speedtigger

iTrader: (16)

This is an interesting article. It may have an influence on my carb choice if I choose to upgrade:

http://www.carcraft.com/techarticles...son/index.html

S10xGN

iTrader: (11)

I read that when it first came out and promptly went out and bought a ProForm 750 annular body for my Holley HP-750. Seems like it's got a bit more bottom end, but I'm still tinkering with it (still blows black smoke rings on the floor when first started).

Luke_PCScarbs

Good article, though I would like to see results after messing with the emulsions on both. I'd bet there isn't much difference. Just my $.02

Pop N Wood

iTrader: (1)

Sort of hard to draw any hard conclusions from that article. I think the off idle bog most LS guys complain about is exactly what they are addressing with the annular boosters. But at the same time the article admits the down leg "might have" gotten the same results if they had experimented with different air bleeds.

So in other words they didn't do a very complete job?

Not sure what to make of that.

NemeSS

iTrader: (127)

interesting....

ZONES89RS

iTrader: (25)

That is what i take from it, you need some guys that really just tinker with every possibility of the tuning adjustment.

brngrhd

to me the off idle bog that your guys are talking about is from a big carb that these motors tend to like on the mid and upper end not having good signal down low..... could this be tuned out with pump shot? IDK

as i see it annulars allow for bigger carbs on small motors.

the annulars make bigger carbs flow less like and 850 with downleg will flow more then it will with annulars but they also make it more drivable down low and because of the atomization run better through out the rpm band.

to me your best bet is talking to a carb builder and getting what they think is good for your combo...... when i was talking with patrick at prosystems about my last carb i was looking at an HP950 style carb he said not to go with annulars......

speedtigger

iTrader: (16)

The NASCAR guys use annulars. I know those guys spend massive money for GURUS to work endlessly on flow patterns and distribution trying to squeeze the last little ounce of power out of those combos. But, they are also very concerned with fuel consumption where street and drag guys may not be. So, they may have other reasons for choosing than we might.

I have owned an 850 annular but it never made it on the car before I sold it. So, I have no personal experience. The low end torque difference depicted in the article is very appealing to me because I am trying to run a tighter stall than most guys might.

brngrhd

you an me both.

as for the engine builder stuff my old engine builder left WI and went to nascar and now builds for greg andreson back when he was building our stuff he even said then you have enough CFM, what you need is better atomization to make more power and better power through the RPM.

xpndbl3

iTrader: (23)

I don't believe that article because who would open up either 4 barrel at 1800rpm to get readings. In the higher rpm range 4000 and up if they tuned them similarly there would be zero difference IMO. I have a holley book from the early 70s and it even discusses the proper rpm operating range to have all 4 barrels open. That test was not properly done IMO and misleading in its results.

speedtigger

iTrader: (16)

I had to really think about this response xpndbl3. The things you say above I have never heard stated in my life. Don't get mad at me here please! But, when I read this response, I immediately wondered if you have ever owned a car with a mechanical secondary 4 barrel. Since you have a car with a high stall and a brake my first thought was probably not correct. I will say that us carburetor guys mat the throttle right off idle. And, if the set up is correct, we are rewarded with the perfect response. So, for a guy like me who is going to run a 2500 stall converter, extra low end torque is just what the doctor ordered.

xpndbl3

iTrader: (23)

A big cam'd car like in the test would not be running a 2500 rpm stall converter. Obviously they had fueling issues running a box stock 4 barrel at WOT on the dyno, no mention of a/f ratio issues, etc. Other than "we added fuel and picked up no power down low" At the dragstrip I don't believe there to be that big of a difference in ET or mph showing up at all. Otherwise annular carbs would be under everyone's hood and dog leg boosters would go the way of the dinosaur. Stock torque peak on an untouched ls1 is what 4400 rpm? So conventional wisdom would be much higher than 2500 for best results for a max effort combo. You can have low air flow signal through a double pumper at super low rpm, and yes there is a holley chart on rpm vs cubic inches. Even after playing with my carb for a few months, the wideband still shows it's not perfect and I've made several adjustments getting it closer. Box stock testing of a big cam combo at WOT 1800 would show the better fuel signal to the annular, if they started the test at 4000 and tuned the dog leg carb, this wouldn't be such a big difference was my whole point.

speedtigger

iTrader: (16)

I would agree with all that 100%. Once the RPM get up, low speed atomization advantages would no longer be of value. I think their test shows something like a 5hp advantage in the upper RPM which could easily be tuning margin.

