now i am planning to port n polish intake n exhaust, most probably about enlarging 2mm in diameter, but i heard that it will hit the water jacket, is it true? but i saw Tomei selling gasket for 34X44mm intake port, that means we can port this much? i try to search on this website but seems that no relevant information inside...

second is milling head, how much i can skim? 1mm will help performance or not?

thx.

can anyone help?

What #'s are stamped in the head?
Odds are it's an emissons low compression head. Those aren't good for porting.

Skimming... you mean to raise compression, that works somewhat, but changes the valve timing a bit, so you'd want an adjustable cam timing gear.

Different pistons could raise the compression without skimming the head.

What is your final goal? Do you want to be committed to burning high octane fuel?

Is it a round or oval port head?

H89 head

my aim is to get higher torque, and also high hp in high rev. so i am considering raising compression ratio a bit. maybe 10:1, that normal fuel burn without knocking.

i measure intake port is 29X36mm, exhaust is 29X30mm, i m planng to port to 31X38 and 31X32

you can also match the manifolds to the gasket, there tends to be bit of gasket sticking into the ports.

What sort of fuel and ignition system are you using?

torque usually comes in at lower rpm than the hp peak, so increasing one tends to decrease the other. ( HP is a artificial number calculated based on the torque )

Skimming the head will have some minor effect on cam timing in an OHC engine, but the A15 is an OHV engine with the cam in the block, so there will be no changes in the actual cam 'event', ... however, .... since the valves will be positioned closer to the piston, just be sure that you have adequate piston to valve clearance, particularly if you use a modified cam with more lift than standard &/or use flat top pistons.

If you include some basic location details in your profile, it could actually help in the identification of the version of the head that you have as some heads were not used in some markets, while others seem to have been used worldwide.

i m from Malaysia, the A15 is from and C20 i think.

now my friend told me that you can only port 0.25mm for intake, is it true? i also found another thread about one of member porting his H95 head ended up poking big hole in the intake port, too close to water passage.

http://datsun1200.com/modules/newbb/viewtopic.php?topic_id=22017&forum=1#112453

i am planning to port from 29X36 to 31X38, is it safe? i think 1mm for each side is very minimal only, i can only remove the rough cast aluminum ssurface.

Quote:
Here i m using Shell V-Power, should be 97RON i think. ignition is electronic distributor, with original ignition coil.

i think A15 torque band is more toward low end, and the "efficiency" is not high as well. so i think increasing compression ratio would have help in raising torque and widen torque band, thus increasing hp all round.

porting is to increase high end HP. two of these combine together for drivability and fun

can anybody help me? thanks in advance.

if you have a spare head or can find one feel free to try.

one would think there is a mm or more you can take out, but not much more.

You can probably polish the intake and not do any damage... Porting not so much.