The 100 mpg carb - does it exist?

[shrinker]

hello David; Adelaide is still the same, still the retirment village of Australia, just with a bit more traffic thats all.

hello Cammer; yes EFi already is good at part throttle but that doesnt preclude the same features being incorporated into carburetors. Its just that it isnt a development priority area. I have done examples of carburetors that are setup for economy etc and they give cleaner emissions and better fuel economy during the government drivecycle test than the EFI. Unfortunately we usually compare carburetors by also comparing older technology design of the engines they are fitted on. There are not many people that turf out EFI to install carburetion. Admitedly you have to use carburetors designed for the intention and you have to tune them and modify them etc but you have to do that when you fit up a custom EFI system as well.
Carburetors have a better flow of fuel into the engine, that is the fuel is delivered more continuously than the intermittancy of an injector. The air enters an engine in a relatively smooth continuous manner that could be described as 'analog' and a correctly functioning carburetor can deliver the fuel in the same manner. This results in elimination of dry pockets of air etc. When you inject the fuel close to the valve you dont allow much time to get the fuel gased and evenly spread throughout the chamber. So the designs of squish etc become very influential to the quality and consistancy of the burn.
The old throttle body injector designs are a classic example of dry air.
If you shine a timing light of the dial back type onto the injectors of these systems you can dial the light so you can see there is large degrees of engine rotation where there is no fuel being injected. This is the best way to visualise a drawback of EFI. Its still like that in the runner. The engine doesnt run very well on dry air.
A carburetor can be designed to have air speeds of 300 mph at idle if you want to, that sort of air speed is very effecive at fuel atomisation and mixing and gasifying the fuel. And seeing as most of the fuel economy running is done on the idle and transition circuits that design is good for economy. Not all carburetors are the same in their abilities just as not all EFI designs can optimise any application.
Providing mechanical equivalency of a computers abilities is just about impossible and it certainly wouldnt be economical, but the difference in the delivery techniques of carburetors and Direct port injection accounts for a lot of the abilities of the computer.
It is important to consider cam and head flow design when choosing FI or carby as these things are very integral to the function of either system.

As a side note, just because all cars are now EFI doesnt mean its the best thing, manufacturers have gained a tremendous advantage at the end of their production lines by using self tuning EFI. No longer do they have cars hung up in the side getting the engine tuned by rows of tuners and now they can charge the world for servicing complex systems that cant be fixed by cleaning them in a bucket.

[BMac]

Originally Posted by DavidVizard-GFN

Then there is the Kendig carb - those guys have something there but don't listen to advice (or at least they didn't).

DV

What do you mean by that?
I have two of them and they are very clean. One doesn't even look like it was ever used! I've got nothing to test them on though.

I read somewhere that one fellow in the early 70's put one on a 351W and got over 50mpg! Wonder if he just tuned it or modified it.

B~

P.S. This is my 3rd post. Wonder if it will show up! Weehaw, look at that!

[BMac]

I have a set of Strombergs from a '75 TR-7. Do you think they'd work on a 318 Magnum? I certainly have the ability to adapt them! I'm looking for higher mpg with no loss in torque and still decent power to 4000 + rpm.

B~

[seattle smitty]

Mr. Vizard, this is the discussion I've been looking for. I will notify all the gear-heads at Ford Six Performance: The Web's Leading Resource for Ford Inline Six-Cylinder Engines and Cars!, many of whom have a keen interest in building street engines for maximum fuel efficiency. We have our own discussions including setting a good tight squish-height for detonation-resistance so we can add a bit of compression. Some of us want to really squeeze down on the heads, while using water-injection so that we can still burn the low octane gas. Of course, a lot of our discussions are specific to our engines, concerning camming and rocker ratio, the well-worn rod-length:stroke arguements, and so forth. If you get a chance, pay us a visit. I think a couple of the posters were students of yours. (I just typed a web address up there; why did it turn into an advertising slogan? But it's a great site).

I have a project you'll like. Ford 300 inline six for a van. Stock cam, stock valves, the standard 1.6 rocker ratio for the intake but maybe 1.7 rockers on the exhaust. Squish at .036-.039" using either the early 240 closed-chamber head or the recent swirl-head. I have two compression ratio targets, one for use with water injection, one without, but I'll ask you about that some other time. I'll fabricate an exhaust system per Philip H. Smith's design.

Here's the interesting part. If I wanted to spend a lot of time and cash, I'd carburate with three sidedraft Webers, OR use the late factory fuel injection hardware for this engine combined with the do-it-yourself Mega-Squirt programmable controller and its various sensors. But first I want to try what I have now, which is a Clifford single 4bbl manifold and a Holly Pro-Jection 2bbl 670cfm throttle-body injector with oxygen sensor.

