OK, so a couple days before Christmas I cut off the stock mufflers on my '00 Monte SS and replaced them with straight pipes. Right before the mod, my Avg MPG read 22.6, and I reset it to see what it would do. In the past few weeks since taking the mufflers off, my MPG has varied from over 24 MPG to about 19 MPG, and now it sits at 21.5. Of course, it goes up when I just drove on the highway, and it goes back down when I've just been driving in town the past few days. But does anyone know if the loss of backpressure from removing the mufflers can have a bad effect on gas mileage? And what about power? It's winter, so I havent had the chance to take her out on a back road and really open her up, so I'm not sure what happened as far as performance. I am considering installing a performance chip (I've been looking on eBay and there are ones that are only about $1, and one called the Redline Power Chip that's about $30, is there any difference between the chips or are they all the same?) so will this help my performance even more, or correct any problems the loss in back pressure may have caused? Also, I want to put an aftermarket intake filter on and fabricate an air box to surround it. Will doing those two things help my performance/gas mileage or hurt it? Thanks for the help.

 

I dont think the mufflers would change the backpressure enough to change your gas mileage. There are so many restrictive parts of the exhaust system before you get to the mufflers. I think the change you saw was either a normal fluctuation or just from you playing around a little bit more after you cut the mufflers off. As for chips, I wouldnt recommend ANY. I would either recommend apower tuner or a custom PCM. I have heard good things from DHP tuners as well as HP tuners. Also ZZP makes a good PCM for the 3800. As for an air intake, the best bang for your buck would be a fender well intake. You have to move the washer bottle I THINK, im not sure. Talk to z34pheonix about the tuner and the FWI. He has a good how to site that will give you some good info.

 

OK thanks, where can I get a PCM and how much to they cost?

 

Go to zzperformance.com/grandprixand look at their 1.0 PCM. I think the price on it is $90 dollars or something. I would talk to someone there first. Tell them what you want to see performance wise from your monte and ask them if they recommend the 1.0 PCM for your application. It will most likely work for you but it doesnt hurt to talk to them before you buy. Who knows, they might even have more recommendations for you to get more power.

 

I looked at the 1.0 PCM and I think that's what I'll end up doing. I e-mailed customer support at ZZPerformance and they didn't give me much help; they just gave me a list of expensive parts to buy. This winter I still plan to put on an aftermarket cold air intake and delete the exhaust U-bend, so combined with the muffler removal and a ZZP 1.0 PCM, about how much of a performance/MPG gain do you think I could make? I'm not sure how much HP the stock 3800 has, but how much do you think I could gain there? Also, the stock governer kicks in at about 105(?), and since the 1.0 PCM disables the governor, what kind of top end do you think I would have?

 

Though a lot would argue with this reasoning keep in mind that no backpressure is ideal for all out power.. but going overboard on a street car could hurt the low end torque a bit and when going stop light to light might require a tad more throttle.. though this might not be an extreme enough case, and it really takes a few fill ups to gauge avg mpg. So see how it is over time..