Audi Quattro rebuild

4v6 · Post by **4v6** » May 9th, 2009, 12:01 pm

Ive had some experience of modifying these particular cylinder heads so hopefully the following contribution may be useful and appropriate to post here.

The Audi Quattro in 10 valve guise, comes in two basic types- WR and MB, the designations applying to the engine types fitted.
Intake valve sizes are 38mm with exhausts being 34mm across the engines.
Essentially the engines are almost identical but they do have some differences, namely compression ratio, dimensional differences with the conrods, big end journals, gudgeon pins and pistons being the main ones.

The cylinder heads are again essentially the same apart from the combustion chamber shapes/volumes but there are some other differences that are not readily apparent until you look inside.

The earlier WR heads appear to have an intake port that is very much better finished as standard than the later MB heads and it shows up as having a higher bare port flow than the later MB heads to the tune of around 10cfm@28" depression, the WR heads flowing ~150cfm as compared to the MB at 141cfm@28" depression.
The improvements I have found on these ports are attributable to the short side radius and the extremely intrusive guide bosses on MB heads. I have not experimented with valve seats as of yet.

The exhaust ports are as far as I can see identical and flow similar amounts, however after modification, although the bare port flows have increased by a similar percentage to the intake ports, the valve in flows dont appear to alter.
I would venture the opinion that valve sizes, seats or shapes would seem to be the limiting factor on the exhaust side, however I have not investigated this further at this point in time due to the limitations of my flowtest equipment.
Im sure Guy could offer his expert analysis regarding the above issue.