4 Barrel on a stock slant

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Seen this thread and red a few post, wish I knew this back 13 years ago, but I did drive mine daily for 6 years this way, split exhaust manifolds and a 390 tuned for my 170 by @CudaChick1968 boyfriend, I bolted it on and it liked it from the get go, 3.23 gears three on the tree.
That jeep breather sent nice cool air to it, and she liked it .

Just thought I would post this, you all have some great tec posts in here, thank you :thumbsup:

View attachment 1715710227

View attachment 1715710228
 
Seen this thread and red a few post, wish I knew this back 13 years ago, but I did drive mine daily for 6 years this way, split exhaust manifolds and a 390 tuned for my 170 by @CudaChick1968 boyfriend, I bolted it on and it liked it from the get go, 3.23 gears three on the tree.
That jeep breather sent nice cool air to it, and she liked it .

Just thought I would post this, you all have some great tec posts in here, thank you :thumbsup:

View attachment 1715710227

View attachment 1715710228
 
This file not found, 404 error @Bugman
Like to see it, but I will delete this one sir
 
Should work now
afb vac.jpeg
 
the formula
CID x rpm/3456
works just fine.
Why it doesn't seem to work, is because most carbs have ADVERTISED flow-ratings that are grossly exaggerated, or are at non-standard pressure drops, or at pressure drops that are different between manufacturers.
Or worst of all, your street engine cannot produce the pressure drop in the first place. Or the engine under your hood cannot come remotely close to the required VE.
So you are forced into bolting something on that you guess might work, and until you figure out that the roar thru the air cleaner on the street, does not translate to performance across the board, you might extol the roar as power, when in fact it is just a roar.

I'll say it again
if you put your 225 on a dyno and measure the maximum air uptake at 235 cfm, then, you can install any larger than 235 rated carb on that engine that you might want to, no matter it's advertised rating; if the engine can only pull 235 cfm, anything bigger, will only pass 235 cfm; whether it have One barrel or six, 235 is all the engine will pull.
So now, your job is to wade thru the advertising hype, and find a carb that will flow the required cfm, at the measured pressure drop, and to heck with the advertised rating. And that carb still has to perform under all other rpms and load settings, to make it streetable.
Lemmee explain;
suppose you have a true and accurate 500 cfm carb rated at 500cfm @1.5 inches vacuum. But your slanty , with this carb installed, only pulls 3 inches. This 500 is now, a 354
But suppose you have a true 354cfm @3 inches rated carb, and your slanty pulls 1.5 inches thru it. This 354 is now a 500
The formula calls for 225 x say 4800/3450=313 cfm@100%VE. / 250cfm@.80 VE
Now; a 250 2-bbl is so, only at it's rated pressure drop, usually 3 inches. So,assuming it was rated at 3, then at 1.5 is 354. Where it stalls I have no idea; but the dyno will show it.

Either carb will work at WOT, at the listed parameters. Just remember, the engine only pulls what it can pull, and as long as the carb can meet the demand, more is rarely a good thing.

The conversion factor I used is 1.414


for other pressure drops;
From Speed Talk;
To convert from one flow pressure to another, you divide the cfm by the square root of the pressure it was flowed at, and multiply that by the square root of the pressure you want to calculate for.

500cfm / (sqrt of 3) = 288.675134595
288.675134595 x (sqrt of 1.5) = 353.553390593

Mike Jones
Jones Cam Designs

Denver, NC
jonescams@bellsouth.net
Jones Cams
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
 
Seen this thread and red a few post, wish I knew this back 13 years ago, but I did drive mine daily for 6 years this way, split exhaust manifolds and a 390 tuned for my 170 by @CudaChick1968 boyfriend, I bolted it on and it liked it from the get go, 3.23 gears three on the tree.
That jeep breather sent nice cool air to it, and she liked it .

Just thought I would post this, you all have some great tec posts in here, thank you :thumbsup:

View attachment 1715710227

View attachment 1715710228
Love those old engines! They had class, and takes someone with great patience to fine tune it! Onward!
 
[QUOTE="Bewy, post: 1973392880, member:

Post #41. No 500 cfm AVS carbs, only 500 AFBs.[/QUOTE]
you might be correct, about the original Carter AVS.
The Edlebrock AVS does come in 500 cfm size
 
Not all afb's were equipped with an air flap. Not sure about chrysler afb's but I know some ford and gm afb's were not equipped with secondary air flaps.

1962 AFB 3131s from a 318. Notice the boosters are from the side. I also have a 3108s the same but can not find an application.

P1010004.JPG


P1010002.JPG
 
Last edited:
[QUOTE="Bewy, post: 1973392880, member:

Post #41. No 500 cfm AVS carbs, only 500 AFBs.
you might be correct, about the original Carter AVS.
The Edlebrock AVS does come in 500 cfm size[/QUOTE]
Lol, post #46, but I'll be honest that I'm not sure what stk. AVS's actually flowed.
 
Correct, Edel does have a 500 CFM AVS. Carter didn't. It had only two sizes in AVS, 625 & 750. 625 was used on 340 & 383, 750 on the 440.

