 65 cruise speed we got this 3800 lb behemoth to deliver just under 18 to the gallon. On street tires it ran high 13's at 107 mph (left tire smoke like a Destroyer laying a smoke screen).

The point about fuel Injection vs carbs for economy raised an intersting point. I had a good friend who worked in Chryslers combustion lab. He had done some serious testing of carbs Vs F/I for economy. Results - a carb beat the typical F/I - untill the injection pressures were raised substatially above the currently accepted norm of around 30 to 45 psi. At 100 psi fuel economy vs pressure leveled out and no gains were seen from added pressure.

Those Khien (or however it's spelt) carbs are good in terms of fuel atomization and combine the best of both fixed jet and constant vaccum carbs.I would add that carb to the list If I had to design a maximum economy carb starting with an already existing example.

Hey Srinker, how's the beautiful city of Adelaide looking these days - hve not been there since '94.
DV

[Cammer]

A new Corvette will run with the best of them and return 25+ mpg on the highway!

I challenge readers to achieve this performance with a carburetor!

I will concede that a good carburetor will match EFI in full throttle applications.

Under part throttle and transitions EFI will prevail over a carburetor.

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