SSI Before and After Dyno Results for SC
 

Dyno runs were several months apart, but at the same shop and same machine. First test, the car was stock except for Flowmaster 1 in 2 out muffler. Second test was with new SSI's and stock Porsche/Dansk 2 in 1 out muffler for 74 Carrera. A/F was too high on both. Torque stayed the same both times @ 160.

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Wow! Thanx!

It looks like the one graph that shows an air/fuel line legibly is running between 11-13:1. The "max" of 17.5 seems to only be where it hit the rev limit or something at the high end. Isn't 12-13:1 right where we want it? If anything, isn't this just a tad rich at some points?

Gawd how I hate to admit this, but it seems that Sweet Old Bruce is right. All things considered, the original (pre 1974) exhaust is the most efficient exhaust for street use. Thankfully, Government got involved. Thus, "improving things".... ;)

I agree on the A/F reading, it looks to me like it's maybe on the rich side thru the rpm band..Was the 17.5 at the low end?

Can't tell what the second graph says, unless it's real low on the scale until 5800 r's.

Now the disclaimer, I'm no Dyno expert!

I agree with Jeff, that thing is too rich over much of the spectrum if that print out is correct. Anything richer than 12.5 to one is counter productive unless you are running boost and even then it is only a band aid. Only other thing that would cause it to read that rich would be an ignition problem and the HP readings don't reflect that.
If you leaned it out a tad it would make more power.

Based on the dyno reading we are talking over $100 per hp? I like power as much as the next guy but I'm a cheap SOB and have a hard time justifying that ratio.

Yeah, I now it's too rich and spoke with John Walker about it. He thinks I may have a bad WUR. Just haven't gotten around to checking it out.

Yup.. agree with that. Too much money for too little HP. You want HP...pump it up! Otherwise you might as well spend the coin polishing the Fuchs.

Mark -
I recall that G Class SCs were getting 177-179 hp at the MRPCA dyno day last winter. I'm pretty sure they were running racing headers. So it looks like you're right in there as far as hp at the rear wheels goes.
Bill M

It depends on what you want. I would do such an upgrade just for the look, the sound improvements, and cooling improvements. I bet it sounds fantatstic.

Don

It does sound good. With the Porsche muffler, it has a nice report, but is still quiet in the cabin. All in all, prolly the best upgrade for the bucks.

it'll clean up you mid range torque nicely.

this thread is a little old, but.... Mark, did you have a cat bypass installed in the "before" dyno, or a regular old cat?

The WUR should have nothing to do with it. Your mixture should be set with everything warmed up. That's when the WUR is basically doing nothing. Bad WUR's cause A/F problems during warm-up. I think. I'm pretty sure. But if JW says something, he's right. If what he says disagrees with what I say, he's still right.

ditto, Ditto, DITTO. i did the same exact upgrade, down to the 2 in 1 out dasak and have loved it. the mid range power is a huge difference, it runs a bit cooler, and the sound alone is nearly worth the price of admission. not some big 1 in 2 out coffee can rumble sound that i have heard from some 911's so equipped, but a raspy mean sound. i got some good reviews on the sound at the track last week.

by the by, i have the larger intake runners 78 and from what ive heard that is the motor that benefits most from the ssi install.

did i mention i love the upgrade, and even if it was $100 per horse its cheaper and more smoggable (in calif) than a supercharger, turbo, or a 3.4/3.6 motor replace.

Blue,
The before dyno was with the stock cat. I had tried a bypass with the Flowmaster and it was way too loud so reinstalled the cat.

Cool, thanks Mark.

Mark,

Are those numbers the raw HP number, as measured at the rear wheels, or has a correction factor been applied.? The numbers seem pretty high for RWHP, don't they?

If you use a 15% correction factor the stock system flywheel HP estimate comes out at 193 HP.

Regards,

Jerry Kroeger

I checked the graphs again, but more closely this time. It looks like the hp is almost identical in both runs, except when above 5500 rpm.

So basically the modification nets a couple of hp throughout the power band, but it's letting it breathe better on top end where the stock system was choking it off.
It's easy to see the peak numbers and say wow, with those I'll get 10 extra HP!
That's true, but only for 700 rpm.

Bone stock 78 SC, tested two weeks ago. I needed a baseline for the thermodynamics project.

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