Tractorsport Flowbench Forum Archive

Posted: **Thu Aug 06, 2009 12:39 pm**

[color=#000000]This is an addendum to what I just wrote:
You are looking at velocities in the port. Don't expect great gaines in CFM. And further more don't worry too much about cfm. On my cousins where the peak HP is at 7500 rpm and shift points at 8300 rpm the CFM demand is 325 cfm through the head. Minimum CSA would be between 2.696 and 2.804 square inches. That would give a port velocity of 260 - 270 fps at 28" h2o.

His engine has a radical mechanical roller with 281

Posted: **Thu Aug 06, 2009 5:50 pm**

Thanks for that info. mate! Thats an excellent idea making a rubber port casting, im in very tight with the local engine recon. guys over here (they love it when i walk in to get work done!!) so they 'donate' a variety of u/s cylinder heads to me for free to practice on. I'll scratch around over here for a similar product and give that a whirl!! Funny you should mention i should be more concerned with 'velocities' over 'cfm flow', as my software indicated that the valve efficiency of the DART PRO-1 heads was just above 95% and predicted a maximum 'potential' flow of 167.7cfm @ 10" (100% efficient). If DARTS bench says the heads flow 164.9cfm @ 10" and my bench 'sees' this as 160.2cfm (but really its 164.9cfm), would i be safe to assume that there is very limited 'extra' flow to be found from this valve/head combo or should i just ignore the software? Also, do you know what the best port velocities are at 10" test pressure?

Posted: **Thu Aug 06, 2009 6:04 pm**

I almost forgot, iv been taking my practice heads and getting one of the end cylinders cut vertically straight through the valve guides on both an intake and exhaust valve so i can see the 'true' shape of the ports, valve/port inclination angles and how thick/thin the port walls are (similar to what your doing but far more destructive!!). This would also allow you to measure inside the ports! :;):

Posted: **Thu Aug 06, 2009 7:29 pm**

yes cutting a head is very beneficial and you are very fortunate to be able to do that. I still like the mold as you can trace it straight to the graph paper if you want to.

Here is a spreadsheet that was on the forum that converts velocity 2 ways - from your "H2O reading on your pitot velocity probe and gives you the velocity in FPS at you test pressure and then converts it to 28" H2O velocity.

If you are testing at a test pressure of 10" H2O and velocity probe gives you 6" H2O reading that is 162 FPS at 10" H2O test pressure and that converts to 271 FPS @ 28" H2O test pressure. 5.5" reading on your velocity probe would be 155 FPS at the 10" test pressure and converts to 260 fps @ 28" test pressure.

John

Posted: **Sat Aug 08, 2009 4:49 pm**

Got a question about exhaust testing with my PITOT bench. Im running a Flow-Quick set-up (i will post pictures soon!!) that has the motors after the 'measuring pick-ups' at the very end of the 'flow circuit' which, during exhaust testing, applies heated air to 'both' the 'measuring pick-ups' AND the test item. Conversely a SF-110 pulls cold air through its 'measuring orifie' and heats the air before being applying it to the test item. I realise there is a need for a temp. correction of the SF-110 reading (due to temp. change from orifice to test peice & vice-versa) but if my Pitot bench is applying the SAME 'heated' air across the 'measuring pick-ups' AND the test item, (and exhaust is actually 'HOT' in real life!), why would i need to correct these figures?? Would'nt a 'hot' measurement be more REAL? ???

Posted: **Sat Aug 08, 2009 5:18 pm**

It might work if everything in the flow path (after the blower) was thermally insulated, because all that hot air is going to cool down fairly quickly as it comes in contact with the rest of your flow bench and the test piece. So where do you measure the actual temperature to correct with ?

Drawing in ambient temperature air, and flowing and measuring with that same ambient temperature air, everything remains at the same temperature. That vastly simplifies the while deal.

I suppose a lot depends on the type of blower too. Vacuum motors use the air to cool the motor windings, and they do run very hot. Every electrical watt going into that vacuum motor passes into the air.
A large single blower fitted with an external induction motor does not create anywhere near the temperature rise in the air as a vacuum motor will.

Just one more small detail to ponder I suppose.

Posted: **Mon Aug 10, 2009 3:28 am**

Tony my bench is a Flow-Quick, which uses 2" rigid pressure pipe to connect a 'vacuum motor box' to a large box-shaped test plenum with adaptor (Flow-Quick pick-up is in the middle of the circuit). Would there be much of a temp drop, on exhaust testing, from my motors to the pick-up and test piece?

Posted: **Mon Aug 10, 2009 4:04 am**

Posted: **Fri Aug 28, 2009 10:45 pm**

Johno in addition to this here great site and all it's members, if you want to read great in depth tech about porting heads go to --> http://www.speedtalk.com

tip ( if you don't already know ) go to google and type csa site:speedtalk.com

Posted: **Fri Aug 28, 2009 11:59 pm**

John is the trial size of the Smooth On @ enough to do a intake 95 cc and exhaust port 73cc ??? thanks for the tip

Posted: **Sat Aug 29, 2009 1:22 am**

Posted: **Sat Aug 29, 2009 11:04 am**

Thanks John

Posted: **Sat Aug 29, 2009 1:26 pm**

btw I think there is an online calculator at that website to help calculate how much you need.

John

Tractorsport Flowbench Forum Archive

Best way to flow exhaust ports?