S4 Heads vs RS4 heads

[s4woody]

well apparently its all in the port design and amount of flow that makes the NA heads a good mod on our cars..and if ya cant find or afford RS4 heads then it,ll do for me..or to be more precise i just got a pair and they are gonna have to..

[BRETTCOLLINS]

I am thinking about porting and polishing a set of S4 heads to keep low down torque, Like the way the My S4 pulls from an RS4 through the gears. don't like the way RS4's make power... it is all to high in the rev range for me.....

[KayGee]

Two very important features of head design are combustion chamber design and mixture speed through the head. Bigger ports aren't the be all and end all of head design. Larger than optimal ports will slow down gases coming into and escaping from the heads actually reducing power.

However we are talking about turbo charged vehicles so we have an advantage "boost". Typically turbo charged vehicles run smaller ports because the gases are under pressure you don't need as big a hole. However like everything else when you start tuning a vehicle you find you need to either increase port size or speed up the gases. Hence porting and polishing of heads.

NA heads have bigger ports are more readily available and cheaper than RS4 items.

Cosworth did a fantastic job with the RS4 heads, they flow really well in the high revs just as cosworth intended. However they designed them to run around 1 bar of boost, tuned vehicles are running considerably more than that....

Now the question is really whether NA heads are upto running 1.5+ bar of boost reliably. Is there enough cooling potential to stop them from warping under high stresses. Are the oilways capable of deliverying enough oil. It would appear there is. So NA heads become and attractive option for those wanting more power.

Strip your S4 heads and drop the parts into the NA heads. Possibly think about RS4 exhaust cams and springs and you have a cheap alternative to RS4 heads. With possibly more potential for power than RS4 heads (you need to speak to someone like Mihnea who has tuned a few cars with these heads to get his opinion as to which are better).

It is worth noting that MTM do head work on their big hp RS4 cars indicating that ports on the RS4 do need some work when you get around 500 Bhp mark.

[saf]

Thank you Kevin.

Top info there.

Helped me understand a lot.

I shall speak to mihnea tuesday when i am there.

Thanks for the tyre advice too.

Thanks guys as well. great advice. very very much appreciated.

[Paulm]

great post.

So we are saying a N/A head flows along the same lines as the RS4 head but at a fraction of the cost. Sounds good to me.

According to what I have read, at the same boost pressure the RS4 head can produce 40 to 50 bhp more than the S4 head.

So, can the heads be changed insitu?

[s4woody]

the NA heads are the way to go if ya cant afford the RS ones..and as for removal insitu..alotalota work i,d say if its poss,and i wouldnt wanna try it..

[MarkB]

Worth remembering if I ever burn out a valve. Probably cheaper and easer to source than even an S4 cylinder head.