Valves

[DCIV]

anyone have any clue how much it cost for a machine shop to do the OS valves? I just want some ball park before I go walking into a place.


Coop

[Wolf_Zero]

[quote=""vr4""]you also have the turbine housing restricting flow and backpressure in the exhaust manifold due to the turbine and x amount of boost.


forced induction cars overcome intake rectrictions much easier than exhaust restrictions. from now on ill save anything technical for 3stech. see ya there [/quote]

Making the exhaust valve larger isn't going to help at all if the real restriction is the turbine/housing. It's like making the opening for a funnel bigger but leaving the opening at the bottom the same size. You might be able to fight a little bit more in, but it's going to become just as backed up.

Assuming your point is truly correct, it makes me wonder why automotive manf. (including the Turbo era of Formula 1) have always used significantly larger intake than exhaust valves.

Unless there's a lot of damn good information on the AEM on 3stech you won't see me on there. Even than I doubt I'd get an invite for it. I'm not to worried about it though, any EMS info I need I can get on AEM's forums.

[DCIV]

I get what wolf is saying. The piston pushes out the exhaust gas so a bigger valve is going to help but not as much as bigger intake where the turbos are pushing air in. If what I am saying is what your trying to say then I agree with steve.


Coop

[Wolf_Zero]

That's not what I'm saying...

I'm not going to bother going into any more detail why either, it doesn't look like it's going to make much of a difference no matter what I say at this point.

[DCIV]

just trying to make sense of your post man, dont get all in a tissy.


Coop

[Wolf_Zero]

Sorry, had a bad day at work. After I eat maybe I'll try to make more sense of what I was saying.

[Wolf_Zero]

The piston doesn't do that much pushing as it would appear that some people think. A majority of the exhaust gases leave the cylinder once the valve opens up because those gases are under pressure. More pressure than your intake charge is likely to have. For example, most exhaust valves open before the piston reaches BDC which means that the piston is trying to suck the gases back in. Despite this the gases are still exiting the chamber, this is because of the pressure that those gases are under. However the piston does push out what's remaining in the cylinder.

Since vr4 was kind enough to mention the fact that you have an exhaust side of a turbo blocking the path of the exhaust and causing a restriction it makes it initially a moot point to go with a larger exhaust valve versus a larger intake. I'll use my funnel example again, but this time I'll go ahead and include adding the equivalent of an intake valve to the example.

Ok, just pretend you have a closed system with a funnel at the end of it. There are two openings on this funnel, obviously the narrow end would represent the turbo exhaust housing and the wider end is essentially the valve. Obviously you can only flow X amount of water through the narrow end under normal circumstances. This makes creating a larger top opening a little pointless because yes, you now can allow more water to go through the funnel. But you didn't actually do anything to change the amount of water being able to flow through the bottleneck of the system. You could increase the size of the top opening 10 fold, but you are still limited by how much the narrower opening can flow.

Now pretend you add a few psi of pressure into the system. This represents any extra air/fuel that would go into the cylinder from a larger intake valve. Well what happens? Despite the fact that you made neither of the exit openings larger, more water is going to flow through that exact same funnel. Why is this? It's because a pressurized system is always trying to get to a point of equilibrium, with the added pressure the water is "trying" harder to find the easiest way to equalize the pressure which means that more is going to get forced out of the narrow end faster. This does however, cause more stress on the components themselves.

Finally going back to normal motors. What's the main goal of making power? Getting as much air/fuel through each cylinder as possible. Replace the water in my example with air/fuel (which is much more compressable than water and flows better), and the closed system with the cylinder/motor and hopefully you get the point of this little exercise. Obviously, like with everything, there is a point of diminishing returns and there is a point that larger exhaust valves will help. But you first need to remove the original bottleneck for the larger exhaust valve to become really necessary.

Hopefully that makes more sense. And like I already asked. If having larger exhaust valves is such a good thing on FI cars why don't more auto manf. (racing engines or street performance engines) use larger exhaust valves more often?

[green-lantern]

COOP just put the fucking car together

[My92Stealth]

[quote=""green-lantern""]COOP just put the fucking car together [/quote]

X2