xctasy wrote:....... Source of CFM's is David Vizards Modifying your Aseries Engine, and some other Modifiying Fords SOHC engine. They were measured in a Supeflow flow bench at 1.5" hg, and have conversion to the 3.0"Hg rating Holley 2-bbls use via a 1.41 multiplier used for pressure head conversions
Here are flow figures for Triple DCOE carbs with the best trumpets fitted to the ends.
40 DCOE , 24 mm, 202 cfm at 1.5" Hg = 286 cfm at 3.0" Hg
40 DCOE , 26 mm, 241 cfm at 1.5" Hg = 341 cfm at 3.0" Hg
40 DCOE , 28 mm (Fiat 2300S), 279 cfm at 1.5" Hg = 395 cfm at 3.0" Hg
40 DCOE , 30 mm, 316 cfm at 1.5" Hg = 447 cfm at 3.0" Hg
40 DCOE , 32 mm, 336 cfm at 1.5" Hg = 475 cfm at 3.0" Hg
40 DCOE , 34 mm, 346 cfm at 1.5" Hg = 489 cfm at 3.0" Hg
40 DCOE , 36 mm, 350 cfm at 1.5" Hg = 495 cfm at 3.0" Hg
45 DCOE , 32 mm, 324 cfm at 1.5" Hg = 458 cfm at 3.0" Hg
45 DCOE , 34 mm, 376 cfm at 1.5" Hg = 532 cfm at 3.0" Hg
45 DCOE , 35 mm, (Torino GR) 397 cfm at 1.5" Hg = 562 cfm at 3.0" Hg
45 DCOE , 36 mm, 418 cfm at 1.5" Hg = 591 cfm at 3.0" Hg
45 DCOE , 38 mm (E37 Pacer), 438 cfm at 1.5" Hg = 619 cfm at 3.0" Hg
45 DCOE , 40 mm (E49 Charger/Tornado 380 Motor w TC), 444 cfm at 1.5" Hg = 628 cfm at 3.0" Hg
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If a Weber DCOE 38 or 40 had a 29 mm venturi , it would a flow of 421 cfm . A similar size early AMC/IHI/Ford 275 cfm Holley 2040 flows 53% less due to a choke air horn.
A Weber with a 30 mm venturi flows 447 cfm. It would outflow a same size venturi 350 cfm Holley 7448 by 27%.
If there was a Weber with a 31 mm venturi, it would flow 461 cfm, or 8% more than a 425 cfm Holley 7508
A Weber with a 34 mm venturi flows anywhere from 489 to 532 cfm, so it flows the same as a similar size 500cfm Holley 4412. Either 2% less or 6% more. An example is the Renault Torino 3.8 L6 with 215 hp triple Weber 45 DCOE with 35 mm chokes is similar to three stock 500 cfm 4412 Holleys with its stock 34.5 mm chokes. Peak power rpm is incidently about 4700 rpm with this carb on the 3.8 liter Kaiser based six see
forum/viewtopic.php?f=13&t=29958,
With 40 mm chokes and a better cam, theTornado 380 w TC did 248 hp at 5000 rpm. See
http://www.torosite.com.ar/torinoytornado.htmlIf a Weber had a 37 mm venturi, it would flow 598 cfm, and that is 9% less than a similar size 650 cfm Holley 6245. An example close is the E37 265 Charger/Pacer, which gave 248 hp at about 4800rpm from 4.3 liters
Small 275 and 350 cfm Holley’s flow a lot worse than a similar sized DCOE Weber’s, due to the restrictive choke air horn.
Larger 500 and 650 cfm Holley’s flow just as well as large Weber’s.This implies that venturi enlargement is advantageous on 275 to 350 cfm Holleys.There is enough space for a 150 thou rout out of a stock small 2040 or 7448, and that would bring cfm up significantly. I'm looking a 1.277" for my 7508 and 9117 list Holleys which would make an extra 11% on a Weber, but more likely to be up to 27% on a Holley 275/350. Note that the smaller carbs often come with truck or economaster boosters, which loose 15 to 30cfm on the 500 cfm boosters. Annular discharge boosters from the Holley 2380EG and 4180G Ford truck and bus carbs bring back the loss, adding 15 to 30 cfm. Additionally, there is a new batch of US Coast Gaurd approved return line 2300 carbs for OMC under new Holley part numbers which allow later bits to be fitted to earlier Holley carbs. Adjustability with the Holley 2300 2-bbl is now total.
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