thinking of building or buying a flow bench?



thinking of building or buying a flow bench?

Postby grumpyvette » October 8th, 2008, 8:57 am

flow bench & porting links you might use

Image

http://www.cfmperformance.com/cfmproducts/flowbenches

http://www.flowbenchtech.com/plans.html

http://www.flowperformance.com/system.html

http://www.superchevy.com/how-to/engine ... w-testing/

http://www.superchevy.com/how-to/engine ... omparison/

http://www.flowperformance.com/flowbench.html

http://www.flowperformance.com/shopvac.html

http://flowperformance.com/basic25.html

http://www.4cycle.com/karting/html/flow_bench.html

http://www.watermanracing.com/flow_bench.htm

http://www.flowperformance.com/

http://www.pontiacpower.com/FlowBench.htm

http://www.gofastnews.com/board/technic ... bench.html

http://ljs.academicdirect.org/A14/031_049.htm

http://www.waekon.com/PS/ocifb/technical.html

http://www.performancetrends.com/pfa.htm

http://www.performancetrends.com/ez_flow_system.htm

http://www.mercdog.com/motorsports/68_flowbench.html

http://www.diyporting.com/flowbench.html

http://www.performancetrends.com/ez_flow_system.htm

http://www.aces.edu/~gparmer/articles/flowbench/

http://www.chevyhiperformance.com/techarticles/95518/

http://www.sa-motorsports.com/diyport.shtm

viewtopic.php?f=52&t=10602

http://victorylibrary.com/mopar/bench.htm

http://www.fordmuscle.com/archives/2006/12/MakingMolds/index.php

http://www.diyporting.com/molds.html


1) open throat to 85%-90% of valve size
(2)cut a 4 angle seat with 45 degree angle .065-.075 wide where the valve seats and about .100 at 60 degrees below and a .030 wide 30 degree cut above and a 20 degree cut above that rolled and blended into the combustion chamber
(3)blend the spark plug boss slightly and lay back the combustion chamber walls near the valves
(4)narrow but dont shorten the valve guide
(5) open and straiten and blend the upper two port corner edges along the port roof
(6) gasket match to/with intake and raise the port roof slightly
(7) back cut valves at 30 degrees
(8) polish valve face and round outer edges slightly
(9)polish combustion chamber surface and blend edges slightly
(10) remove and smooth away all casting flash , keep the floor of the port slightly rough but the roof and walls smoothed but not polished.
(11) use a head gasket to see the max you can open the combustion chamber walls
(12) blend but don,t grind away the short side radias




http://www.eecis.udel.edu/~davis/z28/buildup/plenum/

http://www.babcox.com/editorial/us/us110128.htm

http://www.diyporting.com/Shrouding.html

http://www.babcox.com/editorial/ar/eb120121.htm
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


Re: thinking of building or buying a flow bench?

Postby grumpyvette » December 7th, 2010, 5:13 pm

Article by Will Handzel in Circle Track magazine

GET IN THE KNOW ABOUT FLOWBENCHES.

How a Flowbench works Flow Numbers

bullet
Racing is a competitive sport that requires much more than superior mental and physical ability on the track. Having a race car, or for that matter, an engine, that is developed to its ultimate potential for that class of racing can make an OK driver look great and a good driver untouchable. This is why teams in the top forms of racing have engine departments that are constantly developing and testing engine components and engines for more power and durability.
bullet
One piece of equipment that is required in these engine shops is a flowbench because it can help an engine department document whether changes in the combustion chamber, intake, and exhaust tract improve the ability of the engine to get more of the air/fuel mixture in the cylinder and therefore make more power. Because flow-benches are used by race engine shops across the country this article shows how a flowbench works, how most engine development people test with a flowbench, and how to interpret the flow numbers to help you become a more educated customer and a more successful racer.

