Guide on Head Porting

[Jamo]

Taken from pratical performance magazine quite a good read

[Fat Audi 80]

I've seen that red cross before somewhere...

[Flat on my back]

Glad to see there are other fans od David Vizard, my engine builder and tuner used to work with him.

Guess where i go for my engine work?

[v8 coupe]

Nice read. I am going to be porting my own V8 heads here in a month or two. I have technical hands on experience with good and bad P&P work so I know basically how I am going to go about doing it. All my seats will be cut with a radius cutter and the valves with a single seat angle. # angle grinds are not any better flowing IMO, and just take way to long to do. My practical info is all chevy based, where it has Allot more valve area. though the wrx stuff is very similar to the Audi head design they also show little to no improvement with 3 angles on the valve. JM2C

[karthur]

Sean, How did the head porting go, what were you before and after flow #'s?

[Jamo]

Reminds me I need to move these images over to the forum gallery.

[Bram]

So if I read it correctly, the biggest improvement is by choosing the best valve cut design (even taking a 0.5mm bigger valve) and valve seat design the gains are much higher then just porting the head and leave the valves and valve seats stock?

Section 'A' (the port) has little flow restriction compared to section 'C' (the valve and its seat).

[philS2]

i had some good experience with my 10v head and a guy who specialised in ford and vauxhall heads.he hadn't even done a golf head.i gave him a head to practice on and he came back with 15% extra flow on the inlet and 10% exhaust,iirc.that was including the 3 angle valve seats.then i took the practice head away and went nuts on it.i took the venturi right out to the bottom of the seats and ground the valve guide and boss away.he checked the flow again and i'd completly wasted the inlet,but the exhaust side loved the fact that there was no obstuctions.he did say to press the guide out,then grind the boss away and press the guide back in,as they're short enough already.so i ground out the venturi and the boss on the exhaust on the finished head but left the inlet alone.but i took a slight bit too much out and ended up with water seeping into the exhaust tract.i took a while to find that.don't know how our heads respond to being flowed.i do remember that even after my 10v was done,it still didn't flow anywhere near as much as a 4v per cyl.head.

[S2central.net]

Good info... I've only started my porting work - quite cautiously it must be said...

Can you post up some pics to give an idea how much is too much on the exhaust side or what the inlet & exhaust ports looked like at the improved figures you had benched ?

I need to get my valve guides pressed out before I can do much more on mine.

What were the flow numbers BEFORE any work ?

I'm assuming this was on a 20V I5 head or maybe a 16V Golf head ?

[Jamo]

I've been told the biggest gains can be had from going to a 7mm valve stem from the OEM 8mm

[JP]

A good 10v head can flow the same on the exhaust as a standard 20v, whereas the intake will come up shy by 12% unless you oversize the intake valve in which case it can be matched.

The 4v 20v heads respond extremelly well to 3 and 4 angle multi cuts as have been shown on the test results of my car.

Once you go into the territory of 5v heads the ball game changes due to the port divisions on the intake which require the most attention.

I think what people have to remember is that general articles such as the above are always from single valve per port configurations based on the US V8's which prosper best from high lift cam profiles. Unlike multivalve heads which benefit better from a longer duration low lift profile.

Hence Audi's radical redesign on the RS6 heads which allow for almost a round lobe profile maximising the time spend at the optimum point of flow for the port design.

[4WheelDrifter]

I just cleaned up and port matched the inlet.




And a similar story on the exhaust, but I smoothed out the guide boss.



I'm aware you can do more harm than good if you take too much away. I looked at quite a few professionally ported heads before I tackled my own. A lot of the pros go a bit mad.

[S2central.net]

I need to proof of this multi-angle valve seat stuff - I have this intuition that is just FUD - one of those things that can maybe make a small gain on a very high spec engine, but will be lost in the noise of umpteen other things going on. I could be wrong - just never seen objective results.

Do you have back to back test data on a head with and without such valve seats ?
And let me clarify that question by asking if your before/after comparisons on road tests or rollers also included other modifications to the head at the same time. I can easily see how better port profiling increases the head's efficiency - just not sure about the exotic valve cuts.

Then again - maybe its not so exotic - are these 3/4 angle cuts normal at a machine shop and are special valves required - or does one simply grind in OEM valves as per the norm.

I've also not heard of the 7mm valve stem theory but that at least has some logic... Less air restriction in the port and its a lighter valve too. On my head I need a full set of new valves so this something to think about.

[S2central.net]

@4wheel - thx for your pictures... Interesting you smoothed away the guide boss on exhaust side - i haven't done that - was worried about the reduced thermal capability a little as I had no reference point.

Whilst the whole process can be thoroughly boring, it is also quite compelling - inspiring even - cutting metal and reshaping things - scared half to death that you are gonna grind your way into the water jacket anytime soon. Its a bit bonkers - I've been quite conservative so far but managed to get a feel for it reasonably well.

I really need to get back onto it... I did 4 ports on each side - leaving one each for reference purposes on a bench test, but I think I'll just bite the bullet and get on wiff it... Doing the last port each side up the same point as the others... Then I'll get the guides out and go for the deeper cuts and some knifed & polished zorst ports.

[Jamo]

I've also not heard of the 7mm valve stem theory but that at least has some logic... Less air restriction in the port and its a lighter valve too. On my head I need a full set of new valves so this something to think about.

It came from master Aelred when we were discussing the pro and cons of large valve in the I5 head.