AR Headers and fuel Mileage

[dukeofpg]

Last week I installed the 1 7/8 LT headers from American Racing with cats and X pipe, stock mufflers. The install went well. It took two of us about 3 hours. The results are fantastic. This is not just a little difference, it is dramatic.

At the same time, I installed my own catch can and a tune from Livernois Motorsports.

The car also has a Roto-Fab CAI and I run Royal Purple 100% syn oil. For fuel I pump Chevron 91 Octane and add Torco Racing octane additive to bring it to at least 96 octane.

I ran the car hard for the first two tanks then filled it for a gas mileage run on a trip to Las Vegas from Pleasant Grove UT (about 4500 ft elevation)

When I got on the freeway, I reset the average GPM, set the cruise at 73 and kicked back while listening to XM radio in my leather seated, air conditioned car in 85 degree sunny weather.

Peeking down, I noticed that the indicator was at 41.6 MPG. "Okay, I have been drafting a bit, so this will settle down" I was just about to climb a hill so it will drop back down, I thought. No way!! It kept climbing a tenth at a time. Up up up until it stopped cold at....


http://forum.grrrr8.net/attachment.php?attachmentid=2638&stc=1&d=1247959250


This is crazy!! It stayed at 50 for about 160 miles. Then I got a DIC code. Four to be exact.. “catalyst misread low”. I pulled to the side of the road and did a reset and kept going. The stop and start dropped me to 42.6 and I had a mountain pass to climb, two of them in fact. So it took a little longer before the MPG started to move up. When I got to St. George Ut it was reading 37.7.

I now had the best part of the drive going through the Virgin River Gorge. It is a spectacular canyon with 500 ft sheer red rock walls and lots of twists and turns. I averaged 100 MPH+ thru the canyon. Traffic was light and the car was running like a champ. To my surprise, as I exited the canyon into Arizona, the MPG was now at 43.1.

When I drove past LVMS (the speedway) it was at 46.8. We went into town for dinner and met with some friends. He is a fellow racer, but drives Lexus on the road. The wives stayed and visited and we went out to smoke (tires). By the time we got to the hotel the gauge was at…

http://forum.grrrr8.net/attachment.php?attachmentid=2639&stc=1&d=1247959250

I wonder if 50.0 is maxxed out for the DIC. I filled the tank with 93 octane Chevron and added one bottle of torco. I have been checking the mileage the old fashioned way and it over 30 MPG, but going down because of everyday traffic and idleing at the drive thru ect. The down low is that on the trip to Vegas and back, I got about 33 MPG. I will be going out to the track next week to let it rip.

I did not buy this car for MPG and I don’t care where it ends up. It is just fun to have the results that I have. I really wont take the time to monitor it in the future. I would not have done this except that when it was 41 MPG, I was intrigued and the result is this story for you to enjoy. Skeptics invited. Fans appreciated! Go G8 Go!!

[blackoutgt]

Dang, That is very nice!!! I'm quite impressed! especially for hitting 100+

[majesticix]

the pictures show it, but I still can't believe it.

[dukeofpg]

the pictures show it, but I still can't believe it.


I am with you. I can't believe it either. The only problem is that it is throwing the codes for the cats and I need to have Livernois tune them out for me. I wrote down the #'s for most of the trip and only took a few pics that were good enough to see. The reflection on the dash was bad and a lot of them did not work with my camera phone.

[WickedMom]

Mpgtune.com is an awesome online log. It is also smart phone friendly.

[SpeedRacerX]

How is this possible?

I will put on headers TOMORROW and drive to Livernois for a tune if my car will see 30++ MPG on the highway.

Right now, I get like 22 on the highway, 18 with mix of mostly highway, 15.5 with mix of mostly city, and 13/14 city.

