My head is now showing signs of age...
The stem seals are beginning to leak and I am not up to the task of replacing them... So I have been looking at getting a new head unit that has been ported & polished...
I am not looking for "Ultimate Performance"... Just a little more power over stock but I need the car to be;
1; Reliable as its my daily..
2; Economical as it my daily..
3; maintenance free as far as that is possible...
I don't want to stress the engine to destruction point... Just improve what was there in the 1st inst..
I have been sent this info from a guy who does the work and I wondered what peeps opinions were about it;
8v small vs big valve
G60 cylinder heads, like other counterflow 8v VW/Audi heads, suffer from 2 issues. Firstly, the exhaust port is at a poor angle to the port and the port too small, likewise the intake valve is too big for the port.
Subsequently after a long time in R&D with respect to these heads we've worked out how to make them the most efficient possible for peak hp and tq gains across the rev range in respect to the chosen cam configuration.
First step is to maximise the port efficiency in relation to the standard 33mm exhaust valve, achieved by careful sculpting of the valve, seat and the port. Such is the gain in efficiency (51% average gain across lift range) that it rivals the exhaust flow of a standard ABF and KR 16v head. We subsequently tried to push gains further in the past by oversizing the exhaust valve to 34, 35 and 36mm. The end results in all three cases being either no better than (34mm) to actually worse as the valve size increased.
Although very small gains were to be had in the very low end of the valve lift range, the refitting of a larger seat caused port shape issues resulting in turbulent airflow with a drop of flow in the mid lift range.
Secondly the flow of the larger valve ultimately exceeds the flow capability of the head casting even when opened to the max, causing choking at high lift. So by fitting larger exhaust valves an average flow gain of as little as 20-22% was found instead of the 50+% gains from the standard 33mm exh valve when tested on a G60 8v head.
Similar findings have been found in the R&D of the intake port where mathematically the intake valve operates at an optimum when it is approx 50-55% of the bore diameter hence VAG's choice of the 40mm valve over the earlier 38mm ones. This choice however has been compromised in the head design with respect to the actual port size. The restriction in this case no longer being the valve or how far the casting can be machined but instead the intake manifold itself. For optimum gains we realised that money is best invested in opening up the original port mouths and repeating the same procedure to the latter part of the intake manifold runners as it meets the head. The end gains in doing an intake manifold and head combination are far more favorable than increasing an already optimum valve size.
It's these two factors established from ongoing R&D through the years that have resulted in the end choice of not offering the oversized valve option anymore. As the costs of the intake manifold option are equal to that of the oversized valve option it is simply put better value in respect to end flow gains and performance.
All VAG 8v incl the 2.0 x-flow heads
Standard - £250
Our most basic option giving your old head a fresh leash of life to a higher standard than the day it left the factory; pressure tested, new guides and seals, seats recut, valves reconditioned, wetblasted, chemical cleaned and skimmed.
Performance Heads - All consist of our standard recon with additional port work up.
Street/Strip - £495
The first of our performance packages, a straight bolt on option, good for standard and mild performance cams. Improved throttle response and midrange, smoother power delivery with improved top end power gains.
Weekend Warrior - £650
A good performance head ideally suited for med to high lift/duration cams. Good midrange and top end power gains subject to a remap.
Race Head and Intake Package (1.8 & 2.0ltr counterflow only)- £895
Taking our 8v head to the max with larger port dimensions requiring the modification of the intake manifold (or throttlebodies/carbs) to ensure there is no restriction of flow from the standard runner sizes thus capable of flowing equivalent to a standard KR head. High lift/duration cams are required along with a remap to make the most of this animal.
n.b. any replacement valves required unless stated otherwise are additional in cost to the above prices, prices are on exchange basis.
----------------------------------------------------------------------------------------------------------------------------------------------
By number one do you mean the stock refurb or this one?
Street/Strip - £495
The first of our performance packages, a straight bolt on option, good for standard and mild performance cams. Improved throttle response and midrange, smoother power delivery with improved top end power gains.
Stock refurb should bring you back to factory spec assuming that everything else is healthy.
The street strip combo can yield various results depending on the rest of the system so very difficult to put a number on it. As a general rule of thumb I describe it more by how the car will feel compared to stock as it is the change of the way the power is delivered and the shape of the power curve with more predominant gains in the midrange that make it most noticeable.
As a reference point though one customer fitted the mildest US autotech cam to his street/strip head and fitted a generic chip for it done by someone in Holland. The car made 125hp and 147ft/lb running out of fuel over 3500rpm hence the low hp figure. But like anything what dyno was it on how accurately calibrated and all the other pub nonsense.
Best way to look at it is it will pull stronger, be smoother to drive, have more mid range torque and providing the fueling is there carry on pulling nicer through the top end of the rev range.
