EvolutinIX

iTrader: (10)

So I looked and searched but did not find a thread about this topic. I am just learning how to tune and just ordered a MAPerfomance external dump o2, and now after the fact I got to thinking...If under full boost the wastegate is open and dumping exhaust gas to atmos. won't this throw off my AFR that is being measured by the wideband?? I don't know how/if this will impact the car when I begin to get more involved in the tune. Any advice would be great, thanks in advance.

lan_evo_mr9

iTrader: (10)

Interesting thought that had never come across my mind.....good question. I just ordered one of those myself.....

Evoryder

iTrader: (55)

no issues tuning. you'll love it

EvolutinIX

iTrader: (10)

So you were able to log and change afr's accurately even with the dump??

3SgteGuru

iTrader: (3)

A dump vents exhaust gases out. A wideband mesures the amount of oxygen in a small sample of the exhaust stream. So dumped gases have no effect but to simply lower the volume of gasses flowing past the sensor. But the sensor measures oxygen to fuel or oxygen/fuel not the volume. Thats how we get air (oxygen) fuel ratio (represents division). So if your wastegate is dumping exhaust gases to the atmosphere it only lowering the volume of the exhaust gases (not changing the AFR), but as long as no fresh air makes it was back into the wastegate and through the turbine housing and to the WBO2 sensor you will still get an accurate reading. Air cannot flow back into the dump tube because the exhaust gases have a positive pressure in relation to the atmospheric pressure. But there is a phenomenon that happens when you have and exhaust leak. Exhaust gases move in pulses much like waves at the beach, especially at or around idle. The front of each pulse has a high pressure but the back has a low pressure. When the low pressure part of the pulse passes through a section of exhaust with a leak it can suck in fresh air that will lean the AFR of those gases.

Evoryder

iTrader: (55)

^ what he said. You should net a few hp increase with the o2 dump also. o2 read out should be unchanged.

EvolutinIX

iTrader: (10)

Makes perfect sense, dont know why I didn't think of that. Thank you very much no I don't feel like i wasted $264!! Thanks again.

hediki12

not to prolong this but i have a question similar . if u have a wast gate flanged off one of the runners would that throw off afr in exhaust pipe? i remember reading a thread here that each cylinder produces difrent afrs so if your venting one ur not truly getting the "cumilative" result ... correct?

3SgteGuru

iTrader: (3)

In that exact situation you could theoretically alter the AFR measured by the sensor. Each cylinder can be running at a different AFR like you stated and you only have one WB02 (which has to be a certain distance from the exhaust port not to be destroyed) so the exhaust gases mix in the exhaust piping and we assume the sensor should measure the mean of all the cylinders AFR. Basically lets assign weights to each cylinder, 1 for each to simplify the calculation process, so we have (1a+1b+1c+1d)/4=mean AFR "a" is the AFR of cylinder one, "b" is cylinder 2, etc. Now if you have the dump on the cylinder 2 runner and you are dumping 90% of the gases from that runner your would have to alter b's weight (its simple to find the percent value of any number but for those who don't know this is how its done. First we are loosing 90% so we need to subtract 90 from 100 and were left with 10 so 10% is whats in the runner. 10% of 1 is found like this, even though its obvious, x/1=10/100. The value of x is .1) so b's new weight is .1b. Now put it in the formula (1a+.1b+1c+1d/4=mean AFR with dump open. You will see it will have an effect on the afr of course but the effect is marginal unless your afr on that cylinder is excessively off (like you have some kind of mechanical/maintenance problem). So my point is you will know from physical symptoms that you have a problem thats significant enough before you would even attempt to tune the car. In a nutshell, if you car is in a tune-able condition the afr of each cylinder will be close enough that the dump won't have a measurable effect on the sensor reading.

3gEclipseTurbo

iTrader: (12)

Yes a o2 dump will effect your tune and will most likely require a retune. The purpose of a o2 dump is to free up the exhuast system thus your car makes more whp. If the car is making more whp then it needs more fuel. So if you put on a o2 dump after you have been tuned your afr will be leaner under load. Which can cause knock possible blowning your engine. And this is not just "theory" I tuned my afr before i had my o2 dump then installed it and my afr where as much as 1.0 leaner under load. Which caused knock so i retuned.

It will not effect the ability to tune the car, if thats what you mean.

fostytou

iTrader: (15)

Cars can definitely make +/-10 whp easily based on changes in weather. If that kind of power difference is changing your load and fueling requirements enough to require a completely new tune ..... then you probably weren't tuned that well in the first place (no offense, but the car should run proper across the load range if it is MAF based.

That said, always retune when you change parts, or at least check your tune.

3gEclipseTurbo

iTrader: (12)

I gained 20+whp and 20+wtq from the dump which will effect a tune. And the logs showing the afr differneces where within 3 hours of each other so i doubt the wether was a factor.

EvolutinIX

iTrader: (10)

Thanks again for the insight guys, great info.

Boltz.

iTrader: (42)

+1. A proper tune on a MAF based EMS will compensate for additional airflow. /Thread.

jedibow

iTrader: (1)

I have the issue that when my wastegate opens with an external dump downpipe my AFR jump 1.0 AFR, I have been in the process of recalibrating my MAF sensor, so it is very evident. However it I run through the same tune with the wastegate forced shut with the table WG 100% below this load in Tephra V7 my AFR are absolutely fine, and my MAF Calibration is spot on based on MAF Hz logging. Are you saying that I have an exhaust leak to cause the 1.0 AFR difference when the wastegate opens to the dump tube? If that is the case the only place that would make sense would be the downpipe to turbine housing correct? Please enlighten me