i found out that i have to replace a couple of my valves, so i am going to get some aftermarket high-performance, what are the advantages to oversized valves. i have seen that VWs have 2 intake and 3 exhaust valves for turbo use. if i go turbo, should i use bigger exhaust valves than intake valves? does anyone have suggestions on what brand to use???

 

Ferrea I got .5mm oversized valves for my prelude. I have a link at home that explains a little about the benefits of oversized valves. I'll try to post it later.

 

please do post it, id like to learn a little more about this topic. thanks.

 

"high-performance" valves are usually designed to be lighter... being that the less mass there is to move in the opening/closing process, the less wear on the parts that control them. Also the less mass, the less energy required to start them in motion as well as to stop them. This is generally geared toward high rpm operation and tied to the use of and upgraded valve-train(stiffer springs). As to oversized valves, granted they are properly fitted and seated, the increased diameter would ideally lead to an increased area for either intake charge entry or exhaust gas exit. If a signifigantly larger amount of air/fuel is being burnt, larger valves could potentially lead to open up the entry/exit space allowing more travel in the same amount of time or faster fluid velocity. Personally I find that in general smoother fluid travel paths leading to higher velocity are more important than path size. Of course there is always the point where the conditions the original part was designed for are surpassed at which time it becomes a bottleneck. Vw 1.8t motors use the 3 comparably smaller exhaust valves in place of the standard 2 in most part to help w/ emissions and fuel economy. Basically it clears the combustion chamber faster so that they can play w/ the timing a little bit more. It also helps marketing by being able to claim a "20valve 4cyl turbo engine" and so on. Don't get me wrong, audi knows their car stuff... but they also know how to sell them

 

good info i was also told you compensate lower end power when upgrading to os valves, but then again you gain some on top end... but we all know how lag sucks so its one thing or another i guess.

 

ive read before that using oversize valves on vtec heads is useless unless your going forced induction.the stock valves are considered oversized already from the factory.I do have to admit,the stock valves are very good pieces for all motor.

 

i plan on puttin turbo on my lude, so that's why i considered oversize valves, i've also heard you loose low end torque but seriously gain in high end power, especially with FI, which is what i plan to do

 

Oh, also valves must be made of a material that can withstand the ignition/power stroke indefinetly and be able to transfer the heat to the engine block everytime it seats in the closed position. The water jackets in the head help to take the majority of the heat. If the oversized valves or any for that matter don't transfer the heat properly, you'll have a nice set of burnt valves. If they don't seal well, you see nice white smoke coming out your shiny chrome pipe. And just a note, w/ any valve upgrade... make sure that retainers and clips are solid and quality. Don't go cheap here or you may just find a bunch of valves having a party in your combustion chamber. Ask JG. go on, do it.