dimples won't help..................

They're only good with balls.......

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NEXT

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

in the 70's (and down here) they sold an extra thick carb spacer with some sort of a twirl on each throat... they claimed increased HP and torque... well, I guess that snake oil is universal, huh?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

They still sell them.................

Check out summitracing and you'll find variations of the theme......


Actually if not carried too far (the tornado comes to mind) it might help at part throttle to mix the fuel mixture up a bit and maybe you could get better mileage.....

I was thinking of this when I mentioned the inducing a swirl with the booster (have adjustable little flaps to play around with )

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Oh man, now you tell me! I didn't know the alternatives could be so attractive...

But seriously... I did notice, on Ed's most excellent drawing of the highly-acclaimed Mazda Rotary 4Bbl carburetor, that the main venturi cross section is decidedly in the shape of a wing or airfoil. Which certainly does point toward a lot of correct assessments on page one of this thread, where people were pondering 4 or 5 different shapes. Nice work.

Partly to play devil's advocate, I must ask: is it really worth spending so much time on a carburetor, a device which suffers a huge penalty against the laws of physics in its attempt to deliver a steady fuel-air ratio across a wide range of driving habits? In my experience, each circuit of a carb can be well-tuned for only one operating condition. As soon as anything changes, most notably vacuum draw but also temp or air pressure, it's no longer dead-on. And it's not dead-on from cylinder to cylinder even at its best.

I used to think carbs were awesome and fuel injection was just an over-complicated, unnecessary expensive mess. But then I spent most of a summer experimenting with a Carter BBS and an air/fuel gauge, "rolling my own" metering rods of various diameters and shapes, messing with air bleed diameters, taking notes, and attempting to understand what I found... and learned surprising things about how well a carb simply cannot function. The need for fuel (load) and the signal to supply fuel (manifold vacuum) are inversely proprotional, and there's not a blessed thing we can do about it. Multi-stepped rods, power jets, all of those things are a way to jury-rig from one stage to another, but within each stage the damn thing is calibrated backwards. For example, I can tune for stoichiometric at a given load, say 65 mph on a level highway, but then if I slow to 60 the vacuum increases, thereby sucking more fuel when I don't need it. If I were to speed up to 70 the vacuum is lower so it leans out (which is when I do need more fuel). Without some method of feedback, a carb will never be optimum. And of course, the carbs with feedback were a royal headache. Thankfully, they weren't made for too many years before EFI has taken over the world.

On another note... could there be any use for a venturi in an EFI system, either in the "wet" or the "dry" portion of the airstream? I can't think of any, off the top of my head... I would think that the fuel spraying on the back side of a hot intake valve does a sufficient job of atomization, but I wonder if an improvement could be found. And it's often the silliest questions that lead us into the next dimension of research, so I'm happy to help push. Thanks for an intriguing topic, folks.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Hey man

I know that EFI is the way to go... Is just the cars that I like where conceived and saw the light many years before EFI (well, you had their ancestors out there like the fuelies corvettes, but... never liked my chevvys )

And still, with their drawbacks, carbs are a good intriguing device. I always would look up on a carb rather on a overthinked, tiranic Fuel Injection system

Why tiranic? cuz it does what has been programmed to do. Sure you can fiddle around to try to get some more juice or mpg outta it but your chances (of doing good or screwing up) are never as wide as if you're working with carburetors.

A comparission comes to my mind, and it's front wheel drive versus rear wheel drive. There's nothing more safe, dependable, boring and anti-thrill thing such as a FWD car. Better handling in bad driving condition? sure, if you ain't "Dodge material" as they advertised.... FWD has made it easy for lots of people out there... but I bet that if you like to get your kicks outta body slippage and how you control it on a fast turn, or like to get in control about how your car handles, you won't like front wheel drive. As a matter of fact, I have more than 2 Mega miles behind a wheel, and less than 1000 miles outta that had been on FWD cars (less than 100 miles behind any ricer's wheel)

You can get better power outta the same motor with EFI? I doubt it. You may get better mileage, less emissions, less tune up hassle... but you'll never beat a carbureted engine with a MPEFI one. If yuo do, the carbureted engine is not tuned up. Period. Why? because with carburetion you can tailor things to be as you want them to be. No matter how widely can a MPEFI setub be tuned, you never gonna get below the unproper 14 air/fuel ratio. You can get a carbureted car to be 13... or 12...

Please note that I'm not talking about what's best for economy and emissions, I'm talking about the old as the wind joy that you get when you stomp on it and the seat-of-the-pants HP or torque or whatever rating gives you.

I'm lucky I live in a country where they haven't regulated the emissions stuff yet... and gas prices has increased a lot but I still can afford it... so I'm taking my chances and enjoying my gas sucking car...

Plus: you ain't get that "delay" feeling you get when you step on an EFI car... you know, like as if you where telling someone "Hey, I wnna go wot" and that person tells that to another and so and so till finally some old man scratch his ass and wots.... you know what I mean.

As for venturi principle used on EFI, that's tuned port manifolds.... anything that has some taper on it and is flowing something (air, fuel or mixture) is using the Bernoulli's stuff....

As far as for stoichiometric rate is concerned... 14.6 is the ideal ratio for mileage and NOT COMPROMISING SO MUCH POWER.... You can actually have a li'l bit more power if you go towards the 13 side of that ratio... but you'll loose mpg

I'd say what's obvious here: mpg and emissions controls are AGAINST power, not just for $#!+ and giggles, but because you can't achieve good power if you're after emissions or mpg stuff... and so on you can't get good power if you're aiming on to pass emissions and keep the mileage attractive for the average "I don't know nothing about this car I just fill up the tank if I have to and I take it to pep boys I like my hands clean never opened the hood"car owner (who may consider that FWD cars are a bless for his underdeveloped driving skills) I mean, you can't get 240 HP out of a slant and still get 25 mpg can you? now, if you want 240 hp and use a starved, tortured 426 hemi with restrictive ex and intake, leanburn, all that crap, you'll prolly end up with a li'l more than that, but we're talking about getting all the juice outta the fruit, ain't we?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

some misc comments about some recent posts (I don't feel like quoting) and other stuff.........

