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Old 22-06-2020, 11:48 PM   #1
Luddite
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Porting

Interesting.



It amazes me how much material is removed during the process.
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Old 23-06-2020, 02:27 PM   #2
Uncle Bob
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It's a pretty common mod on cars. I've had it done on various parts before (heads, inlet manifolds). For me, unless you're going to go to extreme lengths to squeeze the last ounce of performance out of the engine with induction mods, exhaust mods, fuelling\remaps then the benefits of this practice in isolation are minimal.
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Old 23-06-2020, 02:33 PM   #3
Darren69
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One improvement that can easily be made apparently is the smoothing of the join between the throttle body and the inlet tract as there is usually a ledge there that can easily be smoothed down which can make a difference.
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Old 23-06-2020, 03:07 PM   #4
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carvernous 2V head





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Old 23-06-2020, 04:08 PM   #5
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Like Darren says, the "obvious" stuff - like lips and misalignments between manifolds etc are easy.

If you've ever taken the head/manifolds off something stone-age and low power (old Fords, Moggy 1000 etc), there's some very obvious things that can be laughably bad and don't help.

But then - and especially for half-way decently designed/made performance engines, like ours - it quite rapidly descends into the Black Arts and non-intuitive/opposite of what you expect effects - especially for a motor which won't run WOT 99.999% of the time.

For example; if removing a large casting cack or lip is good, then so would be polishing the ports, right?

Not necessarily; turbulence can result in better fuel atomization/mixing - and thus better power, economy, response - than mirror-polished.

Surely making the ports bigger adds power? Only if the ability of the port to flow gas in CFM is a bottleneck. If not, then by making it bigger, you're slowing gas flow. Which certainly provides less throttle response, and perhaps worse mixing. Like adding a huge carb/throttle body may make you slightly more power flat out (or not). But it won't run as well everywhere else.

Sure, if you can identify places where the factory was constrained by cost/manufacturing concerns (like only wanting to take 2-3 passes with a mill), you may be able to do better just by applying basic physics - like "gas doesn't like to go around corners".

With a well-designed/built motor, it's usually more complicated than "make it bigger" and "make it smoother". Otherwise, every muppet with a dremel and a bench vice would be Jerry Branch. Or Xtreme Cylinder Heads.

Without a flow-bench and some specific aims/goals, you're probably better off leaving that to the professionals. For a street motor with no obvious "duh" factor in sight, a good 3-angle valve job (the narrower the valve seat, the shorter the life between servicing - and also the earlier it opens/later it closes) and getting the motor right on factory specs (or better) is generally a wise use of time/energy.
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Old 23-06-2020, 04:15 PM   #6
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Quote:
Originally Posted by spuggy View Post

For example; if removing a large casting cack or lip is good, then so would be polishing the ports, right?

Not necessarily; turbulence can result in better fuel atomization/mixing - and thus better power, economy, response - than mirror-polished.
I had the heads on both my M900 and 916 ported by Chris at CJS Racing in Bristol, both make very good power.

But (generalising) the intake ports have a 'rough' finish whilst the exhaust ports are smoother. My understanding is that this for turbulence for the intake and less resistance for the exhaust...
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Old 23-06-2020, 04:56 PM   #7
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This is a fascinating subject and is as Spuggy says, often counter-intuitive.
The "rough" surface of the tracts works like the dimples in a golf ball. the little eddies on the surface irregularities act like roller bearings for the charge hurtling down the 'ole. So the main air mass is not in fact so turbulent as in a smooth tract.
That would be counter productive on an exhaust tract as the little eddies would probably not pass the heat away so well as they will probably continue to hold the same air for a relatively long time and pass the heat to the head. Much as the water in waves doesn't move along but rather circles in the wave and creates the effect of a moving wave.

I was briefly involved with ERM (English Racing Motorcycles), they manufactured their own AJS and Matchless 7R and G50 engines and developed their own heads. The tracts were made in reverse out of wood or hard rubber and used to form the holes in the sand castings. The ones that worked the best apparently were long tapered ones like a carrot with narrow end at the valve whereupon they opened to a bulb shape behind the valve. It was always work in progress, as you don't necessarily know what part of the shape is having what effect.

Peter Williams Father (who's name escapes me atm!) worked in AMC's race department developing the 7R and G50 back in the 50's and probably earlier. He had a novel way to test the atomisation and mixture pattern of various tracts. He would line a cylinder with paper and rig a vacuum cleaner at the bottom of the cylinder. Then introduce a charge of air and ink via the tract and examine the paper to see the result. How he put the ink in I do not know. It would make sense to use a carb I suppose. That was the state of the art in those days... Good old human ingenuity.
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Old 23-06-2020, 10:31 PM   #8
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Reminds me of the joys of port matching and transfer hacking during my mis-spent youth on 2T's.
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