Has anyone experimented with the different size dog leg boosters? What effect did they have on AFR? will they affect tune ability?

Thanks, Rod

ANYTHING you do to any of the metering circuits / passages can have an impact on the AFR. You won't know how it's changed unless you can do before & after testing.

Not sure if you mean larger as in leg ID or venturi hole ID, but both have the potential to change the tune.

A bigger ID leg can flow more fuel, but can also be less responsive to changes in the air bleeds, etc. And it may only flow more fuel if the engine combination it's being used on can generate enough fuel flow to max out a smaller ID leg. Otherwise, it could have the POTENTIAL to flow more, but actually flow less due to it being harder to get started on the main circuit.

A larger ID venturi hole is supposed to improve booster signal, but I suspect that depends upon the shapes of the boosters being compared, too. I have two similar main bodies on hand, one with the original boosters it came with and the other has modified boosters from an aftermarket carb company. However, the way the modified boosters were opened up in the boosters' venturi, I think I'm going to need to add a radius to smooth the transition from where the modification simply left a machined edge where it was enlarged.

I know nothing, but from what I have been reading over the last five years, the straight leg boosters and the downleg boosters will have very different fuel curves. Annular boosters have yet a third.

Look at all the Holleys, the straight leg booster seems to be majority, but every now and then there's an application that calls for a downleg booster. Here's an example - The first 780 Holley that came on the 425hp 396 had downleg boosters. We'd call it a 3310. Then came the later iterations and boosters changed to straight leg once it became a "one size fits all" carb. Maybe BradH or someone else like Mark Whitener or Mr. X our resident carb rebuilder can explain some basics like what are the general characteristics of the three types of boosters. I'd prefer not to get into air bleeds, idle fuel restrictions, and such because it's hard enough to remember the characteristics of the boosters.

How about it, guys, I'm slowly learning the second layer of Holley carb knowledge.

R.

Experimenting with boosters is like experimenting with head porting. If you don't have a flow bench and some other data gathering tools then you are probably wasting your time. You'll need some way of knowing if you are making things better or worse. You can't just look at it and tell if you improved anything.

Vizard has some stuff in his books on booster design. He shows some tricks on booster porting and booster placement. His goal was to increase total airflow while keeping a good booster signal.

As for me, I'm spending most of my time these days learning EFI so I'm gradually selling off my carbs and slowing forgetting what I used to know.

Yup, I'm 20 years behind the times.

R.

Generality: an annular booster provides a stronger signal and will deliver more accurate metering at low air speed, and a cleaner transition to main metering without excess richness. The penalty is that the thickness of the booster slightly reduces CFM. In a Dominator this matters less, of course. Holley boosters appear all the same size, which means the obstruction is more important in a 390 than an 850, etc.

BTW: for highest efficiency a booster is supposed to terminate about .030" after the "vena contracta" (smallest point) of the venturi it's in. The discharge tube should be positioned the same distance after the booster's minimum diameter.

Start with THIS.

My quick fuel carbs on the 572 Hemi have annulars on the primaries and downlegs on the secondary's: quick off the line and lots of air flow when the secondary's are open. Spec'd out by quickfuel. Tim

That's pretty much the exact opposite of what my last annular combination did on the street; it came up on the main circuits too quickly during part-throttle street use and drove like a pig compared to the downleg config I compared it against.

I'm hoping my tuning capabilities are better the next time I run 'em, though. I'm still interested in seeing if I can get a big venturi annular 4150 to work for me.

They work really well on the dyno. The last round of testing I did with a 1050-AN from QF made more power than any downleg booster carb that I tried. As for the street, well that is more complicated.......

When I worked on carbs back in the fuel lab
we tried to develop a moveable booster that
would change in height... that never happened..
EFI came to soon which was far better

Then there's booster impression and it's location relative to the pinch in the venturi but I see no use myself for a straight in a 4150 when a downleg puts the boosters in a better location accordingly...........But I am the guy that sees no place for a VC carb in a performance application either.........

OK I am at fault for the usual mistake of not giving enough information. Thank you for everyone who has replied. What I was curious about was the different size Dog Leg boosters and the effect they have on carb set up. This is for an all out stick shift Stock Eliminator 340 6pack. I would expect that any Holley carb with dog leg boosters would show a similar trend as a 2300.
What brought this question up is I have several sets of carbs One has a loose booster and one has a melted booster, in looking for replacements I found out they come in many bore sizes. So I was curious if anyone had experience in changing the bore size of the boosters and how it affected the tune up mostly at WOT.
Thanks, Guys

BradH thanks for the link.

They are DOWN LEG not dog leg...

[quote=astjp2]They are DOWN LEG not dog leg...

"Booster 3 is a dog-leg booster version of 2 with a step machined into the underside."

astjp2
Above is a quote right out of the book that BradH sent the link to. Perhaps you should read it. Do you have anything positive to add to the discussion?

http://www.hotrod.com/articles/carburetor-showdown/

If you read the article, its downleg, dog leg is slang
and yes, if you use annualar in the primaries and downleg in the secondaries, you get the best of both worlds, good low end with most of the top end....

You didn't read the question and your immense knowledge (I didn't do 4 years and 9 months of Graduate School to be called Mister) has added nothing to the discussion.

And, I suspect, some "interesting" fuel distribution behavior w/ the different flow & atomization characteristics between the primaries & secondaries.

Center and/or outboard carbs?

I've seen fairly consistent booster leg sizes used that probably depend upon the venturi & throttle size combination. With your all-out Stocker, I'd guess you could try out a slightly larger than standard leg size and see if you pick up anything... or screw the pooch w/ your tune. /

Hey, boosters are cheap and Class racers are rich, right?

my 1050 AN works great on the street, much better than the large venturi down leg I had before, love it !! BUT EFI is in the future.