MotorHead

I wanted to try the annular booster and swapped out the downleg boosters today. The annular booster are much bigger and are more of a restriction in the barrel but my 825 Race Demon flows 975 CFM so I can probably spare a few.

Anyway here is the idea behind it copied from a this Car Craft article.

http://www.carcraft.com/techarticles/116_0508_boost/

"The annular booster, which is slightly larger in diameter than the downleg and employs a series of small discharge holes drilled into the inside circumference of the booster to improve fuel atomization. This annular design accomplishes several things. At lower engine speeds, slow air speed creates a weak signal, which reduces the amount of fuel moving through the booster. An annular discharge booster�s multiple holes offer many points for the fuel to enter the venturi as opposed to a single discharge point. At lower air speeds, this offers measurable advantages, especially when combined with the annular�s better signal strength. This is important for situations where large-volume carburetors are used in conjunction with a long-duration camshaft. With a weak manifold-vacuum signal at idle, annular-discharge boosters can greatly improve throttle response and driveability."

Anyway I went for a spin and sure enough the off idle throttle response iis much better and it seems the motor runs smoother all around. As for power it is very hard to say, seems like it has a little more but I would have to put it on the dyno to tell for sure. Anyway I think this is way to go for a street motor

This paragraph is what I thought was very interesting :

" In this particular case, the peak power difference was a solid 7 hp, but even more impressive was the 20-lb-ft average torque increase. This illustrates why Barry Grant recommends using the annular-discharge carburetor on any engine with a camshaft duration of 220 degrees at 0.050 or more. What you can expect is that an annular-discharge carburetor would be an excellent choice to improve part-throttle driveability on a street car equipped with a long-duration camshaft and lots of overlap while also promising a slight overall power improvement. Annular boosters could also be a great addition to a slightly oversized carb as a way to improve its part-throttle manners. "

Comparison of annualar to downleg boosters


Two downleg and two annular in same carb body


All four annulars installed


On the motor

ratflinger

Thanks Motorhead Great info & even better, real world testing!
You can't get this kind of info anywhere else.

MotorHead

I just went for another spin, definatley more punch to the motor now

Maine Vette

Sweet! Thanks for the info. I've heard the annular boosters are great for low end throttle response which is why I got my speed demon with annulars.

It's good to hear a first-hand testimonial!

MotorHead

I want to keep this thread going as I think not alot of us know about this. THe test that Car Craft did on a 500HP test mule says they picked up 94ft/lbs of torque in the 1800-2400RPM range.THis is the range in where you cruise.

I don't know any modification for this cheap that is going to get you this kind of power. After a few test runs I can really feel the added power and it is much smoother and there is no stumble at all from off idle. A very good modification for carbs that have downleg booster and you could also buy an annular booster carb off the shelf, so it doesn't cost any extra

"What we learned from this exercise with this particular engine is that the annular-discharge boosters did a much better job atomizing and distributing fuel and air compared to the downleg boosters. This is especially true at lower engine speeds. If you look at the power differences in the 1,800-2,400-rpm test points, it’s clear how well the annular boosters work. The annular discharge carb was worth a staggering 94 lb-ft of torque at 1,800 "

Gordonm

Oh great! You keep finding ways for me to spend money! This might solve some of the low speed problems I'm having.

Steve439

Excellent, thanks! I was thinking of sending a Speed Demon in to have it changed - I didn't know you could do it yourself.

1BAD80

I put annular booster's in my twin 700 dp Holleys and woke up my cross ram.
Much better responce, only way to change a carb.
There are different type of annular booster's, Ford truck type are thicker on the top section and gives a stronger signal.
Parts were around $250. for both carb's.

MotorHead

Unfortunately you probably have to send it in unless you have the removable boosters. I think the Race Demon is the only one that has them , I don't even thing think the Mighty Demon has them. They can change them though, your local speed shop might be able to do it.

Gordonm

There is an 850 Mighty Demon with annular boosters. All the other Mightys caome with standard boosters. I just checked my 825 Mighty Demon and it does have removable boosters.
Where did you get the annular boosters from. Did you change jets or high speed air bleeds?

SmokedTires

Wayne how did the annulars change your carb settings, did/ do you have to retune?

Not sure about the Mighty Demon being replaceable, but it sure sounds good. I wonder why they recommended the 750 Mighty Demon for me instead of the larger annular model I went with the 750cfm to keep the velocity up for throttle repsonse, which is all the reasons for the annulars.

Steve439

That's OK - I just saw the post about how much the parts are!
The article I read said BG will swap 'em for only $100.
I was debating whether to bother, but now for sure I'll do it.

MotorHead

I did not change anything on my carb except the boosters and A/F seems to be pretty much where it was with the downleg booster.

I did do a alot of work to it to get it right with the downleg boosters though. Not sure why it is so right now with the annualar as the only difference between the two is more power, smoother and better throttle response so I am not going to argue

Doug S

Only the Race Demon series carburetors come with "Screw-In" boosters. The Speed Demon, and Mighty Demon Series carburetors have spun in or swedged boosters. Most sizes are available in either down leg or annular boosters now.

The Screw in Boosters for the Race Demon carburetors are under $100 for the set of 4, and we'll convert a Demon over for about the same price.

1BAD80

The booster's are available thru some good speed shops.
They sell a tool to seat the boosters into the body about $250.00
I made one from a "C" clamp and ground the tip
(look's like a center drill in a C/L cut section & works like tube flaring ).
This was posted a long time ago along with the sites that sell the parts.
Good new information.
Annular booster's will help any motor with throttle responce.

http://www.aedperformance.com/Tools.htm

gkull

I might just have to try it If i take off really easy and then give it gas the motor doesn't grab below 2000 rpm. Maybe the annular will help it get going by restoring some TQ

1972warship

Why did you have to post this...I have a less than perfect edelbrock 750 for my mild 383, and want an annular 750 speed demon. I have to get another tvmadeez cable, air cleaner, and all of the jets,etc for tuning. I do not have the money at this moment so if anyone wants to give to the married with kids corvette fund of mine then let me know ....anyone, anyone, bueler, bueler....

brian76

Anybody know where or if I could get annular boosters for a plain ole Holley 750 DP?

SmokedTires

That's so cool that the tune stayed I will continue to fine tune as I have time. Maybe my carb can go back to BG during the snow months for the annular swap

1BAD80

Under $50. a set.

http://www.aedperformance.com/Tools.htm