Question about rattle in CR sidepipe

[C5GTO]

Firstly, thanks again for all the info and especially the pictures!

Secondly, here's my observations after commuting with the Cobra for a week now and doing no repairs per see on the pipe. The baffling in the drivers sidepipe has broken down to the point that the rattle is completely gone and the exhaust sound levels have gone up a lot, especially when accelerating hard. I haven't seen any large baffling parts come out so I'm guessing the now broken baffling parts are laying on the bottom inside of the muffler. The exhaust noise is bearable on open country roads but not really (for a daily driver anyway) on roads that have concrete barriers or curbs. The amount of sound that bounces back to the car for practical purposes is bordering on ear damage level. I do think I can feel a power difference (could be placebo effect from noise though) but I'm guessing I now have an imbalance between right and left cylinder banks because of back pressure differences.

So I'm now convinced I should do a muffler replacement and I now need to narrow down the choices to make. The car has a 5.0L Ford Motorsports "X302" crate motor with EFI. Ford advertises this motor as potentially making 340HP but I've never got that much from it, could be the overly restrictive CR sidepipes.

Questions:
1) Several people have recommended the Classic Chambered Cobrapack muffler. For the "packed with insulation" 2.5 inch version of these, how does the exhaust noise level compare with the original CR sidepipes? Is it a little bit louder or way louder?

2) For those who have used Classic Chambered Cobrapack muffler, did you stick to a 30" model (same length as original) or go with something a bit longer? Their website says the longer the quieter they are. If longer, does the 32" model look OK on a CR Cobra or too long?

3) Is Classic Chambered the best choice or are there others that should be considered. For example, others that might have low back pressure but might be quieter? I don't mind some noise but it's a daily driver and I do like to hear the stereo as well

4) After welding in replacement mufflers, were you able to have the sidepipes re-coated with a ceramic, high heat coating again? Did this require the previous coating be completely removed? I've got Jet-Hot on mine, it generally is in good shape but there's certainly a bunch of small rock pits closest to the front tires. If coating removed, was it via sandblast or manual?

5) After muffler replacement, did you need to "re-tune" the motor because of back pressure change. I've had my EFI computer calibrated on a dyno to get A/F ratio right. Will I need to have it re-calibrated because the lower back pressure could introduce a risk of an overly lean condition?

Lot's of questions...thanks in advance for any insights you can provide.

[olddog]

Originally Posted by C5GTO

Questions:
5) After muffler replacement, did you need to "re-tune" the motor because of back pressure change. I've had my EFI computer calibrated on a dyno to get A/F ratio right. Will I need to have it re-calibrated because the lower back pressure could introduce a risk of an overly lean condition?

If you have Mass flow EFI (has a mass meter in the intake piping) I doubt there will be any tuning changes needed. If it is speed density (MAP sensor) you may need some tuning. If it is alpha-n (uses throttle position only) it definately will need tuning.

Even Mass Flow has a Alpha-N type table that is used when the MAF fails. That table is also used during rapid throttle changes, when the MAF is not fast enough to give accurate data. It is not a precise control strategy. I do not think it will matter, but you may want to speak to someone more knowledgeable.