The Exhaust Upgrade

Message

revxus · #1 Unread post by **revxus** » Fri Nov 10, 2006 9:16 pm

I just received my new exhaust for my cruiser, unfortunately I later learned that I need to re-jet the carburator with a jet-kit that will cost me another hundred, but I want to do this correctly without jeoperdizing performance - is this a must-do task when installing (louder) exhaust? Will it cause any damage or trouble simply installing the pipes and later re-jetting the carburator? Which task is to be done first?

#2 Unread post by **Sev** » Sat Nov 11, 2006 3:33 am

All I know is that if you reduce backpressure (freer flowing louder exhaust) you increase the amount of air being sucked into your engine. However, if the amount of fuel remains constant you've just leaned out your system, and it'll be running hot.

To compensate you need to increase the amount of gasoline being pulled into the engine. Otherwise you've dropped the level of performance on your bike in exchange for making it louder.

If you don't feel comfortable doing it yourself, get the shop to do it.

revxus · #3 Unread post by **revxus** » Sat Nov 11, 2006 7:48 am

Makes a lot of sense, so the jet-kit will definately have to be performed. Thanks!

Shorts · #4 Unread post by **Shorts** » Sat Nov 11, 2006 2:10 pm

Related question, and I hope you don't mind the hijack

When you add a high flow airfilter to a car/truck, the ECM changes fuel delivery (due to various sensors input) to keep the same fuel/intake ratio. I'm curious as to if you need to do anything to FI motorcycles and why? Is it only carbed bikes that need rejetting since it is a mechanical fuel delivery? Or all bikes?

jstark47 · #5 Unread post by **jstark47** » Sat Nov 11, 2006 3:49 pm

Shorts wrote:When you add a high flow airfilter to a car/truck, the ECM changes fuel delivery (due to various sensors input) to keep the same fuel/intake ratio. I'm curious as to if you need to do anything to FI motorcycles and why? Is it only carbed bikes that need rejetting since it is a mechanical fuel delivery? Or all bikes?

Good question, and I figure I should learn about this since we just bought our first FI bike. A little quick Googling and I found an answer to a similar question on another bike forum (BTW, question was apparently asked by our own forum member 'Dichotomous'):

"**the answer is because a civic has an O2 sensor, the bike doesnt. so when you added the intake and exhaust to your civic, it ran lean, but only long enough for the 02 sensor to pick up on this and tell the computer "hey we are lean add fuel!!" in simple terms anyway most cars (and all after 1996) use a closed loop fuel system...alot of bikes dont"

FWIW.

Shorts · #6 Unread post by **Shorts** » Sat Nov 11, 2006 3:58 pm

jstark47 wrote:
Good question, and I figure I should learn about this since we just bought our first FI bike. A little quick Googling and I found an answer to a similar question on another bike forum (BTW, question was apparently asked by our own forum member 'Dichotomous'):

"**the answer is because a civic has an O2 sensor, the bike doesnt. so when you added the intake and exhaust to your civic, it ran lean, but only long enough for the 02 sensor to pick up on this and tell the computer "hey we are lean add fuel!!" in simple terms anyway most cars (and all after 1996) use a closed loop fuel system...alot of bikes dont"

FWIW.

That sounds inline what I was thinking on the O2 sensor. Makes sense. Thanks jstark. So even FIed bikes have no O2 sensor? (Not that I'm asking for more electronics! I just want to know)

#7 Unread post by **ZooTech** » Sat Nov 11, 2006 4:16 pm

Shorts wrote:So even FIed bikes have no O2 sensor?

Correct. Fuel-injected bikes simply have an electronic fuel delivery system which injects fuel based on a pre-programmed "map", much like a firmware version of a jet kit. It can make minute adjustments based on incoming air temperature, but not enough to compensate for a drastic increase in air flow. When you add a TFI or Power Commander, all it does is monitor the positive leads going to the fuel injectors and increase the duration in which they spray based on the programming (or potentiometer settings) you give it. Without the ability to "sniff" its own exhaust, an engine cannot set its own A/F mixture.

jstark47 · #8 Unread post by **jstark47** » Sat Nov 11, 2006 4:19 pm

Shorts wrote:That sounds inline what I was thinking on the O2 sensor. Makes sense. Thanks jstark. So even FIed bikes have no O2 sensor? (Not that I'm asking for more electronics! I just want to know)

I'm gettin' to the ragged thin edge of my personal knowledge here, and someone else should really chime in...... but in the December issue of Cycleworld, they reviewed the '07 Yamaha YZF-R1 sportbike. The theme of the article is "riding electronic", and they emphasize how much digital technology is making it into street bikes from race bikes. (I doubt any of this would be considered new or startling for cars.) The R1 has an oxygen sensor, but my impression from the article is the primary purpose is to control for emissions, not for engine output.

For most bikes, new pipes means remapping the FI in the ECM or the bike will run lean, backfire, etc.

Shorts · #9 Unread post by **Shorts** » Sat Nov 11, 2006 4:51 pm

Ohh ok, now I'm seeing it. Zoo, good input, I didn't know what mapping was about until you said it.

jstark, I was curious about how emissions was going to play into this. I've been hearing how "its time to crack down on motorcycles for all the polluting they do". Tell you true, I don't want any extra emissions junk on a bike. That's what took the fun out of big engines, muscle cars and 4x4 trucks - aside from gas prices. Makes working on them a bit of a pill needing extra expensive equipment and know how on the computers. Not that we're flat-headed monkeys that don't learn, but really

What happened to slapping a bored over gas burner and going? Hook it up, run your lines and be on your way. Now you've got to make sure the ECM is lined up and the emission police under the hood is satisfied if you intend to make it legal.

Ehh, off the soapbox. I guess EFIed and non-EFIed systems have both pros and cons. Its up to the user as to preference of the lesser evils

I just assume KISS