[WickedMom]

I doubt they are open TOMORROW!!! lol

[SpeedRacerX]

I doubt they are open TOMORROW!!! lol

LOL. Oh yeah. Hey, my wife would support me driving there and waiting at their door Monday morning if I could prove that kinda mileage.
:)

[WARLOCK]

+1 I already have a roto and a tune. Did not effect my mileage at ALL. I got 24 interstate, roughly 18 town.. before and after. If I just need the headers to gain +5mpg
I need to order mine monday.. Thats amazing, congrads on a G8 on a diet. mine's a pig.

[fiveoh]

Hmmm I wonder if the computer not reading the o2s right is causing it to think it's getting better mpg then it is.

[dukeofpg]

Hmmm I wonder if the computer not reading the o2s right is causing it to think it's getting better mpg then it is.

I am thinking this could be a possibility. No doubt there is a lot of stuff going on inside those little black boxes. (Thank goodness MS does not write the software)

I just put the car on the rack to check that all sensors are plugged in and in the correct spot. It is a go.

I also rewrote the HP tune to the ECM. I did not touch the TCM or BCM.

[Chocolate]

How about doin it the old fashion way. Hand Calculation?

[johnbell2]

How about doin it the old fashion way. Hand Calculation?

+1

[GNSS]

I don't know if our cars would be the same, but I have a Duramax with a Preditor tune on it and it somehow skews the MPG reading on the DIC. I went from 20mpg to close to 30 according to the DIC. Hand calculated of course I don't get anywhere near those MPG's.
I think it used those MPG readings or tables for some other calculations.
Maybe some programmers can give us some insight?

Jeff

[dukeofpg]

How about doin it the old fashion way. Hand Calculation?

I would have done this if I knew that I was going to be confronted with such an issue. Until I plan another lengthy road trip, I probably wont be monitoring the mileage. I plan to go to the track this week for test and tune. I will be going with a Mustang club to Miller Motorsports Park in Tooele Utah.

I will be getting loads of crap being the only GM vehicle out on the track. I am a bit nervous because I need to behave because I am a guest, but I also have to drive hard to show that this big 4 door is no slouch. Lots of respect issues going on here. Not until the drivers meeting will I know if they are going to agree to let me drive with them. If one guy says no, then I will be relegated to an occasional hot lap by myself when they take breaks. I know at least one guy that is going to freak when he sees an LSX motor wants to be out with his precious "KR 500"

[Eidolon]

Correct me if I'm wrong on this, but the mileage on the DIC should be calculated from the amount and temperature of the air coming in to the car as detected by the MAF/IAT sensors. The fuel mapping table for those values versus the throttle position should be static, so it should always know how much fuel it's using. Changing your intake and the fuel/throttle/air mapping tables could throw off the readings.

But this car will not get 40 MPG. It's simply not possible. :P Not unless you're going down a 45-degree incline in neutral.

[-Ray-]

As far as I know, my 30.1 mpg over 350 miles is the highest anyone's posted. This is with a Roto-Fab, ARH and a Vector tune. Of course my AFM was engaged for 330 or more of those miles.
Verified with calculating on fill up.

[dukeofpg]

Correct me if I'm wrong on this, but the mileage on the DIC should be calculated from the amount and temperature of the air coming in to the car as detected by the MAF/IAT sensors. The fuel mapping table for those values versus the throttle position should be static, so it should always know how much fuel it's using. Changing your intake and the fuel/throttle/air mapping tables could throw off the readings.

But this car will not get 40 MPG. It's simply not possible. :P Not unless you're going down a 45-degree incline in neutral.


I was not traveling at 45 degrees downhill in neutral. For a while I was sucking up behind every vehicle I could and running with a super light foot. I tired of the effort it took and all the people I was pissing off, so I just drove at a moderate pace rolling into and out of the throttle gently.

I am convinced this is a fluke. I do not propose that I have a G8 that will maintain 50 MPG. I am a racer (hobby) and did not buy this car to compete with priuseeseses. (sorry, that is a difficult word for me to say and spell)

Can anyone else say though that they have seen the MPG at 50.0? The pics are not fabricated.