HOW A FLOWBENCH WORKS
bullet
A flowbench measures the resistance of airflow through a passage by either sucking or blowing air at a specific pressure through that passage. On intake tract passages like carburettors, intake manifold ports, or cylinder head ports, the air is drawn through the passages into the flowbench, while on cylinder head exhaust ports or headers, air is blown out of the flow-bench. The pressure of the air flowing through a part is measured in "inches of water" on a flowbench. This is measured on a manometer, often called the test pressure meter and resembling a large thermometer. It is filled with a coloured fluid and placed vertically with the lower end open to the atmosphere and the upper end attached to the cavity at the base of the test fixture.
bullet
With the flowbench turned off, the test pressure meter should read zero, but when the blower motor is turned on, the fluid will rise up the meter, which has gradations spaced an inch apart-thus "inches of water." The number of inches the fluid rises up the meter correlates to the lack of pressure, commonly referred to as vacuum, in the space below the test fixture. A control on the flowbench, called the flow control knob, opens and closes a valve that will vary the pressure differential or "inches of water" across the port being tested. An inclined manometer, called the flow meter, is used to determine the percentage of flow the passage being tested allows. By changing the size of the opening, called the orifice plate, between the passage being tested and the blower, the maximum quantity of cubic feet per minute (CFM) of air that could be flowed through that part can be altered. The flow meter has one of its ends plumbed to the cavity area just below the test fixture, and the other end plumbed to the cavity below the orifice plate but before the flow control plate, which is attached to the flow control knob. The pressure differential is represented on the flow meter in percent of flow.
bullet
If you were testing a bad-flowing passage you would get lower percentage numbers, while a good-flowing passage would have higher percentage flow numbers. Multiplying the percentage flow times the maximum flow for the orifice size at which you are testing (which is determined for that orifice and provided with the flowbench), you can determine the actual amount in CFM of air that passage flows. With the head bolted to the Flowbench and the 'valve installed with a light spring, a valve actuator is needed to open the valve a specific amount for each test point. This is just a threaded bolt with a dial indicator that rests on the valve so that when the valve is opened by turning the bolt, the dial indicator reads the amount the valve opens.
bullet
Flow-testing is usually done at 0.100, 0.200, 0.300, 0.400, 0.500, 0.600 and possibly 0.700-inch valve openings. Some people test at closer intervals but usually these intervals suffice. Before the test on the intake port is run, the net valve area must be determined. The valve is in the head because that is the way the engine will be run. The air/fuel mixture must flow around the valve so the testing with air must be done with the valve or else the flow numbers are completely useless.
bullet
To calculate this, use this equation: Net valve area (in2) = 0.785 [(diameter of valve ) 2 - diameter of stem ) 2 This is the actual opening at the end of the port and by referring to a chart you will know what CFM setting the flowbench should be set at to perform the testing. That port and valve area combination should be tested at the same CFM every time so that the data can he related to each other. To begin a test, open the valve to the predetermined lift, turn on the blower, open the intake flow valve to set the test pressure, and read the percent flow. Record this. To determine the CFM flowed, multiply the percent flow times the max flow setting the flowbench was set at. Repeat this on all the lifts for that combination.
Top
WHAT THE FLOW NUMBERS MEAN IN THE REAL WORLD
bullet
Put simply, flow numbers provide a representation of what the passage would do in a running engine. When comparing flow figures for a carburetor, intake manifold, cylinder head port, or whatever, don't just look at the CFM of air the part flowed and compare that to someone else's testing without knowing what test pressure (inches of water) the test was conducted at.
bullet
Often, purposely or not, CFM numbers will be compared, and the higher CFM number was tested at a higher test pressure (which will provide higher CFM numbers). To correct test pressures, multiply this conversion factor times the flow figures you wish to convert to a different test pressure. As long as you are comparing apples to apples, the data will help you make an educated decision, if you compare apples to oranges (data from different test pressures), you are going to make a poor decision that probably won't get you going faster.
bullet
While flow-testing can be very helpful in determining what modifications will allow more air and fuel to enter the combustion chamber and the spent gasses to escape in the same amount of time, the engine should be tested on the dyno and/or the racetrack to determine whether the changes really work. The flowbench is testing airflow at ambient conditions not the air/fuel mixture the engine is fed at. Temperatures vary everywhere from freezing to 1200 degF so other engine variables should not change the actual flow.
bullet
Flow numbers are used daily to provide insight into what is occurring inside an engine. While there has been a lot of testing and scientific papers written on airflow, most engine builders or head porters rely heavily on experience with testing stock and modified components to determine what improves performance and what doesn't. That might sound foolish, but in a very competitive atmosphere where any gain is critical, information that can make you power is very valuable. As a customer, you should be able to get a straight answer to a question regarding flow figures and why a component is improved because of flow testing.
bullet
Hopefully, this basic overview of flow-bench testing and the data gathered from that testing will help you go faster at the races.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby grumpyvette » December 7th, 2010, 5:20 pm

