So as I asked a question about valves on the race only forum, that got me thinking about the size of valves in a boosted engine, specifically when it comes to the intake to exhaust ratio. I know that NA engines like bigger intakes and smaller exhaust when making max power per cubic inch but in terms of boosted engines, I don't really know.

So in racing boosted applications, what type of intake to exhaust ratio do these engines like. In a theoretical sense it seems they might need to have a little bigger exhaust to get things out of cylinder more quickly. I'm sure some of the boosted gurus on here can answer this question. Thanks in advance guys!

it may not be so much a % ratio but designing the cam to your engine needs. a longer exh dur than intake.

You will want a bigger exhaust valve compared to a NA engine. I run a 1.625 ex and 2.225 intake on my w8 turbo motor. Alot of the NA w8 ex valves are in the 1.55 range.

The sizing is not your only worry in a boosted application. You need to use a nice valve from quality material. .

True. Exhaust valves have hard lives in turbo engines.

I'm pretty sure my exhaust valves are a stock 2 piece design and I've really been thinking it may be a good idea to take the heads off and replace the valves for a better one piece design. I've seen some n/a failures from 2 piece designs that obviously are catastrophic. Not cool.

Has anyone here used a 2 piece valve in a boosted application (I don't know if that is standard for being 'stock' or if it is a Magnum engine specific thing) and if so how well have they held up? It sucks to soak up probably 300 bucks in parts to replace the valves but it sure beats chunking a piston and still having to replace all of the valves, haha.

Careful when thinking about going to a larger size exhaust valve...Going too large will reduce pessure, which spins your turbo

There's a lot of theories on this, most of them not very well thought out. An engine doesn't know it's boosted. It only sees pressure differentials. So let's say you add 15 lbs of boost to the intake manifold. That's a total of 15 plus your atmospheric which is dependent on elevation, barometer and a few other things. So you shove that mixture in past the intake valve, it closes and BOOM! Now how much pressure do you think is coming out the exhaust? The more air you get into an engine, the more air you will get out of it. Plain and simple. Does this mean I wouldn't port on the exhaust side because I don't think it's as important as the intake? No. That is not what I'm saying. I'm simply saying don't choke the intake in an attempt to make the exhaust better. You will find that if you pick up the intake flow and nothing else, your boost will go down, the intake temps will go down AND you'll make more power. Boost is, after all, a measurement of restriction. And definitely put the best valves you can afford in that puppy.

Big exhaust valves allow some important things in a turbo engine. First, exhaust flow at the valve is only as important as you make it. Having the flow capacity in the head is useless unless you are using a good flowing downstream system.(headers/turbine/wheel)A good flowing head with bias on the exhaust, combined with a complimenting downstream system will allow the use of a camshaft with more characteristics of a n/a cam.
Another advantage is valve cooling. Most of the valve cooling is thru the valve seat. With more surface comes more contact, and with that comes a better cooling, which allows longer durations(less seat time) with adequate valve temps.