i am getting 3in catback installed tom...and i am worried about running lean

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i have my car tuned to a 12.5 a/f ratio @wot...
(5psi of boost) w/ a stock 98 prelude exhaust...
if a bolt on a 3in catback...aprox. how much leaner will my a/f become??

+1 point? 13.5? ...+2points??14.5?

i know the only true way to find out is the dyno...but the closest dyno shop around where i live thinks that for some reason i should be around 13.5 to 14 under boost...(domestic tune shop)

so i am a little weary of going back...but until i find a reputible shop..i was just wondering if it would really be that big of a deal

[uoboarder]

I don't think it'll do anything to the a/f. Think about it... You're running a restrictive as hell 2" piping exhaust... (that's what it looked like in your post) and all you're doing is removing a little back pressure...that shouldn't change the a/f. What will change the a/f ratio is air temperature outside (i.e., hot days and cold nights) and the amount of fuel, fuel pressure, and injector size and pulse width you have. Exhaust flow shouldn't effect it.

[lazyassbrian]

what size is the downpipe? the less backpressure would allow the turbo to spool up a little faster which mite cause some leaning. but with 5.5psi i don't think there'll be much dif in a/f.

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2.25 -2.5 on the dp...i'm not sure