The Flowbench thread.

The first Perspex tube arrive today - I will now complete the fixture so I can test the Honda head flow.







Also did the final bit of IDF type testing with the flow test of the 45 IDF style throttle body - This really stretched the bench and brought up on of those anomalies that crop up with testing - with Four motors I could get 10" depression and the comparaitive value at 28" was 335 CFM - however when I tested at the full 28" - requiring 7 motors ! - I think some of the smaller motors are a bit weak to be honest - the flow dropped off to 310CFM I did get some flow back when I messed about with a larger radius of the bellmouth - but somewhere at the higher flow velocity something is changing.

The Strato's Honda C27A special brew - grasstracker IDF manifold got some work carried out on it by RBE to open it out and reshape it to accommodate the 44mm IDF's that I bought and today I dropped it on the bench quickly to see if we made much in the way of gains.

If we summary the previous tests the original flow from the grasstracker carbs and bodged 32mm chokes was 185 CFM and at most 188 with the choke horns.

When fitted with the 34mm chokes and horns the flow lifted to 204CFM and then when fitted to the manifold it dropped to 196CFM - a decent enough gain all the same.

I suspect there would have been losses with the 32mm 188CFM original carbs dropping a few CFM on the manifold maybe 5CFM to 183CFM as an initial benchmark.

The 44mm on the manifold giving a final result of 206 CFM on the unported manifold

44mm IDF open on the bench - max flow - 253CFM

40mm IDF + 32mm Chokes Stock manifold - 183CFM - estimated
40mm IDF + 34mm Chokes Stock manifold - 196CFM - Measured
44mm IDF + 36mm Chokes Stock manifold - 206CFM - Measured

Ported manifold on the bench raw



I did not run the bench up to full 28" capacity today - I just used a 10" drop and a comparative calculation

Open manifold reference figure - 240CFM open



Bolt on the carb open up the throttle and let it rip





44 IDF + 36mm Chokes Ported Manifold - 222CFM Measured

The manifold mods have picked up 26 CFM

So from the start point of 183CFM we are now at 222CFM an increase of 39CFM or 21% flow gain.

I suspect that the total flow available will be greater than the 222CFM as the fixture I made does not enter the bench at the correct angle - I will open the fixture up to remove a step and then look at the flow again - there could be a few more CFM available but as we only have 253CFM from the carb available to us the gains would not be dramatic and for comparative flow the same restriction would have been there for the other carbs tests but due to the lower flows the restriction may not be so significant.

Better start looking at getting a head on the bench.

We are pretty pleased with the reward for the effort.

Had a bit of time so spent an hour on the flowbench redoing a few tests on the Honda manifold. The adapter plate for the bench was only quickly drilled straight through at for the initial testing and was not quite the right profile/angle for the manifold so I took a carbide to the MDF and shaped it to remove a large step in order to give a better representation of the head/port.

I also note above that I did not test the manifold with any radius - just the hard edge when I tested the flow at 240CFM.


I stuck the 200CFM cal plate on and did a quick test to check the bench settings



Fitted the manifold - and did an open test and the new adapter upped the flow to 256CFM.

A full radius around the inlet increased the flow further to 284 CFM





With a 44 IDF fitted at what the flow had increased significantly from the 222CFM @ 28" measured on the original adapter shape.





Because its a different adapter this is not a comparison flow in regard to any modifications because if I had used this adapter in the first instance all of the flows would have been higher - What it does is give a final flow figure for the complete assembly of 236CFM @ 28"

Exhaust is another aspect that feeds the system - it all needs to work together to delivery the best outcome.

It has been a bit of a while since the bench was powered up and the laptop that runs the software is really getting pretty old - Windows 2000 ! - connected up the power and familiarised again with the set-up.

Popped a 200 CFM calibration disc on and set the bench at 10" - with a 28" comparison setting








Four motors on a minimal setting





A few willing test subjects were gathered from the shed.




45 DC0E with 36mm chokes
40 Weber ITB
CD 125 Stromberg
CD 150 Stromberg

I will also go grab a 40 DHLA to see how it compares with CD150








Just need to make a couple of bench adapters.

I was getting a bit too much variance on the bench so got some assistance with a well overdue calibration.








It was getting a bit late to do any test runs at high depressions so that will have to wait for another day.


Next task is to make a mount jig for an Imp manifold to see just how much it flows.

Whilst doing the testing on the K ITB I figured it was worth spending the time to modify one of the mount plates for the Webcon DCOE style throttle body to see what that flows.








Tested without a radius first as it has a nice large taper into the body - then for a bit of fun I dropped a F1 DFV trumpet onto it to see what it did. I have been given a few of these as they are not to the regs as they are oversize - therefore they did not get finished and the injector boss welded on the side.




A bit of parcel tapes holds it on and covers the hole where the injector boss should sit








As the trumpet picked up flow I then did flow with a radius





Figures @28"





Due to the generous taper there is not a huge gain with the stack or the radius - less than 2% but its a gain.



They flow pretty well - I will drop a DCOE 45 on next for a comparison