Nitrous jetting and SCT tunes, with Zex or NX wetkits...
11/8/06, 07:38 PM
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Nitrous jetting and SCT tunes, with Zex or NX wetkits...
Hey guys,
I've done three cars now on the dyno using nitrous and found that when you use a SCT tune with the nitrous that the jetting specs from Zex or NX are one size to small on the fuel jets.
For example, when using a 75 shot this weekend we used the recommended 26 fuel jet and 40 nitrous and it gave us a A/F ratio of 12.8-12.2 which in my book is too lean. When we used the next step up fuel jet, the 30 fuel, we ended up with a nice 12.0-11.0 a/f ratio.
Like I said before this has happened on every Nitrous application that I've loaded a tune onto at the dyno. So from this information I would recommend that if you are using a SCT tune and haven't had the a/f checked then I would run the nitrous jet for the recommended shot you want to use and the fuel jet for the next size up. This will bring you down to a proper a/f ratio, maybe a bit rich but its better to be rich then lean.
Now this information doesn't replace the need for a dyno session to check a/f ratio's with nitrous. I would always recommend this.
Below is a dynochart from this weekend with a 75 shot, the first run with the recommended jets and the second with the larger fuel jet. I've tested this all the way up to a 150 shot, I couldn't find the dyno runs but he made 420 rwhp with it. I've got a email into the dynoshop for the runs.
Thanks, Doug.
I've done three cars now on the dyno using nitrous and found that when you use a SCT tune with the nitrous that the jetting specs from Zex or NX are one size to small on the fuel jets.
For example, when using a 75 shot this weekend we used the recommended 26 fuel jet and 40 nitrous and it gave us a A/F ratio of 12.8-12.2 which in my book is too lean. When we used the next step up fuel jet, the 30 fuel, we ended up with a nice 12.0-11.0 a/f ratio.
Like I said before this has happened on every Nitrous application that I've loaded a tune onto at the dyno. So from this information I would recommend that if you are using a SCT tune and haven't had the a/f checked then I would run the nitrous jet for the recommended shot you want to use and the fuel jet for the next size up. This will bring you down to a proper a/f ratio, maybe a bit rich but its better to be rich then lean.
Now this information doesn't replace the need for a dyno session to check a/f ratio's with nitrous. I would always recommend this.
Below is a dynochart from this weekend with a 75 shot, the first run with the recommended jets and the second with the larger fuel jet. I've tested this all the way up to a 150 shot, I couldn't find the dyno runs but he made 420 rwhp with it. I've got a email into the dynoshop for the runs.
Thanks, Doug.
11/8/06, 08:59 PM
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best before doug=12.62 @110 with doug's tune 12.29@110!!!!!!!!
and that was just my first time out with doug's tune in it. thanks to bamachips my 11 sec n/a auto goal is within reach...maybe this spring.
thanks doug!
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