Why is my dry-shot lean at lower bottle pressure?

Gary Z · 10-08-2009, 11:04 PM

I am spraying a 125-shot downstream from the MAF using an IAT-tricker to pull timing and add fuel. With commanded AFR = 10.6:1, wideband measured AFR is 12.5-12.8:1 I reduced the commanded AFR to 10.4:1 in preparation for stepping up to a 150-shot. The result was a leaner AFR, wideband measured above 13:1 The only difference (other than commanded AFR) was bottle pressure. Bottle pressure for the rich pass was 900 psi. Bottle pressure for the lean pass was 775 psi. May not be related to bottle pressure but I can’t see any other difference. Any ideas?

ATVracr · 10-09-2009, 10:44 AM

if you dont hit the MAF with enough N20 it wont richen it up as much.

We used to put the nozzle closer to the MAF to richen it up.

Put a fresh bottle in and try it before you change anything.

Nick@HSW · 10-09-2009, 11:20 AM

I'm not a big fan of the resistor mod. If going this direction I would just use the Interface to do your fueling. Its much more complicated than a simple resistor to accomplish a post maf dry shot.

Nick

Gary Z · 10-09-2009, 11:36 AM

ATV, Thanks but I am spraying after the MAF - nozzle is in the bellows between MAF and TB.
Nick, the interface is a good suggestion but I would still like to understand why I am seeing an unexpected lean condition. Charts of two passes are attached.

Kaltech Tuning · 10-11-2009, 06:33 PM

Your fueling will be dictated by your maf and if it is a pressure related issue I wouldn't be surprised if some of the nitrous on the higher pressure pulls were maybe cooling the maf and causing the maf to add more fuel.

Any particular reason you're running your dry setup like this? You have a nice setup in your sig so why run your spray setup like this?

Gary Z · 10-12-2009, 02:24 PM

Quote:

Originally Posted by Kaltech Tuning

Your fueling will be dictated by your maf and if it is a pressure related issue I wouldn't be surprised if some of the nitrous on the higher pressure pulls were maybe cooling the maf and causing the maf to add more fuel.?

Thanks for the idea - I will investigate this possibility. My 90-degree nozzle is pointed directly at the TB but I suppose there could be some nitrous backsplash that is disturbing the MAF. I could replace the nozzle with a plate and see if that makes a difference.

Quote:

Any particular reason you're running your dry setup like this? You have a nice setup in your sig so why run your spray setup like this?

I am new to nitrous and still experimenting with my setup. The usual method of spraying the MAF (upstream) doesn’t appeal to me - I wanted the MAF to work normally with the PE/IAT Table adding fuel for nitrous. This method seemed like a better way but I’m starting to see the value of something like the HSW interface.