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Old 06-26-2014, 08:56 PM   #1 (permalink)
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Aftermarket Intake/Exhaust Good Or Bad For Fuel Economy?

Aftermarket Intake/Exhaust Good Or Bad For Fuel Economy?

I read mixed reviews online from people who have likely never tested their mods in a professional fashion. Obviously doing these mods will likely result in rider being trigger happy and see less MPG.

Only thing I can think of is less torque when intake/exhaust is "opened up"

My main reason would be to shave off 10lbs of rusty black steel exhaust.

Any knowledge on this?

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Old 06-26-2014, 09:30 PM   #2 (permalink)
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Its a tough call. Do you do short or long trips? Most cars respond better to a warm air intake or a short ram so they suck in heated air from the engine compartment. Some cars and those that make longer trips than 7 miles likes cold air.

Where is the power? Down low or up high? If up high, then a 4 to 2 to 1 tri y header will lower the power band and allow you to short shift.

A 4 to 1 collector raises the power band.

Mufflers add weight and reduce torque.
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Old 06-26-2014, 09:37 PM   #3 (permalink)
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Diesels seem to really benefit from being able to breathe better. With a gas car, you'd likely never make up the cost of the mod unless it needed to be replaced anyway or you sell the old parts for good money.
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Old 06-26-2014, 10:54 PM   #4 (permalink)
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There is very little chance you will see any gains. Unless the new intake incorporates a wai. And the added exhaust noise will actually make you more aware of throttle position and engine load
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Old 06-26-2014, 10:57 PM   #5 (permalink)
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Sorry I shoud've said this is for a motorcycle, 250cc, fuel injected (so I guess it has an O2 sensor among other things I really have no clue about) But thanks for the info pertaining cars. I drive those too!
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Old 06-26-2014, 11:10 PM   #6 (permalink)
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Typically, an aftermarket exhaust will be tuned for more performance and biased toward making more power up top. The tubing diameter is usually larger than stock, so velocity will fall. If you are looking for mileage you aren't operating in the peak HP range much, so I would expect to see a loss of mileage.

I've added a slip-on muffler to my stock system, and other than sounding better, I don't think it made any difference in mileage one way or the other.

An air filter that flows better most likely won't help mileage much, as the throttle opening is small when cruising and the flow required is minimal.

Biggest gains will come from significant aero improvements.
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Old 06-26-2014, 11:53 PM   #7 (permalink)
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If your muffler was tuned to give power down low in the RPM's I Imagine it would help your mpg , a bit , if you were to use the low RPMs you may save a fair amount.. I am thinking a port and polish with a slightly shaved head to remove restrictions and raise compression a few lbs. Also add a smaller rear sprocket or larger front sprocket to lower the rpm.
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Old 06-27-2014, 12:00 AM   #8 (permalink)
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http://ecomodder.com/forum/showthrea...aust-9429.html

This thread along with the comments of air flow have me really thinking...

FMF makes headers which may require second thought for motorcycles with mini "2 stroke style" chambers.


FMF: "The redesigned PowerBomb is a four-stroke header that incorporates FMF’s patented PowerBomb module at a precise location in the initial stage of the header. By positioning this “Bomb” at a key point in the system, increased performance and flow is achieved through the expansion and contraction of exhaust sonics through the system. Result is a flow increase of nearly 10%! The outer chamber in the Powerbomb allows the air to expand, cool and ramp back up at a higher velocity. Additionally, the PowerBomb is a “pre-muffler” of sorts which helps to lower the bikes sound output by providing more sound absorbing surface area for the sound medium (exhaust gases). On some models, you can choose between a moto or supercross version. The supercross version is designed for more low to mid-range power where the moto version is focused in the mid to upper RPM range."

So is the goal of fuel efficiency less turbulant exhaust air? Or more smoother flow?
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Old 06-27-2014, 01:50 AM   #9 (permalink)
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An opened up exhaust will not give you less torque. It will always give you more torque at some rpm in exchange for a possible loss at other rpms. If you're lucky, and it's a lot better than stock, you get extra torque everywhere.

