Weber Carb Edjumakashun

[cr_bobcat]

So I'm not making any plans or anything, but I'm curious about the side draft webers. I really know nothing about them. I have 3 heads on hand, and I'm contemplating what I would do with all 3 of them. I've documented what I'm up to with the C9 head in the small block section. I've kicked around the idea of a 6 SU or 3 Weber DCOE configuration. My assumption is that I can just swap heads when the mood strikes. At least that is until I'm able to secretly build a Mustang compound that my wife knows nothing about...

Anyway, I tried doing some searches about the Weber's and, while there's a lot of information out there, it seemed to be mostly about how to tune as opposed to "how do I pick the one that is right for my application". To lay some ground rules, we'll just assume I never get my harem of mustangs and it'll have to play in my relatively stock configuration '67 coupe. So there's no hood scoops or anything like that. I would entertain options that included lowering the engine a la something like CoupeBoy derivative motor mounts. This is why I'm specifically thinking about the DCOE, but I bow to superior knowledge here.

Let the lesson begin!

[xctasy]

About 33 mm chokes ought to do it.

Comming up with that sizing requires the late Eudardo Webers sizing chart. Venturi area has to be optimised, or it will never run right.

Study this graph,





http://img.photobucket.com/albums/v223/ ... ing_II.jpg


By some rearranging to this, it produces the carb size in mm's via the LN function at 6, 8 and 10 000 rpm, so its out of range for the 3500 to 5000 rpm our stock sixes often do.



http://img.photobucket.com/albums/v223/ ... nerCar.jpg



Triple DCOE 40 Weber with 33 mm chokes for a 2.2 liter DOHC Alfa Romeo engine = 200 cid Ford Falcon six reving to 5000rpm. 135 micron Weber jets = 251 cc/min





All that does is syncs the peak power rpm point with the right carb throat size. Once that's done, the rest is easy. You can use 40, 42, or 45 DCOE Webers with 32, 33 or 34 chokes.

You can't change the intake runner length or port diameter a whole heap, its all locked into the throttle and venturi diameters.


There are a bewildering array of Weber DCOE's, they have a type model, and its never a good idea to have a mixed set. There are a lot of minor things that have a hughe impact on tuning. The emulsion tube recomendations and jet sizes should get you close. To get the power peak to 5000 rpm, you'd be looking at a 260 degree cam with 400 to 450 thou lift.

There is no one solution to jetting Webers for an independet runner instillation, but you'll get a great result if you follow these rules.


/viewtopic.php?f=5&t=31668

....... 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

...............

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.html

If 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.

.....

For SU carbs, they have a target ventui area as well.


On six Cylinder cars, they are best kept in the HS6 1-3/4" size range (HIF44, HIF6, HIF7 range), but there is a large range of sizes from 1" to 2", and they don't pacakge or flow at the right rate to work unless they are just right. H2'S, HS2's, H4/HS4's don't work as well, but anything is possiable if the carb venturi area suits the cam duration.

[cr_bobcat]

Thanks xctasy ! Looks like I've got plenty of readin to do. I was assuming that if I went the 3 sidedraft route, if smaller would be better. Do these need a balance tube that would run between each tunnel? Across all 6?

These all programs/scripts you've written yourself? What do you use as a language? Python? I typically use Matlab because I have it at work. The scrits will also run on a freeware version without translation, so that's what I use at home.

[xctasy]

Thanks xctasy ! Looks like I've got plenty of readin to do. I was assuming that if I went the 3 sidedraft route, if smaller would be better. Do these need a balance tube that would run between each tunnel? Across all 6?

These all programs/scripts you've written yourself? What do you use as a language? Python? I typically use Matlab because I have it at work. The scrits will also run on a freeware version without translation, so that's what I use at home.

No, the scrpits were done in the pre Windows Vista/Windows 7 era from the Zee 240/260/280 forum. After that time, the scripts have to be MetFram compliant. So the screen dumps were down back in 2003 from a Windsows NT98 computer.

The best book is David Vizards A series Mini book (the 1988 edition), which covers Weber tunning in a non idependent runner format. Best read ever. It also covers all the issues of making proper rocker ratios out of stock rockers, and timing chains and its your best primary asset. I red it in 1993, and nothing else compares to DV's simplicity.

He actually answers every question in a roundabout way. You have to go through the process, and then explain, not the reverse.

[cr_bobcat]

Thanks! I'll snag a copy. I already have his book on porting, which I read a couple times before I hooked up my first stone. With 3 kids at 5 and under, reading is what I actually have time for. So many parts building up in the garage but no time to get out there. So I'm trying to document the road and learn as much as I can so I reduce the fumbling around when I actually have time to get out there. Shop time is an extremely precious commodity as this stage of the game....

