I am just curious if I needed to retune my car after I changed my whole exhaust to 3in from 2.25in. I was tuned to 280whp on 10-11lbs with a 3in downpipe going down to the 2.25in exhaust. A couple months later I switched the whole thing to 3in. I decided to throw in some pistons and rods a few weeks ago so I took the engine out and tore it down and found that the ringland just fell off 3 of the pistons and there was a crack on the other. I did notice the car was burning more oil than usual so I am wondering if it leaned out some and blew the ringlands after going with the 3in all the way back?

 

yes, going to a bigger exhaust than what was originally on there for the initial tune leads to running lean

 

im kind of in the same boat as you...i'll be upgrading my 2.25" exhaust to 3". Is a/f the only thing that will be affected? Or will timing be affected also? I tuned my car on Crome so changing the a/f will not be a problem(I also have PLX wideband). Changing timing will be since I would need to get on a dyno again.

 

There was definately a great boost in power after going with full 3in. I was trapping at 103-104mph and after it was 108-110mph! with 1lb of boost less! I guess that should have made me think about the retune but I probably blew the ringlands that track day.

 

7-8mph faster traps would be upwards of 50whp more. I'm not suprised you ended up cracking 2 ringlands. Assuming it was tuned to ~11.5 afr's, you gained a good bit of power from less backpressure, and then even more from afr's leaning out to almost stoich. If timing was fairly conservative, you can usually get away with the same timing maps, but if you're really pushing the stock internals, you may want to retard the timing a little bit more.

With MAP-tuned cars, basicly any modification will alter AFR's at some point in the rpm's, since the ecu will make NO changes to the fuel tables by itself.