David Vizard

OK so you have built the budget flow bench detailed in part 2 (http://www.gofastnews.com/board/tech...low-bench.html ). While this may allow you to establish if you have made a move that helps or hinders flow it does not allow you to compare your efforts with the rest of the world (or at least most of it). Within reasonable limits we will look at a simple, low cost, method to fix that.

When I was using the flow bench described in Porting School #2 I never made the connection between using a floating pressure drop and actually calibrating the setup to give CFM. Instead I built a monster of a bench to British Standards with all the corrections then known to man. It is not a job that I would recommend to other would-be porters/cylinder head development engineers. Your time is better spent on developing heads and selling what you are producing. Doing otherwise means investing what is potentially a huge amount of time and effort and, for that matter – money – in a bench that at the end of the day serves you little or no better than one built along the lines described in part #2.

So my recommendation here are build a bench as described in part #2 and if you are looking for more in the way of performance from the bench just build it bigger and with more powerful motors.

But let’s get back to reading out our results in CFM. Here’s where the revelation came in. For many years I knew my good friend Roger Helgesen had a flow bench but the deal here was we always hung out at my place (maybe that’s because the Serdi seat and guide machine was there). But one day I found myself over at his house where he had his flow equipment, porting bench and tools. What an eye opener that was. If ever there was a guy that could come up with ultra simple ways of doing ultra complex jobs it’s RH. (another good friend of mine, Steve Dulcich, the editor of Engine Masters magazine christened Roger ‘Dr. Air’ and I always thought that to be a very appropriate moniker). What really caught my attention here was the calibration plate Roger had made up and the graph he was using to simply read off the CFM at 28 inches of depression. The plate is shown below along with the dimensions to produce it. The size of the holes in it are such as to flow 5,10,20,40 80 and 160 cfm at 28 inches of depression across the plate. Not only can you use this plate to figure out how much flow is passing through a head on a floating depression bench but also it can be used as a reference tool for a regular bench such as a Superflow.



These holes need to be machined with a very smooth surface. As for tolerances make them as accurate as possible (+/- 0.001 is acceptable) The hole sizes and X-Y co-ordinates are:
Hole 5:- 0.210 Dia. on 4.30/3.40 inches. Hole 10:- 0.296 Dia. on 3.95/4.10 inches. Hole 20:- 0.419 Dia. on 3.05/4.30 inches. Hole 40:- 0.594 Dia. on 2.10/3.80. Hole 80:- 0.840 Dia. on 2.05/2.5 inches. Hole 160:- 1.185 Dia. on 3.70/2.40 inches. Radius entry for all holes is 0.25 inches. This is machined such that the edge of the radius goes out to 80 degrees not the full 90. The back of the 5 and 10 size holes must be chamfered with a 90 degree cutter. For the 5 hole the chamfer should be 0.460 diameter and for the 10 hole 0.546 diameter.
For details on making an accurate calibration of a bench be sure to read the main text fully.

A few words about producing/acquiring a Helgesen plate. With Roger’s kind permission I have put up dimensions here so you can produce your own. The intent was not that a GFN reader would go into production with these and sell them as after all it’s RH’s idea and just out of political correctness I would ask you respect that. If you are not in the position to make one then, if the demand is there for say 20 or more, RH will sort out the manufacture of them and sell you one.