[caretaker]

I've seen 100.0 MPG on the DIC.
Going down a hill at about 65 MPH with my foot off the gas,
NOT in neutral, right after resetting the DIC.

My DashDyno has shown almost 120 MPG doing the same thing.

[bobyoung]

The absolute best I ever got was 26.9 mpg going a steady 65 (following a pickup) on a 200 mile trip to Brooklyn NY, the pace drove me nuts. I haven't gotten near that again. I average 17-18 and consider that good for this car the way I drive, I rarely think about gas mileage, didn't buy it for that. I rarely drive slow enough for the AFM to engage for more than a few seconds. I fill it up, reset the odometer and drive almost all the way downhill from there and soemtimes it will be close to 26 when I get home but with normal everyday driving it always goes back down to 17-18. In 1970 most cars with 350+ HP would have been lucky to get 10-12 mpg with careful driving.

[steve b.]

impossible to get that much unless u are going off a cliff.

[WARLOCK]

I got 24.5mpg today on my 62 mile run to work. set cruise at 74 mph, and its not flat alot of hills so overall I think mine does really well i still get 23.8-24.0 with the cruise at 80mph. Problem is the car is to much fun to drive (ahem) spiritedly.. I usually end up avg. 17-19 per tank.
I actually told my cousin today I love the car but when I bought it I wanted a new chevy quad cab 1/2 ton. Im a truck guy at heart, but because I drive so far to work every week I needed something better on gas. If i REALLY was worried about mpg I should have bought a diesel Jetta and got 40mpg. Otherwise i should have just bought the damn truck. So as much as I love my G8 I find myself still passing the lots looking at the silverados.
Overall these cars do well considering...

[dukeofpg]

I got 24.5mpg today on my 62 mile run to work. set cruise at 74 mph, and its not flat alot of hills so overall I think mine does really well i still get 23.8-24.0 with the cruise at 80mph. Problem is the car is to much fun to drive (ahem) spiritedly.. I usually end up avg. 17-19 per tank.
I actually told my cousin today I love the car but when I bought it I wanted a new chevy quad cab 1/2 ton. Im a truck guy at heart, but because I drive so far to work every week I needed something better on gas. If i REALLY was worried about mpg I should have bought a diesel Jetta and got 40mpg. Otherwise i should have just bought the damn truck. So as much as I love my G8 I find myself still passing the lots looking at the silverados.
Overall these cars do well considering...

I was set on a truck too. Then Cadillac put me on the Monticello road course outside of New York City in a 2009 CTS V. It was a drizzly cold day in November, but I had the time of my life. I actually had track time with Andy Pilgrim. See Youtube "Andy Pilgrim hot pizzas" I was in the car with him and we were trading off laps for about an hour. Anyway, I was sold. I just have too many issues with owning a beautiful car like the CTS V in Utah winters. I needed a drivers car, Year Round.

I tried to wait for the GXP, but one day I was at the accountants office doing the business taxes. I was so depressed, I had to go buy a car to cheer me up. The G8 worked. It was fast, fun and easy, just like.... Oh well you know what I mean.

I just hung on to the pickup I had. I will be dropping in a Scoggin Dickey 383 stroker motor this fall.

Thanks for joining the discussion. I was certain that it would get people wound a little tight. It has been good to read every comment. You guys are fun to read and I love the comraderie of this group.

[bobyoung]

I got 24.5mpg today on my 62 mile run to work. set cruise at 74 mph, and its not flat alot of hills so overall I think mine does really well i still get 23.8-24.0 with the cruise at 80mph. Problem is the car is to much fun to drive (ahem) spiritedly.. I usually end up avg. 17-19 per tank.


That's what happens to me, these cars can be really good on gas if you drive like an old lady but....., hey I'm satisfied with 17-18, especially considering what it is.

[WARLOCK]

I just hung on to the pickup I had. I will be dropping in a Scoggin Dickey 383 stroker motor this fall.

