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Can you share your findings, first hand experience, with 30 degree valve angles?
Are you talking about the back cut on the valve or the seat angle ?
From everything i'v READ... multi-angle valve job's are the way to go.
yes and no. Today I was presented with a head and valves that were cut in only one angle (5mm wide) 30 degrees. His reasoning was to remove as much material on the back of the valve to promote flow at low lift.
Then I did a search and found that the 30 deg angle is normally added on top of the actual, let's say 45 deg, seat angle.
Seemingly, both methods work, I would like to learn from more experienced builders what the correct way of doing this is and if it really improves airflow as much as I am led to believe ?
I can tell you now, from first hand testimony, from a guy who owns a very successful tuning company, that multi-angle valve jobs are the only way to go. In fact, this guy takes it one step further and has the valves and seats fully radiused.
30 degree valve angles (as in seat cut not the angle of the valve train in the head) has been/is used by some manufacturers (Pontiac V8 are well known examples) to increase low lift flow. It does this by creating a larger opening than an equivalent 45 degree seat cut would. After about an L/D of .25 the valve seat cut doesn't really have any effect.
Having said all that it stands to reason that multi-angle valve seat cuts are a performance advantage because they help to smooth flow through the valve opening. The user, or the head porter, needs to choose what the actual seat angle (the angle at the contact point) will be and then add the other angles either side.
thank you for your replies. André, can you chip in as well ?
Are you sure you're not talking about the back-cut?. Because 30 degree back-cut is a very common modification.
Sorry @Dynodom, I've never had the opportunity to test valve angles on the dyno so I can't really add much to the thread other than to say that multi-angle valve seats are the norm in the performance world.
"Are you sure you're not talking about the back-cut?. Because 30 degree back-cut is a very common modification."
Marek, I'm not sure who you are asking this question but if it is to me then yes I am sure. Having owned and built a few Pontiac engines (400 ci mostly) I can tell you with absolute certainty that 30 degree valve seats are not uncommon. Yes doing a 30 degree back cut on the valve itself is a common modification for 45 degree valves, anything that adds flow and does not cause reliability issues is worthwhile.
That sums up what the head specialist explained. He reasoned that grinding a rather wide face (ie. 5mm wide, almost "meeting" the valve stem) of 30 degrees angle on the valve will remove a lot more material on the back of the valve than compared to a third angle added "above the (ie.45 deg) actual valve seat angle.
He also said that it is a good idea to run lighter valves with this concept because the wear on seat and valve increase slightly. This concept was learned from looking (yeah yeah, copying it) at valves from a major Japanese performance company.
I left him a Hayabusa head to do a port- and "this" valve job. Cams remain stock. I added my small piece of advice of removing and rounding any shrouded area inside the combustion chamber all around the valves. These shrouding areas are known for restricting flow at low lift time, during which the valve spends the most time, as opposed to the time spent on full lift, twice.