Polishing/Gas Flowing

[mrbeige 0]

I've got a spare cylinder heads that I'm replacing the stem seals on, and have started polishing the ports. What I want to know is, if I just use sandpaper (80 grit through to 240 grit) to smooth the casting marks out of the ports, will it make much difference?

 

I don't want to port it, because I've heard that if I do, I'll loose the only bit of torque I've got from my 2.0l 16v. "Am I right?" :?

 

I'm getting an exhaust cam modified for inlet too, how will this affect my performance?

[Neil VR6 0]

I was reading Practical Performance Car this month and they said that polishing it to a high sheen is a waste of time. Do what you can with paper but don't go any further. The article said that polishing it only serves to advertise what can be done to shift heads and generate business but in reality it doesn't make the engine more powerful.

[coullstar 0]

And only do it on the exhaust port as well.

[Neil VR6 0]

Yep, it said that too!

[rmn 0]

Get a kr head, kr cams, and a few other minor mods, i now have a 2L 16v daily driver with a simular spec including a 50mm inlet and its is damn quick and full of torque too. its all about engine breathing

i had a 1.8 16v golf annd corrado, this one is definatly the nicest to drive out of the lot

[davidwort 0]

And only do it on the exhaust port as well.

 

Don't think that's true, it's getting the air in that's the problem, exhaust gasses (to a certain extent) will get themselves out due to the heat and expansion.

Exhaust ports need to be shaped well and not have any bad steps in the flow, e.g. between head and manifold joints, but it's the inlet that gives the most gains if done properly.

You have to remember that the exhaust ports will soon soot up with deposits anyway, it might be true that polishing them will help to prevent this a bit though.

 

On inlet ports bigger is not better, because you will eventually just lower the gas speed and torque. What you need is better flow and port matching together with removing casting marks that affect flow.

I reckon on a DIY job where you don't have experience of porting and flowing heads it's best just to clean up casting marks and make your manifolds fit the head smoothly, use the gasket as a template and match the faces.

 

David.

[mrbeige 0]

Right, so clean up the casting marks, and port match the manifold to the head? I can port match the inlet as I have a spare head and manifold, but do I port match the exhaust manifold as well? Would it be silly not to port match the exhaust, as this is my daily drive, and cannot be out of action for more than one day (i.e. Saturday's)

 

44mm or 50mm? I'm thinking 50mm port matched, so as to try and retain good gas speed? Would I lose my torque if I go to the 50mm inlet, and if I don't like the 50mm performance, if I've port matched to the 50mm can I go back to the 40mm? I would guess not, but I'm not sure :?

[coullstar 0]

And only do it on the exhaust port as well.

 

Don't think that's true, it's getting the air in that's the problem, exhaust gasses (to a certain extent) will get themselves out due to the heat and expansion.

Exhaust ports need to be shaped well and not have any bad steps in the flow, e.g. between head and manifold joints, but it's the inlet that gives the most gains if done properly.

You have to remember that the exhaust ports will soon soot up with deposits anyway, it might be true that polishing them will help to prevent this a bit though.

 

On inlet ports bigger is not better, because you will eventually just lower the gas speed and torque. What you need is better flow and port matching together with removing casting marks that affect flow.

I reckon on a DIY job where you don't have experience of porting and flowing heads it's best just to clean up casting marks and make your manifolds fit the head smoothly, use the gasket as a template and match the faces.

 

David.

 

 

Just repeating what it said in PPC. Makes sense to me either way but they may be meaning to leave the inlet rough finish to introduce more tumble/swirl. I know there is much more to it than that but I cannot remember thier reasoning.

[davidwort 0]

Right, so clean up the casting marks, and port match the manifold to the head? I can port match the inlet as I have a spare head and manifold, but do I port match the exhaust manifold as well? Would it be silly not to port match the exhaust, as this is my daily drive, and cannot be out of action for more than one day (i.e. Saturday's)

 

44mm or 50mm? I'm thinking 50mm port matched, so as to try and retain good gas speed? Would I lose my torque if I go to the 50mm inlet, and if I don't like the 50mm performance, if I've port matched to the 50mm can I go back to the 40mm? I would guess not, but I'm not sure :?

 

Have a look at the Club GTI Forum posts about 42 v 50mm inlets, as a brief summary 50mm is OK for highly tuned high lift cam engines but the 42mm is the later design and there's a bit more to the shape than just mm bore, the 42mm actually performed better on a 2.016v block with a ported head and KR cams than a 50mm did throughout the rev range.

I'd say use a ported and rough polished 42mm inlet, that's what I've got and the engine is strong throughout the rev range on KR cams.

No point in using the 9A inlet cam with a ported head as the 9A inlet gives good low end torque but poor top end and top end is what a ported and polished head really gives the most benefit to.

 

As far as polishing the inlets and exhaust goes, a mirror finish won't harm the exhaust ports (but won't gain anything much either) but the inlet wants a rough but smooth (if you see what I mean) finish, mirror polished can harm mixing of air and fuel, which I think is where the confusion is - sorry coullstar.

 

Matching exhaust ports is a good idea, so is internally cleaning up the standard exhaust manifold, but it's hard work as it's cast iron!

 

Also, 42 and 50mm should be swappable as the port matching would be the same to the head.

 

David.

[flusted 0]

Polishing the exhaust side prevents carbon build up and aids flow.Match port both head and manifold to the gaskets

Av a look at this as theres some good info

http://www.sa-motorsports.com/diyport.shtm

[craigbeal 0]

Gonna port mine on friday. will take some pics i think. just ordered the gaskets so role on friday :/

[ben16v 0]

beale i`m off on friday so give me a bell and i`ll come over and `ave a goosy!!

[Riley 0]

And only do it on the exhaust port as well.

 

Don't think that's true, it's getting the air in that's the problem, exhaust gasses (to a certain extent) will get themselves out due to the heat and expansion.

Exhaust ports need to be shaped well and not have any bad steps in the flow, e.g. between head and manifold joints, but it's the inlet that gives the most gains if done properly.

You have to remember that the exhaust ports will soon soot up with deposits anyway, it might be true that polishing them will help to prevent this a bit though.

 

On inlet ports bigger is not better, because you will eventually just lower the gas speed and torque. What you need is better flow and port matching together with removing casting marks that affect flow.

I reckon on a DIY job where you don't have experience of porting and flowing heads it's best just to clean up casting marks and make your manifolds fit the head smoothly, use the gasket as a template and match the faces.

 

David.

 

 

Just repeating what it said in PPC. Makes sense to me either way but they may be meaning to leave the inlet rough finish to introduce more tumble/swirl. I know there is much more to it than that but I cannot remember thier reasoning.

 

is it not just to try and even up the flow of inlet vs outet?

 

arent the vw 16v heads a bit of an iffy design on the exhaust side?

 

crazy americans... 8)

[potatonet 0]

hell yes we are crazy

[Riley 0]

hell yes we are crazy

 

all in the name of research though eh... :lol:

[mrbeige 0]

riley, That's quite a good picture you put up there, it shows the water jacket that you would need to avoid if porting!

 

Also, what do I clean the combustion chambers with?

[Henny 0]

riley, what a fantastic photo! Where did you find that? 8)

[Riley 0]

henny,i found that pic on a vortex thread,some guys were messing about editing in lines where they thought material should be removed etc...

 

ill be damned if i can find the thread though :mad:

 

as for the combustion chamber im not sure ma self,maybe just a fine'ish wet/dry paper?

 

neil.