The question is... at what rpm does that happen? Because if that rpm is too high, then you won't see any benefit from it. With a single cylinder, the most you can do is optimize tube size and try to move that sweet spot around. That pulse-scavenging exhaust looks like the bomb, though I expect the operational range for the scavenging effect will be rather narrow.

Intakes are complicated. WAI makes for better economy but good luck finding warm air in front of the bike! Some filter panels make for better economy in cars by altering MAF sensor readings... which is kind of hit or miss... and I'm not sure whether your bike's EFI is MAF or MAP referenced.

On a bike, re-gearing is the most cost-effective way of ekeing out extra MPG. After that, it's fairings and possibly a windshield (unless you'd like to perfect your tuck... ).

Last edited by niky; 06-27-2014 at 01:57 AM..
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Old 06-27-2014, 05:59 AM   #10 (permalink)
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Like it has been stated, messing around with the exhaust and or just the muffler on bikes is going to vary alot with each design with how it affects performance; the necessity for re tuning; and how it affects mpg. My 2014 Honda CTX700, with a 670 cc parallel twin, ports out of the engine and is almost immediately squeezed into one 1.5" pipe right out of the CAT, so, in my case, most mods will do little, since the exhaust is already compressed coming out of the engine and then some more at the CAT. I've fiddled around with going muffler delete only (not messed with any of the header pipe or CAT), and these are my results are shared below:

I'm not one who can give much technical expertise, but I recently played around with removing my muffler from a 2014 Honda CTX700, parallel twin that weighs nearly 500 lbs wet and produces roughly 46 hp and 43 peak foot lbs of torque on the average dyno test. This is a different kind of bike motor; it's much lower revving than most bikes, because it is basically 1/2 of a Honda Fit car engine, and so, unlike most motorcycles, it has very flat torque but doesn't build up so much as it revs; sort of like a diesel some reviewers say, but owning a diesel car, I'd say; not quite.

Reportedly, the torque curve reaches near peak levels around 3,000 RPM and stays there up to about 5,500, and then, the rev limit is just past that point at only around 6,500. What all this means is that, since this is not really a high-performing bike wherein its strength is flat torque and great gas mileage, any small amount of change in the torque and mpg would be very noticeable, especially if one is recording mpg and paying attention to throttle response, which I've done. I'm anal about recording my mpg, and I ride a regular commute at or about the same speed every day and my data is usually very consistent at any given average air temp.

I first removed the muffler to paint it black. Tried the bike out w/o the muffler and was surprised at how good it sounded (though just a little loud, but not as loud as I expected; but a much deeper, big bike sound than what I expected). I decided to ride around w/o the muffler for a full tank of gas. I think that it lost just a little mpg, because my loss on that particular tank was just a little out of my normal range for summer time, commute riding. As for performance, that's a little harder to nail down, because the extra noise may have been messing with my perception, but it seemed like a slight amount of torque was gone in my normal riding RPM ranges, especially on the low end after up shifting, but it may have been that it just seemed like I was having to give it more throttle to get a response due to the noise being created when I'd throttle back.

I really liked not having that big, heavy muffler though, because now I could hear the engine revs and could upshift more smoothly; and additionally, I could much easier clean under the bike after riding in the rain or wet roads, and my research was telling me that no harm would come to the engine from what I was doing, but someone did suggest extending the pipe past the header out end, closer to the original length, because that would communicate back to the engine closer to the stock level for performance reasons w/o having to re tune. So that's what I tried next. I simply went to a muffler shop, and the mechanic swelled one end of a 1 1/2" o.d. pipe where I could clamp it on about 14" long. That cost me $10. I then went out and got a $5, one.point.five muffler clamp, because my stock clamp was too large; painted everything matte black like my bike trim and clamped it on. Now everything was perfect, well except maybe the appearance, but even that ain't too bad. It's quieter at idle, no more popping while engine breaking, but I still have that deep rumble without being offensive. I also seem to have my torque and mpg back, averaging around 79 on my commute tanks and over 80 on trips, which is what I've had since it got hot out and I switched to a low-profile helmet.


Last edited by gregsfc; 06-27-2014 at 06:34 AM..
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