Dyno questions and associated ramblings

GTRFAN · 12-15-2009, 09:27 PM

Hi,

Do most of the dyno operators in the US have twin O2 sensors for the twin Z exhaust pipes? The reason I ask is that when we ran on a local dyno dynamics they only had the one O2 sensor and couldn't take a accurate A/F measurement.

They also said their dyno operates real world mode with temperature and barometric pressure recorded and entered before each run. My understanding is that this gives the most accurate results and is opposite to "Shootout Mode" which they laughed at as a common practice to get higher power figures.

Just curious more than anything

thanks

Modshack · 12-16-2009, 09:44 AM

All dyno set-ups I've witnessed here use a single probe. Probe sampling is not perfect and is off a bit from tru A/F ratios. Good numbers (most accurate) can be sampled from ahead of the CAT with a dedicated probe but few cars are set up to sample there. A good operator will understand the differences and compensate when tuning.

There are various "corrective" calculations applied to raw numbers to make them somewhat comparable. Differences in temps and barometric pressures can be calculated and applied to the raw number. "SAE" is a typical corrected algorythm, but may not give as high a reading. You can play games with the numbers all day long. I once had a Vette dyno'd on a Very cold day. Hit 440 RWHP, but only 410 when SAE corrections were applied..

jpit · 12-16-2009, 10:46 AM

Modshack,

I have a dashdyno that reads A/F ratio from three different sensors. The instructions do say that the car must have a wideband sensor (as opposed to narrow) to get a reading. Two of the sensor readings are very similar while the third seems to read very high (very lean). If our cars have a wideband sensor built in why can't they used that instead of installing a sniffer in the exhaust pipe?

Modshack · 12-16-2009, 12:04 PM

Quote:

Originally Posted by jpit

Modshack,

If our cars have a wideband sensor built in why can't they used that instead of installing a sniffer in the exhaust pipe?

Typical Dyno guys are not electronic technicians. Only more recent cars have widebands built in... the difference between a tailpipe sniffer and an on board sensor is not enough to be an issue......Especially when you're only paying a few bucks for a dyno pull.. As I mentioned, guys that do serious tuning using a Dyno compensate for these small differences, knowing that they are there..

12-15-2009, 09:27 PM	#1 (permalink)
GTRFAN Track Member Join Date: Dec 2008 Location: Melbourne Posts: 586 Drives: 370z Titanium 6MT Rep Power: 17	Dyno questions and associated ramblings Hi, Do most of the dyno operators in the US have twin O2 sensors for the twin Z exhaust pipes? The reason I ask is that when we ran on a local dyno dynamics they only had the one O2 sensor and couldn't take a accurate A/F measurement. They also said their dyno operates real world mode with temperature and barometric pressure recorded and entered before each run. My understanding is that this gives the most accurate results and is opposite to "Shootout Mode" which they laughed at as a common practice to get higher power figures. Just curious more than anything thanks __________________ My Zed

12-16-2009, 09:44 AM	#2 (permalink)
Modshack A True Z Fanatic Join Date: Mar 2009 Location: Greenville NC Posts: 2,883 Drives: 370Z Sport Rep Power: 976	All dyno set-ups I've witnessed here use a single probe. Probe sampling is not perfect and is off a bit from tru A/F ratios. Good numbers (most accurate) can be sampled from ahead of the CAT with a dedicated probe but few cars are set up to sample there. A good operator will understand the differences and compensate when tuning. There are various "corrective" calculations applied to raw numbers to make them somewhat comparable. Differences in temps and barometric pressures can be calculated and applied to the raw number. "SAE" is a typical corrected algorythm, but may not give as high a reading. You can play games with the numbers all day long. I once had a Vette dyno'd on a Very cold day. Hit 440 RWHP, but only 410 when SAE corrections were applied.. __________________ Steal my car! (SOLD)...Now Porsche Cayman S Oil Cooler DIY: Here!

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12-16-2009, 10:46 AM	#3 (permalink)
jpit Enthusiast Member Join Date: Feb 2009 Location: Washington State Posts: 440 Drives: 370Z Tour MT w/Spt Rep Power: 16	Modshack, I have a dashdyno that reads A/F ratio from three different sensors. The instructions do say that the car must have a wideband sensor (as opposed to narrow) to get a reading. Two of the sensor readings are very similar while the third seems to read very high (very lean). If our cars have a wideband sensor built in why can't they used that instead of installing a sniffer in the exhaust pipe?