Holley 390 nascar carb flow. ( mechanical throttles )

[Walter R. Malik]

At 20.4 inches of water depression it will wet flow right around 390. Dry flow will of course be more.

The particular carburetor I was referring to was the R6895 "double pumper" from the early 80's; (the one which had the down-leg but, straight through boosters). Not the 1957 "vacuum secondary" R1847.
The carb R7411 with regular down-leg boosters came later in the 90's.
Then even later came the HP carbs R80507, progressing with dash numbers of the same to follow.

Semantics or ?? I don't know what you are calling a down-leg, but the straight-leg booster is in all the "390" carbs I have seen, '57 Ford R-1273, R-6895, and later HP versions, all have straight-leg boosters. The '57 312 carb is essentially the same casting as the 6895, venturi shape is identical. Later HP versions have the radiused venturi entrance shape, early units have an essentially straight funnel shape venturi inducer, like an R-1850. I trust we are on the same page, a down-leg booster is the type found in original R-3310 and R-4779, 4780,4781, etc.

Believe whatever you want ...
You are not correct with information here and you obviously haven't ever had one in your hands or simply don't remember ... down-leg boosters with the booster venturi bored to straight through were in the original NASCAR 390 "double pumper" carburetors from Holley.
There were not even such a thing as any Holley "double pumper" carburetors until 1969.

[Walter R. Malik]

I just looked it up in the old notes from my Holley days.
All the vacuum secondary 390 carbs did have straight-leg boosters as well as the "for the public" 6895 carbs.
The carburetors Holley manufactured for "restricted" NASCAR tracks had those straight through, down leg boosters.

[Warp Speed]

I've never seen a down leg NASCAR 390.
Do you have a pic of this down leg booster?

[Tuner]

I just looked it up in the old notes from my Holley days.
All the vacuum secondary 390 carbs did have straight-leg boosters as well as the "for the public" 6895 carbs.
The carburetors Holley manufactured for "restricted" NASCAR tracks had those straight through, down leg boosters.

What are you calling " straight through, down leg boosters " ?? The 1273 ('57 312 T-Bird carb) and 6895 have the same boosters ... straight leg .... same as 1850 and 4776-4777 and 3310-3 on up to now. 1848 was not a '57 Ford carb, it is a replacement carb released in the early-mid '60s for 352 FE engines 58 and up, 1849 was for 383 MEL, 1850 was for 430 MEL. After Colt took over Holley the 1848-1849-1850 series and the original 3310 were the first aftermarket pushed units because they were cheapest to manufacture at the time. I don't know about you, but I got 100 Green Stamps per bore for every Holley sold when Colt/Holley started the promotion to Baby Boomer gear heads. This was in 1965 when cross-ram intakes were the new big thing, before T-ram intakes were even on the market.

Is what you are calling a "straight through, down leg booster" in this image?

[Tuner]

I've never seen a down leg NASCAR 390.
Do you have a pic of this down leg booster?

Thank you.

[Walter R. Malik]

I just looked it up in the old notes from my Holley days.
All the vacuum secondary 390 carbs did have straight-leg boosters as well as the "for the public" 6895 carbs.
The carburetors Holley manufactured for "restricted" NASCAR tracks had those straight through, down leg boosters.

What are you calling " straight through, down leg boosters " ?? The 1273 ('57 312 T-Bird carb) and 6895 have the same boosters ... straight leg .... same as 1850 and 4776-4777 and 3310-3 on up to now. 1848 was not a '57 Ford carb, it is a replacement carb released in the early-mid '60s for 352 FE engines 58 and up, 1849 was for 383 MEL, 1850 was for 430 MEL. After Colt took over Holley the 1848-1849-1850 series and the original 3310 were the first aftermarket pushed units because they were cheapest to manufacture at the time. I don't know about you, but I got 100 Green Stamps per bore for every Holley sold when Colt/Holley started the promotion to Baby Boomer gear heads. This was in 1965 when cross-ram intakes were the new big thing, before T-ram intakes were even on the market.

If you bored a standard .140" passage down leg booster to where the venturi section at the end was strictly a straight through .450" diameter hole, is what it is.
I never met the guy but, in my notes someone named Parky Knoll was the NASCAR "requester" for this type booster to be installed in the standard R7411 carburetor which was rated at 370 cfm; (I am almost sure that rating was to simply differentiate the 1 1/16" venturi, 1 7/16 throttle bore carbs from the rest).

Sometime after the 80's Holley changed the main venturi shape from a somewhat concave entry to being convex for the H.P. carbs. I was there from 1976 through 1985 so, those are the only years of my notes.

