When dynoing a 03 w/an offroad will it throw off the a/f heard alot of different things whats the correct answer ????anybody w/offroad dyno w/ a/f yet???
Offroad....Air/Fuel?????
- Thread starter 9900blueoval
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I was told that it will put your car in a "safe" mode that will mess with the A/F if you don't use the MIL eliminator kit. Not sure how true that is...anyone else?
This is mine. Hope this helps. My mods are in my sig.
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For some reason, the site isnt letting me post the pic right now. IF you like I can email it to you.
Or just right click the White box with the red X and copy and paste that URL.
better yet: Here im not really thinking well tonight
:beer::dw: Click Here
Or just right click the White box with the red X and copy and paste that URL.
better yet: Here im not really thinking well tonight
:beer::dw: Click Here
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I would like to hear some input on my dyno graph if someone can. This was my first dyno. When i posted, i didnt really get much feedback. It would be greatly appreciated. Just want to know if my readings are normal. Thanks
Similar to mine.
The lean A/F down low bothers me, though I've heard it's normal.:??:
An offroad X(ie no cats) will change the A/F reading if its done with a tail pipe sniffer. There are settings I beleive to tell the dyno software if the car is running cats or not however so they can be accounted for. The exact accuracy of the reading is not something I am sure about though.
As for the actual real world A/F that the car is running cats will have no impact at all on that. Closed loop A/F is controlled by the O2 sensors in front of the cats and the rear O2's are only their to make sure the cats are doing their job. If the readings do not vary by a set amount then the EEC assumes that cats are bad and will throw a code. You can use MIL eliminators at the rear O2's OR have the rear O2's turned off if running a custom tune so that you wont get these codes when running with no cats.
As for the actual real world A/F that the car is running cats will have no impact at all on that. Closed loop A/F is controlled by the O2 sensors in front of the cats and the rear O2's are only their to make sure the cats are doing their job. If the readings do not vary by a set amount then the EEC assumes that cats are bad and will throw a code. You can use MIL eliminators at the rear O2's OR have the rear O2's turned off if running a custom tune so that you wont get these codes when running with no cats.
This sounds true, but what happens is that most people go from a stock 2.25" diameter to a 2.5 diameter pipe. A bigger pipe means less velocity of the exhaust fumes through the pipe. Also, many use aliminumized pipe, which gives off heat much quicker than SS, in addition to less heat from the extremely hot cats. This might trick the computer into richening things because it see's less temp...a slighly cold motor condition. And the velocity change in the exhaust fumes gives the 02 a different reading as well I would guess.
This is not fact, just my guestimate, feel free to knock down my idea as it may be wrong. This is what I think happens when you go to a 2.5 inch o/r pipe. This is why there is still power to be gained through a tune after adding a 0/r exhaust.
My buddies 99 cobra motor went from 299 rwhp with o/r H, long tubes, flowmaster cb, 4.10 and densecharger to 324 rwhp just by adding pulleys and a dyno tune. My guess is that the pulleys were good for 6-8 of that and the rest was from air to fuel and timing calabrations:rockon:
Then he added a vortech w/ aftercooler with AFM powerpipe and a diablo chip and now has 488 rwhp. Its ran a 11.6 at 123:bowdown:
If headers arent in the equation then there is diameter and material the x/H pipe is made out of will have little if any bearing.
In regards to the A/F of the car, when runnuing WOT on a dyno the O2's arent even used in determining A/F so once again that point is mute. O2's only play a role when running the car in closed loop and then any minro changes determined by the O2's due to headers etc will gradually be accounted for via STFT and after a while committed to LTFT, but as I mentioned none of this plays a role in open loop operation.
Seems reasonable, but the 02 go into the H pipe right, if its different than the stock pipe, like long tubes are as well, then I see no differnence between the a/f effects of adding a o/r pipe vs long tubes
But if a o/r H had no no effect on my a/f ratio, then why did my car smell of unburned fuel so bad, as others do until tuned? Why when i would shift into second or thrid gear at redline did flames shoot out the tailpipe?
Most people felt i was running rich, maybe its just noticable w/o cats and the cats covered up the rich condition in stock form???
I don't know, but i have heard alot of people say that their a/f ratios are out of whack after installing exhaust mods
If your using stock manifolds the exhaust is only going through a few inches of new H/X pipe befor ehitting O2's so the difference it makes is negligable at best. If it goes through longtubes they generally move the O2's back farther and it this change in distance more than materials that make a difference and this is whats accounted for in a tune.
In the simpest of terms, the O2's that have ANY bearing on your cars A/F are BEFORE the cats AND they only have an effect on A/F when NOT at WOT (ie closed loop) and when not at WOT the car trioes to maintain a stoich A/F of 14:1 (far from rich).
Under WOT conditions, O2 feedback IS NOT used. Dont beleive me, weld a bung in your exhaust and put in a wide band O2 sensor, monitor A/F. Cats or no cats will have no effect (aside from back pressure) during closed loop and absolutely no effect at WOT (ie open loop).
I dont know how else to explaine it, but the cats burn off fuel and when they are on the car you will get a leaner A/F reading at the tail pipe than you will with them on. When you dyno a car they input data stating weather or not cats are installed so the sniffer reads properly. You pull cats off your car your going to smell more fuel from the exhaust but that doesnt mean its running richer, it means the cats are doing their job and burning off fuel.
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