Inexpensive 350 Build

[skinny z]

For a street application I prefer to install an Annular Booster.

How would that make it lacking in a drag strip application?
I only ask because my 25 year original Barry Grant 750 VS came equipped with annular boosters. It's proven to be an excellent street carburetor however it proved to be slow when compared to an AED of the same size with downleg boosters.

[Art]

For a street application I prefer to install an Annular Booster.

How would that make it lacking in a drag strip application?
I only ask because my 25 year original Barry Grant 750 VS came equipped with annular boosters. It's proven to be an excellent street carburetor however it proved to be slow when compared to an AED of the same size with downleg boosters.

Doesn't the physical size of the boosters reduce total airflow?

[vortecpro]

I suspect the BLP boosters are, but I have never used their' booster. I would suspect they could use a little dressing on the top of the booster.

The modifications I make do not require the booster to be removed from the carb. It is quicker and less expensive. Another note is to level the booster in the Venturi. This is also a rather simple operation.

For a street application I prefer to install an Annular Booster.

I like your in-carb modifications to the booster. Neat job.

BLP sell a 'machined' downleg booster that tidies up any casting flaws to do with consistency. I have a set in an 825cfm Race Demon and they work great.

Thanks for the pictures everyone!

[tuffxf]

Whether you are foot braking or transbraking plays a big part in carb set up along with the convertor
Cheers

[rgalajda]

Dressing the inlet of the booster to a sharp edge causes more air to flow thru the booster ( improves signal ). The step machined in the booster improves fuel atomization ( shearing effect ).
The more air flow thru the booster makes the booster more responsive.
Booster signal and Fuel atomization at high rpm ( high airflow ) is not much of a problem, but at low airflow ( lower rpm ) can be.

An Annular booster has a larger inlet size ( more flow thru the booster ) and has multiple outlet holes to atomize the fuel.
It is possible to atomize the fuel too much . Hole sizes and number of holes in the annular. This more relates to heated intake manifolds.

Some of the annular boosters are physically large. Airflow can be lost, if you needed it. Larger Venturi may be needed. But remember for a carb that needs to operate at a wider rpm range ,this will still be beneficial. Even a drag car that launches at lower rpm and does not operate at a narrow band of say 5500 to 8000 rpm.

I have some old annular boosters that were physically smaller . I'm installing in an 850 Holley. Picture below

[rgalajda]

Airflow ( Mark should easily relate to this )

There are a few simple things you can do to improve airflow, especially on older carbs.

The first thing I do is shorten the screws in the throttle blades flush with the shaft. The old brass screw heads can be machined thinner to a more domed shape.
I prefer to get rid of those old bulky brass screws . Replace them with button head screws ( easily available ) and shorten them. Loctite is a must here. This is worth about 20 cfm.

Some of the old carbs had slabbed shafts in the secondary. These shafts actually disrupted airflow as compared to a round shaft. Use a round shaft and airflow goes up.

The venturi entrance needs to have the edge rounded leading into the barrels just like the newer style bodies do. About 10 cfm.
If it has a choke horn , radius the top edge , but it’s only worth a few cfm.

These simple modifications ( along with dressing the booster ) not only increase air flow at least 30 cfm but also increase booster activity, so there is no downside to low speed output.

Below is a picture of a carb , after recolouring of the body, I did these modifications to.

[Monza355]

Mark. You talk about a 10hp difference on the dyno with a 750 (950hp) is your carb with a 1.3/4” base plate ? I really think the 950hp would work great on your combo. It has a very strong signal with the small-ish venturies yet has a larger throttle bore than the 750 and should pull harder on the top end. In my experience it is a great versatile carburetor

[rgalajda]

HQM383 is the Braswell down leg booster a larger diameter , particularly inside entrance?

[HQM383]

HQM383 is the Braswell down leg booster a larger diameter , particularly inside entrance?

Inside is under .010” larger diameter- .431” v .440”. However the outside diameter is larger by around .057” and taller by around .060”. The extra height puts the booster air exit lower in the venturi by the height difference and the extra o/d helps create the bigger step shown in pic.

[rgalajda]

Thanks. Is that measurement at( under ) the step? I take the step to .490. What is the smallest inside diameter of the booster? Usually the Holley booster measures .380 smallest portion. Had to correct that.

[vortecpro]

Airflow ( Mark should easily relate to this )

There are a few simple things you can do to improve airflow, especially on older carbs.

The first thing I do is shorten the screws in the throttle blades flush with the shaft. The old brass screw heads can be machined thinner to a more domed shape.
I prefer to get rid of those old bulky brass screws . Replace them with button head screws ( easily available ) and shorten them. Loctite is a must here. This is worth about 20 cfm.

Some of the old carbs had slabbed shafts in the secondary. These shafts actually disrupted airflow as compared to a round shaft. Use a round shaft and airflow goes up.

The venturi entrance needs to have the edge rounded leading into the barrels just like the newer style bodies do. About 10 cfm.
If it has a choke horn , radius the top edge , but it’s only worth a few cfm.

These simple modifications ( along with dressing the booster ) not only increase air flow at least 30 cfm but also increase booster activity, so there is no downside to low speed output.

Below is a picture of a carb , after recolouring of the body, I did these modifications to.

I really do appreciate your information, and the good thing is your going to find out how it works at the track.

[HQM383]

Thanks. Is that measurement at( under ) the step? I take the step to .490. What is the smallest inside diameter of the booster? Usually the Holley booster measures .380 smallest portion. Had to correct that.

Braswell steps out to .525”

The one in the photo I said was std is actually a Demon booster and it measured same as a Holley from Allstate. On closer inspection Allstate have machined the I/d of the Holley to the same as a Demon and recolored them. Small I/d ~.430” step diameter .495”. The BLP machined boosters have been machined to the same dimensions. Found some un-machined Holleys and they measure close to what you stated.

[vortecpro]

New best after carb mods in 1600 DA, thanks everyone for information. I think its possible when we get back to the good track to see a 1.40 60.

[HQM383]

New best after carb mods in 1600 DA, thanks everyone for information. I think its possible when we get back to the good track to see a 1.40 60.

Mods to the 4781 as outlined in this thread?

[vortecpro]

New best after carb mods in 1600 DA, thanks everyone for information. I think its possible when we get back to the good track to see a 1.40 60.

Mods to the 4781 as outlined in this thread?

Not yet, but Eric put me onto the squirter and accelerator mods, but yours are coming next, thanks again! I know there's more there, hell were still working with the jets at this point.

I will be sending another main body to Eric for the booster mods, I'am loyal to Eric he's always worked with me before, I would have you do a carb as well for your willing info, but the Canada thing is problem, if you can get around that let me know.