Exhaust ideas for my GN...

[MaineShark]

Well, my cat-back exhaust is pretty much shot. I got an extra year out of it by welding patches over the holes in the y-pipe, but the patches are starting to fall off, so I'm looking to replace it, and trying to find a better solution than the Hooker exhaust that's on there.

For those who don't know, Grand Nationals have a large amount of exhaust resonance, aroudn 2000 rpm. The factory dual-crossflow (two in, two out muffler) exhaust solves that, but is very restrictive. Aftermarket exhausts are typically two separate mufflers, rather than a single, dual-crossflow muffler, but there are some aftermarket crossflow exhausts. The dual muffler exhausts have all that resonance. The aftermarket crossflow exhausts tend to either be just as restrictive as the factory exhaust, or flow well, but with too much noise (I like listening to the car, but I don't like having to turn the radio past half way, just to even hear it).

So, I've been doing a lot of reading on how people have solved this. I read one solution that seemed quite interesting; the owner had a dual-crossflow exhaust, but added some small racing mufflers before the crossflow muffler, one in each pipe. The resonance was cured, and the car runs in the 10's on pump gas, so I don't think that it can be called "restrictive." They are all straight-through perf-tube mufflers (Dynomax Ultraflo or similar).

Not one to copy others, I figured I'd do something a bit different, and see what it's like. What I'm thinking is to use a single-in, dual-out muffler in place of the "y" section of my y-pipe, then run back with dual pipes to a dual-crossflow muffler. The 3" in, dual-2.5" out Dynomax 17228 would replace the y, and would feed back to a dual-2.5" in and out 17231, out back. The 17228 is a ridiculously high-flow muffler (1400 scfm... good for up to 636hp, according to Dynomax), so I don't think that will be a problem. The 17231 is good for 1800 scfm, or 818hp, so that doesn't seem like it will be a problem, either. They are both 4.5"x9.75" oval mufflers, 14" long (19" with pipe stubs), so they should package reasonably well.

I'll have to find an exhaust shop to custom-bend the pipes, but that shouldn't be too hard.

Anyone have any thoughts on this? I think it has the potential to work well. And the 3" inlet will allow me to eventually upgrade to a larger cat-forward exhaust.

Joe

 

[MaineShark]

Any thoughts?

Joe

 

[WhalePirot]

Sounds like you have a plan; and have thought about it a LOT more than we have.


I appreciate the quotations, too.

 

[MaineShark]

I appreciate the quotations, too.

Thanks.

Basically, I'm somewhat nervous about this, because I've never seen a one-in, two-out muffler used in place of a y-pipe...

Joe

 

[wishuwerehere82]

Joe,

Back in the 70's I worked on a buddies 69 Z-28. We made a custom muffler system for it that involved two separate pipes coming off the headers with two separate Corvette mufflers welded to the pipes. From there, the pipes went to the back of the car and connected to the stock dual crossover muffler and had two separate tail pipes at the rear.
Because of your turbo, you only have 1 pipe off the engine, so to split the exhaust at the output of the turbo would essentially allow for a resonator point closer to the engine which I would think would increase the total power curve.
If you split off the resonator with individual pipes going back to the crossflow muffler, you would essentially reduce the restriction by a factor of two as long as the pipe diameter didn't get smaller, until you got back to the crossflow muffler which would combine the acoustic waves out the tailpipes. Because of the frame design on the Regal there should be plenty of room for two pipes, but do you have enough room in the front for a resonator coming off the turbo output and still have enough split room to get to both sides of the tunnel with the separate pipes?

Back to the Z-28. The sound was very quiet in general, but had a nice low thud at idle. When it wound up, it was very quiet, but had enough flow that the increase in HP was very apparent. We built the 302 to about 500 HP and it was still not loud at WOT, but boy did it move! And pulled the front wheels!
I would say it would work very nicely as long as you don't want any additional sound level.

 

[MaineShark]

Thanks. I'm going for a bit more of a "sleeper" deal with this car, so I want to keep the noise down to a reasonable level. I'll probably pull the cat and install an electric cutout sometime down the road, so I can crack that remotely if I want to make some noise...

Joe

 

[MaineShark]

Well, it's currently at the shop getting the exhaust installed. The guy has had a bit of trouble getting all the bends made to clear the rear axle, and still line up with the crossflow muffler, but I went up there and we both stared at it for a while... think we have it sorted out to where it will work. Gonna cut the inlet nipples off the muffler, and weld some mandrel 90's directly to it.

He's also going to change out the tires, because the BFG Comp T/A's are getting down to the point where they go from "drag radials" to "slicks." Trying Nitto 555R's, this time around. Well, if he can manage to get the Comp T/A's off the rims. Apparently, there's some effort involved. It's like they have a heavily-reinforced sidewall, or something... :L

I hope to hear good news from him tomorrow, so wish me luck. The weatherman says we'll be getting up to 90 or more on Saturday, so I'm really hoping to have it ready to take the tops off and roll...

Joe

 

[Ken]

Joe, I merged the two threads. Hope it's okay with you.

I take it you never did sell the GN, eh? :L

 

[MaineShark]

Joe, I merged the two threads. Hope it's okay with you.

Uh, it sort of is, since I'm looking for headers for the Shark, not the GN

I take it you never did sell the GN, eh? :L

It's still "for sale," if someone offers me a good price. Until then, I'm in no hurry.

Joe

 

[Ken]

Fixed. I just assumed ... :L

 

[MaineShark]

Fixed. I just assumed ... :L

Not a problem. It's the thought that counts, anyway

Joe

 

[MaineShark]

It was a struggle to get it all to fit in there, but it's all installed and working. I'm not overly-pleased with the shop that did the work - they welded things that I asked to have clamped, and they somehow managed to put 30 miles on the car ad

But the system does work quite well. I was previously running an open pipe (not by choice - it just completely rotted out), and I cannot detect any seat-of-the-pants drop in performance with the new system, and it actually has a hair better throttle response (less lag on the turbo).

Plus, I can hear myself think, instead of getting a headache every time the engine came within the 2000-2200 rpm range (which, with the gearing of that car, is almost all the time, in-town).

All-in-all, I'm pleased with the system. And the Nittos just look mean

Add a paint job, and I'll be quite happy, overall. But that has to wait until fall...

Joe