Measuring CFM's after port/muff job

[CHEVYTOWN13]

Is there a way to measure exactly how many CFM's the carb is running after a port and muff job?

I'm trying to figure out ways of measuring but it's all "grass roots" ideas. I've tried searching around at the library/internet and no go.

 

[Banshee]

http://cgi.ebay.com/TSI-VelociCheck...ptZLH_DefaultDomain_0?_trksid=p3286.m20.l1116

I have one of these. It's accurate to +/- 5 percent. You can hold it in front of the exhaust port or in front of a carb (but you have to have the filter off) and it will tell you how fast the air is moving in feet per minute.

It will also read the air temp up to 200 degrees.

I wish I would have took a reading of my stock 372xp before mods and a reading after. Too late now.

 

[CHEVYTOWN13]

Cheers brother.

Now you got me burning the midnight super midnight oil!!!

Thanks Banshee. My grass roots idea consisted of reflective tape on some sort of wheel and measuring it with the exhaust at WOT. Then I was going to look for a formula, but hell, that link is the ticket.

I owe you one.

 

[Banshee]

I changed the link to one on Ebay. If you need to measure a dual port, you'll have to measure both ports and do some math.

Even with a single port if you want an accurate reading you will have to figure out the wind speed and size of the exhaust port and do some more of that fancy math.

Example if you are getting say 3000 fpm with stock exhaust and then widen you port 20 percent you still may be getting 3000 fpm but you are moving more air because the opening is wider. So I'm sure there's some way to figure it out mathematically how much you have gain.

A more accurate way would be to take a reading at the carb. If your using the same carb then more air coming though the exhaust would mean more air coming into the carb.

You maybe able to find one of these meters cheaper at a heating and air supplier. Heating and air guys use these kind of meters.

 

[CHEVYTOWN13]

10-4

Finding the formula will be the fun part.

Cool beans bro.

 

[ShoerFast]

Just a side line to your task....

Timing cuts in known wood and plotting the results will give you a very good idea of performance. Flow under load will show up on a stop watch.

 

[CHEVYTOWN13]

Just a side line to your task....

Timing cuts in known wood and plotting the results will give you a very good idea of performance. Flow under load will show up on a stop watch.

Flow Under Load--what else would play a part aside from the carb and filter to improve times(flow). Carb work? Edit: minus porting and muff mod

Edit:
I'm thinking of modifying the airfilter and using material from an ITG air filter.

 

[Nitroman]

Professionals use a flowbench.

 

[timberwolf]

I'm no chainsaw professional, but do find my homebrew flowbench measures CFM quite nicely.

Usually flow benches are hooked up to a fan bank of some sort to directly flow test each component, I use a large variable speed shop vac, but it works quite well just to use the intake from the saw to pull air through the bench creating a pressure drop over a calibrated orifice that can be used to calculate the real CFM the whole motor pulls.

Another way to figgure CFM for a saw is for test the air filter and develop a flow curve, then measure the pressure drop under the filter to get CFM, more front end work to test the filter, but then less hooking up after.

Ideally there should be a setteling chamber right at the saw to minimize how much the hose from the saw to the bench becomes a resonant factor in the intake. If the hose starts to act like a runner or velocity stack the saws output will be affected. Alternativly a large hose between motor and flow bench can be used to keep the air velocity down and minimize the effect of inertia.



Here is the flow bench I built, have all the stuff and software to hook it directly to computer, just need some time to mess with it.

 

[CHEVYTOWN13]

Professor TW in Grass Roots 101

Now you know why I show up to this guy's classes...

 

[CHEVYTOWN13]

Computers are cool factors...

Here is the flow bench I built, have all the stuff and software to hook it directly to computer, just need some time to mess with it.

This is directly quoted from another site I frequent.

"I have a crazy idea to use the module I use to tune the TBI on the L6 to see if the program will read the firings of the 2stroke on the chainsaw. I'm not sure how I'm going to do it, but it would be cool to see what the fuel delivery is, timing, what the ACTUAL rpm is for every single ignition firing(13,500, in some cases over 15,000 readings of data in one minute!). The ultimate in tuning. Not sure how much can be done with a carb though.

I will admit the L6 had more ponies when it had the Holley 390 4 barrel as compared to the 500 TBI carb it has now."

Right now a buddy of mine who's profession is messing with chips and the like is working on it. We're getting numbers to show up on the screen but we're not sure what it is reading.

He thinks that it might not work, but you never know...

Rick

EDIT: FORGOT TO MENTION I WELDED A BUNG AND ATTACHED THE SENSOR ON A SEARS JUNKIE'S MUFFLER