1997tibby

Ok now i know in MOST (not all) turbo applications that useing your stock cams gives u better results that using performance cams, but does anyone know how a turbo 2.0L would work with a 1.8L cam?

hamhead

Won't make much of a difference since the stock 2.0L intake cam and the 1.8L cam are so close in specs.

a_gut

1.8L cam has less overlap and longer duration, I'll be installing it with my turbo setup.

sharkev

i remember of some topic that we discuss something about that, but i´m not sure.

what I recall its that the 1.8cam in a turbo application is not so good, because you want a more overlap to have more power. NOT SURE.

try to search.

maybe someone here knows about that.

Mad-Machine

The thing you are trying to avoid when going boost is to have both cams "open" at the same time. If the intake valve and the exhaust valve are open, any and all boost pressure you are blowing into the cylinder is going right out into the exhaust. So I think in that respect, duration is fine, it is overlap you need to worry about.

Alex01tib

i know this is a few weeks old but i thought i should let u guys know that having overlap doesnt send your boost right out the exaust, it actually goes the other way, ill explain...

in any turbo set up today, besides the aerocharger i think, there will be more exhaust manifold pressure than boost pressure, usually about twice the pressure. this means that if both valves are open at the same time you will experiance reversion, which is when exhaust gas flows back into the combustion chamber. (max boost pg 119 under reversion if u wanna see it for urself)

i just thought id let u guys know because reversion is alot worse than just blowing boost into the exhaust manifold. if the 1.8L cam reduced overlap it could be a viable turbo accessory. besides reducing overlap an anti reversion cone built into the exhaust manifold is also effective for preventing exhaust gas re-entry.

\/Yes\/

01blacktib

that's an interesting post, basicly its got so much pressure it comes back? is that a simple way to explain it?

Mad-Machine

interesting.. so my facts are a few years old it seems. This would explain why a lot of turbo porsche's I have seen have either a "D" shaped exhaust port or in some cases, almost a heart shaped one. Almost totally round, except for a triangular protrustion into the exhaust flow. No doubt done to keep reversion to a minimum.

a_gut

It makes sense if you think about it. The exhaust pressure drives the turbine, and the turbine drives the intake pressure. When both intake and exhaust valves are open, exhaust pressure HAS to be higher than the intake pressure, otherwise the turbo would defy the laws of energy conservation (you'd have a perpetual motion machine!)

Alex01tib

/\ yup, nothing can be 100% efficient so there is no way to take 20 psi of exhaust manifold presure and turn it into 40 psi of boost. The only way to have more boost than exhaust manifold pressure is to be supercharged too, and thats not particularly easy, but possible