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Discussion Starter · #1 ·
I’ve heard it mentioned several times that when the crossover is eliminated (stock to true duals) that rear cylinder AFR is always affected. So, is that to say that the front cylinder is not affected in the same way as the rear with regards to a crossover? Is this due to the inherent firing order of the V-Twin that only the rear cylinder intake charge gets affected by the front exhaust cycle and the same isn’t true for the front cylinder to experience the same when the rear exhaust cycle occurs?

Another question, does it matter where an O² sensor is placed along the length of the header in a true dual setup? Sensor manufactures generally recommend that sensors be placed near the exhaust port by several inches and never to place sensor low enough or at such an angle that condensation could collect. So, if there is no crossover affect to influence O² sensor, it shouldn’t matter how far down the header the sensor is placed, right?
 

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mlewis said:
I’ve heard it mentioned several times that when the crossover is eliminated (stock to true duals) that rear cylinder AFR is always affected. So, is that to say that the front cylinder is not affected in the same way as the rear with regards to a crossover? Is this due to the inherent firing order of the V-Twin that only the rear cylinder intake charge gets affected by the front exhaust cycle and the same isn’t true for the front cylinder to experience the same when the rear exhaust cycle occurs?

Another question, does it matter where an O2 sensor is placed along the length of the header in a true dual setup? Sensor manufactures generally recommend that sensors be placed near the exhaust port by several inches and never to place sensor low enough or at such an angle that condensation could collect. So, if there is no crossover affect to influence O2 sensor, it shouldn’t matter how far down the header the sensor is placed, right?
Who's system are you using that uses an O2 sensor?
 

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duals and O2

http://www.daytona-twintec.com/TCFI.html

wide band O2 sensors mount as close to exhaust valve as possible. there are some cheaper out there but only 1 O2 sensor. there are tons of FAQ at the site to answer your questions

gonna do closed loop on my 05 in the future
 

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Cster888 said:
http://www.daytona-twintec.com/TCFI.html

wide band O2 sensors mount as close to exhaust valve as possible. there are some cheaper out there but only 1 O2 sensor. there are tons of FAQ at the site to answer your questions

gonna do closed loop on my 05 in the future
Well in that case if they are not set up to preheat themselves you better plan on putting them about 3 to 4" max away from the exhaust port. Go take a look at the 2006 Dynas to get an idea of where they put them and note the angle they are on. If they have the wires for preheating the sensor than you can mount them 6 to 8" away from the head.
 

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Discussion Starter · #6 ·
wkohn said:
Well in that case if they are not set up to preheat themselves you better plan on putting them about 3 to 4" max away from the exhaust port. Go take a look at the 2006 Dynas to get an idea of where they put them and note the angle they are on. If they have the wires for preheating the sensor than you can mount them 6 to 8" away from the head.
Thanks for the info,

I read that the sensors are preheated and that temperature at the bung shouldn't exceed 900°F.
 

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After eating a bowl of chili and some jalapenos, the temperature at my bung has reached close to 900 degrees (at least it feels that way)
 

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fxdl raw said:
After eating a bowl of chili and some jalapenos, the temperature at my bung has reached close to 900 degrees (at least it feels that way)
Well, aim it at Iraq and fire at will. :flames:
 

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Discussion Starter · #10 ·
Road Bag said:
Excellent tool, I've been using one for about 2 years now to map EFI. Be sure to get the optional tach if you decide to buy one.
RB
Thanks for the positive feedback on the LM-1. Any chance you’re running a true dual setup and have noted the AFR differences between the front and rear cylinders?
 

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mlewis said:
Thanks for the positive feedback on the LM-1. Any chance you’re running a true dual setup and have noted the AFR differences between the front and rear cylinders?
I am running duals with 02 bungs front and rear. Once you get the AFR lines matched front and rear, the VE numbers are slightly less in the rear cylinder. The most accepted theory is intake reversion from the front cylinder is being inhaled by the rear resulting in the need for less fuel from its own injector. Thats why the rear cylinder VEs are lower. Theory two is the rear cylinder needs less fuel because its making less power, due to its having a less favorable intake pulse. I tend to believe this because on the dyno, I have added fuel to the rear and seen the AFR on the front change as well from about 4500 up.That blows theory one. An AFR split is easier to tune out than understand for sure. Have fun.
RB
 

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Discussion Starter · #12 ·
Road Bag said:
I am running duals with 02 bungs front and rear. Once you get the AFR lines matched front and rear, the VE numbers are slightly less in the rear cylinder. The most accepted theory is intake reversion from the front cylinder is being inhaled by the rear resulting in the need for less fuel from its own injector. Thats why the rear cylinder VEs are lower. Theory two is the rear cylinder needs less fuel because its making less power, due to its having a less favorable intake pulse. I tend to believe this because on the dyno, I have added fuel to the rear and seen the AFR on the front change as well from about 4500 up.That blows theory one. An AFR split is easier to tune out than understand for sure. Have fun.
RB
Great information! If I understand what you’ve posted correctly, the shared intake charge of one cylinder will likely influence the other. This may not be an issue in the case of my 1999 Magneti-Marelli induction system, as I believe the front and rear cylinder intakes are kept isolated. What’s you’re understanding of the effects of the exhaust crossover (or lack of) on rear cylinder AFR or VE?
 
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