Thanks for joining the discussion. I was certain that it would get people wound a little tight. It has been good to read every comment. You guys are fun to read and I love the comraderie of this group.

:) Yeah, I did the same thing. I have an old 94 Chevy silverado ext cab I got from my dad years ago. It has 200,000 miles on the original engine and still fires up and runs fine. It just looks like its on its death bed. I keep it in the backyard back by the fence just in case I need to haul something.

agreed on the forum. I enjoy logging in. seems alot in common with G8 people.
I think this car really does appeal to a certain group. Look around on here. most G8 owners have owned 20 30 different vehicles for example. and look at the thread started on home audio systems. wow freaks all of us.

Utah looks so awesome, i wanna bring my jeep out there hopefully next year to play. I would love to move out there one day. Job wouldn't be a problem for sure..

[Tate]

The best I've ever pulled was on my trip to Tennessee a few weeks ago to see family. With the mods in my sig. and the car set at 73 MPG (It seems to like that number more so then say 65-70 for me). The DIC was reading 29.6 when I pulled off to get gas again. After filling up and dividing the miles by how much gas it took I got 27.8 MPG. So I do think the DIC is a bit optimistic, but was still very pleased with what I really got.
Tate

[WARLOCK]

WOW. thats excellent numbers. 27mpg at 73mph.. thats the kind of numbers I got with my GTP. hope when I add headers I can come close to that.

[G8-4-Speed]

Ya know, you can recalibrate the speedo to read fast and get great mileage......With my Diesel this was one thing I noticed with my tune before I calibrated it. It was 10% fast making mileage look was better than what it was.

[vert]

27mpg is dman good, I ran 42 miles at 78mph and avg 21.9. That is with kooks, vararam and VMS tune.

[johnbell2]

I'm getting 19-20mpg on the DIC in 50/50 mixed driving with Superchips 93 octane tune and DOD disabled. Hand calc comes in at 19mpg. All else stock. I usually drive like an old lady unless I'm "testing" ;)

[wyd_trkr]

WOW. thats excellent numbers. 27mpg at 73mph.. thats the kind of numbers I got with my GTP. hope when I add headers I can come close to that.Are those mpg numbers of yours including a Roto-Fab Intake and A Intense 93 Octane Dyno Tested Tune in the mix, or did you install the Roto-Fab after you installed the Tune?

[dukeofpg]

The Roto Fab and tune and headers have been on the car before the #'s were recorded. By the way. I have put over 1200 miles on the car and the DIC reads 24.6 now. I also use an iphone app that I input actual miles and gallons and it is at 25.2

[wyd_trkr]

The Roto Fab and tune and headers have been on the car before the #'s were recorded. By the way. I have put over 1200 miles on the car and the DIC reads 24.6 now. I also use an iphone app that I input actual miles and gallons and it is at 25.2You must be doing allot of 70-75 mph highway only driving to attain those 24.6 numbers. Also, what Brand Fuel and Octane Rating are you using, 91 or 93? Also, the tune you presently have is for all of your current mods, correct?

[steve b.]

that sounds about right

[dukeofpg]

The tune is for the mods. I run 91 octane Chevron. I add lucas octane boost (1 ounce to 1 gallon) and Torco racing fuel additive 1 ounce to one gallon. All this with Royal Purple 5W30 100% Synthetic ( not just fully synthetic). I also use Z Max (with linkite) oil and fuel additive.

I know this may seem contrary, but if I drive on the highway aggressively, the mileage seems to creep up

[wyd_trkr]

The tune is for the mods. I run 91 octane Chevron. I add lucas octane boost (1 ounce to 1 gallon) and Torco racing fuel additive 1 ounce to one gallon. All this with Royal Purple 5W30 100% Synthetic ( not just fully synthetic). I also use Z Max (with linkite) oil and fuel additive.

I know this may seem contrary, but if I drive on the highway aggressively, the mileage seems to creep upYou must be doing allot of 70-75 mph highway only driving to attain those 24.6 numbers, correct?