I wish I had a photo as that booster was also available separately.

[Warp Speed]

The HP 390 carbs came in the scene in the mid 90s. Before that, the standard issue 390 that was used in the GN series, both using a straight leg booster, as tuner posted in his pic, to the far left.
That how I recall the late 80s through the 90s anyway?

[Walter R. Malik]

The HP 390 carbs came in the scene in the mid 90s. Before that, the standard issue 390 that was used in the GN series, both using a straight leg booster, as tuner posted in his pic, to the far left.
That how I recall the late 80s through the 90s anyway?

It also lists in these notes here a R7410 which had skirted standard straight boosters and it was rated 340 CFM.
Both of those carbs were available, special order, to NASCAR "cup" teams with "LeMans" style bowls, also.

Holley also made available a special set of model 5200/5210 carbs for NASCAR's "Baby Grand" series in that time frame.

[naukkis79]

This downleg booster is pretty interesting design - they relocate booster from having it's outlet in main venturi to have it's entrance in main venturi? Why? They ruin whole booster, only benefit I can think is that with it that booster flow is combined to main venturi flow at high vacuum situations - carb flows more at high vacuum than with real booster venturi.

I hope that Holley isn't selling those downleg things to people which aren't limited by carb rules.....

[Warp Speed]

This downleg booster is pretty interesting design - they relocate booster from having it's outlet in main venturi to have it's entrance in main venturi? Why? They ruin whole booster, only benefit I can think is that with it that booster flow is combined to main venturi flow at high vacuum situations - carb flows more at high vacuum than with real booster venturi.

I hope that Holley isn't selling those downleg things to people which aren't limited by carb rules.....

In the larger carbs (850, Nascar 830 ect) you either ran an annular booster or the downleg design. Without the drop, you couldnt build any low speed booster signal with the larger venuries, especially on smaller engines. All of our open cup carbs after about 2000 were downleg.

[Walter R. Malik]

This downleg booster is pretty interesting design - they relocate booster from having it's outlet in main venturi to have it's entrance in main venturi? Why? They ruin whole booster, only benefit I can think is that with it that booster flow is combined to main venturi flow at high vacuum situations - carb flows more at high vacuum than with real booster venturi.

I hope that Holley isn't selling those downleg things to people which aren't limited by carb rules.....

IF I remember correctly, the down-leg booster has to much signal strength for the application but, has a bit better airflow curve than a straight-leg booster shows.
I was told, (whether true or not), that opening up that booster diameter and taking away most of that second venturi at the fuel outlet, diminishes some signal strength; especially at high depressions.

[pamotorman]

I just looked at a NASCAR 390 with progressive mechanical secondary and it has straight leg boosters opened to .157

[CamKing]

The HP 390 carbs came in the scene in the mid 90s. Before that, the standard issue 390 that was used in the GN series, both using a straight leg booster, as tuner posted in his pic, to the far left.
That how I recall the late 80s through the 90s anyway?

What was the power difference you remember between the 2 carbs?
I seem to remember a huge power gain, when they started allowing the HP390 in the 90's. I also remember the peak HP RPM increasing a few hundred RPM. I think at that time, I was designing the cams for Elton Sawyer's Ford in G.N., but my memory is a little foggy.

[Warp Speed]

The HP 390 carbs came in the scene in the mid 90s. Before that, the standard issue 390 that was used in the GN series, both using a straight leg booster, as tuner posted in his pic, to the far left.
That how I recall the late 80s through the 90s anyway?

What was the power difference you remember between the 2 carbs?
I seem to remember a huge power gain, when they started allowing the HP390 in the 90's. I also remember the peak HP RPM increasing a few hundred RPM. I think at that time, I was designing the cams for Elton Sawyer's Ford in G.N., but my memory is a little foggy.

I think it was around 8-10 if I remember correctly. That is if the old style carb being tested still had the boosters in the stock height, which most didn't by then.
Then came the booster rules............

[Arthur]

The HP 390 carbs came in the scene in the mid 90s. Before that, the standard issue 390 that was used in the GN series, both using a straight leg booster, as tuner posted in his pic, to the far left.
That how I recall the late 80s through the 90s anyway?

What was the power difference you remember between the 2 carbs?
I seem to remember a huge power gain, when they started allowing the HP390 in the 90's. I also remember the peak HP RPM increasing a few hundred RPM. I think at that time, I was designing the cams for Elton Sawyer's Ford in G.N., but my memory is a little foggy.

Great to see you are alive
Would you please answer my emails
Everyone is busy
Thankyou