Exhaust and Dyno

[79targa]

My 79 targa currently has SSI's with a 2 in and 1 out exhaust. Would there be a usable power increase by going to a 2 in 2 out muffler?

Which brings me to the dyno. I would dyno before any change so as to have a baseline. What is the proper method to dyno an aircooled 911? All other cars I have dyno'ed are water cooled four bangers which can set there idling until they run out of fuel wihout overheating. Big shop fan? In front? In back?

Dr. CS

[911pcars]

My seat-of-the-pants guess is around 5 hp and ?? torque, and this depends on the configuration of the 2-out muffler. I think the SSIs probably uncovered most of the increase already. As for the muffler, the most difference will be the result of internal modifications, some of which may too loud for you; the least from the mere addition of a 2nd tailpipe. There may be air/fuel adjustments to consider in that 5 hp figure as well.

If you have a front cooler, I suggest placing a fan in front of the car. Let us know what you find out.

Sherwood Lee
http://members.rennlist.org/911pcars

[Wil Ferch]

Hi:
2 out would likely not add more than 2 hp, or so.
At my last dyno run, shop simply ran a large fan over the opened rear lid.

--Wil Ferch

[pbs911]

BA reports in the Handbook approximately 7 hp increase was found using the two-in-two-out sport muffler on a 3.2 in conjunction with the SSI exhaust. The hP differed across the RPM range, but I believe this wasthe great HP achieved. I have read other claims of up to 12 HP with this exhaust on the 3.0 with the SSI type set up.

[Steve W]

I've tried six different exhaust setups with my SSIs, and they all seem different in power characteristics. I had a FVD dual out (looks just like a polished Dansk), Triad dual out, Dansk dual out sport, Monty single out sport, a Triad single out with a cat, and right now, I'm running a old Bischoff stock 2 in 1 out which is as quiet as a stock 3.2, and I feel a power choke off compared to the other sport mufflers. Believe it or not, basically the louder the muffler, the greater the response and overall power. It's like for 1 hp, you need to pay for it with 1 db in loudness. Some dbs are more annoying than others, like midrange drone. The most powerful was the FVD, but it sure also sounded like it - man, it was so loud, my passenger and I just looked at each other in shock during the test run, because there was no other way to communicate. I think I also freaked out a hypoed Harley.

[Wil Ferch]

Guys:
Allow me to clarify my original reply.
From BA's book and similar sources...starting from a stock set up that doesn't use the 74 and earlier ( SSI "style") headers....if you "back-date" to SSI ( or pre-74 SSI factory style), this change will gain about 15-17 hp on 3.0's and slightly less...maybe 13 hp for 3.2's.
Similarly, BA says that with the later stock exhaust, if you use a Euro-premuffler in lieu of cat ( Porsche premuffler part...not a simple cat by-pass), in conjunction with a "sport, dual out muffler", this will get you "close" to SSI hp gains...but only on the top end with a slightly weaker mid range than using SSI's. The split seems to be 6-7 hp increase based on the Euro muffler and 6-7 hp increase on the "Sport" dual-out muffler , combined with a sport chip that is usually part of this package. He says RUF at one time offered such a package that included:
- premuffler
-chip
-sport muffler with dual-out tips.

It is supposedly this package that gets close to SSI numbers (with a weaker mid range than SSI's).

If you distill all of this..it would seem the right-side exit ( alone) contributes very little to all of this...I would expect 2-3 hp.

--- Wil Ferch