Weber MAX CFMs (Weber Carbs and Max Air Flow)

I'm playing around with the idea of using Weber DCOEs on a custom manifold, and I would like some information on max airflow of the carbs.

Does anyone know where I can get information relating to max airflow of the DCOE 48's and DCOE 55's.

I'm planning on using 55's only because it does not seem like the 58's are around. Redline does offer 55mm DCOE's that I am assuming are good mechanical units. As far as I can tell the only 58's around are the Berg IDA's

Also, are there any gotcha's specific to the 55mm DCOE's when using them for a max street and track motor.

Thanks for any info.
 
Re: Weber MAX CFMs

For the 48's I think its in the region of 320cfm per choke, my info stated ' that each carb can flow between 630/650cfm'. Bit of an open ended Question really as it all depends on the combo of venturis etc & the type of application they are used in. eg individual choke per cyl or common plenum manifold. Outfits like Gene Berg have a whole bunch of tricks when it comes to increasing flow numbers.
 
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Re: Weber MAX CFMs

I have to agree with Jack Mac. I remember that the total cfm for my 48 ida's were just over 2500 for total set up. That is alot of volume for any engine. What is the displacement of the engine you are feeding with the carbs and what is luring you to the 55's? What is the cam and what is the head displacement? Just curious:thumbsup:
 
Re: Weber MAX CFMs

FosterEast, in my experience you're better off using a greater number of (well synchronized) carbs than fewer of very large capacity. In other words, use four or six two choke DCOE webers rather than two weber (feeding several cylinders). Why? Because the DCOE flows better with a choke installed of a reasonable size relative to the throat size. The DCOEs were designed to work with a choke which is more than just minimally smaller than the throat bore - it is important to accelerate the intake flow to create low pressure for proper and complete atomization. Said another way, your cfm analysis should contemplate chokes installed which scale down the intake diameter, and, cumulatively add up to enough flow by way of utilization of enough separate carburetors.

There's a book written by Pat Braden entitled "Weber Carburetors" which has all the information you'll need - a good read and very interesting.
 
Re: Weber MAX CFMs

One of the 'wrong' assumptions most folk make is to compare that 320cfm per barrel or choke directly against the more common Holley figures like Tom has mentioned.

The Weber is in the GT40 equation one barrel/choke per cyl .eg 320cfm but it is only for that cyl and experiences stop/start reverse pulses every time a valve opens/shuts--thats all unless you connect other cyls by a plenum etc in which case you have simply changed your carb make.

The other thing is to ensure that your comparing apples to apples in flow rates- if both types are not checked at the same pressure drop the data is useless.
 

Randy V

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Re: Weber MAX CFMs

CFM ratings of carburetors are made in a couple of different standards set by the SAE.
I believe it's 3" of mercury for 1 and 2 barrel carbs and 1.5" of mercury for 4 barrel carbs.
Also - The ratings are done dry (without fuel - which will reduce the net flow of air)
 
Re: Weber MAX CFMs

Guys,

Thanks for the feedback. My understanding on the 48mm IDAs or DCOEs is that they run out of air somewhere between 400 and 500 horsepower. (The book I have that discusses the 48mm IDA lists it at 330CFM) I'm building an engine with over 600 horsepower and I am considering the Gene Berg 58mm IDA's, but I am pretty sure if I used a DCOE I would have more room for air cleaners. Either way I have to custom fabricate a manifold, so I am trying to gather data.
 
Re: Weber MAX CFMs

fosterest, if you're building a V8, I can't imagine that four 48mm downdraft IDAs or four sidedraft DCOE will run out of flow, even if your target hp is over 600. Lots of guys here are using the 40mm IDAs/IDFs on engines with 400-500hp.

I seem to remember 50mm DCOEs being available - pretty sure I've had some in the past. Unfortunately, I don't know anything about the Berg 58s.

Sounds like a fun project!
 