Seen here are the calibration plates we use to check our bench. These plates have been run on an accurate bench and so have odd numbers for the holes such as 161.5. With this setup we can calibrate our bench up to 480 cfm at 28 inches.


Let us assume at this point you have a plate – how is it used to give cfm at 28 inches? Here is how that is done. First make sure your bench is sealed up so no leakage will take place except through the test piece. Position the Helgesen plate on the bench with all holes plugged with clay (or any convenient plugs). Next start with a reading on the manometer with the plate completely blocked off for a ‘zero flow’ depression test and note the pressure drop seen on the manometer. Note this stalled depression. (if you did not make your manometer tall enough the vacuum cleaner will have now drunk all the water from it!) Now open the 5 cfm orifice (note – when I was talking about machining this plate they were referred to as holes – now we are flowing through them they are orifices!) and note the depression seen. Next plug the 5 cfm orifice and open the 10 – flow test and note the depression, next open the 5 and 10 cfm orifices together and again, note the depression. Keep going here in 5 cfm increments until all the orifices are open and you have recorded the depression at each 5 cfm increment.

Now go and get yourself a couple of large sheets of graph paper. The larger the better here. I recommend something in the order of 20 x 20 inches. Now for the intake, make up a graph as shown below.




To read CFM off this chart look up the depression on the left hand scale and go across the chart until you intersect with the red line. Drop down the chart and the bottom scale gives you the CFM at 28 inches. Remember the scales on your graph will be different to this example shown here.


If you plot out your results you should get a curve such as that seen here. Where it starts and finishes will be totally dependant on the vacuum/pressure source. Once you have a curve for the intake repeat the test but using the blower side of the vacuum cleaner and the plate reversed. Now blow through all the holes in the same progression used for the intake and make up a graph for the exhaust. At this point you can now flow a head and get some respectably accurate flow figures for comparative purposes.

Accuracy – How good?

Although what we have done here is very basic it can produce results comparable to benches costing ten grand and considered the industry standard. However there are many points at which errors can creep in and considerably reduce the accuracy of the results.

Let’s start first with leakages. For the numbers to stand even a half way decent chance of being right the bench must not leak at any point. The only leak that can be present is the item you are flow testing.

The amount of suction a vacuum cleaner or any electric air mover can produce is influenced by the voltage input to the motor. You must monitor the voltage at the motor input and make sure you test at the same voltage each time. For the record RH (Dr. Air) has a step up transformer that puts the line voltage up from whatever it may be (it varies between 110 and 115) to 130 volts and then a rheostat device is used to adjust it to 115 volts.

The way the plate is mounted on the flow bench also effects the reading it produces. The ideal situation is to mount a box about 9 inches down each side (9x9x9) with a 5 inch hole in the top and whatever size hole mates up to the block or whatever you are using to simulate a block. The calibration plate is then placed directly over the 5 inch hole in the box and flow tested. If the plate is mounted on top of a bore even as large as 4 inches there will be a residual effect from the down stream velocity of the air and the plate will produce numbers that are 2-3% higher than if flowed into an open box.

Big changes in temperature and pressure will also affect the reading but this will only be minor if the bench is in a constant temperature indoors. If there is any doubt about the figures recheck the depression with the plate at say 160 cfm. Using this reading correct the numbers up or down by whatever percentage error was seen.

Be aware the best accuracy is seen when the depression falls between 160 inches and 15. If at high valve lifts the depression drops much below about 10 inches you can figure that when corrected they could read higher than they should. Just how much is dependant on how sever any flow break away that occurs is and at what pressure drop it starts to happen.

