head porting: are all shops the same?

[Gadea]

Hi, fellas. I´ve never had porting&polishing done and so I´m wondering if any machine shop is going to be able to do it properly. I know if I ask them, they will all say they are professionally prepared to do it, blah blah blah. When it comes to cars, we all know too well not everything said is necesarily true. I know it needs to be done just right, or else you´ll end up with worse performance than before, instead of a better flowing surface. If anybody is wondering, its for a M30B35. That said, is there something other than experienced personnel that I should look for in a shop if I wanted to perform such a job?
Thanks!

[whodwho]

Someone experienced with porting could cleanup a head that he didn't have experience with but for a full on porting job they would have to have experience with it before or trial and error with a flow bench to see what works.

Not sure which head you are wanting work done on but BMW heads work fairly well untouched so just a cleanup(smooth the transitions and surface texture) would probably be enough for you.

[jlevie]

The shop you need is one that has experience with the head you are going to have ported. A BMW head is really pretty darned good "out of the box". Achieving greater flow means making subtle changes that aren't necessarily intuitively obvious. The shops that are good at this have probably wasted a few heads in trying things and seeing what the flowbench says. Eventually they figure out a formula for that head that works. I'd suggest that you talk to the folks at Metric Mechanic.

[Bearmw]

I just had Paul Burke build a mild B35 head with one of his custom cams. His work looks great. The motor won't be started up until spring however. His prices seem very reasonable an he can be found via Mye28.com. Make sure you talk to the guys who will do the work and tell them exactly what your looking for and what your checkbook will allow?

[Gadea]

I have visited the Metric Mechanic website before and their sole mention has two effects on me: makes me want to bow before them, and it makes my wallet shake in fear. There isn´t much room for argument here, they are probably THE guys to go to. They explain (very clearly) that smoothing (polishing) out the surfaces in the inlet ports (at least in 80´s and 90´s BMWs) is only a cosmetic improvement, that obviously nobody sees once the engine is put together...and it nets you no other than a loss of flow (and power). They claim that actually roughing up the surface- in a particular and precise pattern - is what increases flow. While I have no reason not to believe them, I just can´t justify spending on a metric mechanic head more than what I´ve already spent on an entire car, plus another engine and rebuild parts and labor. They sell the heads they work on (again, there´s little doubt they´re the best money can buy), but they don´t work on your head, as, for example, just performing a valve angle job.
Basically, I´m just looking for performance gains that won´t cost and arm and/or a leg.
I´m not much in mye28.com lately but I´ll def. check his work!
As always, r3v remains a great source of information!

[whodwho]

Unless you have gone big and already have everything else, headwork will be the last thing you need on the list. It probably would be your least bang for the buck item.

[jlevie]

Short of MM magic and using stock components there are things you can do to the head to improve performance without spending a lot of money. A three-angle valve job will increase flow. The lower portion of the valve stems can be necked down slightly, which will also increase flow. But perhaps most important is having the cam blue printed or buying a new cam. A simple and often overlooked tweak is to trim the intake and exhaust gaskets so that they don't intrude on the ports.

[nando]

unless they've actually worked on your specific head before, no. Especially when it comes to something like an 885 head, there are only specific things that improve flow, and lots of things that make it worse. Hogging out the ports to make them bigger could be considered "porting" but would make things worse, for example.

also, the intake and exhaust gaskets are already larger than the ports - the exhaust by a couple MM. the intake could be somewhat close depending on what brand and how they sit on the studs, but it doesn't matter because the intake manifold ports are quite a bit smaller than the ports in the head anyway.

[Kershaw]

^ i've pulled an m20 apart that had one of the gaskets (cant remember if it was intake or exhaust) covering at least 1/3 of the ports.

They claim that actually roughing up the surface- in a particular and precise pattern - is what increases flow.

this is true. its the same concept a golf ball works on. the little rough patches trap air to them. and then the air that flows in, flows over this trapped air. air over air flows smoother than air over metal.

[nando]

it may have been covering part of the inlet into the head, but like I said, it doesn't really matter much because the intake manifold is a lot smaller.

and if it was covering 1/3 of the port it might have been the wrong gasket (eta?)