Originally Posted by SGAL1

Last night I replaced the emissions and EGR hoses on my engine and I noticed the previous owner had plugged the EGR valve hose.
The A.I.R. / smog pump has also been removed.
I removed the plug that was in the EGR valve hose and replaced all the hoses to the way they are supposed to be routed according to the routing diagram on the inside of my hood.
My question is this: Does plugging the EGR valve hose improve performance?
I have read different theorys on this and I wanted to get your take on it.
Having no emissions testing in Florida I'm not really worried about that.
However I do want my engine to run at it's best performance.
So should I put the plug back in the EGR valve hose or leave it out?
Thanks for your input...

Originally Posted by 427Hotrod

The exhaust comes through the exhaust cross over ports in the center of the heads. If you were to remove the intake you would see a hole on each head between the 2 sets of intake ports that makes a direct connection to the 2 center exhaust ports inside the head. This passage is normally used to warm the intake during cold starts. There is a *heat riser* valve on one of the exhaust manifold outlets that somewhat closes during cold starts to force exhaust through that passageway and on out the opposite manifold. The intake manifold has a cast in passageway that connects the right end left side *exhaust crossover* ports in the heads.

On EGR manifolds that passageway is also cast to bring exhaust to the EGR mounting pad. If you remove it you will see two ports. One will have exhaust flowing out of it from the heads/crossover port and the other goes into the intake runner or plenum area that normally carries the air fuel mixture. There is a gasket that separates the two ports at the EGR. You could have a leaking gasket under the EGR that can cause a vacuum leak or an exhaust leak depending on where it's leaking. The EGR valve opens and allows exhaust to pass through it into the intake plenum/runners. When closed it seals the two passages off. When removing it, must folks install a flat plate to cover both passages and use the stock gasket. This prevents leaks and passage of exhaust into the intake runners/plenum.

The EGR *cools* the combustion event somewhat and reduces detonation as well as helping NOx. Seems strange to say exhaust *cools* anything, but what it really does is take up space that would normally be filled with a clean air/fuel mixture. Since the exhaust won't burn again, there is less good fuel/air mixture in the cylinder to ignite...thus less pressure to push the piston down. High cylinder temps increase NOx so this cools it down some to reduce it. The EGR is disabled at WOT if it's working right and typically only operates at light throttle applications.


JIM