cylinder head help
Turbo Mini Forums

Hiya i just stripped my turbo 12g940 head to start porting and opening out the chamber. Got a bonus it has had hardened exhaust seats in but on the down side all 8 seats seem to have been cut alot lower that mu other heads. they are about 1mm deeper than the casting finish of the chambers. My question is: is there any issues with this or once i grind the chamber roof to the valve height its fine. i know the spring heights wont be as they should but i can sort that and also the rocker geometry. i will try to get some pics.
Thanks James

My small bore turbo project http://www.turbominis.co.uk/forums/index.php?p=vt&tid=473901

Hi, I'm working on a series of what does what on my blog..
As I expected you have to be absolutely anal retentive on valve seat geometry. I just ran some tests and i have one valve (two pairs of identical type) which is pretty much the same (seat widths within 0.05mm) just slightly different in the margin that outflows three nearly indentical other valve configurations by quite a margin around 6-8mm lift. On low lift the difference is absolutely nothing. I retested the whole lot twice because I thought I did something wrong. I messed a tiny bit with the seat in the head an managed to kill the gains i had aquired on three out of four valves
after fiddling arounf with the seats again sort of back where i started with still a few CFM missing on the new valves ..

but as what was supposed to be a simple mod an test turned into a WTF -why does this not work quest- and about 10 valve changes three seat changes and retests. So i need to try and do a decent write-up because otherwise it is just senseless graphs

that said, it will be fine with the seats a bit lower even though it might not be really optimal . Then again when you just put in more topcut you will not lose much if at all and possibly gain some mid lift

The most bang for the buck mod is doing a backcut on the valve.. 10 minutes of work. after that every bit of further gain is hard work..

Oh keep enough meat in the bowls.. I would suggest 84% for a 35.7mm valve because you can just stick in an exhaust valve to check if you are on the mark and still concentric and cutting out is much easier than adding

hope this helps a bit

Edited by Sir Yun on 31st Jul, 2012.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

In short, its fine but not optimal but will work fine

Might be very handy if its going on a small bore block, you "might" not have to pocket the block!

Right where do i start!

sorry about the verbosity .. have to admire BENROSS for his economy of words

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

sorry about the verbosity .. have to admire BENROSS for his economy of words

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Yes keep it easy! .....lol

Cheers guys much appreciated advice. heres a pic anyway but dosent really show

My small bore turbo project http://www.turbominis.co.uk/forums/index.php?p=vt&tid=473901

that lip does affect flow a bit, blend it out it will be fine .

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

yeah i started chambers today. With those lips about the first 1.5mm of lift is really restricted not ideal. I know they usually have a form of machining kir but never seen them this deep. Thanks for your help james

My small bore turbo project http://www.turbominis.co.uk/forums/index.php?p=vt&tid=473901