Summary

Lets assume you are not in a position to make your own Helgesen Plate. where would you get one? Fortunatly a source has opened up here. I seems that Bryce Mulvey of Dr J's Performance and Roger ‘Dr Air’ Helgesen have teamed up and Dr J’s Performance will be selling all of the Helgesen developed porting tools. For more info check out their site as per below. If you have any enquiries email them at: sales@dr-js.com

Dr J's Performance, 436 Montgomery Street, Orange CA 92868 Tel: 714-943-3404 Fax 714 -527-2769 Dr J's Performance - Dr. J's Performance - Home email

What you have at this point is a bench that is both cheap to build and can deliver CFM numbers. The next step for an upgrade here is to write an Excel program that does the number crunching for you. I have a program that I am currently updating that will allow you to input the depression numbers into your PC and produce a professional looking chart of the flow tests. That’s still a ways of and is very work load dependat for a finish date. but if you are interested watch this space (as they say).

But let me ask a question here. How would you like to upgrade what we have built here with an electronics package that, for under about 700 bucks, will allow your bench to read out in corrected CFM and directly integrate with your computer so you can do fancy print-outs? Sound good? (Yeh - almost too good to be true.)This story is in the works right now and will be the next installment of GFN’s Porting School

David Vizard
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby grumpyvette » June 8th, 2011, 7:28 am

http://www.cfmperformance.com/cfmproducts/flowbenches


Image

Sportsman 400 model features:

400cfm capacity at 28” of water
110V powered
Portable, compact design
4 - 112cfm Ametek vacuum motors
Ready to use right out of the box
Stainless steel testing surface
Quality materials and construction
Accurate and repeatable to + or - 0.5%
Audie Technology averaging velocity tube
Digital read out with no complicated manometers
Dual flow directions to test both intake and exhaust
Fully computerized with automatic depression control
Data logging software available, PC and laptop compatible
Cylinder head adapter, valve opening fixture, and radius entrance included

Complete test system $2499
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby grumpyvette » June 8th, 2011, 7:53 am

Article by Will Handzel in Circle Track magazine

GET IN THE KNOW ABOUT FLOWBENCHES.

How a Flowbench works Flow Numbers

bullet
Racing is a competitive sport that requires much more than superior mental and physical ability on the track. Having a race car, or for that matter, an engine, that is developed to its ultimate potential for that class of racing can make an OK driver look great and a good driver untouchable. This is why teams in the top forms of racing have engine departments that are constantly developing and testing engine components and engines for more power and durability.
bullet
One piece of equipment that is required in these engine shops is a flowbench because it can help an engine department document whether changes in the combustion chamber, intake, and exhaust tract improve the ability of the engine to get more of the air/fuel mixture in the cylinder and therefore make more power. Because flow-benches are used by race engine shops across the country this article shows how a flowbench works, how most engine development people test with a flowbench, and how to interpret the flow numbers to help you become a more educated customer and a more successful racer.

