Whisper

iTrader: (12)

So I recently did a heads/cam swap on my M6 98 Z28 from an MS4 cam and GMPP ported LS6 race heads (bought the car with these installed) to a 226/230 Comp Cams and a set of Mamo 220s milled to 62 ccs. The LS6 intake was reused. I'm planing on getting another tune in about a month and a half (PCM of NC) since I purchased a Fast 92mm intake and to tune out the popping the car makes.

I've always been a gas mileage ****. Its one of the things that I love about the LS1 that they can get very high 20s (or more if stock) mpg. A lot of the decision on the cam was based on the most power I could make before fuel economy would truly start to suffer. I know a huge part of fuel mileage is based on the tune. I was largely inspired by what Tony was able to manage in his old Vette in this article: http://airflowresearch.com/articles/article078/A-P1.htm

I was wondering what I could realistically expect in my car fuel mileage wise IF me keeping my foot out of it and driving conservatively is a given? The car does have mods that hurt mileage such as the S60 with 4.10s and 18 inch Z06 replicas that I am unwilling to change. The car has dumped true duals and no cats. The reason I am asking this question here is because I'm wondering if my goals of having as fuel efficient of a 450rwhp car as possible goes beyond what a tuner can/will do and could be helped by getting familiar with tuning software and devices I see on this subforum. Maybe it could be a hobby. But I was wondering first if anyone has an opinion on what is realistic as far as highway fuel mileage first.

Darth_V8r

iTrader: (4)

Similar overall build to mine. I tend to get 16-17 around town. Haven't had a good highway run to gauge highway mpg. I have 7.5 degrees overlap, which hurts mileage. You'll get 1-2 mpg just on less overlap.

Your PCM will hurt you a little. I just recently (like Wednesday) installed the 2002 OS on my 1999 computer, and so far I wish I had done it sooner. A lot more features, tables, better calculations.

There were several minor nagging issues I couldn't get rid of, and the 02 OS appears to have addressed them.

One option it opened up is lean cruise, which allows you to run 16:1 down the highway.

I guess that's a really long answer to say "consider upgrading to a 2002 PCM"

Nicelysedate

iTrader: (3)

Changing your injector timing (EOIT) will help. I get 2-3 mpg better economy going from the stock setting of 5.55 to 6.10.

LSX Power Tuning

iTrader: (4)

Getting the timing and fueling dialed in on a M6 will help your mileage the most. Get your fuel trims within 3% and that will help alot. Getting the timing perfect for the best fuel mileage is something that just takes alot of time and trial and error since each vehicle is a little different.