Re: Weber MAX CFMs

Guys,

Thanks for the feedback. My understanding on the 48mm IDAs or DCOEs is that they run out of air somewhere between 400 and 500 horsepower. (The book I have that discusses the 48mm IDA lists it at 330CFM) I'm building an engine with over 600 horsepower and I am considering the Gene Berg 58mm IDA's, but I am pretty sure if I used a DCOE I would have more room for air cleaners. Either way I have to custom fabricate a manifold, so I am trying to gather data.

Dynoed a 8.2/362 CU with IDA's bored 51.5 with 45 choke result 570@ 6700,500ft torque,will move to Holley with ported/flowed vicor JR manifold for back to back test
 
Re: Weber MAX CFMs

After talking to Redline Weber's, I think I'm going to use Berg 58mm Weber's and dismiss the idea of the DCOE sidedraft. Redline wants to sell carb's but they do not want to help anyone buy one. The fellow I spoke with mentioned a modified 51.5mm IDA or DCOE they had flowed over 1,000 CFM's out of each barrel, which I can't believe.

The engine I'm putting together is a 427 Ford that is stroke to 482

I'm pretty sure the 48's will run out of air at the target HP. The 58mm Berg's have been dynoed on 427 FE's at over 700HP, I suspect the highest a modified 48IDA will go is mid-500's. I guess it would be prudent to use the 48's as RPM governers to limit the top end, but I would like to see how much I can get with the work I am doing.

Thanks again for the help, when I get the engine dyno'd I'll post the results.
 
Re: Weber MAX CFMs

Just a couple questions for ya. How do you think NASCAR teams are able to build the type of HP numbers they do with a single, restricted four barrel? How do you think a Trans Am Ford engine can produce over 700 HP using a single four barrel carb limited to 1100 CFM? That's TOTAL CFM. I think you may be concentrating and fixated on something that isn't neccesarily a determining factor for power output. I have seen WAY more engines "overcarbed" than those that are using the proper carb. You may want to consult with an engine builder that builds serious engines and listen to what he has to say.

Just my .02.
 

Ron Earp

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Re: Weber MAX CFMs

fosterest, if you're building a V8, I can't imagine that four 48mm downdraft IDAs or four sidedraft DCOE will run out of flow, even if your target hp is over 600. Lots of guys here are using the 40mm IDAs/IDFs on engines with 400-500hp.

The standard 48mm (which actually supports only up to a 44mm choke if I remember correctly) will run out of flow with big inch motors if you want to turn serious RPM (greater than approximately 6k):

http://www.gt40s.com/forum/gt40-tec...k-power-choke-size-8-barrel-venturi-size.html

http://www.gt40s.com/forum/gt40-tech-engines-induction-exhaust/17216-twm-weber-manifold-flow.html

A 4bbl is damn hard to beat.

Ron
 
Re: Weber MAX CFMs

After talking to a well respected engine builder and tuner, he stated the a well built 331 SBF with a 7500RPM operating RPM would probably loose on the order of 50 HP at the upper levels using the 48IDA's vs a 750 single 4 barrel Holley. He said the leading factor was the throttle bore on the IDA is smaller than the inlet valve, and causes a restriction, with a resultant vacuum at WOT. Since the Holley is on a plenum, the cylinder and inlet valve sees the larger volume, and doesn't produce a negative pressure. If you could find a Weber or an IR injection that had a 2.05" throttle bore, it wouldn't be a problem.
 
Re: Weber MAX CFMs

Just a couple questions for ya. How do you think NASCAR teams are able to build the type of HP numbers they do with a single, restricted four barrel? How do you think a Trans Am Ford engine can produce over 700 HP using a single four barrel carb limited to 1100 CFM? That's TOTAL CFM. I think you may be concentrating and fixated on something that isn't neccesarily a determining factor for power output. I have seen WAY more engines "overcarbed" than those that are using the proper carb. You may want to consult with an engine builder that builds serious engines and listen to what he has to say.

Just my .02.

The amount of available airflow is THE determining factor, assuming I build the heads correctly and you can properly meter the air-gas mixture.

The Webers are only providing air to one cylinder, where a four barrel carb like Nascar provides 1100 CFM's to any cylinder that's asking for it, not 1100/8. At 330 CFM total from a Weber 48 IDA, I'll run out of air somewhere north of 500 HP.

