[dill]

Which carb does best for mild track and mostly street.annular booster or downleg boosters? I have a big block chevy 68 camaro 454 with 575 comp cam 30 over rpm intake iron heads 400 trans. 410 gear.

[TexasPerfProd]

Here is a pretty good explination of the two.

Annular boosters generate a higher signal strength than the downleg boosters, allowing the use of larger carburetors and/or larger cams while still retaining good metering stability. This higher signal strength however requires smaller jetting than an otherwise identical downleg booster carb.

Annular boosters promote better atomization of fuel because they have many holes for the fuel to flow from, rather than just one big one like in the downleg boosters. This promotes better throttle response, fuel economy, and much better mixture distribution, especially at lower engine speeds.

The main tradeoff with annular boosters is that they are a bigger obstruction to airflow than the downleg boosters, thus lowering the effective cfm of the carb, all other variables being equal.

Here is what a Tech from BG said.

When it comes to annular vs. downleg boosters, there is not a clear right or wrong. It’s a matter of what’s going to work best on the application. There are Pro’s and Con’s to both sides. An Annular booster can give you better atomization on an engine, which can result in better torque, HP, and acceleration. They can also allow you to get away with some components that may be too big for the application. Since the carburetor is generally the last thing that gets bolted onto the engine it has to make up for or compensate for a multitude of sins or mismatched components beneath it. If the cam is a little big, or cylinder heads, or not enough compression, etc. these things need to be taken into consideration. There is not a clear cut one is better than another, it would be much easier than, only having to offer one part. It’s more a matter of giving additional options to help fine tune, or tailor the application. On an engine where a 650 may be a touch small, but a 750 is going to be too large, a 750 with annular boosters may be a great option. Bottom line you need to go over your entire combination with your carburetor builder to determine which one of their carburetors is going to work best on your specific combination.

Hope this helps.

[oger]

Pretty much agree with the above post. I personally know of a 69 with a crate LS-7 (early one that had compression) a 400 and 4.10s. He stuck an annular 850 DP on it and even with that terrible ZL-1 cam it was quite liveable as a street car.

[BigRed-L72]

I find it interseting that the downleg 850 Mighty Demon is recommended for 440"-509" motors.

The annular version on the other hand is recommended for 480"-540" motors. seems backwards to me.

I had an 850 BG Sports Claw that I sent in to have it changed over to annular boosters on my 468" it worked as intended, smooth idle,great throttle responce etc..

It is now on the 406" in signature. Seems to be working pretty good on that motor as well, even though technically the carb shouldn`t be on anything less than 500" (as per a BG rep).
It does have a very slight hiccup on tip in though, but should hopefully clear up as I tune/adjust it.
I simply un bolted it from the big block and put it on the small block with no changes made, we`ll see

[67RS502]

Originally Posted by BigRed-L72

I find it interseting that the downleg 850 Mighty Demon is recommended for 440"-509" motors.

The annular version on the other hand is recommended for 480"-540" motors. seems backwards to me.

(as per a BG rep).

If it was recommended by some tech guy it prably is backwards.
I agree with you, Big.

[TexasPerfProd]

Well he did start out saying

When it comes to annular vs. downleg boosters, there is not a clear right or wrong. It’s a matter of what’s going to work best on the application.

I always did like trial and error with new parts as long as I could aford it. Which wasnt often if at all. But I sure tried some crazy stuff with used junk. Id try the most mismatched stuff just because it was what I had. Dont worry it didnt work to often.

[Tech @ BG]

Originally Posted by BigRed-L72

I find it interseting that the downleg 850 Mighty Demon is recommended for 440"-509" motors.

The annular version on the other hand is recommended for 480"-540" motors. seems backwards to me.

Not sure where this came from, on our 850 carburetors we recommend using a down leg booster carburetor on engines between 480 & 540 ci, and use the annular booster carburetors on 440 to 509 ci.

[BigRed-L72]

Originally Posted by Tech @ BG

Not sure where this came from, on our 850 carburetors we recommend using a down leg booster carburetor on engines between 480 & 540 ci, and use the annular booster carburetors on 440 to 509 ci.

Scroll down to the 850`s

http://www.barrygrant.com/demon/default.aspx?page=15

[Tech @ BG]

That's a typo. The two descriptions were reversed. That has been corrected in the new catalog, and the website will be updated shortly.