Now this Clifford manifold is supposed to be a performance item, with nicely-radiused runners . . . BIG runners, and a BIG plenum. And that 670cfm injection unit seems pretty BIG, too, for an engine that will never see the far side of 4500rpm. The Sixers typically like the Holley 390cfm 4bbl for this kind of work. Well, the Smitty plan is this: since the engine is basically two triples set end-to-end, I have fabricated a divider in the center of the plenum o this Clifford manifold, so that any cylinder will draw a vacuum on just half of the manifold volume, and draw from only one side of whatever injection unit or carburetor I use. In other words, like virtually every factory V-8, my I-6 will have a dual-plane manifold!

Before I obtained the Pro-Jection unit, I had thought to try a Quadrajet o my split manifold. A Quadrajet would normally be far too big for a six like mine, but by effectively splitting it into two 2bbl carbs on a dual plane manifold, it could work. My only reservation is that since I'd have to mount the carb sideways to it's preferred orientation, the float-height and metering might fluctuate a lot under routine acceleration and braking. The Pro-jection won't be bothered by this at all.

But now think about this one. A third possibility might be the Street Predator. A normal orientation of this carb (float-bowl AFT on a street machine, says the manufacturer) is perfect for an inline six, whereas on a dual-plane V-8 manifold the spraybars of the Predator are funneling its charge right at the manifold divider, which seems less than ideal. Of course, the Predator is huge, 1050cfm or some-such. But what if I could fabricate a divider, say 3/8" wide, inside the middle of that carburetor, matching the divider in my split manifold? If I could be sure that the spraybars would meter evenly on either side of the divider, that might be a very functional, easy-to-tune, altitude-compensating carb for my purposes.

What do you think of that last idea (before I call Predator and see what THEY think of it)?

[BMac]

Hey, that's a good move dividing the plenum into a dual plane but remember, it's best to divide by firing order! That way the pulses go left right left right left right.
My friend has a Toyota wagon with a 1.8 and I was surprised of the torque it had so I asked him to open the hood. Sure enough, long runners and a divided plenum!

I think with the constant vacuum type carbs like the Predator/Kendig you won't have to divide it's plenum. In fact, you may not have to divide any plenum. Not sure on that one. I have both those carbs and also a Woodworth constant vacuum carb. If I was running a straight engine, I'd use motorcycle carbs like the Keihins used on Hondas. Actually the older Honda Preludes used two Keihin carbs used on their bikes.

Just a thought but it may be worth a shot.

[Pinhead]

I was thinking the same thing. Use six Keihin carb's, one per cylinder, with good and long intake runners. Parts are abundant, they're easily modifiable, and extremely simple. Six of them would definitely give you enough for the top-end, CMF-wise, and would be excellent for torque. I would personally try to use the CV type. You can usually buy them in banks of four on eBay for less than $100.

[DavidVizard-GFN]

Seattle Smitty,

Big post - lets see if I can give you a short answer. The Holley projection seems to be good at part throttle where the fuel droplets smack into the butterfly and get distributed in the air OK but at WOT the fuel's going in so fast a lot hits the manifold floor and results in wet flow. Be aware of that.
I did a triple SU setup for a Toyta Land Cruiser about 1978. This was used for off road and rock crawing to actually get to almost inaccessable places. (part of the guys job was looking for meteorites in the desert). The carb made this six into the next best thing to a 200 hp electric motor. It would pull smooth from about 400 rpm. Once again good mixture prep paid off. Top end was still way better than stock to boot!

As for the Preditor guys I told them years ago they had a great carb but there were no manifolds out there to specifically take advantage of their fuel dispersion charactoristic. AS a result they always dynoed out behind a Holley.
DV

[seattle smitty]

(please delete)

[seattle smitty]

Thank you. I thought you'd have something to say about the split manifold, but that's okay, I'll do it anyway. I'd heard about that problem with Pro-Jection, so I designed the "splitter" I put in the plenum so that it would tend to shear and hopefully re-attach liquid fuel. Also, I welded a partial water jacket under the manifold. And manifolds on these engines tend to get quite hot anyway due to proximity to the exhaust manifold. Finally, this engine will rarely see WOT.

Are you aware of the poor reputation, deserved or not, that SU carbs have in this country? Have you done an article or thread on the subject? You demonstrated in your book that they can work very well, but why then are there aftermarket kits sold here to owners of old Brit-cars who want to switch to a whole range of alternatives to the SUs that were factory-engineered into their cars? I'm a contrarian, and would be delighted to show off an American engine running happily with a row of those impossible SUs, but I'd need to know a lot more.

[Cammer]

seattle smitty,

There is that little issue of having to carry an oil can in your car for emergency SU lubrication!