Ok... I just bought a New 2006 Monte Carlo SS (with only 64-miles). I had a local muffler shop fabricate a cat-back using FlowMaster mufflers. After which, I noticed a big difference in "Out-of-the-hole" power and between 20-mph to 45-mph the car sounds funny (like it is missing, but it is not).

I am a finance manager for a Chevrolet Dealership, so I had our mechanics look at and they told me I lost backpressure and that was the cause for the loss of power and that funny noise. They recommend I go back to stock which would cost me $600 with my Employee Discount.

OK... Magnaflow says its cat-back system is DYNO-TESTED & TUNED, at $725 and then I figure another $150 to have someone weld it together for me. SO my QUESTION (and my mechanics cannot answer me), Am I doing any harm to my car now using the flowmaster system with no resinator that could cause warranty issues that my warranty would be voided because of the exhaust? SECOND QUESTION: Would you recommend the Magnaflow Dyno Test System or should I go back to stock?

OK one more question:
Just read about the EFM/DOD system and if I understand, the NEW EFM computer is hardwired, cannot be modified, and any modification will be voided by the EFM system automatically adjusting the vitals to compensate, and that even throwing a Cold Air Intake is a waste because of this tamper-proof box???

 

First of all, explain a little about your Flowmaster setup, what size piping, etc....

I have a custom Flowmaster system and I didn't feel any loss, plus it improved my 1/4 mile times. I have 3" from the cat to the Y (w/res delete), my Y is 2.5" into Deltaflow 40s. Maybe your shop went too big???

Unless the removal of your resinator specifically causes a problem AND the dealership can PROVE that it was the cause, you shouldn't have any warranty issues. And, the chances of your resinator causing a problem are slim to none, and slim just left town.

You can find the Magnaflow system for around $500 online, but if you really like the sound of your Flows, I wouldn't go that route. The Maganaflow system sounds good, but not quite like the Flowmasters.

Finally, many of us have 2006s and have had NO problem with installing a CAI. We've also got programmers that can eliminate DOD if you want. So, not too sure what you're talking about on that last paragraph.

Welcome!

 

My last paragraph came about from what I read on GMHIGHTECHPERFORMANCE.com. Trust me, I stopped working on engines when the first black box came out in 1975... yeah they had some stuff in 1973, but 75 is when the blkbox ruled.

I have been asking this question around the internet because I want (no, need) to know, if my car is ok until I can afford to go to a magnaflow or back to stock. I have learned a lot about the LS4 in the past few days... enough to be STUPID/DANGEROUS! So please take everything I say with a grain of salt, because I really don't know and I am regurgitating what others have said.

The LS4 is quite unique in that the DoD/EFM system is designed to self-correct itself as much as it can to maintain factory specs. As indicated by one individual, "Even a Cold Intake" is defeated by the EFM. While more air is incoming, the EFM system adapts and restricts its in the intake itself, and in the case of someone putting a supercharger on the motor, the EFM would sense the massive air and put the motor in "Engine Failure" or limp mode, reducing engine power to half. The EFM system is designed so that it cannot be defeated without total removable and the motor modfied to operate without it, or so I am told.

Mechanics have told me that for a Cat-Back system to function properly, it must me dyno-tuned to the car to maintain backpressure at low RMP and go to zero back pressure at RMPs over 3500 -- like the Z06 works -- something most Tom, Dick, and Harry's at your local muffler shop cannot do. They say my car has lost its low-end torque (and I will validate that, because the steering wheel would rip out of my hands from a standing start and now it doesn't). But that I have probably gained high-end Horsepower, that I will again validate, because my top end speed has difinitely increased. Again. What no one has answered is, am I hurting the motor right now with the no back pressure at low RMPs (by eliminating or severly reducing scavenging), or is the Cat itself going be enough to allow the proper scavenging.

 

There's no mystery about exhaust. You put it on to help your car breath better. Just read over the threads there are a ton of them on performance stuff with LS4.

 

You still haven't told us how big your piping is. If you went more than 2.5" on a stock setup, then you're gonna lose your low end and gain high. This is normal.

And as far as "cutting power in half", that's called torque management. It's designed to pull timing in order to save your transmission. A tune will solve this problem.

Even then, some people on here (Taz) have claimed to be feeling significant gains on an intake even with the stock tune....so there is a bit of grey area as to how much power is pulled and when...

 

If I am not mistaken, they cut off my resinator, welded in a new pipe, and then cut my stock mufflers off flush with the muffler and then put in FlowMaster Delta 40s in and welded them to my stock system and tail pipe.

 

Your fine, no worries. I have a 2006 as well with magnaflow catback and K&N intake. Runs great and is pretty quick. Ran a few 13.9's @ 101 mph quarter mile with just those mods last weekend. I'm in Michigan too, where are you at?

 

3" inch piping is pushing it for stock. I have 3" because I have quite a few mods and a custom HPT tune to account for the loses. If sound is what you are looking for, you always have a custom system fabricated, 3" to the y-pipe, then 2.5" to the tips through bullet mufflers. A lot of people here like the Flowmasters, but I personally value performance over a sound...so I suggest Kooks or Dynomax bullet mufflers.