Evo8 head porting ...now with Stage 3 flow data!

[rado]

To address some of the questions I've been asked about valve jobs and "back cut" angles, I thought I'd share with reference to my most recent data from and evo 8 head.

I'll put up the data first, then discuss salient points in the thread. Questions are welcome!




now the graph...

[rado]

Ok, let me start by saying that the term "valve job" is a misnomer of sorts. This term really refers to cuttting angles on the valve seat, not the valve. Machining matching angles on the actual valves is called valve refacing.

Many believe that the purpose of a "valve job" is primarily for power or more specifically, increased flow. However, without debating importance of power, another key reason is to increase sealing performance of the valve in order to preserve compression.

So the two reasons are flow, and compression. Lets look at flow first.

From the data above, comparing the orrange and the black lines; ew can clearly see that the valve and seat preparation enables or facilitates increase flow accross the entire lift range of the valve. A max gain of 10 CFM is achieved at 0.3" lift!

Gains will vary from engine to engine, and the same combination of angles is no guarantee, but the the gains are certainly not insignificant!.

[rado]

The second and IMHO more valuable reason for valve work is to restore valve sealing, and thereby preserve compression.

Unfortunately these benifits cannot show up on a flow bench, but will manifest on the dyno, and also in longevity. Some high performance engines line the 4G63 have very narrow seating surfaces on the valve seat (<1mm). This boosts performance in the stort term but is ultimately will rob performance when the valve starts to leak.

If you ever have the oportunity to look at the seating surgace of a used valve under a mangifying glass you'ld be hard pressed to believe that any proper sealing cound take place.

Abrasive paste / lapping compound bedds itself into the metal, and causes premature valve seat wear, so the best solution is an accurate machined seating surface.

Additional angles on the valve or the seat, just aid the air while flowing past this critical part on any port.


I hope this sheds some light on the subject.

Richard.

[rado]

Stage 3 performance is on par with AMS evo heads!