In my original post I was asking about the DCOE 55, since it should be able to have bigger chokes than the 48 IDA.

Unfortunately the sites that sell Weber's do not have a lot of information to help you, so I was hoping someone here may have went through a 55DCOE installation since it is pretty much a race-only carb and could tell me how it worked for them or might have some flow data on it that could help me.
 
Re: Weber MAX CFMs

Ron,John,

Thanks for the feedback, as I mentioned I'm going to try the Berg IDA's and see what happens...

I just called Berg, they still do not have the 58mm IDA's available. They told me this November they should have them...
 
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Re: Weber MAX CFMs

Fostereast,
You might wish to get in touch with Dean Lampe who is in the process of sorting out his Dyna Tek injection. This is the only setup I have seen that actually 'looks' like Weber IDA's that may be able to flow enough to meet your requirements.
But if you really want the top end power go with a 4bbl, I have been fortunate enough to work on some 355 Nascar stuff that makes over 800hp and it is all about quality of airflow rather than sheer quantity. But one of those motors would not be streetable without a major rethink in cam & compression, along with a lot of other mods to give any sort of longevity at lower RPM which in turn would remove around 250hp.
 
Re: Weber MAX CFMs

The amount of available airflow is THE determining factor, assuming I build the heads correctly and you can properly meter the air-gas mixture.

The Webers are only providing air to one cylinder, where a four barrel carb like Nascar provides 1100 CFM's to any cylinder that's asking for it, not 1100/8. At 330 CFM total from a Weber 48 IDA, I'll run out of air somewhere north of 500 HP.

In my original post I was asking about the DCOE 55, since it should be able to have bigger chokes than the 48 IDA.

Unfortunately the sites that sell Weber's do not have a lot of information to help you, so I was hoping someone here may have went through a 55DCOE installation since it is pretty much a race-only carb and could tell me how it worked for them or might have some flow data on it that could help me.


As you have eluded to, there is much more going on than just pure CFM numbers, which is what I was getting at, and what Jac Mac is also saying. I mean lets just look at what has been stated so far. Assuming a low given value from the posts above of 320 CFM per throat on a 48, that gets you total 2560 CFM, yet an 1100 CFM 4 barrel will build more power. These are areas that many engineers have spent many hours and $$ on. The result? All top efficiency designs use a common plenum. If you don't want to use a common plenum intake manifold because you think the individual carb bodies "look cool" then at least put the air horns in a common plenum and I will bet you see HP increases once tuned properly. Also, if you REALLY want to get the flow maximized, you may ask around about anular discharge main venturis. I'm not just talking about the fuel venturis, but the MAIN venturis. If you find someone that knows about what I have just told you, they are the ones that will be able to get you the most out of the carbs you choose, but it won't be cheap.
 
Re: Weber MAX CFMs

I think you would gleen a lot of information on 50 & 55 DCOE's if you were to get in touch with a knowlegable Toyota Formula Atlantic engine builder. I think the top runners really learned how to massage the carbs.
 
Re: Weber MAX CFMs

Crash 33, an 1100 cfm 4 barrel will flow 8800 cfm if you use the same logic that a weber engine will flow 2640. Each cylinder can pull about 330 cfm through a weber and the same engine with an 1100 cfm carb will give a max of 1100 cfm to EACH barrel. I have dyno numbers that show the stock 48 IDA could not pull my engine much over 500hp at the crank. My heads are Yates and they will flow over 360 at .7 inches of lift. The webers can't keep up. The dynatek system was at 500hp at the tires and still climbing at 6000 rpms when it hit a rev limiter that I didn't know about. The dynatek system will flow 90 cfm more per barrel than my webers. It is all about the air flow. You will not get all your engine has to offer if it is a big HP engine if you use the webers.
 
Re: Weber MAX CFMs

Dean, so suppose that 4 barrel (with common plenum) was bolted to a BRM V16 then it would be flowing 17,600 cubic feet a minute (cfm). I wouldn't think that's correct.

Whether it's flowing to one or two twenty cylinders, total flow is still limited to a single choke point (the carburetor).
 
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