You have the ability to make that test any time you want, without a dyno. Make a pass on the street with the filter on, another with the filter off. Compare the MAP figures in your data logs.

 

That is what I meant by my post but it might not have been clear. Thanks

 

Thanks guys. What I meant by my earlier post is that I cannot run the test using the vacuum instrument on the dyno to replicate the condition. I did however hook up a dial vacuum gauge about an hour ago. It isn't ideal but I can see the relative change.

Under normal passes down the highway, vacuum seemed normal at cruise and WOT with the cam set up that I have.

I covered the front with a plastic bag to create an intake restriction. At WOT, vacuum dropped to 2 inHG then steadily rose to 6 inHG. The restriction relative to RPM (load). So, vacuum will slowly increase with an intake restriction as stated by cardo0.

I didn't clog the exhaust on my car... but the car I borrowed I jammed in a socket and a rag which was secured with vice-grip pliers. (don't try this at home - disclaimer). At WOT, an obvious loss of power but the vacuum gauge was reading typical, not abnormal results. However, under cruise the backpressure increased. This caused cruise vacuum to steadily drop while under load. Predictable.

Back to my car, the vacuum did not drop after cruising for a while (but my dial gauge is not as accurate as digital) so it seems that the exhaust is not too restrictive.

From 2000 - 4000 RPM I'm at 0.1 inHG.
From 4000 - 5000 RPM I'm at 0.4 inHG.
From 5000 - 6000 RPM I'm at 0.6 inHG.

So, it may be a small intake restriction. Could be that the filters are getting dirty but the dyno operator said it may be the SLP intake. He said he's done these before and they don't seem flow as much as a Moroso. I don't know if that is true or BS. Maybe someone who's tried both would know.

I'd like to replicate that on the street (with and without filters) as suggested above but my dial gauge is not as accurate as a digital reading from the MAP. Are there any GREAT scanners for the OBD-I? Something like the Auto X-Ray 6000 that can be used for both OBDI & OBD-II cars and provides live data. Any alternative is welcomed.

Well, I thought I'd give an update. Thanks for your help.

 

Thanks Cardo0. I had the guys at Haddad Motorsports weld up an additional O2 bung into the Y-Pipe. This way we were able to dynotune the car using a Wideband O2. I can use that fitting to connect an exhaust pressure tranducer. I think one of my buddies has one I may be able to borrow for a weekend. It will give a digital signal based on backpressure.