ngng

at least for me-
- I already have a set of 100mm tips that I piad good money for
- the laguna pipes i am working on bolt to the OEM mount plates
- turnaways aren't enough, at least where I am to pass sound

ngng

do side mufflers even matter? I thought when the car was wide open, the side was bypassed anyhow?

F1CrazyDriver

incognito.
imo- I have seen a lot of tips for exhaust.80/100mm etc , bbi- etc etc - oem look proper / best suited.

FJSeattle

Weight

Spyerx

and heat

Also with the stock sides and valves in place it's not a straight shot, but it is pretty open.

I second allowing the stock tips / style tips to be mounted, AKRO, M&M, etc allow this.

Evolved Rs

It's not as much of a noise increase as a center bypass would be but like Spyerx said, it's straight through. Where with stock sides there's still a small gap for exhaust to bypass to the rest of the muffler, valves closed or not.

ngng

I should rephrase. Do the side mufflers make any difference with sound since I thought the car bypasses them at WOT? I would love to remove mine but am worried about a) sound b) cracking the center muffler

bmwtye

Yes they make difference in sound. With the exhaust valves in the closed position the gasses will enter the side muffler via a 3/4 inch gap in its primary pipe. There's a short piece of ø 50 mm tube in the first baffle. The second baffle has a huge amount of small holes so there's not much resistance there. The rest of the pipes are ø 50 mm as well.

The big pipes of the GT3 mufflers are ø 63 x 1 mm.
The cross section of a ø 50 x 1 mm pipe is 18.1 square cm.
The cross section of a ø 63 x 1 mm pipe is 29.2 square cm.
So the cross section of the ø 50 mm pipe is only 61 % of the ø 63 mm which is fine up to about 4000 rpm. Above that range the ø 50mm becomes rather restrictive.

Larry Cable

+1 one of the reasons I chose the SW ctr bypass due to the ability to reuse stock tips

ngng

Got it, thank you for the clarification. Do we know approx what level of sound the side mufflers muffle?

Jamie@dundonmotorsports

Just finished some track side testing:

Conditions: Clear skies, 75F, 50ft measuring distance on the front straight
991 GT3 Dundon Race Headers (catless, w/ side deletes)
OEM Muffler: ~102dB
Ultra Quiet straight tips: ~92dB

So about a 10dB reduction. With Turn aways would likely be 3-4dB further reduction.

PLEASE DON"T TAKE THESE AS ABSOLUTE MEASUREMENTS. How sound levels are measured, weather conditions, tip orientation, etc... have a HUGE effect on the absolute number.

We have further testing to do on it, should have a loud version to play with at the end of the week.

modoz61

Hi Jamie
That's really encouraging data

We are finding more and more tracks here in Australia implementing noise restrictions at 95db

So with 3db to play with from your measurements there should be enough latitude to meet those requirements.

so I gather your testing was done using a 991, will you be trying to collect similar data on the system with a 997?

Jamie@dundonmotorsports

The data we gathered was for the reduction in dB's by the muffler, not the absolute value of the car. We will be testing 997's as well, but likely those will be beta testers and they will be getting absolute values (from laguna, limerock etc...)

I wouldn't make the jump that a 991 GT3 with Dundon Race Headers and our Ultra quiet muffler is 92dB's. The take away is that the muffler reduces the dB of the car by approximately 10dB...

What's your car at now for dB?

Jamie

modoz61

Hi Jamie

It's been measured at 97 at one circuit, and just heard another local track is now at 90 do unless special consideration is given

So 10 db is quite effective enough

Jamie@dundonmotorsports

OK that we should be able to help with! Would want the Quiet and turn aways, there's also GPS driven valve solutions that can work, not a fan as they spike EGT's from the restriction, but if used judiciously can get you a pass...