HP Question Answered
 

Rather than post new, I thought this would be a good place to add dyno results from my 79SC that I had performed today. After the 0-60 test in 2003, this gives additional proof of the increased HP associated with SSI's on a stock SC. This is the only HP performance upgrade I've done to the car. The cams and everything else are essentially stock. On the second dyno run, I obtained 190HP and 175 ft/lbs of torque at the wheels. I obtained 185 HP on the first run. The 190HP compares to 180 HP and 175 ft/lbs stock; but this figure is at the engine. So if one assumes no losses in the drive train, I've gained 10HP with the SSI's. Since a 100% efficient drivetrain is impossible, and I use a very conservative figure of 10% loss, I'm at 211 HP and 194 ft/lbs of torque at the engine. This is a 31 HP and 19 ft/lb increase over stock figures. These figures support not only the feeling of increased power and quickness, but the results I posted earlier from my GtechPro runs. I think using a conservative loss figure of 10% should preclude any discussions that I'm being too generous to drive the engine HP number up.

The other thing that jumps out from the graph is how flat the torque curve is now. I pulled my owners manual and notice that the torque comes on a little later than stock but goes higher and stays there nearly to redline. In fact it stays in the 170 ft/lb range at the wheels from 4200 rpm up to 5800rpm; a very useful torque band. The HP ramps up quickly but not as fast as stock, but also goes higher and stays nearly flat to redline. This supports the fact that the SSI's allow the SC to breath more freely at the top end.

Needless to say, I'm very satisifed with these results from a 26 year old car with over 209k miles on it.

http://forums.pelicanparts.com/uploa...1111211352.jpg

SSI's added 10 HP to my otherwise stock SC - tested on the same dyno.

Yeah, but do you have the K&N air filter on? :D Just kiddin of course.

Mark what was the actual rear wheel HP the dyno read on your runs? Also what type muffler are you using?

I'm not sure why my car would benefit more from the SSI's than yours. I think the figure I'm seeing is consistent with the 0.4s increase in 0-60 times I saw earlier. I would not have got this improvement from only a 10hp increase.

If you attend any of the PCA events here this year, PM me and maybe we can drive each other's car to try the old seat of the pants test if you like.

Lastly, how similar is your HP and Torque curve shape to mine? Ignore my air fuel ratio curve, that resulted from a stuck open AAR. Did you see the same flat torque curve and did your HP peak at a similar rpm point as mine?

autobon, great thread here, but how do I put this gently ... it would seem that the dyno you're using has the volume set at 11. . .or your SC has cams or non-stock p&c's.

Measuring 190hp, at the wheels from a stock SC, is a bit much.

Also, not knowing what your SC measured before the SSi's, is a big red flag. ... the factory #'s were minimums . ...maybe you started with an extra high output 3.0.

As a side note (question) how well did the g-tech predict HP?

Island, I'll go back and check to see what the volume was set at. Not being familiar with dyno's, what is the relationship of volume setting and the readout? What's it for and what setting should it be? Also, what is your take on the shape of the torque and HP curves? By the way, there's no reason to put it gently to me. My feelings won't be hurt. :) As an engineer, I definitely understand the subjectiveness of figures. I've just made a reasonable effort for minimum cash outlay to quantify the improvement. I think everyone would like to have some idea of the figures before they spend money on SSI's. Bottom line is that there's not much you can do to a stock SC so if you want some improvement, whether it's 10HP or 30HP, SSI's are one of the few options without modifying the engine.

I agree totally that there's no way to determine absolute figures over my pre SSI condition for certain, not having done a pre SSI dyno. This figure is a delta "Porsche published figure". If I did indeed start with a higher output than published, then the increase is less. I try to stay away from absolute numbers as much as we all would like to have them. There's even disagreement of absolute figures when they get published by professional testing firms, and I'm definitely far from that.

I feel better comparing deltas. The 0.4 second increase in 0-60 times is a delta between two runs in similar conditions using the same testing device with the clutch dropped at the same rpm and done by the same driver. The 6.7 second figure for 0-60 was made without abusing the clutch too much. I did not rev it way up like the magazines do before launching. I'm sure that figure could be improved if I was willing to abuse my car but I wasn't.

I never did get around to doing a HP test using the Gtech. One thing I do know is that my car is much faster now than it was the previous 18 years I owned it. The SSI's along with the suspension upgrades has made it like a go cart on the street. It takes curves faster and accelerates out of them much better.

Autobon,
I'll have to dig out the dyno sheets. My AF was really wacked out but was that way for both runs. I had a Flowmaster on the original HE's. I have a 2 in 1 out stainless 74 Carrera muff now. Sounds groovy.

Got here from a link posted by the OP in http://forums.pelicanparts.com/porsche-911-technical-forum/1045669-how-loud-headers-really-plus-bonus-intro-pics-2.html

This is relevant I would think, amounts to saying it runs faster given more gas which it should.

10 Hp seems like a nice bump... " Dual -Out " looks cool, too.

I’ve put on more than a few SSI sets and never had to change the mixture. I bet the engine wasn’t running in an optimum state of tune which is where most of the power increase came from. General drivability and throttle response surely increases.

That's possible. However, I don't recall having the idling problem before I added the SSI headers. I keep the car tuned and running well. Truthfully, it's been 18 years since I posted this and I'm doing good to still be able to spell SSI.

I could go back and look at my maintenance records and tell you when the car was tuned up prior to installing the headers if you have any interest. I have my maintenance records computerized back to 1984.

I had linked to this old thread because I recall measuring actual decibels and one of the recent posters wanted to know how loud SSI's are.