weber dcoe Venturis as orifices,does anybody knows their cfm

[mc-racing]

Hi,

I'm new here...
My name is Max and i live in Austria and i'm restoring an 73' Alfa Gt Junior for historic hillclimbs .
I want ot build a flowbench easy and cheap.

My idea is to use the internal venturis from Weber 40 dcoe carbs instead of orifice plates, because they should be relativly equal all over the world and they are nearly everywhere available. For example i have 27mm, 30mm and 32mm here in stock...

What do you think about this idea?

Please, does anybody has some Weber venturis around and could post some flowdata of this ?

Or if the Venturis are not usable for mesuring, maybe they are good enough for calibrating a flowbench with orifices?



Best Regards
Max

...sorry if my english is bad...

[1960FL]

Max,

Not a real good idea especially if you are trying to work toward some form of standard flow. I suggest you read the Flow Bench 101 thread under Flow Bench General, read specifically the section on Ratio Metric Design. This design is simple, accurate and repeatable; there is no BLACK ART to making orifice plates and or CALIBRATION plates. The real issue is when comparing your flow bench to another flow bench the comparison is based on a known standard (your calibration plate).

Bruce will probably scold me for this but if we were building the very first DIY orifice flow bench we would not have a source for orifice or calibration plates. Thus we would have to make them ourselves. None of the plates used here by the guys on the forum are NIST traceable (Except maybe one, million dollar bench, haha).

So if you were to use the formulae found here on the forum to calculate “flow through an orifice” you will have a good start. These plates can be made as accurate as a CNC lathe can make them or in the beginning, with a simple hole saw on your drill press. Working toward a solid understanding of CD is most important here as this will make your hole saw plates as accurate as possible for the given machine work finish. The key is that you always calibrate to the same plate (your calibration plate) no matter who’s flow bench you are using.

Remember, in actuality the fact that the flow bench can interpret air flow into a value is as big a benefit as it is a hindrance. The real purpose first off is to measure improvements in your work (Comparator) these numbers could be interpreted in simple ratios like “I increased flow by 10%” once we start looking at MAX FLOW numbers we begin to compare ours against everyone else’s; Not that this is a bad thing but it often muddies the water and or causes us to lose focus as to why and what we are doing to the cylinder head or device we are flowing.

Last I would also suggest you read the old forum thread from Steff_1 it will answer many questions and has some great information on CD and pinning down your plate CD based on regression testing.
http://www.tractorsport.com/cgi-bin/for ... ;t=58;st=0

Enough for now,

Rick

[mc-racing]

Hi Rick,


Thanks a lot!

A friend offered to make orifices for me on his cnc, he usually constructs little Star engines on the scratch for his RC-Planes, so this things should be very accurate machined.

The link doesn't work for me because i was not registrated in the old forum.....i got this as answer:

Ikonboard Message
You do not have access to this forum. Are you logged in?

You are NOT logged in

Best regards

MAX

[1960FL]

Max,

PM Bruce your login information for the new forum so he can set you up to read archives on the old forum well worth it alot of information there

Rick

PS.. Orifice plates realy do not need to be done on a CNC but i guess Smoke em if you Got em!

[Brucepts]

Max,

PM Bruce your login information for the new forum so he can set you up to read archives on the old forum well worth it alot of information there

Rick

PS.. Orifice plates realy do not need to be done on a CNC but i guess Smoke em if you Got em!

LOL that's for sure . . . as mine are machined manually on an old circa 1919 18x48" belt drive lathe

[JONATHAN]

Hi Max

I am also building a alfa GT Junior for historic track racing with a 2liter motor +/-210 hp.
I have a lot of head flow data if you need.

thanks
Jonathan
South Africa