2004 Chevy Monte Carlo SS

July of 2010 - ZZPerformance 2.5" Downpipe w/ High Flow Cat

I've been doing a LOT of reading and research in the world of increasing the performance (in terms of horse power) on my Monte Carlo.   Luckily, for me, the 3800 v6 used in my Monte has a somewhat popular following (which has fueled a lot of after market goodies).   The fun part is weeding out the "hype".   I'm a computer tech, not an engine builder (hmm, almost sounds like a spoof on a McCoy quote), so it's taken me a while to figure out what I want to do and be comfortable with executing my decision.

I decided the first avenue to take is mod the exhaust (if it you want to get more power, the engine needs to breath better and the first step in breathing better, be able to output more exhaust).   A lost of people jump towards headers.    I've looked at headers on the 3800 and they seemed very pricy and possibly overkill.   I asked some people on message forums and read what everyone else had done. From people with both naturally aspirated 3800's (like mine) to the SuperCharged model, a lot of people leaned on a downpipe with high flow cat and Power Log (replacement front manifold) from ZZPerformance.   It appears ZZP has done a lot of research to the stock exhaust GM installed on these cars and found ways to "tweak" it by simply removing bottle necks and giving about a 2.5" flow all the way around.   I further confirmed there claims by actual pics of customers on the different forums who shared their findings while making these improvements.

After much research, the journey begins.   I ordered my new stainless steel 2.5" downpipe with high flow cat and new gaskets and it arrived 7/29/2010.   I decided this, as I figure I need to work the system from the back forward (next step I plan is the Power Log).   Below are pics of it after I opened the box.   I took note of nice clean welds and how this looked just like they described, 2.5" flow all the way through.


Saturday, July 30th, 2010, Jeff Lewis and I ripped into this.   I got the front end of the Monte in the air and we crawled under with some tools and went to town.   I took a moment to use some scrape would and stack it to hold the back section of the exhaust (so it did not hang or damage anything).   Since I ordered the downpipe, I had been coating the upper nuts with PB Blaster and I think it paid off (I did not worry about the ones holding the back flange together, as that was apart last year to replace the gasket and hasn't even had 5,000 miles since it was done).   Everything came apart nice and easy (couldn't ask for it to go any better).   Jeff helped hold the original down pipe and slide it out.

Below are some shots of the new and old.   You can see the old down pipe had what is refered to as the "U-Bend".    This is a part where the downpipe takes a large dip (and flattens out) so the rear O2 sensor can sit vertically (it's assumed GM was concerned the sensor might get damaged otherwise).   Many people believe this to be a bottle neck, but from my reading, it really isn't as bad as people believe, as it still moved the same volume of air through it as the rest of the pipe.   Regardless, the new downpipe has a much smoother look and still houses the same O2 sensor.


Looking at my factory down pipe and the new one, it looks like my original one looks like it has an inner ring that creates a bottle neck in the air flow (past that, it looks like the down pipe may have about 2.5" flow, I may cut it open to confirm this before I dispose of it).   It's hard to tell (as I could not get a clean shot and a tape measure was not the best measuring tool for this job), but it looks like that metal ring on my original downpipe reduces the opening for air flow to about 2 inches, but the ZZP downpipe appears to have a full 2.5" opening all the way through, with very smooth bends.

Re-installation was a breeze!   Jeff helped hold it into position and we both started lining up the new gaskets and starting the nuts and bolts.


CONCLUSION - After we finished, cleaned up tools and changed, we took the Monte for a ride.   Zipped around some local roads and on the freeway and such.   The car might be a touch louder (as in a decible, nothing really noticable), but it does feel like it has some improved performance.   Most noticable is when you goose the gas at lower speeds, it feels like it wants to "go" more then it did prior to the down pipe change.   It's not a large scale difference, but it is a noticable improvement.

Overall, I am pleased with the improvement I can feel in this product.   With what I have in mind so far for mods to my Monte, this seems that have been a very good and logical starting point!

2004 Monte Carlo SS Page

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