Advise needed on ported & polishing a cylinder head


Road Burner
Poole, England
VW T5 swb 2.5tdi
Hi just a dim question, i have a bmw 328 and was thinking of getting my cylinder head ported and polished, but do you really gain anything from doing this and what are the pros and cons, and roughly how much could i be looking at to get this done???
It is one of those topics where you will get divided opinion and personal ones too. Probably not as common as it once was due to improved manufacturing processes and much improved quality of all assembled parts. It is still practised today but is probably part of the blueprinting that goes on. I can only speak from past experience when tuning older engines that were poorly designed and manufactured. Polishing is not always the best, a 'rifling' finish has been known to improve the flow.

With the work done you will benefit from improved gas flow. Against are probably costs and length of time to complete. In the old days this was known as stage one tuning, going to two and three with bigger valves etc. Another minus is if doing it yourself you might get it wrong and grind through a water jacket or close to one, you need to know where the thin areas are and where localised heat may be an issue. Best left to a specialist if you want results, but no harm in having a go yourself if you have the time, tools and don't mind if it goes wrong!
im not going to attempt this myself but was going to pay for this to be done, and was thinking of getting the valves done. but was not sure if i would get any benifits...

i am going to get a larger manifold put on my car, replace my headers and the whole exhaust system and maybe next year get my car supercharged but that depends on funds.... lol
If you're throwing boost at it, best look into the bottom end as well. I don't know how the rotating assembly will hold up to boost, most specifically the pistons and rods. You may not have to worry too much about the crank, but pistons, rings, and rods definitely.

If you only do the head and the bolt ons, no forced induction, here's how it should turn out:

You'll get more torque out of the bottom end because the air is more freely moving through the engine. The car will likely run smoother, albeit noisier (a good thing if you ask me, lol) Top end will feel more free and revvy, you'll probably find yourself winding it out further than normal because it's fun and sounds good.

Looking for numbers? No way to tell, really, without a dyno. Off-the-hip, I'd say perhaps anywhere between 15-20whp in the lower rpm band and 10-25whp in the top end. It's not a huge number gain, but gaining in the bottom AND the top makes the entire drive feel crazy fast.By comparison, of course.

Especially if you can find another car with a similar setup to what you have now (pre-mods).

Proof: I put on a pully and I only gained about 25whp at 7000rpm. I however, gained about 60whp from 2000 to 3500. Holy frijoles! That thing killed! I only had 249whp but was beating all the 300-350whp cars that I met. Why? they were turbo cars. They got all their power from 4-7krpm. I got my power starting from 2k. they were always playing catch up.

However you build, make sure you get your power throughout the rev band, not just at the top.
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Thanks for that Waynne, I new I had seen something somewhere! Will have a read up on this in a while ;)

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