Question about rattle in CR sidepipe

[C5GTO]

Yes, the car has an EEC IV EFI setup, larger mass air meter, large injectors and Edelbrock EFI intake manifold. I worry about lean conditions (maybe over worry) because it ran lean before I had it dyno tuned and re-calibrated. I think the intake and heads are capable of flowing plenty of air, once the exhaust side is no longer restricted, hopefully it will all balance out. I seem to recall the dyno had the engine putting out about 300HP after re-calibration.

After doing more research on the different mufflers mentioned (and some others), I'm leaning towards the Flowmaster Slimline sidepipe mufflers. It looks like I'd need to adapt from 3" collector to 3.5" opening/outlet to turnout but that just means a couple more welds per side.

Has anyone heard or experienced anything negative about the Flowmaster muffler?

It sounds like one positive is that they will be cooler to touch with the double siding. I've had my kids and one friend get a "snake bite", that's never fun.

[C5GTO]

I'll start with the punch line first. During the first test ride with new mufflers welded in, my first impression was WOW...OMG...WOW. If I had know this one single modification would result in so much more power, I'd have done it 20 years ago. The external look of the CR1 sidepipe gave no indication about how restrictive and poor that piece really was.

After cutting the pipe open, here's the source of the rattle:



The baffle plate ruptured and the resulting loose chunk of metal was floating around in the muffler until it lodged under the internal piping. The result was a straight through muffler that wasn't stopping much exhaust noise.

I did go with the Flowmaster Slimline sidepipe mufflers. Here's pics showing the installation process.



Hint: make sure the bandsaw is cutting straight before doing this. Also, measure carefully as there's no good way to hold the resulting pieces for secondary cuts.





Original CR1 muffler compared to the 30" Flowmaster after tacking in pipe size reducers. With reducers the 30" muffler grows to about 33.5" in length. The Flowmaster is also 4.5" diameter versus 4". This didn't turn out to be an issue at all.

After lots' of cutting, welding, and metal finishing, here's the resulting raw sidepipe after the first test drive.



With the old mufflers, the power dropped off considerably at about 5,500 RPM. With the new mufflers, power between 5,000 and 6,500 RPM was pucker worthy. I shifted at 6,500 even though the RPM was still climbing fast and there was no fall off in power.

After the test drive, I discovered this:




The blue/purple areas are the uncoated reducers that are mild steel. The mufflers are SS and didn't show any discoloration. The existing ceramic coat didn't show any damage either. The ceramic coat is rated at 1,500 degrees, so the pipes didn't get that hot. I don't know what temp leaves mild steel purple though.

My gut tells me the new amount of muffler flow is resulting in a lean condition at WOT. Especially given the discoloration present after the muffler. I only wound it up 3 times on the test drive so it got hot fast.

Question for you guys who know about the signs of a lean condition. Do you think this evidence is showing it? My conservative side says I should get the computer re-tuned. It would also be nice to understand the HP gain purely from muffler replacement.

[moore_rb]

Originally Posted by C5GTO

Question for you guys who know about the signs of a lean condition. Do you think this evidence is showing it? My conservative side says I should get the computer re-tuned. It would also be nice to understand the HP gain purely from muffler replacement.

I wouldn't necessarily use the blue coloration on the pipes as a sign that you are leaning out too much - mild steel alloys can begin bluing as low as 650 degrees F, and your exhaust gases are running nearly double that.

Still - If I were in your shoes, and if I had the funds, I'd probably be thinking the same way you are, and would be booking a session with my dyno-tuner...

I'd also pull the 4 corner plugs, and look for bright white insulators, glazing, or the little pepper flecks that might indicate detonation.

I knew you would love the performance gain. How about the sound and volume levels? Did they meet up with your expectations as well?

[C5GTO]

Originally Posted by moore_rb

I knew you would love the performance gain. How about the sound and volume levels? Did they meet up with your expectations as well?

I only have one fairly short impression for the new sound and volume levels. I took the car for the 15 minute test drive and then pulled the pipes to send off to get them re-coated with the ceramic shiny stuff.

The sound at idle is now lower pitch, so more bass sounding. It's certainly quieter than the sound after the ruptured baffle and I think quieter than the original CR1 muffler. It's not too quiet though, so about right for a Cobra.

The sound at WOT, well it still sounds V8 healthy and I doubt I could pass the sound check on the Laguna Seca back/uphill stretch with the throttle down. But it sounded quieter than the straight pipe I had. On the test drive, I was on country roads so I don't yet know how it sounds with the exhaust bouncing back off concrete barriers. That's the true test for the daily commute driving

I do like that the mufflers run cooler now. After the test drive, I was able to put my hand on the muffler momentarily without getting burned. I would never of attempted that with the old mufflers. Even getting close to the old mufflers right after shutdown could raise a blister. The external part of the muffler was not too hot even though the mild steel before and after it turned blue.

[C5GTO]

I thought I'd post a final chapter to this story just in case anyone is interested. Here's how the sidepipes look after final coating:



I had the pipes coated with Cerakote Chromex by a local company that is a certified applicator of this product. They came out great and are brighter/shinier than the JetHot coating that was on them prior. I'm very happy with the finish so far.

After driving the car with the new mufflers for a couple of months now, here's my impressions. The thing I like most about the new mufflers (beyond the extra 30+ HP) is that they run much cooler than the old ones. They run cool enough that I don't feel the need to remind everyone who I take for a ride to watch the muffler on exit. The double wall SS construction is far superior to the mega-heat radiating single wall steel mufflers.

I like the new sound as well. They have more of a bass sound, that is lower pitched. More like a big block Cobra has. Unless I tell people otherwise, they assume it has a big block from the bass exhaust note.

As to loudness, they are louder than the original CRL sidepipe muffler but not by much. They are quieter than the equivalent sidepipe glass pack muffler. I don't need ear plugs when driving. I can hear the stereo fine, that is until a speed of 65 is surpassed, but this is just wind noise, not exhaust loudnesses.

For you budget minded guys out there, these mufflers aren't the cheapest option. At about $215 apiece, they are on the pricy side, but save yourself just one snakebite and the extra cost is really worth it Also, given the SS construction throughout, I'd bet that these won't rot out like the old ones.