HOW A FLOWBENCH WORKS
bullet
A flowbench measures the resistance of airflow through a passage by either sucking or blowing air at a specific pressure through that passage. On intake tract passages like carburettors, intake manifold ports, or cylinder head ports, the air is drawn through the passages into the flowbench, while on cylinder head exhaust ports or headers, air is blown out of the flow-bench. The pressure of the air flowing through a part is measured in "inches of water" on a flowbench. This is measured on a manometer, often called the test pressure meter and resembling a large thermometer. It is filled with a coloured fluid and placed vertically with the lower end open to the atmosphere and the upper end attached to the cavity at the base of the test fixture.
bullet
With the flowbench turned off, the test pressure meter should read zero, but when the blower motor is turned on, the fluid will rise up the meter, which has gradations spaced an inch apart-thus "inches of water." The number of inches the fluid rises up the meter correlates to the lack of pressure, commonly referred to as vacuum, in the space below the test fixture. A control on the flowbench, called the flow control knob, opens and closes a valve that will vary the pressure differential or "inches of water" across the port being tested. An inclined manometer, called the flow meter, is used to determine the percentage of flow the passage being tested allows. By changing the size of the opening, called the orifice plate, between the passage being tested and the blower, the maximum quantity of cubic feet per minute (CFM) of air that could be flowed through that part can be altered. The flow meter has one of its ends plumbed to the cavity area just below the test fixture, and the other end plumbed to the cavity below the orifice plate but before the flow control plate, which is attached to the flow control knob. The pressure differential is represented on the flow meter in percent of flow.
bullet
If you were testing a bad-flowing passage you would get lower percentage numbers, while a good-flowing passage would have higher percentage flow numbers. Multiplying the percentage flow times the maximum flow for the orifice size at which you are testing (which is determined for that orifice and provided with the flowbench), you can determine the actual amount in CFM of air that passage flows. With the head bolted to the Flowbench and the 'valve installed with a light spring, a valve actuator is needed to open the valve a specific amount for each test point. This is just a threaded bolt with a dial indicator that rests on the valve so that when the valve is opened by turning the bolt, the dial indicator reads the amount the valve opens.
bullet
Flow-testing is usually done at 0.100, 0.200, 0.300, 0.400, 0.500, 0.600 and possibly 0.700-inch valve openings. Some people test at closer intervals but usually these intervals suffice. Before the test on the intake port is run, the net valve area must be determined. The valve is in the head because that is the way the engine will be run. The air/fuel mixture must flow around the valve so the testing with air must be done with the valve or else the flow numbers are completely useless.
bullet
To calculate this, use this equation: Net valve area (in2) = 0.785 [(diameter of valve ) 2 - diameter of stem ) 2 This is the actual opening at the end of the port and by referring to a chart you will know what CFM setting the flowbench should be set at to perform the testing. That port and valve area combination should be tested at the same CFM every time so that the data can he related to each other. To begin a test, open the valve to the predetermined lift, turn on the blower, open the intake flow valve to set the test pressure, and read the percent flow. Record this. To determine the CFM flowed, multiply the percent flow times the max flow setting the flowbench was set at. Repeat this on all the lifts for that combination.
Top
WHAT THE FLOW NUMBERS MEAN IN THE REAL WORLD
bullet
Put simply, flow numbers provide a representation of what the passage would do in a running engine. When comparing flow figures for a carburetor, intake manifold, cylinder head port, or whatever, don't just look at the CFM of air the part flowed and compare that to someone else's testing without knowing what test pressure (inches of water) the test was conducted at.
bullet
Often, purposely or not, CFM numbers will be compared, and the higher CFM number was tested at a higher test pressure (which will provide higher CFM numbers). To correct test pressures, multiply this conversion factor times the flow figures you wish to convert to a different test pressure. As long as you are comparing apples to apples, the data will help you make an educated decision, if you compare apples to oranges (data from different test pressures), you are going to make a poor decision that probably won't get you going faster.
bullet
While flow-testing can be very helpful in determining what modifications will allow more air and fuel to enter the combustion chamber and the spent gasses to escape in the same amount of time, the engine should be tested on the dyno and/or the racetrack to determine whether the changes really work. The flowbench is testing airflow at ambient conditions not the air/fuel mixture the engine is fed at. Temperatures vary everywhere from freezing to 1200 degF so other engine variables should not change the actual flow.
bullet
Flow numbers are used daily to provide insight into what is occurring inside an engine. While there has been a lot of testing and scientific papers written on airflow, most engine builders or head porters rely heavily on experience with testing stock and modified components to determine what improves performance and what doesn't. That might sound foolish, but in a very competitive atmosphere where any gain is critical, information that can make you power is very valuable. As a customer, you should be able to get a straight answer to a question regarding flow figures and why a component is improved because of flow testing.
bullet
Hopefully, this basic overview of flow-bench testing and the data gathered from that testing will help you go faster at the races.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby 67chevy » January 22nd, 2014, 8:43 am

thank you so much for this info grumpyvette! ive been doing heads for quite some time now but was limited to mild port work bc i had no way of measuring my results, i simply used basic advice from people such as david vizard and you to get good results without going into unknown territory.now i will be able to probe the ports and learn more a ports characteristics with measurable results. im hoping that this all will eventually get me more port work in my area but the learning experience is the biggest benefit. thanks again! this is great info!
67chevy

 
Posts: 8
Joined: January 20th, 2014, 1:55 pm

Re: thinking of building or buying a flow bench?

