About a month and a half ago I removed the IMRC plates in the intake manifold to see what the difference would be. It was theorized that above ambient pressures should negate the effect of the IMRC system. But at the same time I noticed a slight bump in boost at the same point the butterfly valve opened which contradicted this concept. So I was curious as to what the effects would be if I removed the plates.

At first there was no noticeable difference except for about 0.5 more boost below 4k revs. The fact that there was less boost with the plates closed would indicate the engine was able to use the excess air better possibly making slightly more power. However, after more driving and in the heat of summer I started noticing something very interesting.

When stuck in traffic or moving slowly, in other words the engine is getting hot; there was a noticeable lack of power below 4k revs. This power loss was at part throttle inputs; full throttle seemed better relative to with the plates installed. But since I don't floor it from every light it was noticeable. It was almost as if there was a threshold of throttle input which was needed for power; sort of on/off response. Once the revs passed 4000 there was a quick surge in power. The next day when starting cold the power was consistent from the lower revs to higher revs.

It seemed that when the engine got hot and the air, there was a loss of power below 4000 revs with the IMRC plates removed.

Last week I reinstalled the plates and have driven several times in mid 90 temps with complete sun and the power is even through the rev band. This high temp lull in power was not present with a fully functioning IMRC system. So the airflow in the manifold does seem to be affected by the IMRC valve even under boost which is contrary to what I would have thought.

The next step, once I reinstall the boost gauge, will be to disconnect the IMRC actuator and see what the response is like with the valve closed. I expect there will also be a drop in power but who knows, I've certainly been wrong before. It would be interesting if the response was better with the plates closed even at the higher revs.

 

Very Interesting scalbert, and I have missed some of your posts but why all this work? Obviously you are trying to figure out why and how things are working the way they are - but are you trying to come up with anything in particular?

 

these power differences are great enough so that you can feel them from just driving or are you on a dyno measuring them?

 

Mainly for reference.

I have thought about replacing the entire or just portions of the manifold with a custom Liquid/Air intercooler. Before doing so I need to know the ramifications of removing the IMRC system.

Also, I want to know the effect when/if the IMRC actuator goes out on a blown vehicle.

 

You could notice them while driving and primarily at part throttle.

 

It will probably act different with a bigger boost pulley!

 

We shall see...

 

Any new news on the IC and even higher boost project??

 

I'm still waiting on the silicone elbows. I just called and they're telling me the middle of August. :angry: I'm pretty sure I will be able to use the larger IC, but I want to mock it up with the elbows before I decide. Maybe my headers will be ready by then.

I got your pulley off and shipped back today. I sent it to the Cobb Place address, and it should be there Friday. Do me a favor and measure your two pullies. I want to make sure it's 3/8" larger. You know, measure twice cut once. When I double it for the larger one, I don't want to end up at 9psi.

 

No problem, I'll use a Mitutoyo hand micrometer on it or maybe even a laser thru-beam micrometer. Is one micron (0.000039 inches) accurate enough.

 

That's what I'm talking about! I was using a 25' Stanley tape measurer.