Can someone explain to me what the benefits are for running oversized valves? Is there a noticable performance gain? What additional engine mods need to be done in combination with oversized valves? Cam? Will the larger valves affect smog output? I live in the land of the smog nazi's (CA), so I'm a little bit reluctant to modify the engine if it will wreak havoc come smog time... I am looking for a little extra "seat-o-the-pants"...

Ken

O/S valves help increase volumetric efficiency. i'm not so sure on the low end, but they most definitely help the engine breathe at higher RPMs. a good cam really makes things even sweeter...

you can get away with a lot of engine work here. I have already done all of this to my truck (read below) and i passed...granted i lowed my idle to barely keep the engine alive, but hey, passed with flying colors! Take that CA<img src="/forums/images/graemlins/nana.gif" alt="" />

do oversized valves really make that much difference? would it even be a noticable gain in performance? Has anyone done this mod?

I put EB's oversize valves in my old 22r. I also did one of his midrange cams at the same time. It didn't help much off the line, but it made a very good difference on the uphill grades

Besides flow rate, you are also looking for turbulence. Is harder to quantify turbulence though. Turbulence in the combustion chamber creates a fast burn, and combustion pressure develops sooner while the piston is still at the top of its stroke giving more power and fuel economy.
A computer simulation experiment was done on an engine with an extra piston that pumps air through a very small valve creating large turbulence. Even with the extra drag of the extra piston, it still got much better fuel economy.
Another reason why BMW inline 6 engine with variable valve lift get quite good gas mileage and power. The valve opening is matched to engine speed to create the most turbulence in the combustion chamber.
The size of the valve has to be sized to match the engine rpm. For high rpm, larger vavle, and smaller valve for lower rpm.

>>>*Sure, I think I can. The obvious benefit is the opening is larger, simple as that.

This means more fuel/air mix can pass at a given lift. But the situation is vastly more complicated than that, otherwise we would just install the biggest valve we could get in there and be done with it.

The increased head size means an increased pattern across the cylinder, so distribution is improved. Then we know that the first .100" of valve lift offers the best atomization due to high pressure under the intake (Think of that spurt of water you get when you take your finger off the end of a water hose)

So size helps in many ways. Add in that bore size, stroke, and expected engine speed to port velocity has to be taken into account, and there are limits to what is the best size.

So just like a 2.02" intake valve adds perhaps 5-6% to a typical smallblock Chev V-8 over the stock 1.94", the same thing happens with a little Toyota 4 cylinder, or even the V-6.

The effect is less noticeable in the lower RPM ranges, and increases as engine speed increases....*EB

So how much effect will larger valves have on a 3.0?

>>>*So far the effect has been a bit less than we hoped with the 3VZE but it is still there. That engine design is a shade soft for low end anyway, it seems to me.

I need to fiddle with that design some more, but too much to do and too little time...*LOL**

I ran out of those valves anyway, darn it. Some of the big rebuilders gobbled up all my stock, now I have to wait 6 months to have them made again...*EB