30 mpg??
Melting Slicks
Joined: Mar 2005
Posts: 2,891
Likes: 4
From: North Port Fl
Who ever told you that changing your heads and cam would not decrease your MPG didn't know what they were talking about. When you do things like add a high flow intake or better flowing exhaust or headers your are allowing the engine to breath better and also making it more effecient so it will increase both HP and MPG, but when you change the heads and the cam you are doing so to build HP, but you are not making it more effecient your are actually doing the opposite you are cramming more fuel and air into the combustion chamber than you were with the stock heads and cam at the same RPM so you're going to get worse gas mileage. Depending what cam and head combination you go with will determine how much more fuel it will burn. A decrease of 6 or 7 MPG at 65 miles per hour is not unheard of, I have heard of a lot worse. There is no such thing a free HP, it either cost your money or fuel economy and usually both.
Last edited by ljthe2nd; Jan 6, 2009 at 04:12 PM.
Safety Car
Joined: May 2004
Posts: 4,811
Likes: 2
From: Simpsonville SC
I got ls6 heads, ls6 intake, G5X4, LG Pros, no cats, and B&B Bullets, makes 434 rwhp and 415 rwtq and 559 rwhp and 623 rwtq on a 150 shot. I get between 27 and 28 on the highway. Its a M6 with stock 3:42's. Its all in the tune. When mine was bone stock I got 32.5 on longtrips. Get your tunner to tune on it some more
Melting Slicks
Joined: Mar 2005
Posts: 3,335
Likes: 0
From: Buckeye Country OH
CI 6-7-8-9-10 Veteran
St. Jude Donor '05-'06-'07-'08
Who ever told you that changing your heads and cam would not decrease your MPG didn't know what they were talking about. When you do things like add a high flow intake or better flowing exhaust or headers your are allowing the engine to breath better and also making it more effecient so it will increase both HP and MPG, but when you change the heads and the cam you are doing so to build HP, but you are not making it more effecient your are actually doing the opposite you are cramming more fuel and air into the combustion chamber than you were with the stock heads and cam at the same RPM so you're going to get worse gas mileage. Depending what cam and head combination you go with will determine how much more fuel it will burn. A decrease of 6 or 7 MPG at 65 miles per hour is not unheard of, I have heard of a lot worse. There is no such thing a free HP, it either cost your money or fuel economy and usually both.
With my mods and the cruise set @ 72mph I can achieve 27-28mpg vs. 32mpg, stock.
Racer
Joined: Nov 2008
Posts: 484
Likes: 0
From: North Dallas area TX
I've only had my 04', C5, Auto, Vert, grocery getter since the middle of December but my daily commute to and from work is about 30 miles each way on US-95 north from Vegas. It's a long, strait, relatively flat road with a 70MPH speed limit and lots of cops who love pulling over speeding GI's and writing tickets. I normally set the cruise at 75mph and flip the DIC to instant MPG so I can watch what the car is doing. On perfectly flat level road the average is about 28-29MPG but every time I hit any kind of slight uphill in the road it drops to 23-24MPG and on any slight downhill it goes up to 32-34MPG. With about 70% highway and 30% around town driving the best I've gotten on the DIC's average MPG readout for single tank of gas is 22.8MPG. On a long highway drive of a few hundred miles over several tanks of gas I could easily believe a 32MPG average per the DIC.
Do my numbers sound about right compared to what everyone else is getting? I've been toying with the idea of taking everything apart and cleaning the heck out of it just because I don't know how well the previous owner maintained it. I figure it wouldn't hurt to do but I'm a bit paranoid about ripping such a beautiful machine apart and not being able to get it back together. Heck I about had a brain hemorage trying to instal a K&N filter
How the heck do you get the assembly out to put clean it and install the gasket without breaking the tie down straps?
Even if the best I ever average is 22.8MPG it still beating the heck out of the milage I was getting out of the 06' Quad Cab 4x4 Tacoma I traded in on it. The absolute best that thing ever got was 24MPG from L.A. to Las Vegas.
Do my numbers sound about right compared to what everyone else is getting? I've been toying with the idea of taking everything apart and cleaning the heck out of it just because I don't know how well the previous owner maintained it. I figure it wouldn't hurt to do but I'm a bit paranoid about ripping such a beautiful machine apart and not being able to get it back together. Heck I about had a brain hemorage trying to instal a K&N filter
How the heck do you get the assembly out to put clean it and install the gasket without breaking the tie down straps?Even if the best I ever average is 22.8MPG it still beating the heck out of the milage I was getting out of the 06' Quad Cab 4x4 Tacoma I traded in on it. The absolute best that thing ever got was 24MPG from L.A. to Las Vegas.
Pro
Joined: Feb 2007
Posts: 550
Likes: 0
From: Clermont Florida
Damn, I think I have a super c5 then...Its an M6, but all I have is an intake, x pipe, and catback....i reset my MPG button and went 120 miles of straight hightway driving at 65 mph, then about 15 of city miles till I reached my cousins house, and I AVERAGED 37.6....I actually took a picture of it with my camera phone lol...Has anyone else experienced these kinds of numbers, out of curiousity?