[xctasy]

Try some ex race MGB carbs, often Model 13's, as per Mopar Six pack E49.

https://www.youtube.com/watch?v=4dxO1TPWhlE


My son was born in 1993, I have there children (the other two girls). Years of birth 93, 96, 99. I read all of David Vizards old and new versions of Modifying Your BMC A series {Tuning British Leyland's 'A' Series Engine (A Foulis motoring book) and the later Second Edition by Haynes } about six time each while making sure my little nippers didn't get out of bed early in the weekends or eveings after work. To my kids, I was the troll in the hallway. My three Minis and five Falcons, two Cortinas and the Mustang recieved modifications that were birthed from David Vizards accurate information. Its the Q=V.A (Flow equals velecity times area) that David elaborates on in graphic and specfic detail. He showed me how to fit a 350 cfm 2-bbl Holley up to a 1600 Cortina, or a 32/36 DGAV to a 1725 Hillman, and a 390 four barrel on a 2000 Cortina and a 500 cfm carb on a 250 Falcon and 2300 V6 turbocharged Cortina. Gearbox gearing was unlocked with his quarter mile formula and that allowed me to return a 58 Vauxhall Velox with a four speed gearbox, and idealise the axle ratio. He showed me how that was done with just the few formula that all crackpots seem to have. These days, we have vidoes where he is so kick a$$ funny. https://www.youtube.com/watch?v=ow5cGV7bXCw


His Weber emulsion tube tuning is a legand...

https://www.youtube.com/watch?v=1pkFSA_rRFI

His endorsement of the Janspeed type SK/TWM Weber DCOE throttle linkage is pivotal

http://www.fastroadcars.co.uk/shop/inde ... oductId=50

Weber throttle linkage, part number LP2000 to fit DCOE/SP range of carburettors. It is top mounted, supplied with throttle cables, pedal block & full fitting instructions. The 2 levers between the carburettors are included.

This is the best linkage of its type on the market today. Also available are the single cable linkage top mount LP1000 & under carburettor mount in single LP3000 & twin cable LP4000 versions

See also http://www.rallynuts.com/motorsport-car ... e-kit.html

Note that David often overturns his earlier suggestions after experimental detail, and that's the most delightfull thing. Issue1 and 2 show how air flow modification for modern engines has developed. You should read the carb section on "How to Modify Ford sohc Engines" http://www.scribd.com/doc/198984368/268 ... vid-Vizard

There are only three other books to compare, and thats


1. William F and Douglas Milliken's 918 page book on vehicle dynamics,

http://www.millikenresearch.com/tn_rcvdcov.jpg
http://www.millikenresearch.com/tn_rcvdbak.jpg

proof if it were ever needed that the Americans are the vehicle masters, not Lotus and Colin Chapman. In that book, it was F=M.A (Force= Mass times Acceleration). I made 15 years of money out of that book.
Thanks William F. Milliken Jr (who died in 2012) http://www.bentleypublishers.com/automo ... -clip.html


2. Tuning for Speed by Phil Irving. Australian Phil invented Specfic Horspower per rpm, which Group A racer Laary Perkins ACED when he did Qjet and IDA 48 carb modifications.It allows anyone to understand the true net worth of modification. His book covers Weber side draft carbs, and proves that they can be down drafted 5 degrees easily.

The other was3. Del Washburn on the study of numerical sequences in my favorite Hebrew ecclesiastical book, the Bible. Torah is best...


You'll find David Vizard probably a little easier to understand than the other two...


A quick note. Replace the needle and seat valve and floats, and dilligently adjust to specs. Webers have awful reliabity in this area as the carbs are hard worked, as the fuel loads are pretty big. Don't buy any cheap fuel parts, only good quality. In his second book, DV goes into how to step wise tune them.



You can use two DCOE 45's and tune and size them like you would a joined together 1275, 1400 to 1600 cc stroked A series Mini with 38 to 40 mm chokes. This is also like the triple carb E37 and E49 265 Hemis ran. Modern 4-bbl in line sixes do as weel as triple carb engines for peak power if the cams areintense enough. Like a 2.55, 2.8 to 3.3 liter engine. As a matter of fact, ex Ferrari engineer Lampredi used to run 2300S Fiat engines that way with DCOE40'S and 26 mm chokes for 136 hp net. Dellorto DHLA or DRLA will do the same as DCOE's or IDA/IDF's

One carb down on the 265, a twin DCOE 45 will make an easy 255 hp if it can rev to 6500 rpm. I ran two 350 cfm 9117 carbs (ex 1977 302 Ford) with 30 mm venturis, and got a sensational improvement in power and economy using the 16 to 19 thou power valve channel restrictions instead of 59 thou and 62 thou for 350 and 500 cfm carbs, as David suggested for 1600 to 2000 cc engines with this 350 cfm carb in 125 hp and 500ccfm carbs in 155 hp instillations. That's what a good 3.3 will flow, if the cam is Winston cup/NASCAR 4-BBL restrictor plate biased for under scavenging. According to the programs, two 350 or 500 cfm carbs act like a single 4-bbl 496 or 709 cfm double pumper for a possiable 250 to 310 hp horspower at 5800 rpm.