Fuel consumption with catless downpipe

RubberBandMan · 02-09-2020, 11:41 AM

Hey all, I'm curious what kind of drop off in MPG folks have seen after installing a catless downpipe? I have a 6MT 340i with a Mission Performance tune (love it

) and considering going stage 2, with downpipe. However I can't get a good read on how much this will affect fuel consumption. I see the question popped up in a few related threads, but didn't see much feedback on it. I recognize that it will obviously have an impact, just don't know how drastic it would be. Anyone running a tune and downpipe who can chime in?

E90ROXS · 02-09-2020, 11:53 AM

Once you get a downpipe you will ignore the level of fuel consumption. Welcome to the dark side.

Supr3me · 02-09-2020, 12:01 PM

Quote:

Originally Posted by E90ROXS

Once you get a downpipe you will ignore the level of fuel consumption. Welcome to the dark side.

This. Face it, if gas mileage was that important to you, you'd have gotten a 320i. The component that has the biggest impact on fuel consumption on a modified B58 is the one actuated by your right foot.

That being said, I've heard (but not researched) that going catless can actually improve gas mileage.

not1337 · 02-09-2020, 01:15 PM

I can't imagine that decreasing exhaust restriction would do anything but increase mileage.

marcthedark · 02-09-2020, 01:17 PM

Less restriction = higher efficiency
Tune with higher boost etc = less milage if you get into it
Heavier foot = lower mileage
It all depends on your behavior. A simple change won't change much

Rockyca · 02-09-2020, 06:47 PM

Right foot mod if you are worried about fuel economy. But really... who buys a performance car for economy?

Sleeper340i · 02-10-2020, 03:54 AM

I averaged 20.8mpg mainly freeway driving with my high flow catted down pipe recently, but I am heavy footed. When stock, I averaged about 21-22mpg so the difference is minimal in my case, but I would run through 30 bucks of gas in one day somehow on rare occasions, which never happens anymore now on stage 2. MPG decrease would be the least of my worries. It's not like it's 5-10 mpg at least from my experience.

RubberBandMan · 02-10-2020, 05:57 AM

Quote:

Originally Posted by Sleeper340i

I averaged 20.8mpg mainly freeway driving with my high flow catted down pipe recently, but I am heavy footed. When stock, I averaged about 21-22mpg so the difference is minimal in my case, but I would run through 30 bucks of gas in one day somehow on rare occasions, which never happens anymore now on stage 2. MPG decrease would be the least of my worries. It's not like it's 5-10 mpg at least from my experience.

Thanks. This is the type of feedback I was looking for.

RubberBandMan · 02-10-2020, 06:01 AM

Quote:

Originally Posted by Rockyca

Right foot mod if you are worried about fuel economy. But really... who buys a performance car for economy?

No mention of buying my car for the sake of fuel economy, just a specific question about how much the downpipe itself factors into things.

Londoner · 02-10-2020, 11:52 AM

Quote:

Originally Posted by Rockyca

Right foot mod if you are worried about fuel economy. But really... who buys a performance car for economy?

Er...I did! Obviously wasn't the primary reason for buying but the B58 engine is more efficient on paper than it's rivals, which also means cheaper annual road tax in the UK. So yea, whilst i had a list of tick boxes, fuel economy was imo something worth considering.

Briland33 · 02-11-2020, 08:22 AM

Quote:

Originally Posted by RubberBandMan

Hey all, I'm curious what kind of drop off in MPG folks have seen after installing a catless downpipe? I have a 6MT 340i with a Mission Performance tune (love it

) and considering going stage 2, with downpipe. However I can't get a good read on how much this will affect fuel consumption. I see the question popped up in a few related threads, but didn't see much feedback on it. I recognize that it will obviously have an impact, just don't know how drastic it would be. Anyone running a tune and downpipe who can chime in?

I have a catless dp on for a few months now and noticed zero change in economy. Just this past weekend i did a 2.5hr drive cruise controlled at 80mph and averaged ~34mpg if I remember correctly.

conradb58 · 02-11-2020, 10:49 AM

Quote:

Originally Posted by RubberBandMan

Hey all, I'm curious what kind of drop off in MPG folks have seen after installing a catless downpipe? I have a 6MT 340i with a Mission Performance tune (love it

) and considering going stage 2, with downpipe. However I can't get a good read on how much this will affect fuel consumption. I see the question popped up in a few related threads, but didn't see much feedback on it. I recognize that it will obviously have an impact, just don't know how drastic it would be. Anyone running a tune and downpipe who can chime in?