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Le Mans Master
Joined: May 2006
Posts: 6,774
Likes: 363
From: Midland TX
I have a stock 2001 Coupe A4 LS1 with Hurricane intake and Corsa Cat backs and X-pipe.
My DIC reads usually between 30-33 on the highway, but I am never on the highway more than a couple minutes a day... so 30+MPH is just what my car is capable of if I used up an entire tank of gas with the cruise control engaged and never touched the accelerator or brake pedal - never happened in over 8 years so far!
I get 220 - 240 miles for every 13 gallons of gas consistently over the past 8 years. If I ever start seeing 30 MPG I will go ahead and trade it for a Cobalt.
My DIC reads usually between 30-33 on the highway, but I am never on the highway more than a couple minutes a day... so 30+MPH is just what my car is capable of if I used up an entire tank of gas with the cruise control engaged and never touched the accelerator or brake pedal - never happened in over 8 years so far!
I get 220 - 240 miles for every 13 gallons of gas consistently over the past 8 years. If I ever start seeing 30 MPG I will go ahead and trade it for a Cobalt.
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
Who ever told you that changing your heads and cam would not decrease your MPG didn't know what they were talking about. When you do things like add a high flow intake or better flowing exhaust or headers your are allowing the engine to breath better and also making it more efficient so it will increase both HP and MPG, but when you change the heads and the cam you are doing so to build HP, but you are not making it more efficient your are actually doing the opposite you are cramming more fuel and air into the combustion chamber than you were with the stock heads and cam at the same RPM so you're going to get worse gas mileage. Depending what cam and head combination you go with will determine how much more fuel it will burn. A decrease of 6 or 7 MPG at 65 miles per hour is not unheard of, I have heard of a lot worse. There is no such thing a free HP, it either cost your money or fuel economy and usually both.
This is right on !Now with my stock 1998 MN6, I get 16-18 mpg city, 22.5 mpg driving to work, and have gotten 32.6 mpg on the highway. With 345 HP, you can't beat this mileage !
Melting Slicks
Joined: Oct 2007
Posts: 2,724
Likes: 2
From: Holland Landing Ontario
[QUOTE=Tom73;1568450380]Best way to measure highway mileage is on a long trip, one that takes several tanks of gas. That will remove any varables.
On my '04 conv auto, pure stock, I got 30.5 on a trip from central Texas to Las Vegas and back, total of about 2500 miles. And that was cruising at 75-80 mph under cruise control.
I did a trip to the east coast and back averaging 31+ mpg. Since that time I added a Vararam intake and the milage has improved a little due to better breathing.
On my '04 conv auto, pure stock, I got 30.5 on a trip from central Texas to Las Vegas and back, total of about 2500 miles. And that was cruising at 75-80 mph under cruise control.
I did a trip to the east coast and back averaging 31+ mpg. Since that time I added a Vararam intake and the milage has improved a little due to better breathing.
Burning Brakes
Joined: Jan 2008
Posts: 850
Likes: 2
From: Prattville AL
My 408 iron block with Stage 2 P&P L92 heads, L76 intake, 90mm TB,42# inj., custom grind cam,85mm MAF,Vararam B2, SLP LTs, X-pipe, Stock MN6, stock 3.42 diff and ECS custom driveshaft.
Mine is a 99 coupe. I spent the last two weeks on the road. cruise set between 78-82 mph the DIC averaged 33.4 MPG, but the hard math only got me 24.8 MPG. Im cool with what im getting for a 454 RWHP 457 RWTQ car with a 232/236-595/602-115+4 cam...Lots of room left in the motor for more power later on down the road. But she is my DD.
Mine is a 99 coupe. I spent the last two weeks on the road. cruise set between 78-82 mph the DIC averaged 33.4 MPG, but the hard math only got me 24.8 MPG. Im cool with what im getting for a 454 RWHP 457 RWTQ car with a 232/236-595/602-115+4 cam...Lots of room left in the motor for more power later on down the road. But she is my DD.
Drifting
Joined: Nov 2001
Posts: 1,658
Likes: 25
From: Rochester Minnesota
On top of that, your MAF sensor is also measuring air flow and adjusts fuel delivery accordingly. While intake systems may increase hp, they won't increase mpg.
Race Director
Joined: Sep 2007
Posts: 12,899
Likes: 1
From: Denver Colorado
i have to respectively disagree with you.. i have a 98 coupe, a4 with 3:15 gears and i run on the highway at 75mph and get 31.5 mpg....
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
FYI, the DIC's MPG is calculated using the fuel injection pulses. So, if you put in different injectors, your MPG will be off (unless you corrected in program, and I am not sure that you can do this).
Burning Brakes
Joined: Aug 2008
Posts: 1,058
Likes: 91
From: Indiana
I have an M6 and around town get 21-22 mpg. On the highway going 60, I get up to 32. On the hwy going 75-80, I get 27-28mpg. I believe thats about as good as it gets for me, which is the best mpg car Ive ever owned. My mods are z06 box and catback, stock tune.