# Tailpipe A/F on the dyno for tuning? **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [August 26, 2005, 10:12am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816 "2005-08-26T10:12:59Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Viper966](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/viper966/32/7268_2.png) [@Viper966](https://forums.speedlife.net/u/Viper966)\ **Post date:** [August 28, 2005, 7:38pm UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/21 "2005-08-28T19:38:42Z")
no im not… guess i shoulda specified ---
**Author:** ![Adictd2b00st](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/adictd2b00st/32/7625_2.png) [@Adictd2b00st](https://forums.speedlife.net/u/Adictd2b00st)\ **Post date:** [August 28, 2005, 9:34pm UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/22 "2005-08-28T21:34:39Z")
yea what everyone else already said…if you have a straight thru exhaust, then yes its fine…otherwise its not gonna be accurate ---
**Author:** ![jay\_g](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jay_g/32/111288_2.png) [@jay\_g](https://forums.speedlife.net/u/jay_g)\ **Post date:** [August 29, 2005, 5:26am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/23 "2005-08-29T05:26:56Z")
Does anyone have any prof that it will fuck up the readings? My experience with getting a tail pipe 02 sniffer and with my tuning readings have been VERY close. Not identical but close. ---
**Author:** ![rj-92](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/rj-92/32/7310_2.png) [@rj-92](https://forums.speedlife.net/u/rj-92)\ **Post date:** [August 29, 2005, 7:06pm UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/24 "2005-08-29T19:06:21Z")
If you know the cat Eff’s up the readings, it has to do so in a linear fashion, hence this irregularity is predictable and can be acounted for and a correction factor applied to get and acurate reading… Correct? ---
**Author:** ![Viper966](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/viper966/32/7268_2.png) [@Viper966](https://forums.speedlife.net/u/Viper966)\ **Post date:** [August 29, 2005, 8:36pm UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/25 "2005-08-29T20:36:05Z")
yes and no… things like egt will fuck up that curve… ---
**Author:** ![catalyst](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/catalyst/32/7279_2.png) [@catalyst](https://forums.speedlife.net/u/catalyst)\ **Post date:** [August 30, 2005, 5:57am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/26 "2005-08-30T05:57:57Z")
> [@num482](#): > > Does anyone have any prof that it will fuck up the readings? > My experience with getting a tail pipe 02 sniffer and with my tuning readings have been VERY close. Not identical but close. Can you quantify “VERY close” for us? ---
**Author:** ![jay\_g](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jay_g/32/111288_2.png) [@jay\_g](https://forums.speedlife.net/u/jay_g)\ **Post date:** [August 30, 2005, 6:12am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/27 "2005-08-30T06:12:03Z")
With in .2-.3 richer. So for me it showed richer. ---
**Author:** ![Jack](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jack/32/7613_2.png) [@Jack](https://forums.speedlife.net/u/Jack)\ **Post date:** [August 30, 2005, 6:31am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/28 "2005-08-30T06:31:53Z")
> [@rj-92](#): > > If you know the cat Eff’s up the readings, it has to do so in a linear fashion, hence this irregularity is predictable and can be acounted for and a correction factor applied to get and acurate reading… Correct? I don’t think its that easy. Like Bry said… EGT has a HUGE influence on your cat… so if you do a pull, cool down, do another pull… your EGTs will be different (especially if you made some changes) and now the cat will be warmer/cooler than before and working more/less efficiently ---
**Author:** ![Inn-Tune](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/inn-tune/32/7588_2.png) [@Inn-Tune](https://forums.speedlife.net/u/Inn-Tune)\ **Post date:** [August 31, 2005, 8:20am UTC](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816/29 "2005-08-31T08:20:02Z")
> [@Adictd2b00st](#): > > yea what everyone else already said…if you have a straight thru exhaust, then yes its fine…otherwise its not gonna be accurate That about sums it up. It will lag a little behind a sensor that’s closer to the engine, but we’ve tuned MANY cars this way without issue. I’ve found the lag is about 100-200 RPM. I have sniffed the tailpipe on cars with cats if they just want an idea of the shape of their curve and where it is. If your car is way off tune this will still show up. The best option is still to have a bung ahead of any cats, but far enough back that it doesn’t overheat, and in a place that’s easy to access. This is usually 1-5 feet from the head(s) or turbo depending on the setup. > [@Boomin99GT](#): > > Yeah I hear ya but usually you need to hold the gas @ a certain RPM for a few seconds before the meter can calculate whats going on, they’re not that fast and on the dyno you can’t hold it @ a certain RPM. As an FYI…my dyno can hold any RPM I want…even with a vehicle at full throttle. This does stabilize the o2 readings at the start of a pull if you’re using a tail sniffer setup. -Mike [Previous page](https://forums.speedlife.net/t/tailpipe-a-f-on-the-dyno-for-tuning/1816.md?page=1)