On my 250 I'm running a jetted down 500CFM Eldebrock carb on and old aluminum Clifford intake. I think I have it set-up correctly but I saw a few pictures in an old 250 Forum post of Eldebrock carbs sitting the same way as they sit on a V8, small barrels toward the front of the car and big barrel toward the firewall. I thought, but I could very well be wrong so dont bite my head off, that on a straight six since the intake runners are all on one side of the engine that the carb should be "sideways from on a V8" so that the two small barrels face the motor and the two big barrel face the drivers side of the car. This would allow one small, one large barrel to feed the front 3 cylinder and the other small and large to feed the rear three cylinders. Am I correct in my thinking??? The engine with the white lakester header is mine, not a great pic sorry and the other pic I found on here and the carb is mounted the same way as on a V8......
I tend to agree with you. On the 250 I built, it had a Holley 2 barrel mounted "sideways" as you describe. Butch/56sedandelivery.
Sideways tends to even out the mixture better. The more street driven, the more important that would be. The front-to-back guys are usually looking for simplicity.
At WOT all are open. I don't want to say it doesn't make a difference... There is a difference in the distance from the carb barrel to the cylinder. Look at the benefit of a 1 barrel per cylinder Webber setup. It's more efficient because each cylinder is drawing from maybe a 200 cfm bore and that bore sees a higher vacuum signal. The higher vacuum signal causes more accurate metering, faster fuel flow rise and better atomization throught the jets. A webber carbed engine will operate more smoothly with a radical cam than an engine where cylinders share the carb. The Webber carbed engine enjoys the better metering while at the same time greater gross airflow at higher rpm's When you carb a shared carb engine to meet the same high rpm demands the engine becomes over carbed at the bottom end. I used to think the cfm of a 4barrel was divided a**** the cylinders sharing it distributively Contrary to how I originally understood the 4 barrel It apply's it's full cfm to each cylinder individually. Why? Only one cylinder at a time is drawing from it. I didn't understand this until I learned about the physics of the Webber multi carb (and mechanical injection) air/fuel systems. Once you can get your head wrapped around how it's different it's easier to see how only one cylinder at a time sees the entire 4 barrel, they don't share it except in regards to maximum flow
I've spent a bit of time messing with 4 barrels on a 261 Chevy and then a 302 GMC.I always mounted the carb sidways with the primary barrels closest to the head. However I did mount one V-8 style and didn't notice any difference in everyday driving.
My buddy bought another race car last year. We run 230s in our cl*** and are limited to Holley 350cfms. But the thing is our intake on the new car(new to us) sits sideways on the intake. So baically the ****erflys run paralell to the engine. The idea is that the air and fuel mixture won't have to make such a hard turn. In turn starving the outer cylinders. The carb also sits on a one inch spacer. Seems to work well. The only real problem is fitting together a carb linkage that isn't a mile long.
I have found especially on slant sixes but i did work on some 250s as well a few years ago that front mounting like on a v8 produced very poor idle and off idle performance. When turned sideways the difference was dramatically better as you surmised. Here is the last one i did and still have. I am more than satisfied with it. What concerns me is you said you "Jetted Down" Jetting has nothing to do with airflow or engine size. A certain size carb venturi needs a certain size jet to provide the right mixture. What engine it is on is imaterial other than for minor corrections for manifolding variations. All gasoline engines require the same mixture strength (rich or lean) Don
I have run a 4bbl on 230 - 292" chevys and have always positioned the primary's away from the engine for best low and midrange. The little bit of extra distance seemed to help with fuel distribution in these ranges. You can't get it perfect due to runner length variations using a single carb on an inline.
It depends on your intake. A Dual Plane intake (such as the Offy I have on my Ford 300 six) has one chamber for the primarys and one for the secondarys. This will determine the carb orientation. On a single plane, there is one chamber for both, and as such carb orientation will come down to fit, linkages, and other considerations.
Well it sounds like I was correct in my thinking since this is a single plane intake. Thanks for the info guys, I just didn't want to look like a fool but I thought I was correct. HEY - Dolmetsch I read what you wrote...... "What concerns me is you said you "Jetted Down" Jetting has nothing to do with airflow or engine size. A certain size carb venturi needs a certain size jet to provide the right mixture. What engine it is on is imaterial other than for minor corrections for manifolding variations. All gasoline engines require the same mixture strength (rich or lean)" ......so I'll ask this, as long as I'm changing metering rods and jets doesnt this effectively reduce the cfm of the carb? On my 54 chevy I'm running a totally internally stock vortec 350 with a highrise tunnel ram and msd ignition system and two 500cfm four barrels. I am entirely aware that 1000cfm in way way to much for a stock motor, this was mostly done for looks not performance...at first it choked had on full acceleration and i had to pull and clean up plugs once a week. I then ordered the smallest metering rods and the smallest primary jets and next size up for the secondaries that edlebrock makes. It was an instant difference ran great, I still have to pull the plugs but only every month or so and it barely chokes when given full throttle....... This is why I choose to run a 500cfm and jet it down on my 250, if I've been told right double your cubic inches of a stock engine is absolut max on carb cfm, 250cubic, no more than 500cfm, 350cubic, no more than 700cfm and so forth, input??? Again I'm not an expert this is why I post on here, love input and new knowledge!!! Thanks
Oh ya and any ideas on a throttle cable setup ideas would be great, right now I'm just running a really long lokar cable, but I saw a guy on here that had a neat linkage setup using the corner stud as a pivot point instead of wrapping the cable all the way around???? INPUT IDEAS KNOWLEDGE SEND IT!!!
No jetting and or metering rods has got nothin to do with CFM whatsoever. 2 500s is normal for a 2 x4 set up The rules dont apply because you run on one carb till wide open just like with a three duece or 6 pack set up. because of that the engine runs well on the primary carb till the throtttle is around 70 to 80 open then the second carb comes in. The carb size is only so we get decent low speed perfomance and since then we only use one it is not a problem. Tunnel rams by the way do not fall into the catagory figured with normal CFM charts .they have a differnt and stronger signal to the boosters and can operate with CFM that would kill a normal manifold . BTW I am glad you didnt ask what sixze the AFb is on my rail. it aint a 500 or even a 625 BTW. Anyway you are on the right track and asking the right questions All the best with your build Don
I might have to try that...my offy intake with an 600cfm mounted with the primaries next to the head, but i have poor lower end lower rpm power. I have good response on my top end and when the rpm's are up a bit. My thoughts were to run a 22-25 hundred stall in my TH 350 to help.
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