4 Barrel on a stock slant

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flatiron said:
I have a header and A Offy intake for my 71 Dart Slant six. Is a small 4 Barrel to much for a stock Slant ?
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Kinda like a too-big carb that you have to keep taking fuel out of, to make it run? It don't matter how big a carb you put on it ,you are gonna have to keep taking fuel out and out and out, until it matches the 250cfm or so, that the engine is actually able to inhale. So why not just start with the right sized carb, and enjoy the benefits of a proper match?
It's a 225.
A Stocker,N/A, cannot inhale more than 1/2 it's cid at 1rpm.It cannot be done.No matter how you rate the carbs, at 3800rpm, the stock-engine cannot inhale more than 225/2 x 3800/12x12x12 x 100% VE =247cfm; and at a more typical VE it is going to be less.
You can of course, make any reasonably sized 4bbl pass 247 cfm. And with enough time and patience, you might get the circuits worked out.
But the front half of a 500 will do that. and a teener 2bbl will do that.and I think a SuperSix 2bbl might do that too. And with a whole lot less time and effort put into the tune.
I believe the stock cam is about 236/242/111? ADvertised. and the lift is .395.And a compression ratio around 8/1.
I'd be surprised to see that thing pull 70%VE, in that car, at it's age. So .7 x 247 =173cfm. And that's using the formula inputting max-rpm,instead of where peak torque is. So 173 would be generous. So with that in mind; I guess you could put a very small 4bbl on it, and run just the primaries.Cuz if you try to run the secondaries,airflo through the front will drop to something like 50%,and the secondary flow will match whatever the front is doing. So now instead of the primaries all by themselves flowing 173cfm;all 4 bbls are flowing a total of 173 cfm. How you will tune the fuel for that I have no idea.Ima thinking.................... EFI.
Like I said before; I got a lot of respect for anybody who takes the time to make this work, with a carb.
But hey, I once put a teener top end onto a 340 short block with nothing more than fenderwell headers and a freeflowing exhaust. I also put the teener cam into it. So essentially it was a big-bore teener.The 65 longroof I put it into,was a blast, pulling hard to 4500(50mph)! And when I opened the hood to proudly show off my 2bbl, the impressed, no longer were. :( Hey snicker all you want, I just blew your doors off fella.You got smoked by a 2bbl! :)
 
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You guys should be posting this stuff on a Pro Stock forum..they could learn a lot from this discussion. Here they are with 2500 cfm on top of 500 inch engines. No doubt they would go faster with an 850 Double Pumper.
 
whitepunkonnitro said:
You guys should be posting this stuff on a Pro Stock forum..they could learn a lot from this discussion. Here they are with 2500 cfm on top of 500 inch engines. No doubt they would go faster with an 850 Double Pumper.
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But we're posting here because this thread is about appropriate carburetion for a Slant-6 engine in a street-driven vehicle.

I tried to load them on here, but for some reason they wouldn't go.
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Dangit! They would've gone just fine if only someone hadn't informed them that they don't go on FABO. Now they're all educated and stuff; they know the science so they don't go any more, just like flightless pro-stock 500-CID bumble bees with 2500-cfm carbs and stuff.
:lol:
 
I just rebuilt my stock Slant6 and decided to go with a 4bbl 650cfm Edelbrock and I have not had any problems with it, now take in account that the car is only a showcar at the car shows around town and it does not get drove much

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RustyRatRod said:
The AFB is a hybrid design in that area. While the base plate is mechanical, they have an air door that regulates secondary operation.

Chrysler chose the AFB for that very reason on the Hyper Pack.
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Rusty, super old thread, but Hyper Pack Carb, 3083S does not have the secondary air flap.
Nobody is perfect.
 
273 said:
Carb size is more about restriction then it's actual flow numbers since the rating is based on vacuum levels 1.5 for 4bbl and 3 for 2 bbl. So if your engine produces a different vacuum level at full throttle then you carb will flow more or less then rated.
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Not to mention that because of lack of flow, carb metering will be AFU
 
Hyper_pak said:
Rusty, super old thread, but Hyper Pack Carb, 3083S does not have the secondary air flap.
Nobody is perfect.
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Yes it is an old thread and yes it does have a secondary air door, just like every single AFB ever made. Look at the exploded diagram. See item #42 "air valve and weights". The air door on the AFB is under the boosters unlike an AVS or Thermoquad. But you're right. Nobody's perfect. :)

3083S Carburetor Info Page
 
I stand corrected. I looked into my carb and did not see the flap.
On closer inspection I can see where it USED to be.
Thanks, I guess I arn't perfect either.
 