I have not, I still get 30mpg highway driving 80-90mph depending on headwind or not. Your fuel economy is dependent on your foot.

mike@x-ph.com · 02-11-2020, 11:31 AM

Quote:

Originally Posted by marcthedark

Less restriction = higher efficiency
Tune with higher boost etc = less milage if you get into it
Heavier foot = lower mileage
It all depends on your behavior. A simple change won't change much

+1

Wires · 02-12-2020, 06:43 PM

Results might be a bit skewed since I have a ER catted DP + BM3 stage 2 tune, but pre mods, the hilly highway commute to work and back used to burn 10% more fuel than post mods.

The gains are actually better than 10%, but now you need to lay into it on every corner/stop light "'cause it's fun!"

I don't know how much is from the DP, and how much is from the BM3 giving a lot more bottom end torque.

02-09-2020, 11:41 AM	#1
RubberBandMan Enlisted Member 11 Rep 30 Posts Drives: 2016 340i Alpine White 6MT Join Date: Jul 2018 Location: Los Angeles iTrader: (0)	Fuel consumption with catless downpipe Hey all, I'm curious what kind of drop off in MPG folks have seen after installing a catless downpipe? I have a 6MT 340i with a Mission Performance tune (love it ) and considering going stage 2, with downpipe. However I can't get a good read on how much this will affect fuel consumption. I see the question popped up in a few related threads, but didn't see much feedback on it. I recognize that it will obviously have an impact, just don't know how drastic it would be. Anyone running a tune and downpipe who can chime in?
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02-09-2020, 11:53 AM	#2
E90ROXS Captain 225 Rep 676 Posts Drives: E90 Join Date: Feb 2012 Location: SJ iTrader: (1)	Once you get a downpipe you will ignore the level of fuel consumption. Welcome to the dark side.
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02-09-2020, 01:15 PM	#4
not1337 Private 102 Rep 82 Posts Drives: 2016 340i Join Date: Jan 2020 Location: Dallas, TX iTrader: (0)	I can't imagine that decreasing exhaust restriction would do anything but increase mileage.
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02-09-2020, 01:17 PM	#5
marcthedark Lieutenant 120 Rep 410 Posts Drives: M240i xdrive Convertible Join Date: Apr 2017 Location: Phoenix Metro Area iTrader: (0)	Less restriction = higher efficiency Tune with higher boost etc = less milage if you get into it Heavier foot = lower mileage It all depends on your behavior. A simple change won't change much
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02-09-2020, 06:47 PM	#6
Rockyca First Lieutenant 34 Rep 356 Posts Drives: 2016 340i M-Sport Join Date: Jan 2012 Location: Toronto iTrader: (1)	Right foot mod if you are worried about fuel economy. But really... who buys a performance car for economy?
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02-10-2020, 03:54 AM	#7
Sleeper340i Second Lieutenant 94 Rep 255 Posts Drives: BMW 340i Join Date: Nov 2019 Location: Seattle iTrader: (0)	I averaged 20.8mpg mainly freeway driving with my high flow catted down pipe recently, but I am heavy footed. When stock, I averaged about 21-22mpg so the difference is minimal in my case, but I would run through 30 bucks of gas in one day somehow on rare occasions, which never happens anymore now on stage 2. MPG decrease would be the least of my worries. It's not like it's 5-10 mpg at least from my experience.
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02-12-2020, 06:43 PM	#14
Wires Brigadier General 1646 Rep 4,876 Posts Drives: 2016 340i xDrive Join Date: Apr 2008 Location: Calgary iTrader: (0)	Results might be a bit skewed since I have a ER catted DP + BM3 stage 2 tune, but pre mods, the hilly highway commute to work and back used to burn 10% more fuel than post mods. The gains are actually better than 10%, but now you need to lay into it on every corner/stop light "'cause it's fun!" I don't know how much is from the DP, and how much is from the BM3 giving a lot more bottom end torque.
	Appreciate 1 RubberBandMan10.50 Quote