12 replies to this topic

[danie garry]

hi all, just a quick 1 looking for a lil help! i'm writing a thesis on the investigation and improving the air flow the the a-series cylinder head so if anyone can give my any info or links to any relevant info it'd be great! this is obviously being done so i can get as much info on porting and polishing and all that stuff so i can do my own cylinder head along side the paper. kinda looking for the inlet and exhaust dimensions for say an 850 head and a 93 spi cooper 1275 head too if anyone has em to hand, could measure them but the heads are a hundred miles away!
thanks for what ever help ye can give me!

Edited by danie garry, 22 October 2012 - 07:39 PM.

[R1minimagic]

Get a copy of the yellow bible, that will tell you everything you need to know!

[danie garry]

Get a copy of the yellow bible, that will tell you everything you need to know!

ordered from amazon!
have to somehow determine the roughness off the ports and the effects of the polishing etc....any ideas?!

[Ethel]

The grade of abrasive used to produce them?

You might get a comparison from measuring the static friction limit with a soft control piece - push a little rubber ball with a spring & measure the compression. Or maybe time a drop of oil running along the surface? Replicating the test conditions will be the tricky bit.

That's actually a pretty complex subject, for starters there are 2 different (inner, outer) ports of both inlet & exhaust and a stack of variables: valves (size & shape), valve guides, valve lift, valve seats (size & angle(s)).... It might be an idea to concentrate on just one aspect if you are going to do some practical research.

[danie garry]

The grade of abrasive used to produce them?

You might get a comparison from measuring the static friction limit with a soft control piece - push a little rubber ball with a spring & measure the compression. Or maybe time a drop of oil running along the surface? Replicating the test conditions will be the tricky bit.

That's actually a pretty complex subject, for starters there are 2 different (inner, outer) ports of both inlet & exhaust and a stack of variables: valves (size & shape), valve guides, valve lift, valve seats (size & angle(s)).... It might be an idea to concentrate on just one aspect if you are going to do some practical research.

cheers ethel!

after having a talk with the head boss guy over all this it seems that i'l just be reporting on the exhaust ports, reason being that its a gas so we can take it as an ideal situation of just air as opposed to the inlets being air fuel mix! and we can also take the exhaust ports in a near perfect environment, ie. no valve guide.. so its now more of an investigation of the difference in air flow of a standard cast finish and the polished smooth finish of a modified port
the main reason that i went with the initial topic is that everyone talks about a modified head and how logic dictates that smooth exhaust=air out but i'v never really seen the hard facts and calculations behind it all.

[Ethel]

Good call on doing the exhaust, a rough finish is reputedly better for fuel vaporisation on the inlet, so you'll have nicely taken that out of the equation. With the exhaust perhaps there's a difference in heat transfer between different finishes? I expect it's as marginal as any difference in flow you'll find. Of course an exhaust port isn't likely to stay shiny for long, maybe there's another factor to investigate in carbon build up?

[R1minimagic]

Yes was going to mention soot build up too, it wont stay clean/smooth for long!

[danie garry]

Good call on doing the exhaust, a rough finish is reputedly better for fuel vaporisation on the inlet, so you'll have nicely taken that out of the equation. With the exhaust perhaps there's a difference in heat transfer between different finishes? I expect it's as marginal as any difference in flow you'll find. Of course an exhaust port isn't likely to stay shiny for long, maybe there's another factor to investigate in carbon build up?

it'l not get sooty in my ideal testing where only air is used!
cheers for the help lads, nice to see some logic instead of calculations that have far too much of the alphabet in em!!

[danie garry]

so lads, getting somewhere with this, i'd want to be seeing as it has to be handed in friday week! hit a bit of a wall with it though, to simplify it all down the purpose of the paper is to investigate the effects of roughness on airflow, letting me use straight pipes for testing and calculations.
so i'v done all my testing and calculations based on a 800mm long, 36mm diameter pipe, 1 rusted to simulate the roughness of a cast head. the problem i have is that i'v calculated everything to give the results as a pressure drop but testing in a wind tunnel has given a change in velocity, anyone know if there's any way of comparing the practical results with the theoretical calculations?? going round in circles with it all now!! cheers folks!

[danie garry]

howdy folks.......you'l love this 1!!
right so the theory behind this is that air should flow better through a smooth pipe rather that a rough cast pipe, seems logical to me anyway.
turns out that at low revs, 1200 and lower this is true but at the velocity the air is travelling out the exhaust port at say 5000 rpm i seems that 800cm down the line the velocity increases more for a rough pipe! think i'm just breaking physics!!

[mini-luke]

What assumptions you using to equate air flow speeds into RPM's? Just our of interest

[danie garry]

What assumptions you using to equate air flow speeds into RPM's? Just our of interest

cylinder dimensions bore/stroke: 70.6x81.33 mm-volume-assume average port size is 36mm diameter(easy pipe to get!!)-rpm converted to rev per second- half that as the exhaust stroke only occurs every second rev-divide the volume by area and multiply by the exhaust strokes per second
engine rpm velocity (m/s) 1200 3.13 1500 3.91 1800 4.69 2500 6.52 3000 7.82 3500 9.12 3800 9.90 4500 11.73 5000 13.03

Edited by danie garry, 20 April 2013 - 02:15 PM.

[danie garry]

well it turns out i'm a complete and utter moron!! messed up with compressible and non compressible formulae and spent ages trying to work out stuff and crying!!
at higher revs it is better to have a smooth port!!