I have a cut-out installed in my down pipe. It's just capped off, its not an electric open/close one (yet).

I"m going to the dyno saturday and plan to uncap it. I've not been able to log the car uncapped ever because it's so hellaciously loud when open and my apartment complex has 3 police officers that live in it, I'd be caught for a noise violation before i put it in gear..

My question is: Will uncapping the car change my afr values. I know it's going to be better flowing and I will likely see a drop in boost pressure, but I'm not sure if it will effect the AFRs to uncap it. It holds 11.8-12.1 now @ WOT and I don't want to uncap it and then have to stop mid dyno run because it's going leaner than that. (I get 3 pulls so I can tune between them, but I'd like to know what I'm up against before going in).

Thanks!

 

With mine closed it ran around 11.3-11.4afr and open iy was 11.7-11.8, BUT mine is electronic and when i took it off the plate was bent causing a leak which i think altered my afr. I made a cap for it and it now stays the same open and closed. So im pretty sure the leak was causing the difference but I would watch the wideband closely just to be safe.

 

yes, when it's open, the a/f will change slightly.

 

Hey ralli, do you ever get pretty bad burst knock with your cutout open? Im going to put mine back on soon, but before I took it off after I put my meth on I would see 3-5* of KR for a split second as soon as i smashed the gas with the cutout open, but none with it closed.

 

can't say I ever did. That sounds a bit odd for sure.

 

Leaner?

 

yes, open it should be leaner. You are moving more air out, less back pressure.

 

Thats called tip in knock. Its normal to have a small amount of tip in knock.

 

Retuned to an 11.6 in case she leans up. If everything's okay after the first pull I'll flash it back

 

Oh thank you sir! I thought it was burst knock. Is it normal to have that much though?

(sorry for the thread jack! almost done lol)