My Post on 240sx.org list

[guidot]

This is the post I made last night to the 240sx.org mailing list. I haven't gotten a reply as of yet but let me know what you guys think:
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Hello all,
I have been on this list now for almost 2 years. All of you are very helpful, especially those who go out of their way to answer almost every question (asad, errin, asao, jeff b. etc.). I had a quandry that I couldn't find a straight answer to though ( I have all messages in the 2 years archived, thank god for Outlook!<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wink.gif" border="0" valign="absmiddle" alt=';)'>.
If I install the biggest injectors I can without modifing the intake manifold (370cc?) or the ECU, install the 300ZX fuel pump and filter and DON'T do anything on the air side, aka Cobra MAFS, will I run rich? Or will the the stock ECU compensate, if I reset it? Also, is this SCCA Solo 2 legal? I have checked all the resources that I trust and I haven't gotten a true yes or no.
Again this is not something that I would be doing right away but if I do do it, I don't want puffs of black smoke soiling the traffic behind me.

Thanks!

Jeff
240SXONE
Owners of New England
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[Cheater240SX]

The stock ECU will adjust for differences in the system (MAFS, injectors) based the O2 sensor. &nbsp;I think it will generally adjust +/- 20%, but that might be generous.

370cc injectors sound large (how large are stock injectors?)

Mustang 5.0L guys get around this by replacing injectors and MAFS as a set. &nbsp;Thus, for a given airflow, the MAFS sends a lower voltage signal than a stock one would, the ECU sends a shorter pulse to the injectors, and the injectors spray around the right amount of fuel because they are oversized.

This causes some problems with ignition timing though. &nbsp;The ECU determines engine load off of the MAFS and determines spark advance from this. &nbsp;With the larger MAFS, engine load is always determined to be lower than it actually is, and timing is advanced more than it should be. &nbsp;This can probably be solved just by setting base timing back a few degrees (clock the distributer)

[DuffMan]

Is this for a turbo KA? If so I don't recommend doing that. Turbo and NA computers are set up differently. NA fuel maps are based on the volumetric efficiency of the engine, and only adjust for small changes in air pressure. At WOT, they say don't just say "well the MAFS says we are getting so much air so add so much fuel". It's more like "well I know the engine can only breathe in this much air at WOT so I will give it a preprogrammed ammount of fuel."

This is why getting a JWT program on an NA engine with boltons will show so much improvement. The stock program is limited to what the theoretical limits of the engine are. With turbo cars it's totally different. Turbo ECU's realize that many factors can change the amount air being fed into the engine so they take the MAFS word for it when it says there's more air coming in.

This is sort of an oversimplification, but its generally correct. In your case a JWT reprogram would be the easiest solution. You could also try messing arround with a Greddy Emanage if you are really into tuning your own car.