Cylinder Head Guru?

[Ned Loh]

Who is the MX5 cylinder head guru for a basic / pocket port?

There are plenty of people who will take money but who really knows where to touch up for Best gains, and where can be left alone?

Just looking for mild port to work with stock cams. nothing outrageous.

Would probably aim to keep standard valves and new standard springs, although 1mm oversize valves and aftermarket springs could be considered if worthwhile gain

[hks_kansei]

http://mx5cartalk.com/forum/memberlist. ... ile&u=8804

aka Warren Heath

From my understanding, he doesnt own an MX5, but works on a lot of Escorts with B6/BPs in them, so knows the engines well.

[ralt]

Hi.
Your question regarding what to modify an what to leave alone is what is called the secret. Ever model of head is different and it takes much work trying different things until you are satisfied by using a flow bench.
I would suggest go to race meetings speak to competitors about who does their cylinder heads or ask the question here I am sure people won't bite. It may be an idea to have your location on your sig.

[hks_kansei]

It;s also worth noting that I doubt there would be much gain (for the cost) in doing port work with standard cams.

If the head is fried and needs to be rebuilt anyway then you may as well go for it, but if it's a good head then why not also go for some bigger cams? (or just skip the head work and go cams from the start?)

[Ned Loh]

I am not really interested in moving peak hp to higher rpm, hence not a lot of interest in cams.

Bowl job is porting low hanging fruit, shouldn’t be overly expensive. Not expecting massive gains. Not trying to debate if worthwhile on a dollar / hp basis.

I appreciate the lead to Warren heath performance.

[93_Clubman]

manga_blue on here has done & posted a few times over the last couple of years about the kind of work you're considering:

Also, casting and machining quality on B6 and early BP heads was pretty variable. On my original head about 35% of the available inlet port area was lost to mismatches in inlet manifold flange and gasket positioning. I see nothing wrong with matching ports to manifolds and removing casting dags and machining faults inside the ports (so long as you don't reshape or polish). Depending on the original quality you can pick up quite a few hp there.

Sometimes the manufacuring on B6 and early BP heads was pretty sloppy. That means that on some motors there are quite good gains to be made throughout the range and especially at the top end by just doing the simple things on them.

Check that the inlet manifold, gasket and head ports line up well without any overlaps, You can correct this with simple hand sanding with rolled up 120 grit general purpose sandpaper. If it's too bad (like manifold ports are offset more than 2mm over the port opening) then you may have to oval out the bolt holes on the inlet manifold mount and work out a way of lining it all up correctly again at final assembly, typically with either dowels or alignment marks.

Take out any casting faults and dags in the inlet tracts in both the manifold and the head by sanding and scrapng. Focus particularly on the areas between the valve seat and valve guide - the "bowl". As StillIC said, don't polish anything on the inlet side - always leave at least a 120 grit rough finish.

Likewise clean up the exhaust side and polish it there if you've got too much time on your hands - there are small gains from polishing there but they're only temporary.

Check the fit between throttle body and inlet manifold too. It may be necessary to file and sand off bumps and ridges in the manifold side of the union that are protruding into the main air flow.

As an alternative to turbo or mad n/a builds you could now consider a low cost natural build. This would involve getting rid of the lousy NB8A manifolds. Get an NB8B exhaust manifold. Also get either an NA8 inlet manifold with an adaptor plate or an NB8B inlet manifold - there's no real difference in performance though the NB8B option is a bit simpler to fit up. Get some low-level porting done on the head and inlet manifold; match up all the ports and flow the throttle body into the manifold. . You can do this yourself with a die grinder or a dremel as long as your keep it all very modest. Just remove the dags, smooth the ports, match the mating faces, open the bowl above the valves out a fraction, etc. If you're putting in hgh-comp pistons you can take a bit of metal out from around the valves (unshrouding) but just be really, really conservative with it all. Serious port shaping needs serious skill, experience and equipment. Anyone with patience and common sense can do a reasonable modest tidy-up.
If the head work is done effectively and you decide you are happy to drive the car between 3000 and 6000rpm with the odd squirt to 7500 then you don't need to spend on cams for a street car.

[bruce]

Sounds like you'd gain minimal hp, which I don't think you'd even notice.

[manga_blue]

It all depends on how well or badly manufactured the head and manifolds were to begin with. The first NA8 engine in my car started out with 45rwkw on the dyno. We pushed that up to 48 by cleaning the injectors but couldn't find anything else wrong on the outside. Cleaning up the ports and matching the manifolds got us to 68rwkw, then we finally got to 75 when we put a better exhaust on it. We calculated that inlet manifold flange and head bolt hole machining errors had reduced the available port areas by almost 40%. I think we moved the manifold 6 or 7 mm to get alignment. A couple of the ports had some big casting ghoulies near the forks and some big ridges where the valve seats were cut in as well.Obviously this was a really badly made head, but some of the early BP ones were like that.

I've done a couple more BP05s since then but they haven't been that bad to start with. Butt dyno suggests you get 5-10kw and the delivery is better after cleaning up an average head. I've done one BP4W and felt it was very well made compared to the BP05s, except that the BP4W manifold design was total crap. This is what I'm running now: tidied up BP4W head, standard BP4W cams and buckets, flowed NA8 throttle body and manifold on an adaptor plate, good exhaust and a remapped OEM ECU. Pulls like a train compared to a stock NB8A or 8B from under 2000 and still running on 91 octane.