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polishing ports

504 views 8 replies 5 participants last post by  DarrenH 
#1 ·
i was just reading the rally head thread http://www.migweb.co.uk/forums/showthread.php?t=121324

what sort of state are the standard ports in? how much work is needed to make a real difference?

16vastra is talking about drill attachment (is this the sandpaper flappy type things?) what sort of gains are available here?

if i got really **** and sat off with some wet and dry and really fine grade stuff will i get any sort of significant power gain?

is it worth doing the manifolds too?
 
#4 ·
You have to be carefull with headwork as you can just as easy make it worse!
If you have a go yourself dont change the actual shape of the ports just get rid of any bad casting marks.
You could polish the exhaust ports but you want the inlet slightly rough,you can also polish the chamber and piston crown,but be carefull you dont catch the valve seats else you might have to re grind the valves in or worse,have to have the seats recut.
Regrinding the valves in while the head is off is a good idea anyway.
Also match the inlet manifold and head so there is no step and they line up.
You want the exhaust manifold slightly bigger than the head port causing a little step,this can help pulses going back into the engine.
Dave
 
#5 ·
ok, that's good gen.

but the big question has to be... if i didn't screw it up, would i stand to make enough gains to justify taking the head off etc etc?

i could certainly do it, but if were to gain, say 2-3 hp, it wouldn't really be worth the bother. the time would be better spent fitting the new clutch that is still in it's box...

what are the likely pwer gains, or what other benefits am i likely to see (drivability, fuel economy etc)?
 
#6 ·
Personally i wouldnt bother until the head had to come off for some other reason,you would prob only gain a few bhp with matching and a polish.
Its changing the port shapes and valve size where you get power increases,even then its only 15% or so for a properly done blydenstein head.
Still,saying that,its not a hard job,it took me a few hours to do a head gasket change on my XE,allow another couple of hours for matching etc.
Use a new gasket to match too,put it on the inlet manifold and marker pen the material that sticks into the port shape,do the same on the head,then grind away the marked material smoothing it gradually into the port/manifold.
Dave
 
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