New exhaust setup leading to different AFR ?

[Yspen]

Hi all .
Engine setup : 2F-E with aftermarket ecu using MAP sensor fueling ( Delta 250S cam ). I have a Wideband commander fitted to monitor AFR and help tune the fuel maps
Yesterday I added an extra silencer box in the exhaust pipe . There setup was headers ( 3-2-1) leading to 57mm pipe , large box halfway and out the rear . Now we added another box ( 40 cm ) at the very end of the pipe ( I think OEM is the same ) as I wanted the car less noisy .

When I left the shop I immediately noticed that the AFR ratios were richer . Eg where the gauge showed 14.7 before it now ran at 13,8 .
I actually had to adjust the maps a bit . ( not an issue as I save the maps and can revert if need be)

Now what could have cause this?
1. Change is exhaust setup leading to less scavenging or more backpressure and this affecting fueling ?

2. Welding on the pipe leading to damage to the sensor ?
I contacted Dynojet and they say welding is unlikely to damage the sensor and their sensors cannot be calibrated .

Interestingly the car actually feels like it has more torque ( could be wrong here but this is my perception).
If it is the exhaust setup then it will be great as I will be using less fuel as the maps has to be leaned out to get stoich ?

Is there anybody with so insight as I do want the fueling perfect ( do not want to start burning valves cause AFR was wrong )

 

[AussieHJCruza]

I can't help regarding the change in the AFRs, but in a N/A diesel such as a 2H, there is way more low-down grunt with the standard, more restrictive exhaust than with a high-flow system.

 

[Yspen]

http://www.veryuseful.com/mustang/tech/engine/exhaustScavenging.pdf

 

[TobyB]

Yep. The resonance of the exhaust system will affect the fuelling. Usually you don't get 'something for nothing'
as your top end may suffer, or you'll get a torque dip at 4275 rpm or something, but you really can tune the
exhaust system for a particular 'band'.

Honestly, over 10 years of camming, compression ratios, piston design, porting, blah de blah,
one of the biggest rejets I had to do on the 2L race car was when it got a better,
more- open exhaust... that had quite a bit more volume, as yours does...

t

 

[Slow Left]

Hey Yspen, I like your approach here. I've still got the carb'd 2F, but your experimental approach has got me interested in looking into adding some sort of feedback loop so I can make adjustments (like adding on larger exhaust pipes...or engine tuning...) and measure the affect.

So it sounds like what you are doing is using the data collected from the Commander to test for the affects that changes in your system have on performance.
So you are measuring Air to Fuel ratio as the performance metric for determining whether a change has a positive or negative affect on performance.
To do that, you've hooked up the A/F sensor to the exhaust downpipe (before the CAT) and receive a Tach signal from the coil (as a measurement of engine speed).
Do you use either Analog 1 or Analog 2 for additional measurements to make the calculation more accurate (like air temperature)?
Does the Commander communicate directly with the ECU?

On your 2F-E, was that an aftermarket kit or did you take it off a later Land Cruiser model and marry it to your engine block.
What components/sensors does the ECU use to adjust the amount of fuel injected?
MAP or MAF (and where is it located on the engine)?
How/where does it measure engine speed (crank sensor?)?
How/where does it measure gas temperature?

According to that .pdf you posted on Backpressure, it seems like what you are trying to optimize is the negative pressure (or 'suction') behind the main pressure wave.
The question I think you are trying to answer is whether or not the decrease in AFR ratio that you measure (from 14,7 to 13,8) on the Commander as a result of the change you made in the exhaust system is an indicator of increased or decreased engine performance (efficiency).

 

[Yspen]

Hi Slo
I am not so much interested in performance as in efficiency and economy . ( suppose it goes hand in hand )
The ecu I am using is a locally made product with good support locally and it is easily tunable on the road .
Unfortunately it does not have Wideband support but only a narrowband sensor ( it is switched off while I am tuning ) .
The wideband gives me an more accurate indication how to tune the Aftermarket ecu effectively . Even though I can log on the Wideband commander I am not doing so and use the ecu for that purpose . With the Wideband connected I do runs at low , cruise , high cruise and WOT and can then set the fueling in the ecu to reach the optimum AFR for a particular rpm / load level

Here is an example of such a map - mine does not look like that but it gives an idea of the type of AFR one looks for

The Ecu used in my setup has the following inputs : MAP sensor ( vacuum in manifold ) , water and air temp, Lambda ( narrowband ) , Throttle position sensor . It uses the stock dizzy , coil and ICV of the 3FE . It was way easier to set up the 2F-E with this setup than using stock ECU . ( no VSS or EGT )

The tuning is something that takes time though and after fitting the new exhaust all changed as the AFR reading were lower ( richer ) . The ECU uses MAP sensor and rpm to adjust fueling . You can use TPS as well but I have it set up to use MAP only to determine load .

So I was trying to increases backpressure in the exhaust , I was just trying to get a quieter one . But I seemed to have gotten some backpressure or reduced clearing of the cylinder . That though lead to AFR changing , probably due to the reduced scavenging of the cylinders and fueling remaining the same at a particular load / rpm range . With the same fuel and less oxygen in the cylinder the car is now running richer and I thus need to change the fuel settings . How it is afffecting power output can only be determined on a dyno - I suspect the car has lost a bit of horses in the process event though it still runs well with the 2F-E setup .