14.7:1 is ideal mixture for emissions
(15-15.5):1 is ideal mixture for economy (15.5 may be pushing it)
(12.8-13.2):1 is ideal mixture for power

Carbs (and throttle body injection) have 1 great benefit I never seen mentioned...................(well maybe very rarely)...

Have you ever seen all the crud that builds up in an EFI intake manifold??????? Having gas in the mixture for the length of the intake manifold runners keeps them clean. EFI runners clog up with an oily residue....

Air bleeds are also a carb tuning aid that's rarely touched.. You usually hear about jet sizes, power valves, rod diameters, rod springs..... All these pieces control fuel flow, but not air flow like an air bleed; there's plenty of tuning in a carb, and if you have the time you can actually figure out what is going on...


Now here's another type of carb that might be interesting to try:
A constant velocity design.. Unlike most carbs, they have some altitude adjusting capabilities.. There is a variable opening slide that is controlled by how much air is going thru it, with a needle that controls mixture. When you're not on the idle circuit, or the slide is all the way open, it does adjust to altitude (not fully, but much more than a normal carb)

See
http://members.aol.com/roundr1/CVK40.html

With the variable size, you can get both economy and power...


BTW, the CV40 is a sidedraft, might be interesting to see a custom manifold made for multiple carbs............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Wow! what a carb! a 6 carb no plenum manifold would be great to build with these, of course that pulsing is gonna be an issue past certain rpg range, but this little carb is very interesting.!!!

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I was just thinking of 2...........

Split them front/rear, and have equal length runners. The suction pulses would be evenly spaced and each carb and it wouldn't be to hard to tune them.

With 3 carbs, you'd get uneven suction pulses unless you have a really strange manifold setup, might be harder to get the mixture the same between the pairs.


BTW, there's a CV44 if you need more airflow.

BTW2, CV40 show up on ebay alot since they're stock on Harley's, and people change them out for mikunis........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

in other words using the CV40 in the dual 1 barrel manifold.... That might work really good...

I'm not a big fan of 3 carbs setup neither, unless you go all the way deep into trouble and build a 1-6 / 2/5 3/4 manifold for them, and deal with runners lenght (not an easy task) so you have even pulsing like in the rear/front setup from dual 1 barrels 123/456 layout. For a 3 carb setup I think that prolly the easy way to go is 3 2 bbl carbs no plenum setup (a weird custom manifold with this arrangement showed up on ebay some time ago) anä if I were to dive in such a trouble I might as well go 6 1 barrels. Tuneability would suck as much as the 3 2 bbl but you sure would get a strange looking induction sistem

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

"and there's not a blessed thing we can do about it"
It's called "air correction", and it's present in all carburetors for the last 90 years. In some it's an adjustable feature (emulsion tube, air bleed etc.), in others it's a combination of leakage and a sized orifice.

Stoichiometric has nothing to do with power, mileage or emissions. It's the mixture which causes complete combustion - neither air nor fuel left over. It does not produce the cleanest exhaust byproducts.

Vizard reports increased mileage up to 20-1 mix.

6 cylinder manifold design is a lot more complicated than it appears - read Smith.

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"No matter how widely can a MPEFI setub be tuned, you never gonna get below the unproper 14 air/fuel ratio"

It's called "wide band closed loop", and it's almost 20 years old.
Vizard describes in detail how to use the older and more common (= cheaper) lamda sensor to get the mixture table values down to 12.5. It requires lots of work though - 5th grade arithmetic.

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well I least I missed for 20 years only...
Now seriously. panic:
A) didn´t know $#!+ about the wide band closed loop thing you describe. As I didn´t know $#!+ about booster when I begun this learnin adventure.
B) can you get it below 12.5? or that's the sistem's limits?
C) being the theoretical person you are (I've read your articles and they're very clear and nice written) I'd like to ask you a question, for real and leaving all aside. I did read about tunnel ram intakes, and I got most of it, with its 5th grade formulas and all. I don´t understand what's the ram pipe diameter formula talks about. I get the runners lengs, plenum stuff, etc etc etc but I don't know how to interpretate the ram pipe diameter value. Is that the opening you should have as carb throat? also it says that if the air filter is bolted ontop of the carb this kind of setup is just not worthwile, so I´m guessin that you have to chanel the air long before the carb?

and last but not least, I'd like to thank you for your slap in the face. Seriously, not being sarcastic here, I've learned not to be sarcastic with someone that is more intelligent than you It pushed me to learn and read and think a li'l bit more before open my mouht wide and start asking nonsense bs. Not that it will show on my posts... but

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Don't forget that the CV40 is a sidedraft carb............

Any manifold designed for downdraft carbs won't work.


And Panic......... yes 14.7:1 is stoichiometric, but that's where you need to be for all the emissions stuff to work.............. And with the the 15.5:1 or so I was thinking of having a good chance of being able to smoothly run the engine.... Don't think 20:1 would run very well with a slant

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

CV40?

It is a keihin bike carb...

Works the same way as a su carb, but is 15-40 or so years newer.

Just an observation: some applications using constant depression carbs have a "balance tube" built into the manifold, just downstream of the carbs. It connects the two or more runners, and is normally less than half the manifold throat size. It serves to smoothe the idle by suppressing the suction pulsing. I think it also might ease tuning.

The impression I get is that balance tubes are something of a compromise, used for production engines.

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Last one out , turn off the light