I have a spare head for my A12 and I wanted to have a go at porting and polishing it, which I have never done before. Can anyone give me any tips before I start? Other than take it to someone else to have it done cause I want to try for myself.

Also it was my understanding that the roughness in the inlet ports improved turbulance to mix the fuel with the air, wouldn't polishing the inlets reduce this turbulance and would it matter that much. And if you polish the inlets, should you do the inlet manifold as well?

Also is there anywhere with direct instructions on how to do this or is it just something learned with practise.

By the way is is just a round port head if that makes any difference.

I'd go find a closed chamber oval port A14 head. Definitely a better starting point, but also involves a new manifold to suit. The basics of mild porting are not too difficult.

This article is worth a read:
http://www.sa-motorsports.com/diyport.htm

Keep the ports as small as possible to keep air speed up. And don't drop the short side of the intake port, you want it as high as possible to try and swing the flow around the valve seat. You want to keep the port shape as consistent as possible. Polishing is out these days for the reasons you stated.

Without a flow bench you are probably better off just doing a basic cleanup and port matching the manifolds. Don't forget to give the manifold a cleanup also (internally).

Do a few before and after tests, stopwatch, dyno, flowbench, what ever you have. No use guessing on the effectivness.

OK, thanks for the redirection to that article L18_b110, very interesting reading.

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cable tie, thanks for your input as well, it looks like the best option for me is to match the head and inlet to the gasket and then just to have a general clean-up of sharp edges etc.

next question, other than to say that I have done it, is this small amount of work really beneficial to performance? I know, anything that increases the efficiency of the engine is beneficial, but realistically is it worth it without doing any other work to the top end.

I've added a few photos of a DIY job me and a mate did on my old L series head. Just have a look in the photo album while their still in the recent listings.

I wouldn't go for massive porting either, big gains can be found with minor reshaping of the inlet port: specifically the guide boss, valve pocket area, and unshrouding valves in the combustion chamber (if that's a problem the head your doing). But the round ports heads are really a bit on the small side for performance applications. To get significant performance improvements on these small engines (that aren't exactly big on torque) means improving volumetric efficiency at higher engine speeds, where you want to be able to flow a large volume of air in a short period of time, and the small port heads won't cut it. Even Datsun acknowledged that - look at the GX head. The oval port head is a much better starting point.

Just saw you last post Datto7, it really won't make a big difference on an otherwise standard engine. There's bigger improvements to be had for much less effort in changing the carb, adding extractors, a cam regrind first. Then maybe pop the head off for a bit of a skim to raise CR a bit and do the porting at the same time.

But if you've got a spare head and the desire to have a go, I'd say do it. If nothing else, you'll learn from the experience and have a much better idea of it all. Remember the ear protection though! You don't want to end up with industrial deafness or that annoying ringing in your ears -can't remember the name for that.

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OK, I acknowledge that the head I have is not the best for performance, however, its the same as the one I have on there now for comparison (apples to apples), and I also wouldn't want to be messing with a GX head on my first time doing something like this.

Anyway I will have a play on the weekend with my spare head and see what I can do.

And thanks for the pictures

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Tinnitus. I had it for three weeks after a concert when I was in high school

I also want to thank you, L18_b110, for the great information. I too, am learning and the basics you showed help a lot. I have a coouple of A12a, circa 1980, Nissan heads that would make great learing tools before I try my hand at an oval port head.

Thanks again

Jack

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I have extractors, I wish I had a different carby (have a standard one that is absolute crap, not because it is standard but because it is shagged), and a cam regrind would be good.

I was looking through the engine section of the photo album earlier and found some very useful A series port pics posted by various members...

A15 In Port sectional veiw



A15 Ex Port sectional veiw



Feral's A13 race engine porting...drool...



JTS A15 race porting on stevo1000's engine
[img]http://datsun1200.com/modules/myalbum/photo.php?lid=1747[/img]