Incredible Datsun Cylinder Head Redesign

Tony Knight from Knight Engines in Adelaide has posted up some amazing things over the years, including reworking a 24L V12 tank engine and countless alloy V8 porting jobs.

His current work is a Datsun cylinder head for a competition engine.  He has welded up most of the combustion chamber, ported it and has even moved the entire head across the block 2mm!

Tony explains:

Starting with an open chamber U67 L20B casting – it doesn’t really matter which head I started with as long as it is a big port one, you’ll see why in a sec.
Aiming to make a really, really powerful 2L datto:

Got it all stripped down, seat inserts & guides out back to a bare alloy casting, then out with the TIG welder & spend a couple of hours making rods disappear”P1131391_zpskakloexr

Tony also commented on his willingness to share his experience with the broader automotive community:

“I have an accutig 300 – 300A capable & 100% duty cycle with water cooled torch etc.
Depending on the area I was using between 130 – 220A, it could be done with a 200A machine, but only just. The chamber design will be the secret squirrel stuff, but I’ll post it up anyway, along with an explanation of how/why it works.
I’ve drawn from the knowledge of others on many occasions, you can’t learn all this stuff on your own, there is far more than a lifetimes knowledge to obtain – may as well pass on what I can.  I wouldn’t be where I am without the help of guys like Peter Schaeffer, Peter Michaels, Bill Hanson, Bob Sherry etc.
Nor would I be here without the information posted online by yanks like Darin Morgan, Chad Spiers etc.
I’m just passing it forward, just like they did, it’s only fair”


“Snip some time while I straighten out the head (bent about 1.5mm from all the welding), then on to the mill, rough the welds down to .040” from the original face & then peen the bejesus out of the welds to compact & work harden the softer welds:

Mill it down to a clean surface:

Head17 head6Top face gets a light skim to get it nice & flat:


Same goes for manifold face:head9

Now I’ve got a clean slate casting to play with, I’ll be putting in my own design combustion chambers & doing some other stuff as well.

It seemed to me that the head bolt holes would be better off about 2mm further away from the manifold face, so that the head sits off to the side about 2mm & get the intakes valves closer to centred in the chamber at full lift.
You’ll notice I welded up some of the water jacket holes on one side, that’s to allow the head to move over on the block a bit.

I started offsetting the head bolts holes in the mill with a core drill, but it wasn’t going to work – too much flex in the drill, so I ended up just doing it by hand with my grinder, not the prettiest job, but hey, it’ll work:

P1131402_zps58eiwmsc Next up I gotta finish stripping down the short motor (needs a freshen anyway) so I can sit the head on & mark out the bore onto the head.  Got the short pulled down & the head dummied on the block, you can see how much I’ve moved the head over:

P1131405_zpscx92jirf P1131406_zpsnizjmvjwHead face scribed with bore locations, you can see the offset in the welds:

P1131412_zpsqeixikch(1) P1131410_zpszjqlhjgc(1)Belted the guides in, they’ll have to come out again for porting, but they have to be in for seat inserts & seat cutting.
Reamed them to size in the seat & guide machine & then on to fitting the seat inserts.

Machining insert recess’s for the intake seats:

Head17 Head18De-burr the holes & belt them in with some never-seize so they don’t gall on the way in – .007″ interference fit:

Head19 Head20Repeat process for exhausts: Head21 These are tool steel seat inserts – pretty tough, they’ll hold a good seat for quite a while.

I’ve dug up some ecotech V6 valves that are 8mm stem & slightly larger than the valves I’ll be using in this, I just turned them down to the right size in the lathe & bingo I’ve got some dummy valves for cutting the seats etc.

Cutting seats, as there is nothing left of the original chamber there is no datum to base seat height on, so I measured another head, figured in the difference in thickness of the heads (how much had been milled of the other one) & used that measurement as seat depth.
Intake seats cut to height:

Head22 Head23 Head24Throat cuts done: Head25 Head26That’s all I can do on the seat machine, no room for a top cut, I’ll have to do the top cut by hand with a grinder (yay).
Out of the machine, bump intake guides down out the way for porting (exhausts are just going to get ground flush with the port roof), run a tap through the plug holes & on to the porting station: Head27 Head281st chamber done, haven’t CC’d it yet. Head29 Head30 Head31 Head32 Head33 Head34 Head35 Head36 Head37 Head38Ok, done 1 whole cylinder, took a little while to nut out the shapes I wanted, especially on the exhaust side.
The exhausts on these things are the real problem, abrupt short turn & not much you can do. So rather than try to perform a miracle I instead concentrated on unloading the turn as much as possible – I threw away all the existing info & port designs & started from scratch with the focus being on getting the correct cross sections in the correct areas, getting the port to taper out as required & unloading the turn.
Intake is also a little different to what I’ve done in the past, the new chamber shape allows for a more aggressive short turn, which in turn allows for more flare after the minimum cross section just before the guide.
I’ve gone for a 40mm port at the min cross section, the port tapers down to 40mm (or 1.9^”) from around 42mm at the head face, then flares back out. Head39 Head40 Head41 Head42 Head43 Head44 Head45 Head46 Head47 Head48 Head49 Head50 Head51 Head52 Head53

Chambers all done bar final sanding – I’ll do all the sanding at once when I’m done with all the carbide work.
Took a few pics of the junk head, it’s been messed with & cut for bigger valves, but you get the idea:

P1141454_zpsicrube1j P1141455_zpstmivmrfa P1141463_zpsnhstv6fo

Grinding, plus a bit of grinding & some grinding

P1141459_zpsft8rkph0 P1141460_zpsn2huejwn P1141462_zpsraeibtkg

Here’s the full thread on Performance Forums.

We will revisit this as it progresses!



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