Barksavon
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| posted on 7/1/18 at 06:45 PM |
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Polishing Ports....Worthwhile or not?
I have the head off my engine at present (ST170) and stripped down. Is it worthwhile polishing the ports while its off. The ally casting is quite
rough but I don't think I want to spend hours polishing to gain a few HP.
Thanks
Ian
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Nickp
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| posted on 7/1/18 at 07:14 PM |
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If you don't want to spend time doing it then you've answered your own question 
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jossey
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| posted on 7/1/18 at 07:20 PM |
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Do you want the best horsepower from the engine or a cheap engine?
Thanks
David Johnson
Building my tiger avon slowly but surely.
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Barksavon
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| posted on 7/1/18 at 07:29 PM |
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Perhaps a better question then would be What sort of gains can be expected from polishing the ports
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r1_pete
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| posted on 7/1/18 at 07:39 PM |
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Taking out any casting irregularities, and producing a port of as near common ‘diameter’ will provide better results.
A 300 - 400 grit finish is said to be preferable to a mirror finish.
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Barksavon
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| posted on 7/1/18 at 08:25 PM |
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Thanks Pete....advice always appreciated
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jossey
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| posted on 7/1/18 at 08:25 PM |
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It's more about what other parts you mix it with. With just standard cams and inlet etc then very little gains but if you get throttle bodies
and bigger exhaust, cams and Pistons then it's more that it needs to be done as it will maximise the results.
Thanks
David Johnson
Building my tiger avon slowly but surely.
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Barksavon
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| posted on 7/1/18 at 08:44 PM |
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That's helpful thanks, I'll be putting bike carbs on but don't intend to swap the cams or pistons so im thinking it may be
unnecessary...
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jossey
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| posted on 7/1/18 at 09:27 PM |
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Good luck with the build.
Thanks
David Johnson
Building my tiger avon slowly but surely.
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snapper
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| posted on 8/1/18 at 07:59 AM |
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Port polishing does not produce any more power, the rough cast finish actually helps prevent fuel drop out and pooling.
In the bad old days polishing ports was used to convince people a good porting job had been done when in reality it was merely a cosmetic con job.
I would look for 3 angle valve seats bigger valves, waisted stem valves with penny on a stick valve heads rather than shiny shiny ports.
Matching the inlet port to the head is a worthwhile job though if you want to do something to help flow and will probably take less time than
polishing your ports.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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chillis
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| posted on 8/1/18 at 01:06 PM |
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As snapper says you don't actually want polished ports, just remove sharp edges. Most 4 valve heads are pretty good these days straight off the
line. Race engines often have polished ports but they are looking for max port velocity at very high engine speeds and even then the % gains are
small. The Zetec head design is also aimed at exhaust emissions performance rather than max power and the ST170 was a cosworth tune up on the original
engine so I doubt there would be anything gained in polishing the ports. As for bigger valves etc if memory serves the valve size increases are small
as the valves are quite close together. I would work on cam design and intake and exhaust design for maximising performance.
Never under estimate the ingenuity of an idiot!
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SPYDER
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| posted on 8/1/18 at 01:10 PM |
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The latest vogue is to machine dimples into the inlet tract, like the ones on a golf ball. Some dimple fanboys go even further and dimple the
combustion chamber and the piston top!
There is something to be said for polishing the exhaust port to slow down the build up of carbon but even that would seem to be a waste of time given
your average kit car mileage.
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Barksavon
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| posted on 8/1/18 at 06:10 PM |
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Don't think I'll bother with the polishing , thanks for the advice everyone, much appreciated
Ian
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