3.0 SSI Upgrade Questions

[poorshe911]

Hello fellow P car enthusiasts.
I have an ‘83 SC that I’m thinking about doing an SSI updrade to. The car has 89k total miles with a motor rebuild about 2k ago and 3.2 pistons & cylinders 300 miles ago.
I have a few projects planned, Carrera cooler, windshield & sunroof seals but am also thinking about SSI’s. If a 2 in 2 out muffler is necessary, I’m curious about what’s been done with the rear valence to accommodate the extra exhaust pipe.

Thanks!

[rngreenejr]

You can either remove the valence entirely or m&k and I'm sure others sell replacement valences with the two holes. They need to be painted to match

[Bill Verburg]

Originally Posted by poorshe911

Hello fellow P car enthusiasts.
I have an ‘83 SC that I’m thinking about doing an SSI updrade to. The car has 89k total miles with a motor rebuild about 2k ago and 3.2 pistons & cylinders 300 miles ago.
I have a few projects planned, Carrera cooler, windshield & sunroof seals but am also thinking about SSI’s. If a 2 in 2 out muffler is necessary, I’m curious about what’s been done with the rear valence to accommodate the extra exhaust pipe.

Thanks!

Cut the right end to match the left

buy f/g or salvage if you don't want to cut the original

[David Inc.]

Think hard on the mufflers and how you want to use the car, SSI with 2-in-2-out can be LOUD.

[jaxxon99]

2 in 2 out muffler is not necessary. I have a 2 in 1 out Dansk Sport muffler with SSI's, sounds great and no bumper modifications

[MrBonus]

I just put 830 miles on my car to and from a rally with SSIs and two-in-one-out M&K and at 5000 RPMs (which is 88 mph in 5th for me), I couldn't even hear my Bluetooth speaker in the passenger seat at full blast next to me.

Below 4500 RPMs, it's totally livable.

If I had two-in, two-out, I likely would have had hearing loss without ear plugs.

[Bill Verburg]

Originally Posted by MrBonus

I just put 830 miles on my car to and from a rally with SSIs and two-in-one-out M&K and at 5000 RPMs (which is 88 mph in 5th for me), I couldn't even hear my Bluetooth speaker in the passenger seat at full blast next to me.

Below 4500 RPMs, it's totally livable.

If I had two-in, two-out, I likely would have had hearing loss without ear plugs.

The drone and dB level are not the fault of the 2 out design, they are the fault of the muffler design and construction

I've had 2 out for decades w/ multiple mufflers, the only 2 that didn't have drone and loudness issues were a B&B and a Fabspeed, and early Fabspeed didn't drone but it was loud.

SSI w/ 2x out just need the right muffler

[Showdown]

I've had 5 mufflers with SSIs; only two didn't drone to the point of nausea: M&K 2-in 1-out, and AchtungKraft GT/k

[poorshe911]

Had no idea about the noise issue. Guess I’ll have to think about what a “nice to have” addition it would be.

Thanks
Michael

[G450X]

I went through some trial and error myself with my ‘82 SC.

I agree with the comments on the 2/2 drone. I sold my M&K 2/2 (GT3 style) and picked up a ‘74 factory 2/1 that I ran for a while, but it was a bit too quiet. If you live in a “quiet” neighborhood the factory type 2/1 is nice.

I eventually picked up a M&K 2/1 which has been on for 10 years now.

Don’t forget to remove your O2 sensor if you still have one.

[poorshe911]

Is the ssi performance benefit still there using a 2/1 ?

[David Inc.]

Regarding droning: Using one silencer insert in a 2-in-2-out is apparently enough to disturb the exhaust pulses where droning goes away, at least for mine. Using both inserts takes away the exhaust snarl and aggression (also afterfire pops), but it's not really noticeably quieter than open.

[Bill Verburg]

Originally Posted by David Inc.

Regarding droning: Using one silencer insert in a 2-in-2-out is apparently enough to disturb the exhaust pulses where droning goes away, at least for mine. Using both inserts takes away the exhaust snarl and aggression (also afterfire pops), but it's not really noticeably quieter than open.

A similar strategy was used on the non-droning B&B that I had, the exit hole on the right side was much smaller than the one on the left side. The difference in sizes wasn't apparent to the casual observer because the ensuing exit pipes hid it.

The muffler was good sounding and not overly loud.

[Bill Verburg]

Originally Posted by poorshe911

Is the ssi performance benefit still there using a 2/1 ?

In the muffler there are several concerns
one is flow, a single and dual can flow the same or one can be better than the other, it just depends on design and construction.

another is efforts to enhance pipe acoustic tuning benefits, again design and construction details matter.

lastly the aural characteristic is going to be determined by design and construction.

You will have to listen to a given muffler or take someone else's word for it.

[RarlyL8]

As Bill stated, the abatement of drone in the dual inlet dual outlet mufflers requires extra design considerations. All muffler types can drone, the only generalization you can make is that dual inlet single outlet mufflers have less propensity to drone than their dual outlet counterparts.
As for the M&K examples, we have two basic types of mufflers for most applications, Street and Sport. The Sport mufflers were originally designed for track cars with an emphasis on weight savings. The drone zone on the dual out Sport mufflers is below 3500rpm which is under the typical operating RPM for a track car. The mufflers weigh 15 pounds or less.
M&K Street Mufflers are designed to pass California, European and race tracks with sound regulations as well as significantly reducing or eliminating any drone. This comes at the price of extra weight, complexity and cost.
A third option is hybrid mufflers. If someone wants a Sport muffler then finds that it drones for their driving style or application we can add Street muffler tailpipes and other features to the Sport muffler to calm it down.
Lastly there is the Active Exhaust option. Best of both worlds.

This car has our MKM29 Sport muffler installed. Small case, no baffles.




This car has our MKM29ST (street muffler) installed. Long case with baffled tailpipes.




We also have an Active Exhaust version that combines Street with Sport. Long case, baffled tailpipes, bypass valves.