David L. Lutz

I seem to be having this same issue, searching for that "wonderful" right level of V8 roar.

I can tell you this, running stock manifolds, X pipe, S4 big resonators, and RMB is just too Loud. So after discarding my orginal muffler years ago (before SC and X pipe) I got a GTS muffler from Roger and now there is just not enough of that "wonderful" roar...

So just last week during the CV boot replace, I when back with the RMB, and there is really lots of vibration/resonating going on!

ShawnSmith

Someone needs to invent the "RMC" - Rear Muffler Compromise. Half the weight and half the muffling of the stock muffler, but not quite as aggressive as an open pipe RMB...

David L. Lutz

Exactly

hacker-pschorr

Were any of these tests on a boosted car? I cannot remember.

Z

That's basically what this is:
That's the configuration I have on my car, only I also have two of the small round mufflers in the rear muffler location, as as mentioned above.

Okv

Yes, I have been searching for a solution for this.
A rear muffler just smaller than the original, with same outlet pipes.

Thought about making one from parts of the RMB and original muffler, but still need a reasonable fitting smaller muffler then.
The cost, including manufacture, would of course be very high for this.
(Labor intensive, destroys rmb and original muffler, new muffler, case of beer for the welder..)

Now, perhaps one of the 928 suppliers could come up with a solution?

aggravation

That's what I had before I cut out the resonators and replaced them with a pair of flowmasters. Doing that it's damn near perfect, just a touch loud still but roll up the windows and you can then enjoy the music and just barely hear the engine unless you go above 3500 rpm.

After getting to drive it some today with the window down I realized just how great it sounds and the only time I really wish it was quieter is at idle. Sitting at a light or the drive through window at the bank it is annoying but I realized today it isn't the combustion noise that gets me, it's the blower.

My blower has a high pitch that gets loud above 800 rpm's and unfortunately my engine wants to idle at 800. That blower sound overpowers the rumble of the pipes at idle when you're listening from inside the car or at the front or side of the car...from the rear the pipes cover it pretty well.
Once underway the engine sound hides the blower or else the blower gets quieter above 1500 rpm's, not sure which.

Since my idle needs to be lowered still maybe I need to wait and see how I feel about it when I get the idle down to 675-700 because right now sitting still at idle, if I slip the clutch just a touch with the brakes on to get some load on the engine, the idle drops to that range and the blower sound disappears leaving only the engine sound and it is intoxicating without that blower bearing whistle or whatever it is.

Tampa 928s

Some other info for you: https://rennlist.com/forums/928-foru...-86-on-rm.html

As I said by gutting the rear pumpkin and welding it back up the sound is just right.

andy-gts

I remember louie's picture of his set up as headers-no cats-4inch glass pacs-then crossover-borlas-and rest 3 inch pipes for the exit. there for the crossover was a couple feet back of the headers to help upper rpm hp . I couldn't quickly find the pics.

Darien

Yup, but I'm not sure if he tested both types of SC's?

slate blue

Use a variable bypass valve, it will take it down the volume down to what you require but have the flow there when you need it. I think it will be your cheapest solution too as you don't need to buy a new exhaust, just fit the valve at the rear and away you go.


Greg

With bypass valve.

Louie928

Darien,
I think that setup is probably louder than most people want, but does make good power. The twin 4" straight through mufflers in the rear is a good helper too. I gave up trying to advise people or try to answer exhaust questions because everyone has a different idea of what sounds good (right) and what doesn't.

Darien

Don't get me wrong, I too have the x-pipe and stock pipes with resonators and RMB and she does sound great. But I thought the 2.5" pipes were the way to go for better flow? As for the right sounding muffler that will fit where the resonators are located, I'm in the dark.

Louie928

Darien,
I've done testing with the )( pipe and stock rear exhaust with RMB, or with rear muffler on, vs the 2.5" rear exhaust with aftermarket mid mufflers and RMB on my S4. There wasn't enough difference, on the S4, to bother building a 2.5" rear exhaust. For my taste, the )( and stock rear exhaust and RMB was too loud especially using the small resonators. I found the stock rear exhaust with small (GT style) resonators and the GT rear muffler to be just right. Might not be right for someone else. I could never find any repeatable measurable difference in power whether the rear muffler was on or not. That's on an S4.

I have done comparison testing on a couple of GT's between the stock rear exhaust and a 2.5" rear exhaust. The GT does benefit from the 2.5" rear exhaust. Maybe around 5 - 8hp, not huge but it's something. The Bullet brand mid mufflers fit easily, but tend to be loud and raspy. I've never tried those with using 4" dia mufflers at the rear, but I bet that would help. I made a system using 2.5" pipe and Dynomax mufflers and that worked really well on a GT. They are larger than the Bullet brand mufflers and would be hard to fit beside an automatic trans, but this was on a GT. That car had no rear muffler. It was loud when you got on the throttle, but not bad at all when cruising. The new owners love it, but for others it might be too loud, not loud enough, have a wrong tone, too raspy at 2385 rpm, etc. I tend to go for what makes good power first, and how it sounds is secondary, or thirdary. This GT did really well. It had ~ 295 rwhp stock which is about normal for a GT. From memory, fitting the )( pipe (stock rear exhaust) brought it to around 316hp. The 2.5" rear exhaust got to around 325. That's about normal power for that configuration too. Then I put on Devek L2 headers. That required a new )( pipe to fit up to the headers. Then it made 338 rwhp with tq all the way up to 349 lb ft. at both peaks 3200 and 4400 RPM. This was after Sharktuning. The work was done over about 2 yr period, but the car wasn't driven much during that time. It had 150k miles on it and was a real sweetheart to drive. I guess you could say, "perky".

I've thought a lot about exhausts on a SC engine, and I have nothing concrete on that. I do have reservations about opening up the exhaust too much with boosted intake. There is a very real possibility of blowing some of the intake charge right out the exhaust during the valve overlap period. GTs would be more sensitive to this than S4. The listed valve event specs are at 1mm lift and while they don't show any overlap, there is a period during which both valves are open a little. Anyway, it would be interesting to see the dyno results of different exhausts on a SC car. The boosted engines do really well with minimal exhaust changes. Better than you'd think they would. Seems like I read of someone who put headers and a dual 3" exhaust on his boosted engine and lost power compared to what he had before. I don't know any particulars on that setup, but I did file it in the back of my mind as something to consider. For Jim Hurtt's GT with TS SC, I was going to use headers, but decided against it. I made a 2.5" rear exhaust with Dynomax mufflers and X pipe. It made 500 rwhp at 9 psi boost. Whether headers or 3" exhaust would have done better, I'll never know. It is quite loud when above 4000 and on boost. I could put a stock rear exhaust on it and try, but the new owner doesn't care enough to let me try the experiment.

Darien

Thanks Louie...that rings a bell