Of interest when talking about flow ratings & cu in, Pontiac had a Hi Perf 230 cu in inline 6 in 1967 that had a 750 cfm 4bbl Quadrajet carb. Engine made 215 hp, not far off 1 hp per cu in.
 
the formula
CID x rpm/3456
works just fine.
Why it doesn't seem to work, is because most carbs have ADVERTISED flow-ratings that are grossly exaggerated, or are at non-standard pressure drops, or at pressure drops that are different between manufacturers.
Or worst of all, your street engine cannot produce the pressure drop in the first place. Or the engine under your hood cannot come remotely close to the required VE.
So you are forced into bolting something on that you guess might work, and until you figure out that the roar thru the air cleaner on the street, does not translate to performance across the board, you might extol the roar as power, when in fact it is just a roar.

I'll say it again
if you put your 225 on a dyno and measure the maximum air uptake at 235 cfm, then, you can install any larger than 235 rated carb on that engine that you might want to, no matter it's advertised rating; if the engine can only pull 235 cfm, anything bigger, will only pass 235 cfm; whether it have One barrel or six, 235 is all the engine will pull.
So now, your job is to wade thru the advertising hype, and find a carb that will flow the required cfm, at the measured pressure drop, and to heck with the advertised rating. And that carb still has to perform under all other rpms and load settings, to make it streetable.
Lemmee explain;
suppose you have a true and accurate 500 cfm carb rated at 500cfm @1.5 inches vacuum. But your slanty , with this carb installed, only pulls 3 inches. This 500 is now, a 354
But suppose you have a true 354cfm @3 inches rated carb, and your slanty pulls 1.5 inches thru it. This 354 is now a 500
The formula calls for 225 x say 4800/3450=313 cfm@100%VE. / 250cfm@.80 VE
Now; a 250 2-bbl is so, only at it's rated pressure drop, usually 3 inches. So,assuming it was rated at 3, then at 1.5 is 354. Where it stalls I have no idea; but the dyno will show it.

Either carb will work at WOT, at the listed parameters. Just remember, the engine only pulls what it can pull, and as long as the carb can meet the demand, more is rarely a good thing.

The conversion factor I used is 1.414


for other pressure drops;
From Speed Talk;
A 225 doesn't "only pull" any amount of depression, & 3"Hg is indicative of more demand, not less than 1.5"Hg. It boils down to the head's ability to supply the cylinders, then the cam timing used to crutch the level of ineffectiveness of said head(s) in the desired operating range. The rating of a 4bbl was standardized to represent a "performance" oriented depression of 1.5"Hg at peak HP, but the demand at say 6K, is of course way more than the demand at say 2K w/a stock converter....yet many have done just that, thrown a cam in an otherwise stock setup, which decreases the efficiency at low rpm w/reversion...the carb has to have enough depression to pull fuel up out of the mains to stay running, let alone well...the accel pump can be tailored some, but can only cover for so long,.a Holley's most notable feature, lots of pump capability. The depression may be only .4"Hg at "1st romp"(maybe worse depending on how poor a mismatch), and the carb has to have the right calibration of air-bleeds & jetting to deliver fuel at such poor signal depressions.
I'm trying to figure out why it seems the Title & intent of the OP seems to get drowned in "Big Carb Bravado" & senseless anecdotes about irrelevant applications.
Simply put; when the carb ceases to be the primary restriction to atmosphere, & the head takes over, unless You want to add fuel jets to the ports fuel flow will suffer/cease.
The formulas are accurate for most street cars, not near-race setups posing as street cars. Which I have no problem with.
 
That formula is accurate telling your the dynamic displacement and ruffly how much air your engine will displace but nothing to do with picking a carb for your engine.

1st I never see anyone measure what vacuum their pulling before even thinking about swapping carb sizes which so easy to do and 2nd we already knows what works for most applications. stock to 350 hp 600-650 cfm 250-500 hp 750 cfm 450-700 hp 850 plus cfm, under 200 hp you could go with a 500 cfm but i'd would be overly concerned about it. Obviously this ain't meant to be set in stone just ballpark.
 
1962 AFB 3131s from a 318. Notice the boosters are from the side. I also have a 3108s the same but can not find an application.

View attachment 1715710674

View attachment 1715710675

I have several early afb's without an air flap. Like 66fs's, the boosters are from the side. The secondary barrels are small enough that I reckon the air flap wasn't necessary. Don't know the cfm's, but I'd bet they are all well less than 500, maybe less than 400.

The one on my 63 Valiant is a 3249S from a 1962 poly 318 automatic (I think last year for power pack poly 318).

20151031_192248 (2).jpg


Also have a 2991S from a 1960 318 poly and a 2856S from a 1959 361.

20210327_154938.jpg


By the way, 66, your 3108S shows as being from a Chrysler Marine 413
 
That formula is accurate telling your the dynamic displacement and ruffly how much air your engine will displace but nothing to do with picking a carb for your engine.

1st I never see anyone measure what vacuum their pulling before even thinking about swapping carb sizes which so easy to do and 2nd we already knows what works for most applications. stock to 350 hp 600-650 cfm 250-500 hp 750 cfm 450-700 hp 850 plus cfm, under 200 hp you could go with a 500 cfm but i'd would be overly concerned about it. Obviously this ain't meant to be set in stone just ballpark.
LOL! You've never test drove with Me then, & stock to 350hp....on a stock Slanty?
 
I think you will find that the carbs in post #73 have smaller secondary t/bores & venturiis than the 625 & 750 AFBs that came with 1 11/16" & 1 9/16" respectively. They are probably about 450-500 cfm.
 
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