Poor Gas Mileage, is it me or is it my tune?

[HellsBells]

Hey guys,

So since I got this car, I threw on a C&L racer, a Brenspeed 91 octane tune, Corsa axlebacks, and an O/R midpipe.

I get an amazing 8mpg in the city. Now, let me explain my situation and driving habits:

MY CITY DRIVING (8mpg):
-Typical trip: 2-5 miles, no more than 7 miles (extremely short trips, many cold starts, a lot of the time, my temp gauge barely just made it to operating temp and I'm parking).
-I have a bad habit of shifting at 4000+ RPM, in every gear. I tend to coast/engine brake at 3000-4000RPM (by this should shut off the injectors). I don't floor it or take off at lights, I actually just tend to apply throttle very lightly (maybe 20-30% throttle) and let the sucker rev up because of the terrain in my area (city, hills).
-With that said, a lot of uphill/downhill in my area. Lots of traffic lights. Lots of stop signs. Speeds never exceed 25-30mph.
-I run 91 octane Chevron gas exclusively. I don't use any additives.

MY HIGHWAY DRIVING (19-22MPG):
-Basically, 75-85mph the whole way. I'm talking 450mile trips here. Just one cold start, engine stays hot the whole time (I stop once for gas/food/bathroom).
-Same gas, 91 Chevron, I cruise in 5th and occasionally downshift to 3rd and punch it to red line when I am bored. I'd say I do this maybe 5-6 times over the 450mile trip.

Does this sound right to you guys? I've always wondered if my tune from Brenspeed is excessively rich (exhaust pops a lot and occasionally spews flames). I emailed Brenspeed and they never got back to me.

Thanks guys! I'm not so worried about my highway MPG, but my city MPG is horrific!

 

[fdjizm]

If your city driving is accurate that's probably about right.
I don't see a reason to shift at 4k on the street def. part of your issue.
I shift at 2500 or less on the street comfortably.

 

[HellsBells]

If your city driving is accurate that's probably about right.
I don't see a reason to shift at 4k on the street def. part of your issue.
I shift at 2500 or less on the street comfortably.

No real reason other than it's a bad habit that came from driving my previous car (small displacement import, 9000RPM redline, had to rev it to the moon and back to get going).

I'm not complaining that it's terrible, I just wanted to know if it's me or the tune. If it's the tune, then I need to go do something. If it's me, then whatever, it's me.

Thanks for the response though! I figured the 4K shifting, super short trips, cold starts, etc... were all contributing to it.

Suppose I do just as I am doing but I shift at 2500. What kind of MPG should I expect in your opinion?

 

[JeremyH]

+1, Sounds about right for the driving habbits you described. Im sure not revving as high in every gear may help a little but probably not a noticeable differene. When im just normal driving I usually shift around 2800-3000rpms.

 

[fdjizm]

No real reason other than it's a bad habit that came from driving my previous car (small displacement import, 9000RPM redline, had to rev it to the moon and back to get going).

I'm not complaining that it's terrible, I just wanted to know if it's me or the tune. If it's the tune, then I need to go do something. If it's me, then whatever, it's me.

Thanks for the response though! I figured the 4K shifting, super short trips, cold starts, etc... were all contributing to it.

Suppose I do just as I am doing but I shift at 2500. What kind of MPG should I expect in your opinion?

I get 17-18 in the street, around 27 or so on the highway (cruise control).
I've been very smooth with the pedal (gas prices)
2500 rpm is a good shift point on the street, just don't bog the car or step on it in 5th etc...

 

[HellsBells]

I get 17-18 in the street, around 27 or so on the highway (cruise control).
I've been very smooth with the pedal (gas prices)
2500 rpm is a good shift point on the street, just don't bog the car or step on it in 5th etc...

How fast are you going on the freeway? I can't seem to ever break more than 22-23mpg ever. My best was 24mpg and I was going 60mph the whole time.

+1, Sounds about right for the driving habbits you described. Im sure not revving as high in every gear may help a little but probably not a noticeable differene. When im just normal driving I usually shift around 2800-3000rpms.

Gotcha. What kinda mileage do you get driving city exclusively?

 

[JeremyH]

Gotcha. What kinda mileage do you get driving city exclusively?

10-11 mpg city only

21-22 mpg hwy cruising

 

[HellsBells]

10-11 mpg city only

21-22 mgp hwy cruising

Okay cool, I don't feel so bad anymore

Thanks guys!

Totally random question: I have 3.55 gears and I'm planning to go with hot rods or detroit rocker cams. I do not plan on changing the gears at all. Does fuel mileage tend to suffer more with those cams?

 

[JeremyH]

In general yes, aftermarket cams means more air which means more fuel.

 

[Drex]

I am averaging 17.5 overall, but I drive alot faster on the autobahn. I am pleased with milaege I get considering the conditions.

 

[whyask]

Also with the cams your going to loose some low end .... so a set of gears may be an upgrade idea in the future...