[dukeofpg]

Sorry,
I did not mean to dodge your comment. Most of the driving is highway. I don't cruise the neighborhood too often. I just drive to the airport and back a couple times a week. With a customer visit thrown in once in a while. There are spots here in Utah where the speed limit is 80 and I get as close to 90 as I can without passing the flow of traffic. The miles per are slowly creeping down overall. If you read the beginning and look at the pics, you will see the whole story.

[wyd_trkr]

Sorry,
I did not mean to dodge your comment. Most of the driving is highway. I don't cruise the neighborhood too often. I just drive to the airport and back a couple times a week. With a customer visit thrown in once in a while. There are spots here in Utah where the speed limit is 80 and I get as close to 90 as I can without passing the flow of traffic. The miles per are slowly creeping down overall. If you read the beginning and look at the pics, you will see the whole story.

Well to be honest with you, I was definitely qestioning your fuel mileage, but now that you have explained the highway driving, I can see you can get pretty good fuel mileage. However even with my new 2009.5 GT the best mpg I got on a trip to North Carolina running 72 to 75 mph was only 25.6 mpg running with just the Superchips Cortex 93 Octane Tune with a Stock Intake System.

I can understand even with your Roto-Fab Intake and other modifications, because of your running the Livernois Tune from someone elses Dyno Tested and Proven Tune and it was installed into your car, that you would be getting better Fuel Mileage, over others of us that just bought an off the shelf programmer and it does not accommodate a Cold air Intake into the mix!

My car has now lost 2 mpg since installing my new Roto-Fab Intake system this past weekend and running the Superchips Cortex 93 Octane Tune in it, without a Good Cold Air Intake Tune. I sincerely hope that Superchips does a good job on programming the Roto-Fab Intake into the Superchips Cortex 93 Octane Tune and I see a Major increase in Fuel Mileage.

I have been told that the Roto-Fab Intake "Will" increase your Fuel Mileage between 2 to 3 mpg increases "With" a Good Tune!. However, by just installing the Roto-Fab Intake you "Will Not" see an increase in your Fuel Mileage, as "It Will" Decrease it, until a Good Tune is performed into the mix!

If anyone tells me by just installing any Cold Air Intake on a GT improves Fuel Mileage "Without" a Good Tune, then I will have to raise my "BS Flags"
Hope this helps!

[dukeofpg]

Just want to be clear... I am not bragging or trying to win a prize for the highest mileage. I just was wigged out when I saw the 50.0 mpg and I wanted to know if anyone had ever seen the gauge read higher than 50. Is that the max? Putting the tune to the car. Disconnecting the battery when the headers went on all may have jogged the system into a false reading. I don't know and I really don't care. It was just a chance to publish the readings that I took pics of. I don't have anything to prove. I have never, never, never purchased a car for fuel mileage. Other factors influence why I have 6 cars, all with V-8's. In todays "green" world, I could be considered the evil anti environment devil. I don't care about that. Enjoy your prius while you save gas for ME to use.

[wyd_trkr]

Just want to be clear... I am not bragging or trying to win a prize for the highest mileage. I just was wigged out when I saw the 50.0 mpg and I wanted to know if anyone had ever seen the gauge read higher than 50. Is that the max? Putting the tune to the car. Disconnecting the battery when the headers went on all may have jogged the system into a false reading. I don't know and I really don't care. It was just a chance to publish the readings that I took pics of. I don't have anything to prove. I have never, never, never purchased a car for fuel mileage. Other factors influence why I have 6 cars, all with V-8's. In todays "green" world, I could be considered the evil anti environment devil. I don't care about that. Enjoy your prius while you save gas for ME to use.No doubt, with your DIC reading those higher than normal readings, you might have had a "Fluke" in there after installing the headers etc. Anyway, my point was being realistic in stating no GT can achieve those mileage numbers with those modifications you are running! Of course I did not buy my GT for fuel mileage either, however anytime I can gain in that area I am game for it!

