Hi,

I got a APS ST Z. Since I was busy yesterday, my buddy took my car to a shop to dyno it. Well, looking at this chart I'm a little concerned about the AFR. It's quite lean up to 4700rpm. I'm not concerned about the AFR reading before 2200rpm. I assume they are like that because AFR wasn't getting measured before 2200rpm. Where I'm concerned is between 2200rpm to 4700rpm. I should have called the dyno shop, but instead I stopped by my turbo mechanic and he said that often times rpm is revved up gradually (NOT WOT) while dyno testing therefore the AFR doesn't drop dramatically to 11's. What mechanic said kind of makes sense because I've actually seen this when the turbo was first installed in my car. If I slowly raised the rpm upto 4000rpm, AFR would stay around 14 or high 13's, but if I do WOT, AFR would drop to 11s and 10s.
Well, I'll find out what the dyno tester did tomorrow, but what do you guys think about this chart? Did the dyno tester do the WOT or gradually revved the RPM?

 

remember that if the afr was taken at the tail pipe, it's most likely reading a full point leaner than it actually is...

 

Good point.. I'm gonna have to ask them where they put the O2 sensor. APS ST comes with an extra bung on the exhaust pipe.. So, I'm not sure if they put the O2 sensor in there or at the tail pipe...

 

BTW the torque reading is in kg*m.. Yes metric... I'm also only boosting 0.5 bar, which is about 7psi. I'm going to raise my boost up to 0.7bar when the zeitronix arrives. I'm hoping for 400rwhp.

 

Ive had pipe sniffers on a car with no cats read almost identical to widebands way closer to the motor in my car....they are only way off if you have an exhaust leak. Id question the shop they should have gone WOT sooner imo. BTW what was your TQ?

 

Yup.. first thing tomorrow... My torque was 56.72 metric.. How do I convert that to US measurement? It's been a while doing the conversion in my physics class....

 

I had my APS ST at the tuner last week (dynocomp - authorized APS shop) and I asked him the same thing. I had done 2 dyno runs on a dyno jet a few weeks before and noticed that it was kinda lean. He said that the fuel system must be up to operating temperature to work as designed and to give accurate measurements. In other words, it might start out looking lean but as the car warms up the ratios will move down. That's why when he is tuning on the dyno dynamics load based dyno, he gets the engine nice and warm before looking at the numbers. This was proven by the results he showed me.

 

Interesting.... But did he say anything about the diff b/w WOT and gradual revving?

BTW 56.72kgm = 559.2592Nm = 412.49Lbft <- If my calc is correct, 56.72 metric torque is equal to 412.49Lbft (US) torque.

 

So are you saying before your car is completely warm it will run lean or that it will only register as lean but in reality be normal. ??

 

I just spoke to the dyno guy. He did WOT at 2200rpm. He said since the single turbo doesn't build full boost until around 4000rpm, AFR doesn't have to drop dramatically to 11s. He said when he saw the result, he really liked the AFR curve. Also, they put the O2 sensor in the tail pipe, so the actual AFR should be 0.1~0.2 lower.

 

I have done back to back to back to back testing on this thory, and the difference is within .1-.3 points , nothing to be alarmed at...When I do Dynos I use the tail pipe, when I tune I use both for reference, and their almost always dead on.

 

Not too sure, just repeating what I was told. I think it's more like it will run leaner until warm.

 

If thats the case then it could explain why so many people get blown motors since it takes about 15 minutes to completely warm an engine. I guess it also depends on what he means by warm. This kind of vague statement would make me go crazy.

 

Just curious.. Does installing much more free flowing exhaust alter the AFR?

 

If your car is running the same amount of fuel as before, but is flowing more air because of a less restrictive exhaust the AFR will be leaner (more air/fuel). How much depends on the change in flow. On a turbo car, any and all exhaust restriction is the enemy.