And as for the miliage your about par with me and i shift at 3000-3500 (auto with the rachet shifter) and i have 4:10s , Did the Knotts trips in April and driving normal on the freeway i was gettiing 27.8 doing 80 the whole way for about 8 hours of driving, ... thats boosted with the gears,....

 

[HellsBells]

Also with the cams your going to loose some low end .... so a set of gears may be an upgrade idea in the future...

And as for the miliage your about par with me and i shift at 3000-3500 (auto with the rachet shifter) and i have 4:10s , Did the Knotts trips in April and driving normal on the freeway i was gettiing 27.8 doing 80 the whole way for about 8 hours of driving, ... thats boosted with the gears,....

See, your highway MPG makes me feel like maybe my tune is whack? I drive pretty mildly and I can never get that high, even from NorCal to SoCal.

Will gears still be necessary for going with the detroit rockers? A lot of people report no loss of torque whatsoever, some report gaining a bit of torque along with the HP bump. My reason for not changing gears is because I will sooner or later get a blower (yeah yeah, everyone says this but my issue isn't money at this point, it's time). So I felt like sticking with 3.55's would be good, especially since my car rarely sees the strip, it's a street car and daily driver

 

[fdjizm]

umadbro?

I was doing it prius style here, extremely boring ride but the 4.6 3v is capable of some good mileage.
btw I NEVER hit 30mpg ever ever no matter what so close though.

 

[UltraKla$$ic]

Wow, yall get terrible mileage. My tanks of gas last 9-10 months at least!!!

 

[fdjizm]

Yea with all that driving you do sell your car already!

 

[UltraKla$$ic]

Thinking of parting it out and just keeping the body. How MPG's will just the body get?

 

[VTXFrank]

With my C&L Intake, tune and O/R X-Pipe, I get, depending on my right foot, from 11 to 14mpg city. The C&L has been rumored to have the worst gas mileage. I can't recall where I heard that, it was in a thread on here somewhere I think. On the hwy doing 65-75 with four or five blasts to 110, I got 25mpg over a 200 mile trip last week.

If I REALLY baby the gas pedal, I've had 16mpg city and 27mpg hwy. But that' some boring ass driving. Conversely, while really getting on it and be damned the gasoline,I've gotten 10mpg city and 17 hwy.

I don't think it matters too much if you have a 4.6L, 5.0L, boost or no boost, these V8's are thirsty bitches. How thirsty depends on you. And your making trips where the car doesn't even get fully warmed up is going to kill your MPG. The car WILL run rich the whole time until it is warmed up fully. The fact that you're getting some popping and some flames just illustrates this.

 

[gil_t2]

I used to get 18-19 city, 26-29 interstate,that was with all my mods. Then I installed the C&L racer and it went to shit. 15-16 city and 23-24 highway.

 

[Franchi]

I get 10 to 11 city so doesnt sound all that abnormal. But I do have Thumpr cams, 4:10 gears and every other bolt on. And I beat on it when I do drive it, I shift 50% of the time probably about 5k and rest of the time around 3k.

Why would you do cams now though if thinking of getting a blower down the road? You would benefit far better from blower specific cams. The Detroit Rockers do have a line up specifically for blown cars.

 

[HellsBells]

With my C&L Intake, tune and O/R X-Pipe, I get, depending on my right foot, from 11 to 14mpg city. The C&L has been rumored to have the worst gas mileage. I can't recall where I heard that, it was in a thread on here somewhere I think. On the hwy doing 65-75 with four or five blasts to 110, I got 25mpg over a 200 mile trip last week.

Gotcha. That sounds like the exact same scenario as me, we have the same mods other than the X/H difference. Who wrote your tune by the way?

I used to get 18-19 city, 26-29 interstate,that was with all my mods. Then I installed the C&L racer and it went to shit. 15-16 city and 23-24 highway.

Thanks!

I get 10 to 11 city so doesnt sound all that abnormal. But I do have Thumpr cams, 4:10 gears and every other bolt on. And I beat on it when I do drive it, I shift 50% of the time probably about 5k and rest of the time around 3k.

Why would you do cams now though if thinking of getting a blower down the road? You would benefit far better from blower specific cams. The Detroit Rockers do have a line up specifically for blown cars.

Well, I figured installing the cams before the blower would be a good idea. That way I don't have to take off the blower again and also, I could make sure the car ran good with the cams and then boost it. I'm not sure, I'm just going by what seems like the right order for me. Also, cams are only $800 vs $7000 for a blower and as I understand it, the cam install takes much less time. What exactly is the difference between the blower and N/A cams? And suppose you had to get cams before a blower. Would you be better off running the N/A cams first and sticking a blower on it. Or running the blower cams without a blower, and then sticking the blower on. Power gains aren't a huge concern, so long as I get at least 10-15hp out of them eventually. I also want NSR cams for sure.

I'd also like to clarify that I'm not complaining about my gas mileage. At 9MPG, I fill up about once a month at most (I barely drive and when I do, I don't go far). I was just wondering if this was normal or something was wrong with my car/tune.

Thanks for all the responses!