ported your own cylinder head before??

Post by **picky** » Sun Feb 25, 2007 11:45 pm

Ive spent the last two weeks working on porting a 12G940 cylinder head myself, anybody else out there do their own heads?? Ive got the shapes right I think, Ive based it on some very detailed photos of a MED Engineering head that someone was selling on ebay. But, the inside surfaces dont look very smooth, which I think will restrict flow a fair bit

Im using a dremel grinder with a flexible end, and a cheap set of diamond grinding bits that I bought on ebay, they seem to last!!

What are other people using???

Picky

Post by **8009STEVE** » Mon Feb 26, 2007 2:45 am

To mooth off the inside, try a six inch nail. Cut the head off, cut a slot into the end and wrap a strip of emery cloth round it. make sure that it is wound the right way.

Post by **bmcecosse** » Mon Feb 26, 2007 7:42 am

Tim - m,ain thing is to enlarge the inlet valve throat as much as possible - leaving only a thin valve seat - and take away much of the guide boss. Also the 'short' radius side - a good deal of metal can be taken away there to enlarge the X sectional area where the gases turn the corner. Similarly - in the exhaust throats - the short radius side is very restrictive (try sticking a finger round the corner) - and a good deal of metal can be removed there - but don't remove the exhaust guide boss. I'm amazed a Dremel can do anything - I use a leccy drill and the big mounted points from the Pound Shop! The final finish is not important - in fact they say DO NOT polish it - a slightly rough surface is better.

Post by **Stig** » Mon Feb 26, 2007 1:46 pm

I can't believe no-one's plugged David Vizard's book yet (Tuning the A-Series Engine). It's got various diagrams showing "remove this bit down to here" kind of stuff and advice as to what's important and what not to waste your time on. There's one on Ebay for a fiver.

Post by **picky** » Mon Feb 26, 2007 4:26 pm

Dont worry stig I have the book in question! I have read all three chapters on cylinder heads in detail. it just looks a bit of a mess inside as the surface is not really "rough" it has jagged edges from the edges of the tool. I have had some success with a small emery cloth tool, I guess it will just take a long time to smooth it all out completely, even to a rough finish.

David vizard suggests smoothing the short side radius, but only on the exhuast, not on the inlet. this is to stop flow going up the inlet valve during the overlap period apparently.

Post by **bmcecosse** » Mon Feb 26, 2007 8:09 pm

That's not how I read it! But in the real world - I rather doubt if it matters all that much. But you are going to supercharge this anyway I think ?? So these head mods are not quite so important when the gas is being pushed in - rather than sucked!
Crank is on it's way to Minispeed-should get there tomorrow.

Post by **picky** » Mon Feb 26, 2007 8:48 pm

thanks bmc

this head is only a practice really, it was the standard midget head that came with my engine. I am hoping to sell it, and depending how much I get for it I may do more of them. I also have an mg metro turbo head, which I will do some porting on for the supercharged engine. I think you are right bmc, that for a supercharged engine it is less important. Will probably spend tomorrow grinding out the marks and scratches, and take some photos see what people think.