[-Ray-]

Just want to be clear... I am not bragging or trying to win a prize for the highest mileage. I just was wigged out when I saw the 50.0 mpg and I wanted to know if anyone had ever seen the gauge read higher than 50. Is that the max? Putting the tune to the car. Disconnecting the battery when the headers went on all may have jogged the system into a false reading. I don't know and I really don't care. It was just a chance to publish the readings that I took pics of. I don't have anything to prove. I have never, never, never purchased a car for fuel mileage. Other factors influence why I have 6 cars, all with V-8's. In todays "green" world, I could be considered the evil anti environment devil. I don't care about that. Enjoy your prius while you save gas for ME to use.

You said skeptics invited. Anytime someone posts 41 mpg avg going up hill you are going to find them. If anyone posts avg fuel mileage gains 100 percent more than what the majority of G8 owners are getting, you will have lots of non believer's. Nothing personal.

[TrUcKeR]

Just a tune and front muffler/res removed, driving from Rapid City, SD to Gillette, WY, steadily increasing elevation the whole way, with the A/C on 1/2 speed the whole way, 91 (10% ethanol blend) octane.

http://forum.grrrr8.net/attachment.php?attachmentid=2724&d=1248913614

[dukeofpg]

You said skeptics invited. Anytime someone posts 41 mpg avg going up hill you are going to find them. If anyone posts avg fuel mileage gains 100 percent more than what the majority of G8 owners are getting, you will have lots of non believer's. Nothing personal.

I would not take it personal Ray. The whole purpose of the forum is to stimulate discussion. I hope I have not offended you or anyone. It is just chat.

It was not an uphill drive. The elevation from Salt Lake to Las Vegas is about 2500 foot drop. So it was downhill all the way.

[danno111909]

one time for about 20 seconds my mpg was listed at 99.9 I kid you not!!!

[Grey Ghost in NOVA]

The best I have seen with a Vararam & Cortex Milage tune is 29.4 mph @ 75 mph in Northern VA!!

[TurboSS]

there are ways of getting higher than normal mileage. i think he said he was drafting....mythbusters did a show on this and using a dodge charger i think it was v6 at 55mph behind a semi showed the closer they got the better the mileage...at 50ft back ( about 2.5 cars, av car being 20ft long ) i think it showed about 30% better mileage. now do the same thing in a g8 with the dod in 4 mode the entire time...big ass increase. now think about the wind. most people dont think about it unless its from one side of the car or the other. but if the wind is behind you at 10kts and your going 55mph i have seen in my g8 the mileage go up by 2.5-3mpg at 78* and flat road. so if you can get 25mpg yourself and draft a larger vehicle and get 30% more that gets you 32.5...now 10kts wind pushing you could see ~35mpg. now if you throw in some down hills with idle power ( at idle you burn NO fuel above 45mph ) so you could ride the entire downhill drafting( reducing drag ) and the wind (reducing drag and pushing) and now no fuel coasting you can add alot to your average mpg. just something to think about.

[Patrick G]

A lot of you are missing the fact that most of Utah is at much higher altitude than other parts of the US. Thin air makes it easier to push these cars at highway speeds. I regularly see my mileage increase 2-3 MPG when driving across Colorado compared to the lowlands of Texas.

Back to the original topic: I commend you for posting on your gains with AR Headers. They are excellent!

[TurboSS]

A lot of you are missing the fact that most of Utah is at much higher altitude than other parts of the US. Thin air makes it easier to push these cars at highway speeds. I regularly see my mileage increase 2-3 MPG when driving across Colorado compared to the lowlands of Texas.

Back to the original topic: I commend you for posting on your gains with AR Headers. They are excellent!

great point

[SMOKINV8]

Just to add to the discussion a bit...

If the fuel injector table(s) are tweaked in the tune, it will alter the values for the DIC fuel economy. I haven't come across a Livernois tune for a bolt-on car, so I don't know if they do or don't, but some people adjust the IFR table on bolt-on cars, which would affect this.