ported head

hello everyone, i tuck the head off my mk1 golf 1.8 8v gti yesterday and noticed it has had the inlet ports ported and polised but the exhaust ports have not been touched is that the best way or should i have some work done to the exhaust ports to mach the inlet ports?. i know big ports are better but some engines react differently. any advise?

up to you really, Inlets are the best bet to go for on a normally aspirated engine as the more air you can get it the better, work done on the exhaust ports will minimise pumping losses but it all needs to be done in a structured way by someone that has actually tested the heads and knows what works, not some monkey with a dremel :-) polishing doesn't really make any difference to airflow it just makes the heads look pretty and sells them to people that should know better you can also make the ports too big and in the wrong places quite easily which affects gas velocity which is detrimental to the gas inertia in the exhaust  causing power loss.

Basically the answer is, you can quite easily lose power by porting if done incorrectly so make sure you get it done by someone that has a few good ones under their belt!

i think ill keep it as it is then, and your advise has been most useful. you have now got my brain ticking woundering if its been done right lol. i think when its been put back together it's going on the rollers to see what the power derlivery's like and what its making lol. cheers .

It does make a huge difference to airflow. Smoothing off the exhaust ports will allow the air to escape more easily as friction is reduced and airflow through the port is far smoother, increasing its velocity. So long as you only smooth off and not port you wont do any damage.

What you DONT want to do is polish the inlet ports. If these are too smooth there is not enough turbulence in the air to allow proper atomization of the fuel, causing it to settle on the port walls, not good. Thats why when you buy a gas flowed head from TSR or the like the inlet ports are left slightly rough.

The 8valve heads all benefit from work to the intake ports but its very definitely NOT a case of going bigger.
Bigger isnt necessarily better, trust me.
Big ports flow a lot of air, but you need a big valve to match and a cam thats matched otherwise youll not derive the full benefits.
Having said that, big ports on a road engine arent any good for normal driving because the port may be bigger but it also flows slower which hampers cylinder filling at lower valve lifts.
In other words its better to have a fast flowing port than a slower flowing port.

The exhaust ports on these heads will flow more with work, but the big issue with them is the exhaust valve size and possibly shape.

Ive found on multiple occasions that the flow of the ports can be improved somewhat on the exhaust yet once the valve goes back in and the ports are tested with the valve being lifted at 1 mm increments to mimic the cam opening it, the increase isnt as dramatic.
The big gain on the exhaust port comes from a bigger valve but the flow ratios of exhaust to intake need to be retained if at all possible so that you dont have a situation whereby the intake underflows.
This possibly explains your heads lack of any work on the exhaust side, but its not really professional to do only one side as gains are gains even if they are only small.

How much do your ports flow? Who can tell until its tested?

Heres an example of what im talking about.
I recently tested a big valve audi head (same basic head as the 8 valver plus 1 cylinder extra) whilst at the same time porting another stock sized valve audi head.

Heres what i found.

Exhaust ports.

Lower plot is the stock exhaust and stock valve.
Middle plot is the modified exhaust port and the stock valve.
Top plot is the big valve in the exhaust.



As you can see, it flows a lot better than the stock or even modified exhaust port, however, take a look at the intakes for the same heads.

Blue trace is the stock intake port.

Green is the big valve head.

Read is the modified "stock" port.



This big valve head makes more flow than the stock port at all points.
However the modified port with the stock valve size only loses out right at the top of the cam lift where the valve spends only a fraction of its time.
Its making more flow and stays right with the big valve head almost all the way to the top of its lift, so although this particular big valve head is an improvement over the stock port its very definitely not an improvement over a modified port and stock valve in this case, but its probable that i could have made the big valve head flow better still as it came to me done by someone else- (no idea where it originated).

If you were wondering what such a modified port stock looks like btw, heres a photo of mine that i did.

Intake.





Exhaust port.

Nice reply, good info and airflow results to back it all up, have you  'polished' the ports on the 8valver to see if it makes any difference to flow, I would doubt it would considering it doesn't make any difference on an old A-series head which has one of the most restrictive heads known to mankind in the universe I would agree that cleaning up some of the casting marks would increase flow ever so slightly but not polishing the ports, that would be crazy!

I havent actually tried to apply an optically polished surface as it just promotes fuel puddling.

That finish you can see on the ports i did is about right as its generated with 80 grit carborundum tapes and is smooth but very definitely has a rough feel to it compared to one finished finer at say 120 grit which is what i use in the exhausts…it helps on the exhaust to keep them from choking up with carbon.

The casting mark cleanup actually does in some cases yield quite a good increase by itself and some of the heads ive done from different years were dire in that respect with lumps of flash sticking out and ridges right where you dont want them.

Anyway apologies for hijacking the thread, ill buzz off now and leave it free for others to chip in!

brilliant info really appreciated nice one. well im having no more work done to it but  should be having it on the dyno in a month or so. so ill have to let you know what it makes.i am quite curious now thanks again .