semi on the topic - does anyone have flow ratings on weber carbs? please
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| Too much Carburation?? https://slantsix.org/forum/viewtopic.php?t=32906 |
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| Author: | Bigd [ Sat Dec 20, 2008 1:00 pm ] |
| Post subject: | Too much Carburation?? |
The motor is a stock 225ci bored over to 242ci. It has custom Aries pistons, a Clifford solid camshaft, 320 deg duration 595 lift int and ex. Custom 1.6 roller rockers from Clifford Performance. The block deck was o-ringed . Compression ratio is approximately 11-1. The head was ported and polished extensively. Oversized valves from a 318cid were used as well. The header was custom made. The rotating assembly is balanced. The intake is from Clifford as well as the three Weber side draught carbs. They flow approximately 1000cfm combined. I purchased this 72 dart swinger as is and it came with time slips running 9plus seconds in the 1/8th mile...The question I have is......1000 cfm is way too much for this combo isnt it?? I have always only ran BB chevs etc and have yet to run a 1000cfm or larger carb....850 mostly...Any Ideas???? Im not in love with the webber idea anyways so if its slowing the car down it will be going on the shelf and the holley will be purchased. Any input would be very much appreciated...Thanks |
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| Author: | terrylittlejohn [ Sat Dec 20, 2008 3:02 pm ] |
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i have never run webers but some have had great succuss with them, my high comp engine is close to what you have and i found a 750cfm holley to be the best with 4.88gears, 30in tires and 3900rpm convertor.if this is you first slant six`s you better start by not comparing it to a v8(chevy or other) i have found for racing that more cam and carb rather than cube`s work with /6`s |
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| Author: | Joshie225 [ Sat Dec 20, 2008 3:48 pm ] |
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What size chokes in the Webers? You can't expect individual runner intake systems to have or need the same flow numbers as a carburetor on a plenum. If you do decide to ditch the Webers I'd be interested in buying them. I have a late model Clifford intake with bosses for nitrous or fuel injection and water heat for trade. The manifold has been mostly polished in preparation for powder coating and has been fitted with a divider to improve carburetor function and improve torque at low speeds with a big cam such as yours. I also have a few 4bbls to choose from that could round out the package. |
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| Author: | VG-265 [ Sat Dec 20, 2008 4:27 pm ] |
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A LOT of people would question the idea of removing Webers and installing a Holley... The Webers are far more expensive to initially install and set up, but work extremely well. Somebody has already spent the $$$, and it would be a backward step to go to a 4 barrel. |
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| Author: | FrankRaso [ Sat Dec 20, 2008 5:05 pm ] |
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The flow rating of any carburetor is relative to a standardized pressure drop. On 4bbl carburetors, the pressure drop is 1.5" Hg and would equivalent to the manifold vacuum level. 1bbl and 2bbl carburetors are rated at 3.0" Hg. Since the Webers are 2bbl carburetors, we can assume that they are also rated at 3.0" Hg. With your 242 CID engine and assuming your VE is 85%, you will require about 298 CFM at 5000 RPM. Your set of three Webers (1000 CFM @ 3.0" Hg) will flow exactly what the engine needs at any particular RPM, but the pressure drop (and manifold vacuum) will be about 0.26" Hg at wide open throttle (with 85% VE) and 5000 RPM. The lower pressure drop (0.26" Hg vs 3.0" Hg) means that the air-fuel mixture density is greater inside the combustion chamber, which results in more power. The problem with oversized carburetors is poor low speed operation. However, the Webers may work fine in this application. See Carburetor Flow Rating for more information. |
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| Author: | Joshie225 [ Sat Dec 20, 2008 6:17 pm ] |
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Frank, individual runner manifold and carburetor systems are not like plenum manifolds and carburetors. You cannot add the flow capacity of the carburetors together because the cylinders do not draw from all the carburetors. According to my Weber book an engine with 660cc cylinders with one venturi feeding one cylinder and a maximum horsepower RPM (power peak) of 6k RPM the carburetors should have 42mm chokes. |
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| Author: | FrankRaso [ Sat Dec 20, 2008 6:34 pm ] |
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I agree with you that individual runner manifold and carburetor systems are not like plenum manifolds and carburetors. I was only trying to make the point that the flow rating of a carburetor is not an absolute number. |
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| Author: | emsvitil [ Sat Dec 20, 2008 7:13 pm ] |
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see this post/thread on multiple carbs http://www.slantsix.org/forum/viewtopic ... arb#200195 |
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| Author: | steponmebbbboom [ Sat Dec 20, 2008 7:17 pm ] |
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if that guy ever builds a six-barrel slant, i want pictures. |
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| Author: | 68barracuda [ Sat Dec 20, 2008 9:15 pm ] |
| Post subject: | Weber flow ratings |
semi on the topic - does anyone have flow ratings on weber carbs? please
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