Had an insightful visit at Keegan Engineering, where the boss dropped knowledge on how they port their BP heads. It is possible that they've forgotten more about porting than most people ever knew.

All the words are here. Some numbers, too.

"Also, he's found that the VVT heads are generally much better from the factory than the early NB or NA heads in terms of casting quality and core shift. The early heads often have a 0.040-0.050" step where the port meets the valve seat that the factory doesn't bother to clean up.

As if you needed another reason to use a VVT head on your Miata hot rod."

 

that intake port looks so much better than mine after working on it...

 

That is good info!!

Some I knew and do, some I didnt and learned.

 

I'm impressed! I'll be porting my own head soon enough so this is relevant to my interests.

 

What would a lowly pleeb such as myself expect to pay Keegan Engineering for such masterful service?

Excellent post, I've enjoyed reading these updates!

 

/\ THAT

 

Just a guess... Spending 15 hours to port is going to cost, figure $50-75 /hr then add in the valve job, surfacing and any other machine work and parts.

 

J j j JKAV IS GOD


ok big question. Does all that velocity advantage stuff matter if you are boosting? For boost dont you just want max flow?

 

Yikes! I've got a VVT head sitting in the garage mocking me, but that's $750 on the LOW end, just for port work. That's like, an entire new Supertech valvetrain. It's sexy, but not in MY budget.

But wait!
Now THIS is something I could get behind. I understand that hand-porting will almost always be superior to CNC, but for outright cost, this has always looked like the way to go (other than DIY.) I honestly would have no issues sending a head to KE and having a service like this performed.

I'll be watching this closely.

 

One thing that became very apparent is that if you don't know what you're doing when porting, it's easy to end up worse off than if you left it stock. I'm all for DIY and experimentation (have you seen my lemons car?). But head work is like valving shocks - best left to the pros, in my opinion.

EO2K, Keegan will work to the customer's budget and needs, suggest dropping them a line - 562.301.3277, info@keeganengineering.com. Mike's super friendly.

Faeflora, it is true that boost provides a nice dose of port velocity. If you had a land speed record car or drag car you might get by with an oversized "dead" port because you'd be in boost all the time. For a boosted track car or anything that involves part throttle modulations and transients, you want your ports to have inherent velocity and flowicity (I might have just made that word up).

 

Curious. I would have expected blunt leading edges on the intake ports. I can't tell though from the head-on picture if it might be.

 

Are you talking the point between valves? They are sharpened on my cyl head as well. I would have to assume having them sharp maintains speed. It is what I see on most ported heads.

 

Awesome, thanks for sharing.

 

Yes that. I read the Inside Line blog entry and he does indeed keep the leading edges blunt on the intake side.

The reason I asked is because I read elsewhere that some engine builders dont like sharp edges. Their justification was not the same as Keegan's. Keegan says thin edges crack. Other builders (I can't remmeber who now) say that subsonic flow leading edges are always blunt.. like any aero body would be and that you would only see benefits from a leading knife edge as you start to get into supersonic flow.

Or something to that effect.

Trailing edges, as you have on the exhaust ports, are another story. Sharpness there makes aerodynamic sense. But maybe not strength sense.

Anyway I was noticing in the photos after looking closer that the edge profile is probably not a big issue since it's significantly narrower than the projected area of the center wall and the bluntness is likely a miniscule contributor to drag around that wall.

 

I took a look at my head, and they are sharper than stock, but do indeed have a somewhat blunt edge. I would say similar to the OP's pic. The exhaust side seems to visually have a similar edge.

 

Its for off boost throttle response.

For a street driven car, its nice to have.


To me,what would be the best is have the head casting CNC ported, to get all the proper locations and sizes set, then have the CNC port work hand blended so it is clean and smooth.

Both CNC port and hand port have there pros and cons.

 

It is a bit of an optical delusion. The port divider/septum on this head is fairly blunt, esp in the saddle point. Definitely not sharp, anyway.

 

Not sharper than factory?

 

I have studied in aeronautics and worked in a machine shop where we ported heads by hand and with a 5-axis CNC machine, and I can tell you that for intake ports, you definitively want to have a blunt transition between the two runners, because it reduces the boundary layer's height (http://en.wikipedia.org/wiki/Boundary_layer) and turbulance, which is not characteristics you want in your runners. Picture an airplane's wing leading edge (http://en.wikipedia.org/wiki/Leading_edge), it is not sharp for the same reason.

 

Isn't that kinda what I said?