RaceCarRyne

setup:
h22 stock bore
95mm stroke
skunk 2 pro 1 cams locked in vtec
13to1 compression
ported and polished head with 3 angle
custom drag header and custom intake..


what size carbs.. i know some ppl are running them and have good results.. i am looking for wot throttle only..

RaceCarRyne

no 1 has any imput?

d16dcoe45

Either a set of 50 DCO/sp or 55 DCO/sp Webers. As I understand it, the 48 DCO/sp, 50 and 55 all have the same outer bodies (55), its just the diameter in front of the throttles on the head side is smaller with the 48s and 50s. I think you can run a up to a 46mm choke in the 50s and up to a 48? in the 55. The size of the choke, not the carb is going to dictate how much power you can achieve.

Even on a big rpm, big power, large displacement setup the biggest chokes (venturi) aren't always the best, even if you are only worried about peak power.

You can tell the "big" DCOE style carbs (48,50, 55 sp) are made just for performance because they don't even have a provision for a manual (starting) choke--the casting is blank!! All other DCOEs (38 to 48 DCOE) come with a manual choke.

Just to clarify, when I referred to "choke size" in the first paragraph I was referring to the main venturi, the starting choke is just a starting device that dumps alot of extra fuel on a cold start--most people don't run them anyway.

RaceCarRyne

well do you have any cfm numbers on a throttle body.. and how do you go about running that big of a carb beacuse the atomization takes place from how strong the signal is through the carb. less signal=less atomization=less power. if you take a cfm reading you should be able to come close to a carb size in that method.. currently i have 2 holley 2 barrel 350cfm a piece for it and the butterflies are 38mm arround.. even tho they are smaller than what most ppl would say will work they have a high cfm flow rate and wiht the smaller butterfly they will also have a strong signal..

SOHCinWA

Ask Bisi. He is the King of Carbs... He can lead you in the right direction

RaceCarRyne

i was hoping that he would respond to this thread
how should i contact him pm. or waht

SOHCinWA

Yeah you could PM him I know that he is online today trying to catch up on all of his emails.

d16dcoe45

When you are running 2.2 liters plus, with 13:1 compression and alot of cam, you are going to need a choke at least 42-46mm (maybe more, although I doubt much more than 46-47mm) , the only commonly available sidedraft carbs that can support that choke size are the 48,50, and 55 DCO/sp Webers.

The carb body size doesn't determine the airflow, the choke size does. A larger ID carb with the same choke size will flow a bit more than a smaller carb with the same choke size, but the choke (venturi) size is how you determine what size carb body to get.

With a fixed venturi carb like most Holley 4-barrel type (except for the King Demon RS(?) the carb is rated by CFM--the venturi is cast into the body. With a DCOE or DCO/sp you can have a 45 DCOE with a 45mm throttle plate but you can size the carb to different power levels and displacements by running from a 28mm to a 40mm venturi size, and changing sizes whenever you want.

The "sporting" DCOEs--the 48-55 DCO/sp have a more limited off the shelf venturi selection (I believe from 40-48mm) because they are desgined for sporting motors with high specific outputs that aren't worried about low end power (a huge venturi will make low end jetting more difficult and will hurt low and mid range power compared to a smaller venturi)

d16dcoe45

Also, you are comparing a 2 barrel Holley which is on a plenum to an individual runner design. A DCOE or DCO/sp being an individual runner design has very powerful individual pulses which can give you good carburetion even when running a large choke size for optimum high rpm power (provided the choke is not too large for the application). I know a 38mm choke in a DCOE 45 Weber can flow around 215-225 cfm per barrel, going from a 38 to a 40 in that carb body (dcoe 45) gives a minimal airflow increase but really starts to hurt low end power and smooth carburetion. Its hard to directly compare CFM numbers from an individual runner to a plenum system.

I myself run a 38mm venturi in a 45 body, for my application it gave more top end power and alot more midrange and low end than the bigger 40mm venturi. When the venturi size gets close to the size of the body (throttle plate) the carburetor becomes less affective at actually carbureting--giving you an accurate amount of fuel througout the rpm range.

A 48 or 50 DCO/sp will let you run a large venturi for unrestricted top end and still be able to meter fuel effectively at low and mid rpm ranges.

RaceCarRyne

how do i measure venturi size?

SOHCinWA

Call Bisi and that will solve all of your carb needs

d16dcoe45

Venturi sizes are cast into the venturi themselves--in mm. Otherwise just measure the ID of the venturi where it necks down to its thinnest point.

Flashmn

Technically with webers you're running one carb per one cylinder, although they are together as two. Also you dont measure a DCOE as 2.2 liters, you measure it as the cylinder size, exact size. I think honda 2.2 is something like 2160cc, so you'd be running 540cc per carb.

Also as for compression ratio, the carb doesnt know what the compression ratio is, only things affecting it are cam overlap, duration and lift. As for going for carbs that are too big, its a pain in the *** to adjust, because your carb doesnt flow all that great on low RPM. Also you'd have to choke it alot. For example I was running 40mm DCOE's on my 1.6 with 33mm chokes. I'd have great power from 2000 to 7000 when it would instantly cut off, then again I cant rev over 7000 with the valvetrain. If the carb is too large, your flow will be interrupted by the amount of material at the choke point, with a carb too small, you cant find chokes that work over the maximum allowable for the carb.

Then we come to the problem of manifold length, which you can fine tune the resonance pulse to a specific rpm range, thus you'd get a small boost at that area. Key points a long manifold is good for medium RPM power, short one to high rpm.

I've fiddled enough with carbs, its EFI for me now.