Im looking to get the most flow out of this b16 head. Head has a nice port polish job, de-shroud and im thinking of upgrading to .5mm oversize flat valves. Obviously ima need a valve job and rework the radius to get th benefits of the larger diameter. My question to the engine pros is do i need to replace the valve seats or could i open these stockers just enough to fit .5 over?

 

.5mm isn't that much when you're talking in the circumference of a circle. If you're going. 5mm why wouldn't you just get 1mm over. I have skunk 2 1mm on my turbo b series and made huge difference without porting and polishing. I do believe i still have stock seats. Almost 100%

 

Don't do it. The valves in the B16 head are plenty big. Oversize your valves and sure, you will see better flow... but your cam timing will be WAY less than ideal due to interference.

Just get a good sized cam and valvetrain work to support it.

 

most head porters will tell you that oversize valves on a b-series head is pointless for most of the builds. An H-series is more beneficial. Don't bother doing it.

 

for small bores oversize valves wont help....specialy if your not gonna port it to match...your putting a bigger wall that air has to go around to get to the combustion chamber...if your not changing seats there is no point you are just restricting flow...rlz and 4 piston can get over 300cfm out of stock size valves...more than you will need on a b series and also you v2v clearances will be too tight to run large enough cams to take advantage of it...

unless your building a 1000+whp outlaw car you dont need oversize...

 

So can anyone explain WHY oversized valves don't make "power" or I should say is "worthless".

 

My buddy put flat face over sized valves in his car after having a stock head on and his car ran wayyy diff.. Much more top end.. Pulled madddd hard

we had identically built cars except his head and it was a poor mans r setup.. Overtime after 3rd he'd pull on me about 3 cars and keep pulling. Id say makes good diff. It does cost lot. Many other things factor too.. Intake. Intake manifold with exhaust manifold.. Etc...

 

That's a pretty basic statement. If you look at what I said and what cibao2ner said, you'll have somewhat of an answer. In a smaller bore, increasing valve size usually increases valve head restriction on the incoming airflow as well as out going if you use oversize the exhaust valves as well. It limits the size of the cams you in run in some cases and affects their adjustability for tuning best power etc. Larger valves in a small bore B-series tends to cause more compromises elsewhere that will cost more power than would be possible by increasing the valve size. The fact that a competant head porter can get a B-series head to flow 300cfm on stock sized valves is just another reason why there's little point in doing it. The H-series heads are a slightly different story, on some builds.