Would be interested to see a comparison since this method would be ultra repeatable.

I think for most, this wouldn't be as DIY, but a service that is otherwise financially taxing. Not everyone is privy to such awesome techniques. I'd be interested in pricing but this is one of those black magic areas that I wouldn't have the experience of knowing the difference for the amount of $ spent.

This looks fantastic though, and I can appreciate you sharing the steps and methods as you are now.

 

Emilio/949 does CNC Miata heads, I think that's the only "market" right now.


This thread is interesting.

 

If through Keegan Engineering, there's some serious experience behind the magic

 

This isn't really DIY given the need for a CNC machine however I really like how modern tools and software like smart phones, photoscan and some quick modelling in 3Ds max are enabling anyone to do this sort of work. The CNC machine I'm using is a 15year old Roland 4 axis machine. It can't cut that quickly but in the time it took me to mount the head to the machine bed, the tool pathing was complete and ready to go and it was off cutting.

Emilio's CNC heads are cut with a 5 axis machine with probably hundreds of hours of 3D modeling time, machining and several prototype heads as tests. You really need the extra two axis to get the cutter into the ports. Even then it's a challenge due to the angles in the ports.

I think I could cut the ports with my machine but I'd need a ball cutter that has a bit of overhang. I figure I can make a rubber mold from my race head intake and exhaust ports, then photoscan them to generate the surface model and use that to cnc. Maybe do a few ports and average them. I know that head flows well so its an excellent starting point.

From here I'll most likely do some CNCing of the bowls as they are fairly critcal and I'll hand port the rest.

 

Here is a quick video of the CNC machine cutting the combustion chamber.

 

Giggidy Giggidy

 

nice!!

 

Bling! Shame no-one will see it...

 

+1 more Giggidy

You might as well look at the larger (7mm) exhaust valves cause they're sodium filled. I would imagine you could use Mazda or Nissan valve guides. Simple matter of making them fit.
I have some seat time on a few of these heads at this point and it helps to have a good set of headphones to listen to your favorite whatever. If you feel it's necessary, you can CC the combustion chambers and the intake runners in the head. 180-320 is common on the intake surface. 400 grit and then a light buff is sufficient for the exhaust.
cheers- JB

 

This is a super-cool way of doing this.

 

Do you think it's worth running the sodium filled valves? The benefit is they will handle more heat but the larger stem will obscure a little more airflow. I think if heat was a problem it would be better to go for an inconel valve. I could fit the 7mm stem by either boring out the valve guide a little more, or fitting the nissan valve guide, which would require machining the head to fit the larger diameter.

As a side note, I made a tool to punch out the valve guides as I need them out to port the head properly. I lathed it out of some 4140 as the valve guides are in pretty tight.

 

Did you knock them out from the lifter side or the port side. we always use an end mill and cut down the stock guides from lifter side until the circlip comes loose. then we knock them out by hand from the lifter side. seems to help from pulling metal through.

I vote 5 or 5.5mm valve stems its lighter and flows more. no brainer if you are going to change valve stem diameter.

 

I knocked them all through from the port side... I tried to take the circlip off but I couldn't figure out how to get to them. The first one came out ok but scored the last half of the bore, it's like they are pulling with grime that's baked on the tip through with them. So I soaked the rest in CNC and they came out nice and clean, without dragging any crap through the bore. Some of them required a lot of persuasion to move... It felt like I was going to break the head in half!

I think I'll pick up an air hammer to install the new ones.

 

I would avoid an air hammer. iv seen them crack heads usually on porsche heads but anything is possible. best thing is freeze the new guides.oil the bores and knock them in. only takes a few mins.finish with a light reem on the top side and then hone to fit your valves.

 

Awesome... I also thought that maybe I could pull them through with a threaded rod and tighten them in with a nut. Freezing them makes more sense but I guess you have to move quick. Anything special to get the heights correct? I have another head so I figured I'd measure the installed height from that and match.

 

the new guides should have a machined lip on them. stop hitting when you hear them stop going further. The heights might be off ever so slightly cause of the way the heads were machined at mazda.

 

There is an installed height spec in the manual which I'll have a look at when installing them. From what I can find it looks like a 6mm carbide reamer is all thats required to fit the valves. There is a fairly large window on the clearance spec.

 

did you buy miata specific guides or guides for something else? i run a tapered ream over the top side incase any mushrooming happened while installing them. Usually the guides are undersized and get honed to fit the valves in.

 

I have purchased the bronze miata guides from miataroadster. I can also get tapered carbide 6 flute reamers designed for bronze valve guides that are meant to produce an excellent finish without the need for honing. From the specs it looks like Mazda speced the valve stems so that the required tollerences are correct for a 6mm hole in the guide. The Nissan valves seem to be the same. Given I'm trying to do as much as possible DIY, my plan was to purchase a 6mm reamer and give it a go on the new installed guides. I think it should be fine but I'm open to suggestions here given I really don't know how it should be done.

 

The purpose of the hone is to help oil retention as well as ensure a concentric guide after its installed. A reamer doesn't do the former too well. Look into a sunnen honall