For guys like brngrhd and I who are running tighter street converters, it could be very useful if the test results are a-typical in the lower RPM ranges.

xpndbl3

iTrader: (23)

That's why staying on the front barrels for a quick second and rolling the throttle will allow you to keep up air velocity throughout the lower rpm range. Wish I had a functioning scanner to show a few pages out of this book on all the theories behind it.

stinkybutt

My wifes car has run 11.0's@119 with a gen 1 406, dished pistons,5.7 rods, GM Fast Burn heads. Edelbrock RPM air-gap. Comp flat tappet solid, 520/540, 244/252@ 0.050". On our chassis dyno I had to reduce 6#'s in jetting after going from a down-leg 750 to an annular style booster . The car instantly improved it's 60' from high 1.5's to 1.40's. It also now carries the wheels about 30' out and 3-4" up. The car has a 3.50 gear, and is 2975 with her in it. The converter is an 8" that was custom built and pulls the motor down when put in gear. My wife leaves the line just off idle 1,000-1,200 rpm, leaves the car in drive,it shifts @6,000, goes thru the eyes at 6,000.
The new 6.0 with LS3 heads and comp cam XR281HR-12. I'm also using the GM intake with a 750 Annular carb. I hope to get the car running and dynoed in the next few weeks. I'll be using the same turbo 350 and converter.
I know from tuning on our chassis dyno and stealing my wifes carb to show customers how well the annular boosters work vs the down-leg and straight boosters I sell a bunch. The throttle response is amazing.
BUT you cannot just throw a booster change with-out re-jetting. Also we noticed you don't need as much pump shot as the boosters are more sensitive to the airflow, hence they pull fuel quicker.
Annular boosters are great for a street car.
BE CAREFULL with dyno #'s. A bigger carb can make more power, BUT the low end throttle response WILL suffer.
AND YES the car pulls the wheels leaving on the foot brake at 1,200 rpm.

Aleck

stinkybutt

Again I return after reading the artical. The ann boosters made more top end power, BUT read that 90 lbs/ft below 2,500 rpm. So why are some in here bashing the annular boosters? We look for average hp/torque #'s when we tune as well as peak #'s. Remember when you shift @ 7,000rpm the engine drops to low to mid 5,000. You need a good shift recovery to get to peak hp. Also on the street when you slow down to go around a corner it's ALL about booster signal for response down low. We use a wide band for tuning and also use the airbleeds and the emulsion tubes in the metering blocks.
Some off idle stumbling you guys have is probably due to the idle air bleeds and idle restrictions, not all about pump shot.Timing plays a big roll in all this too.



Aleck

Luke_PCScarbs

Most carburetor builders will choose a down leg booster, pick the venturi size, and meter the fuel properly in the metering block to control booster flow. By properly tuning the emulsions and high speed bleed to the down leg booster, the carburetor will come close to the annular at low rpms. Around 5800-6500 (depending on engine specs), the down leg will surpass the annular in flow and power. Inlight of this, the annular is not better than the down leg, and the down leg is not better than the annular. Each are application specific.

Luke_PCScarbs

This is also dependant apon whether or not the carburetor is the correct size, too small, or too large for the engine it is going on. Also there are many people that believe, in drag race applications, that you are wasting your time dynoing carburetors and headers. I have seen instances where this is very true. Just because it makes more power on the dyno, doesn't mean it will go faster down the track.

I haven't seen any NASCAR carburetors, but I have seen carburetors from some of the best competition eliminator engines in the country, and haven't seen annular boosters in them. Again, application specific.

Pop N Wood

iTrader: (1)

Werd that. Made all the difference in the world with mine.

speedtigger

iTrader: (16)

I like hearing from the guys who have been there and done that. Thanx Aleck.