Postby grumpyvette » January 22nd, 2014, 9:40 am

I'M ALWAYS GLAD TO HELP WHERE I CAN!
IF YOU BUY OR BUILD A BENCH OR DO SOME CYLINDER HEAD PORT WORK ,POSTING A BUNCH OF clear DETAILED PICTURES WOULD BE VERY USEFUL
By David Reher, Reher-Morrison Racing Engines

“The pursuit of a big cfm number has ruined countless cylinder heads.”

“What’s it flow?”

Whenever a conversation about cylinder heads begins with that question, I cringe. I know where this discussion is going, and it’s not good. When a racer wants to distill the performance of a highly developed cylinder head down to a single number, I know I’m dealing with someone who is fixated on the flow bench.

I can speak from hard-earned experience, because there was a time when the flow bench was the center of my universe. When my partners Buddy Morrison and Lee Shepherd constructed our first flow bench in the ’70s, it was a revelation – or so we believed. We were addicted to airflow, and like three flow bench junkies, we convinced ourselves that big flow numbers translated to quicker elapsed times. But that was more than 30 years ago, and since then I’ve learned to avoid the pitfalls of flow bench testing.

Unfortunately many racers coming into the sport haven’t been taught the lessons that Buddy, Lee and I learned the hard way. Cylinder head manufacturers, porting shops, and engine builders constantly advertise flow numbers – and I confess that I’m sometimes guilty as well. In this environment, it’s understandable that some racers think it’s all about maximum airflow. They shop for the biggest cfm number at the lowest price, like finding a screaming bargain on a 52-inch TV at WalMart.

The strategy to win the “Biggest CFM Contest” is simple: Grind the largest port that will physically fit in the head, use the biggest valves that will fit the combustion chambers, and test it on the biggest fixture you can find. That head might win the prize for airflow, but it won’t win on the dyno or on the race track.

The factors that determine the performance of a cylinder head are complex. A head that is ported without considering air speed, the size of the engine, the rpm range, the location of the valves, and a dozen other parameters isn’t going to be the best head, regardless of its peak airflow. And yet I see racers who are seduced by big cfm numbers bolt a pair of 10,000 rpm cylinder heads on a 7,000 rpm short block and then wonder why the engine won’t run.

The most critical area in a competition cylinder head is the valve seat, and the order of importance works its way out from there. There are many questions that are much more important than airflow: How far are the valve heads off the cylinder wall? What’s the ratio of valve size to bore diameter? What’s the ratio of the airflow to the size of the valve? What’s the size of the port, what’s its taper, how high is the short-side radius? The answers to these aren’t as simple as comparing a flow number, but they are what really make a difference in an engine.

Airflow is simply one measurement among many that influence engine performance. With the availability of affordable flow benches and computer simulation programs, it’s easy to fall into the airflow trap. A builder works on a cylinder head, sees some bigger cfm numbers, and keeps working for more flow. But if he doesn’t stop and test the engine on a dyno and on the drag strip, it’s very likely he’s gone down a blind alley. What the manometer on a flow bench sees at a steady 28 inches of depression is not at all what the engine sees in the real world. The pursuit of a big cfm rating has ruined countless cylinder heads in terms of what will actually run on an engine.

I put more faith in dyno pulls and time slips than I do in flow benches. I’ll cite an example from back in the day when Buddy, Lee and I were winning Pro Stock championships. Lee came up with an idea for a tuliped exhaust valve. He filled in the back of the valve with Bondo, and tested the new design on our flow bench. It was killer. We instantly saw a tremendous improvement in airflow with a small exhaust port, a nice tight radius below the seat, and much more stable flow. So we had some titanium tulip exhaust valves made and tested them on the dyno – and the engine didn’t run well at all. We had great airflow on the bench, but the engine didn’t care.

