Offsetting cylinder head

[mutantZ]

I was over at the ratsun forums and came across an older thread about someone doing some extensive head mods to a L20b. It included welding some of the water passages and slotting the cylinder head bolt holes to offset the valves in the cylinder. I did some searching here to see if anyone has tried this but I didn't find anything. This is way beyond anything I plan on doing but the numbers he is listing is pretty impressive.

 

http://www.performanceforums.com/forums/showthread.php?67302027-Doing-some-stupid-shit-to-an-old-datsun-head

https://racemagazine.com.au/cars/incredible-datsun-cylinder-head-redesign#more-13007

[Xnke]

That's Tony Knight's L20B build. He only did it because he wasn't allowed to open the bore up, once you bore the block to 89mm (as he's doing for the new owner of that cylinder head) it's not of much utility anymore, and he moved the head right back over.

 

I've moved heads over trying to get more valve unshrouding after reading and discussing with TK why he did it, and yes, it does net you some gains but it's not a massive gain. TK's massive gains in that head are in the port work and the fact that the chamber is now a modern design, that uses pressure recovery to keep flow through the port high even as it transitions from the port, around the valve, into the combustion chamber. Moving the head over 2mm to unshroud the valves was mainly to get the valve to open through the maximum diameter of the bore, instead of opening into the passenger side and actually shrouding the valve more as it approached the bore wall. Once the bore is cut to the biggest it can be for the block he's using, it isn't needed anymore.

 

EDIT: It's pretty obvious from the photos and the quotes that the magazine article listed is pretty much cut-and-pasted from Tony's post on PerformanceForums. That's really dissapointing.

Edited May 3, 2016 by Xnke

[mutantZ]

Ah I didn't realize that's what it was for. I thought he was experimenting with valve placement for combustion, which I guess was the case given the rules. His workmanship is pretty amazing.

[Xnke]

The reason isn't for any kind of combustion advantage, it's only to make it so the valves don't open up directly into the cylinder wall. Once you bore the block, it's a non-issue so he moved it back over onto the dowel pins.

 

Bolt a head onto a block and look up through the bore while you move the valves, and you'll see that as the valve opens, it approaches the bore wall and thus shrouds the valve curtain area the further you open the valve.