Hyper_pak said:
I stand corrected. I looked into my carb and did not see the flap.
On closer inspection I can see where it USED to be.
Thanks, I guess I arn't perfect either.
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Wow, it surely needs to be there! It will run MUCH better with it installed.
 
RustyRatRod said:
Wow, it surely needs to be there! It will run MUCH better with it installed.
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Wow, it would surely run better if it were an AVS,......
Really, comparing 1" lift, 500ci, aftermarket headed &Pro-hogged, tunnel-rammed Pro-Stock All-out-all-in-for-the-$$$$,....to a stock Slanty with a head that chokes it(assuming a 225) at 4,600rpm, WTF?!
lots of folks love the "feel" of oversized carbs dialed in,(goes for FI TB's too) because there is more initial "go" for a given throttle angle, despite no more or even less actual performance. A small VS/Airdoor 4bbl won't be too much since it works half(or just over) based on demand, & leaves room for other upgrades.
 
In 1969 here in Australia, mother introduced an in line 6, in three sizes 215, 245, 265 cubes.
The bigger size was available with a 4bbl, a 625 cfm AVS. From memory, #4934.
 
Bewy said:
In 1969 here in Australia, mother introduced an in line 6, in three sizes 215, 245, 265 cubes.
The bigger size was available with a 4bbl, a 625 cfm AVS. From memory, #4934.
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And also a six pack. Those were badass. I want a Valiant Charger Hemi Six Pack.
 
RustyRatRod said:
Yes it is an old thread and yes it does have a secondary air door, just like every single AFB ever made. Look at the exploded diagram. See item #42 "air valve and weights". The air door on the AFB is under the boosters unlike an AVS or Thermoquad. But you're right. Nobody's perfect. :)

3083S Carburetor Info Page
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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.
 
oliver said:
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.
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I think these were pretty much earlier models. I had an "oddball" (in Chevy speak you know how THOSE guys are!!) When I was young had a 327 with an AFB I think off a Poncho. It had the big center air bleed screw--which adjusts idle speed by means of an intentional air leak. Also, the carb head passages are different, and being young and stupid, took "a bit' to figure this out. The thing always made a lot of noise, a distinctive high pitched "hiss" when idling.

ponchoafb.jpg
 
oliver said:
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.
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You are correct. Not all AFB's had velocity valves, MOPAR included. Usually earlier engines and larger engines.
 
My 1966 GTO came with the AFB type in post #43. Mixture screws plus the large brass centre screw which admitted air to adjust idle speed. Notice there is no idle speed screw; the primary t/blades bottomed out in the bores & speed was adjusted via the brass screw.

Post #41. No 500 cfm AVS carbs, only 500 AFBs.
 
No Carter AVS, but Eddy makes a few of 'em(Thunder), incl. 4x4/offroad version IIRC......
 
oliver said:
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.
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Well learn somethin new everyday. Thanks. That carburetor in question did have one though, as that diagram clearly shows. I'd sure like to know how the early AFBs that did not have the air valve fought off the horrible bog it would cause without one. I've seen a LOT of AFBs and I've never seen one without it......not that that means a thing. I'm sure if you say some didn't have them it's true, because stuff like this goes through evolution as it's evolving through time. I'd like to see one without it so I could see how they managed the bog. Maybe a tighter secondary venturi?
 
RustyRatRod said:
Well learn somethin new everyday. Thanks. That carburetor in question did have one though, as that diagram clearly shows. I'd sure like to know how the early AFBs that did not have the air valve fought off the horrible bog it would cause without one. I've seen a LOT of AFBs and I've never seen one without it......not that that means a thing. I'm sure if you say some didn't have them it's true, because stuff like this goes through evolution as it's evolving through time. I'd like to see one without it so I could see how they managed the bog. Maybe a tighter secondary venturi?
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I think they only used them on larger motors with small bore venturis. Most of the ones I've seen without the air door have the secondary boosters coming in from the sides vs the back.
 
oliver said:
I think they only used them on larger motors with small bore venturis. Most of the ones I've seen without the air door have the secondary boosters coming in from the sides vs the back.
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Maybe that makes up the difference.
 
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:

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Tim Morlin Visit 7 22 2010 017.jpg
 
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