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Actual cfm used vs carb size

General engine tech -- Drag Racing to Circle Track

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F-BIRD'88
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 02, 2019 11:36 pm

You are limited by the performanve of the venturii of the carb yu are using. 4 big or bigger venturi in the case of a single big holley racing carb. You are limited by its design
And come to a point whrre just making the 4 venturii bigger just does not work.
So use more (8) smaller DIFFRRENT DESIGN carb(s) venturii. Now it is different. Generally more veturii are just better(er) than 4.
You are doing it differently now and has the potential to perform better. Now you can do a better quality job that carburation does. And use more airin and out too.
Multi carbs have a advantage. Thats why rules based class racing separate single carb cars from multi carb cars, or flat out ban the multi carb cars from competing eith the single carbed cars. There is a advantage and they know it well. Thats why the fasted unlimited race classes are dominated by v8's with multi catb setups. Both N/A and supercharged.
Single 4 bbl carb thinking will limit you. Especially on a V8 engine.

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Re: Actual cfm used vs carb size

Post by Steve.k » Wed Apr 03, 2019 10:15 am

IMG_3528.PNG
That makes sense f-bird88. All top pro dual carbs or nowadays individual runner injected.Like a freinds motor just recently done.
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Wed Apr 03, 2019 10:44 pm

That's smooooth... I like that a lot.

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Re: Actual cfm used vs carb size

Post by Steve.k » Wed Apr 03, 2019 11:16 pm

Yes very nice piece.

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Re: Actual cfm used vs carb size

Post by CGT » Thu Apr 04, 2019 12:13 pm

I want to see a picture of the 2 carb to a single carb intake adapter.
"If you pick up a starving dog and make him prosperous, He will not bite you. This is the principal difference between a dog and a man"

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Re: Actual cfm used vs carb size

Post by steve316 » Thu Apr 04, 2019 3:17 pm

Nice looking set up, I have always liked Nova.

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Re: Actual cfm used vs carb size

Post by amc fan » Thu Apr 04, 2019 4:02 pm

I did an over 1 hour search on internet and could not find any 2x4 to 1x4 barell adapter. Mr. Firebird who makes it?

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Re: Actual cfm used vs carb size

Post by Steve.k » Thu Apr 04, 2019 5:01 pm

It's actually a 60's chevy wagon.

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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 10:28 am

amc fan wrote:
Thu Apr 04, 2019 4:02 pm
I did an over 1 hour search on internet and could not find any 2x4 to 1x4 barell adapter. Mr. Firebird who makes it?
Blower Drive Service BDS has a 2 piece combo that stacks up to create a 2x afb carb to single 4bbl adapter.
Search Youtube for the video that shows how to assemble it with a few drilling mods and fastener.
Its pricey. Polished billet ..

AussieSpeed also has some 2 carb to single 4 bbl adapters, (I am not crazy about these.) One piece short height T shaped transition.

Holley #300-217 is a blank adapter top that can be used to adapt 2x4's to single 4 bbl. Flip it over, make the single 4150 flange hole... Add a flat aluminum 2x4 carb top with 2x 4150 flange holes for 2afb carbs.

Contour fill the inside as needed to get the internal plenum shape/contour/ volume you want. Slope, ribs , divider etc.
Whats inside is your lil secret. Make the internal part removable so you can tune/play/reshape it as needed.
Once the top is bolted on no one is the wiser.

There is a 2x4 holley 4150 carb top too. Just a few different ways to do this.# 300-220. ?
Look it up holley.com

At one time B&M sold a 2x4 to single carb adapter that fit 2 holleys inline, or sideways or 2x afb's.
Simular to the AussieSpeed stuff.
Afb's. AVS AVS2 carbs are easier. In every respect.

If using on a Dual Plane hi rise RPMstyle intake and you want to maintain the 180 degree split plenum then add a full divider inside the 2x4 adapter.
Like said whats inside your adapter plenum is your lil secret. To create a decent Y shaped internal plenum plan on a 3.5" total adapter height. You can adjust that with a spacer inbetween the base and top as needed.

Note this: Pretty much every sigle 4 bbl carbed intake manifold gets BETTER as you raise the carb up with a carb spacer. A 2x4 adapter will be no different.
The taller you make the Y shaped 2x4 to 1x4 transition the better it will work.. Think 2.5"+++.
If you only make a very short adapter witha T shaped internal transition that is short the power gain may be modest. Higher is usually better.
Still ends up a bit shorter than a tunnel ram.

For street driving allow a longer engine warm up time and keep and employ the carbs choke and fast idle system to max "drivability".
A dead cold adapter will want richer carb jets than a fully warmed up adapter. Let it warm up for street driving.
The higher the carb (carbs) the longer the warmup time.
You can use the Edelbrock Dual Quad adjustable PROGRESSIVE 2X4 carb linkage.
Now you are driving around town on just the rear carbs primaries, most of the time, until you get into the throttle
Withyur foot. The carbs throttleaction is progressive.
For strictly drag racing (with racing converter- trans brake) you can try it set up non progressive using the same Edelbrock carb linkage.
It is adjustable. Use what works best.
Last edited by F-BIRD'88 on Tue Apr 09, 2019 11:14 am, edited 2 times in total.