We were working late one night, and Buddy decided to yank the heads off the block and have Lee open up the exhaust throats. Well, Lee kept grinding and Buddy kept taking the heads on and off, and eventually we picked up 30 horsepower that night. We were porting from the dyno and not from the flow bench. When Lee finally flow tested the heads the next day, they were down 30 or 40 cfm, but that’s not what that engine saw.

The final test of a cylinder head is on the track. Frank Iaconio was our chief Pro Stock rival, and he was a smart racer. Frankie used to change valves at the track — he’d make a run, come back to the pits and switch from valves with a 30-degree back angle to a 20-degree back angle. We did similar tests on the dyno, but he did it at the track. I was impressed.

I’m not dismissing flow benches. In fact, we use them daily at Reher-Morrison Racing Engines. But a flow bench is a tool, and it’s really not much different than a micrometer. A micrometer can measure the diameter of a piston, but you have to run the engine to learn the correct piston clearance. Knowing the sizes of the piston and cylinder bore doesn’t tell you if the piston is going to gall or collapse a skirt until you run it. And knowing the airflow of a cylinder head doesn’t tell you whether it will make good power on a given engine until you race it.

Experience is the most important tool in cylinder head development. A person with extensive dyno and track experience has been through it all before, and knows how to avoid the flow bench fallacies.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby 67chevy » January 28th, 2014, 12:53 am

i have some questions. ive literally given myself a headache over the past weeks looking into flow bench design. some things confuse me such as the plenums set up on some benches while others dont use any. this basic looking setup is what i was hoping to build. http://www.flowperformance.com/system.html but it doesnt have any plenums. is this a good design to follow bc it looks easy to build. how will this affect readings compared to a design with a plenum ? im just trying to set up something cheap and easy to build with a water manometer setup until i can afford a digital manometer. sorry if this info is included in this thread but my head is literally spinning after going through so many different design setups to determine the simplest and most accurate bench for my requirements. this setup is said to be good for engines around 100hp per cylinder which is plenty for my needs.
67chevy

 
Posts: 8
Joined: January 20th, 2014, 1:55 pm

Re: thinking of building or buying a flow bench?

Postby grumpyvette » January 28th, 2014, 10:08 am

adding a plenum reduces air flow turbulence and acts like a cushion, when you make changes so you in theory should get a more consistent and easily repeatable reading and in theory slows rates of change in flow,but should not change readings, you could easily modify that design to include a larger plenum, if you decided too at some point.
please take lots of pictures , of parts and stages of construction,and post part numbers of all the parts you use if you decide to build a flow bench!
links to any related computer software and bench building experiences ,plus any accessories you find useful would also be helpful
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida

Re: thinking of building or buying a flow bench?

Postby 67chevy » January 28th, 2014, 2:04 pm

thanks grumpy, im definitely going to take pics when i get down to construction. right now i have alot going on and im trying to get my shop in shape before i really get into the build. i already have a bench i use for grinding that could be converted to a basic comparator bc of the size of the motor on it, i just used a filter in between the grate and motor when grinding. its a little weathered from being in a bad area of the shop but still functional. ill take pics of that soon, my ex-gf's father built it for me years ago. i definitely want to share all of the steps in the process of this build bc i understand how hard the concept of building a flow bench seems when you first start looking into it without knowledge of how it works exactly. hopefully that will help others
67chevy

 
Posts: 8
Joined: January 20th, 2014, 1:55 pm

Re: thinking of building or buying a flow bench?

Postby philly » January 28th, 2014, 8:32 pm

+1 in for pics....
-phil

There's never enough money to build it right, but there's always enough to build it twice!
philly

User avatar
 
Posts: 1364
Joined: December 12th, 2013, 4:08 pm
Location: Miami FL


Return to Shop Plans, and some larger shop tool related info

Who is online

Users browsing this forum: No registered users and 2 guests

cron