How is a carburetor calibrated?

Tech questions that don't fit above forums

Moderator: Team

Post Reply
TheWolfMan

How is a carburetor calibrated?

Post by TheWolfMan » Sun Jul 31, 2011 8:24 pm

I'm wondering how both manufacturers like Holley do it, and how the carb modification shops do it.

Coloradoracer
Pro
Pro
Posts: 444
Joined: Sun Mar 21, 2010 9:48 pm
Location: Conifer, Colorado
Contact:

Re: How is a carburetor calibrated?

Post by Coloradoracer » Sun Jul 31, 2011 11:16 pm

I'm not an expert, but I can tell you this, it comes from tremendous amounts of testing and data. There are numerous things that they have to take into account and it's more than just a simple explanation. Fuel demand requirements, emulsion packages, circuit timing, carb sizing, engine applications, and about a million other things. Well, maybe not a million, but you get the idea. It takes alot to come up with a combo that works, and even with the best tuners out there, someone else will tweak it and tune it just a little better......
Mark Goulette
Owner/Driver of the Livin' The Dream rear engine dragster
Speed kills but it's better than going slow!
http://www.livinthedreamracing.com
Authorized Amsoil Retailer

Shopboss
Guru
Guru
Posts: 1026
Joined: Sat Dec 13, 2008 1:55 pm
Location: Georgia
Contact:

Re: How is a carburetor calibrated?

Post by Shopboss » Mon Aug 01, 2011 7:46 am

The same way you get to Carnegie Hall! :lol:

Donny

David Redszus
Guru
Guru
Posts: 5655
Joined: Tue Nov 27, 2007 9:27 am
Location: Chicago
Contact:

Re: How is a carburetor calibrated?

Post by David Redszus » Mon Aug 01, 2011 6:47 pm

Years ago I had the opportunity to spend several hours in a discussion with the head engineer at Walbro. I asked about the calibration of various size carburetors and he replied that they have a carburettor flow bench that is extremely accurate. I asked where I could buy a similar one. "No problem," he said, "we will build one for you. The price will be $250,000. It comes with full instrumentation."

But no instruction manual. :(

robert1
Guru
Guru
Posts: 2541
Joined: Fri Oct 26, 2007 8:26 pm
Location: missippippi

Re: How is a carburetor calibrated?

Post by robert1 » Mon Aug 01, 2011 7:22 pm

I read this somewhere a long time ago. "A carburetor is a uniquely designed device calibrated to deliver the wrong amount of fuel at any RPM!"

David Redszus
Guru
Guru
Posts: 5655
Joined: Tue Nov 27, 2007 9:27 am
Location: Chicago
Contact:

Re: How is a carburetor calibrated?

Post by David Redszus » Wed Aug 03, 2011 12:16 pm

robert1 wrote:I read this somewhere a long time ago. "A carburetor is a uniquely designed device calibrated to deliver the wrong amount of fuel at any RPM!"
David Vizard, "How to build horsepower, Vol 1 , page 79, quoting a "well known physicist."

"A carburetor is a wonderfully ingenious device for providing an incorrect air/furl mixture at all engine speeds."

Damn close to being correct.

Dave Braswell
Member
Member
Posts: 122
Joined: Wed Jul 13, 2011 10:51 am

Re: How is a carburetor calibrated?

Post by Dave Braswell » Sat Aug 20, 2011 4:05 pm

"A carburetor is a wonderfully ingenious device for providing an incorrect air/furl mixture at all engine speeds."

Damn close to being correct.[/quote]

This statement is very close to being true when you try and run a production, mass produced performance carburetor on a high performance engine.There might be one application where the carburetors fuel curve meters correctly, spot on for that motor. Put it on a different motor and it might not be so good. When carburetors were used for OEM road applications the carburetor was calibrated to the specific production engine used in that vehicle. This calibration was verified on a wet flow bench using mineral spirits as a test flow fluid. This calibration could be controlled close enough to match a fuel curve standard that was considered acceptable for the application.

When you get into real race applications things change. Every different motor configuration requires a specific calibration to properly match the fuel curve requiremnts. A lot of this can be achieved through tuning the calibrated restrictions in the carburetor. The ones having threads being the easiest to change.

When you purchase a carburetor from someone who specialises in custom calibrated, high performance carburetors you should be getting a devise that is correct for your application. The price you pay should be directly proportionate to the work involved. This is not unlike race engines themselves. You can compete in limited classes with a "crate motor" and do quite well, but don't try and compete in a Dirt Late Model show. In Drag Race applications a Supergas motor can be built for a fraction of the cost of a Prostock motor. Do they perform the same? I think we all know the answer.

The higher the quality and the better the piece the more you are going to pay. It all depends on what level you want to play.

andyf
Guru
Guru
Posts: 1230
Joined: Tue Oct 05, 2004 12:55 pm
Location: Oregon
Contact:

Re: How is a carburetor calibrated?

Post by andyf » Mon Aug 22, 2011 9:30 pm

Not too long ago it was basically impossible for an average guy to custom calibrate a carb but these days a sharp guy can get it done. The newer carbs have billet metering blocks which are fully adjustable so you don't have to mill, drill and fill anymore. Add in a wide band 02 setup and your average Joe can now sort out a carb if they pay attention to what they are doing. It is also easier than ever to get lost so a person needs to take good notes and think hard about what changes they are making.

The new Holley Ultra carbs are a good place to start if a person wants to try building their own combination. Those carbs allow you to adjust all of the circuits and they pretty good right out of the box. They usually only require some minor tweaks to get a nice fuel curve on a street/strip type of car.
Andy F.
AR Engineering

Post Reply