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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 11:06 am

On a big single plane racey intake manifold a plenum divider either full or partial can be a effective tuning element. As can a Brodix style plenum "turtle"
If you have trouble with distribution, try this...
If the intake was working right with 1 carb it won't be much trouble tuning with 2 carbs on a decent adapter.

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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 11:20 am

Here is the video about assembling the 2 piece 2x4 adapter using BDS parts and a bit of smarts.
https://m.youtube.com/watch?v=zQaCdMiJU ... e=youtu.be

A bit pricey polished billet show car stuff but this is the general idea. About as short height to get a Y shaped internal transition.

You can fabricate your own TEST adapter with bolt on top using bonded WOOD and some carb spacers. Or self fabricate with sheet plate aluminum with a mig or tig.
Make the carb top removable to allow internal and height design changes.

Edelbrock uses Bonded wood and epoxy for making prototype intake manifolds and for making prototype casting patterns to develop, create new stuff. You can too.

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Re: Actual cfm used vs carb size

Post by CGT » Tue Apr 09, 2019 11:37 am

F-BIRD'88 wrote:
Tue Apr 09, 2019 11:20 am
Here is the video about assembling the 2 piece 2x4 adapter using BDS parts and a bit of smarts.
https://m.youtube.com/watch?v=zQaCdMiJU ... e=youtu.be

A bit pricey polished billet show car stuff but this is the general idea. About as short height to get a Y shaped internal transition.

You can fabricate your own TEST adapter with bolt on top using bonded WOOD and some carb spacers. Or self fabricate with sheet plate aluminum with a mig or tig.
Make the carb top removable to allow internal and height design changes.

Edelbrock uses Bonded wood and epoxy for making prototype intake manifolds and for making prototype casting patterns to develop, create new stuff. You can too.
Ok. Im having a hard time understanding why you would think that contraption would be good for power somehow. Blown, and restricted...maybe...maybe. But if your already running that stupid little blower who cares.......NA, that's just gross.

I don't know that you could make things any worse than that thing would. Look at the horrible angles and transitions your introducing....I'd put good money on that thing being a mistake on a decent NA engine....of course if the engine was a turd before that abortion, it would just remain one.

Send one out, we will see how it stacks up. But... It's kind of the not having to build a swimming pool to determine that a bowling ball doesn't float thing...
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 11:49 am

There is nothing there to say this will work badly.
It has been done before and does work.
Expect to meet or Exceed the power of a big dominator carb on a capable motor. 500+ + hp.
Yup it does lend itself very will to supercharged single carb blower applications where 2 carbs are desired.
It will also work in N/A high power engines.
The more capable the engine (power output), the better it will work.
If you show up with this at a single 4 bbl carb rules limited race class, they will ALL bock... Whine and squeel.
Because they Know you have a advantage.
You'll go a bit quicker/faster. Great for bracket racing.
Easy jet changes to weather tune it if needed.
(It will tend to not be so sensitive to different or changing weather conditions)
Yup every guy that sells single 4 bbl carbed engines will whine, squeel, bitch and swear. "That cannot work"
It will.

As said 2x4 AFB AVS2carbs is easiest but on a single plane intake 2x 750 hp double pumpers mounted sideways will work well too. It will breath deep.
It will have extended top end power and rpm range. Gear the car to ,ake advantage of that to max perf gains.
Its going to want to REV UP.
Last edited by F-BIRD'88 on Tue Apr 09, 2019 12:00 pm, edited 1 time in total.

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Re: Actual cfm used vs carb size

Post by CGT » Tue Apr 09, 2019 11:55 am

F-BIRD'88 wrote:
Tue Apr 09, 2019 11:49 am
There is nothing there to say this will work badly.
It has been done before and does work.
Expect to meet or Exceed the power of a big dominator carb on a capable motor. 500+ + hp.
Yup it does lend itself very will to supercharged single carb blower applications where 2 carbs are desired.
It will also work in N/A high power engines.
The more capable the engine (power output), the better it will work.
If you show up with this at a single 4 bbl carb rules limited race class, they will ALL bock... Whine and squeel.
Because they Know you have a advantage.
You'll go a bit quicker/faster. Great for bracket racing.
Easy jet changes to weather tune it if needed.
(It will tend to not be so sensitive to different or changing weather conditions)
Yup every guy that sells single 4 bbl carbed engines will whine, squeel, bitch and swear. "That cannot work"
It will.
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Re: Actual cfm used vs carb size

Post by F-BIRD'88 » Tue Apr 09, 2019 12:01 pm

Sorry guy I got nothin to sell you.
Its up to you to try it. There are many carbs you can use for this.

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