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Exhaust Backpressure

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well clearly this ecu is not capable of doing it - but most good quality ecu's can hit target afr's without an issue.

Would a factory setup be capable to learn such a big change? Only ask as I thought factory stuff had pretty limited learning capability.

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to a point yes - they are always trying to hit target afr's with variables such as water temp, intake temp, airflow, throttle position and load.  But being on a bike id suggest this one just cant deal with the change or it is a 'dumb' ecu and is not adaptive learning.  Hard to say. 

 

We tried to trick the ecu on that V6 I built with a series of resistors to alter water temp readings (to get the ecu to enrich the mixture).  It worked in the low to mid revs but when it hit the dyno the ecu could not keep up in the mid to high ranges and it actual sent it leaner.  We pulled out all the resistors and the POT and went back to straight ECU and it went richer.  Strange but true and an example of how far you can push the stock ecu.  We have a Haltec in there now and it is a whole other world.

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Following on from this - backfires.

 

 

Been tinkering with the bike a bit and done a few little mods - one of them was removing the air snorkel so it's just an open hole to the airbox. Sounds awesome and seems to have given it a little more kick (could also be the fact that I washed the filter out too) but it also backfires on deceleration.

 

Just going by smell the bike's running a bit rich anyway so I doubt it's leaning it out too much.

 

Any idea's what the go is with that? Reckon if I leave it as is, will it hurt anything?

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Could be because you removed the air snorkel or could be all the little things you have done. Yes the ecu can adjust but it's guessing as to what is best as it's only meant to allow for slight changes to a standard system, not modifications as well.

What do you call a backfire? is it crackling and popping on decel or is it a bang? How loud is the bang?

It maybe that the ecu is adding fuel to compensate for the extra air in and when you roll off the throttle because the bike is still essentially standard it can't use all the extra fuel so it explodes. Is it bad? Well it ain't good, might not do terminal damage straight away but over time it won't be good.

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Probably just unburnt fuel banging (exploding) in the pipes.  Pretty common on deceleration.  Even V8 contrived bullshit, I mean v8 supercars do it.  Go to any event and you will here it on the gear cut.  Watch it on telly and you will see the flames and shit out the exhaust. 

 

Its just unburnt combustible material suddenly combusting when it hits hot stuff.  You shut off the throttle but the engine still pumps the stuff for a bit and then bam it ignites in the pipes.  Especially when you have no mufflers or you burn all the glass out of a packed muffler.

 

If that is what it is, then its not bad.  But if you have a header crack or something else then that can lead to bad, i.e. burnt exhaust valves etc etc.

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Hey fellas Im thinking about running a side pipe on the XD for racing next year!  I have 3" system mandrel bent right thought with a Lukey Muffler. (4 into one Pacemaker headers 4V).  Its twin into single using a Y section.  Im running 11;1 comp and im thinking about kicking the exhaust out the side after the Y section with a hot dog or straight through muffler.  What do you blokes reckon before I go cutting up my good exhaust? Im going to make it so I can bolt and unbolt the full exhaust for when I go racing or back on the streets.

 

Cheers fellas!

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Check the regs surrounding side exiting exhausts. Some don't allow them as it directs exhaust at other drivers and officials. Me, I'd run the exhaust back to the factory location with 2 hooker aero chambers. I'd flange and support the outlet and run a turn down tip at the track and then have an over the diff section with 2 moroso spiral flow mufflers in the rear 1/4 area for the street.

 

From memory those Lukey mufflers are a packed glass muffler with a perforated core and sometimes they have an s section. They are rather crap for performance applications. I good chamber muffler like the aero chamber or mangnaflow will shit all over them for sound quality and performance.

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The big group c bangers used to run fat side pipes. I'd like to use a nascar oval side exit pipe. I used to have s link to a cheap supplier. I'll see if I can dig it up.

Just remember that it is possible to build a quiet - no loss exhaust system. Noise does not always equal power. In some cases where the engine has more exhaust percentage a restriction can actually help power. Probably one true of a clevo with alloys but in some instances it does help.

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that's why in the olden days they never went past 2 1/4 exhausts on the EFI crossflows as they were starting to run lean, with 2 1/2 you'd  have to crush the FPR a little to get it more psi

 

friend made his own exhaust on his R1 (big bang) and the thing was running very very lean, had to go get it tuned and the thing was scary 

 

instead of fat side pipes i'd go for the boom tubes, fuck i wish they'd be legal

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