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hp difference between headers and ssi

Anyone have a good guess at the hp gain difference for a 3.0 cis motor going from stock exchangers, cat bypass and stock muffler to:

SSI exchangers, cat bypass, sport muffler

or

headers, cat bypass, sport muffler

I still drive the car to/from the track and like some passive heat (heater blower has been yanked) in January in the desert.
Old 04-27-2007, 08:22 AM
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When I changed my 78 to SSi's & Dual in out MK.. There was a noticeable power increase.. my car was also a Euro Spec car. Its very streetable, but a little loud.

Some say its about 20HP.. but it felt more like 50 to me... worth the $2k or whatever it was.
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Old 04-27-2007, 08:29 AM
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I don't know if this helps but I now have SSi's (1.5") on a 3.2 and was looking into 1-5/8's headers, which will help on the top end but I will lose some bottom end. On a 3.2 from a stock exhaust to SSi's it may be 15-20hp, but I am not sure how that differs from a stock 3.0 exhaust.
Old 04-27-2007, 08:44 AM
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There is no diff bet. headers and SSI's from a power standpoint, but with headers you have no heat. Thus if you need heat SSI's are your only option. Either way you will probably pick up 15 HP, and a slightly cooler running car.
Old 04-27-2007, 08:46 AM
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Quote:
Originally posted by JBO
There is no diff bet. headers and SSI's from a power standpoint, but with headers you have no heat. Thus if you need heat SSI's are your only option. Either way you will probably pick up 15 HP, and a slightly cooler running car.
Yes, the nice thing about SSI's is that they are an equal length system, same as a header setup. My understanding is that the SSI is available in one tube size only, so they may not be the hot ticket for large bore motors. One other thing I can think of is the SSI might run a bit hotter tube inside the exchanger giving a little faster gas flow. I can't imagine it being much of a measurable amount, though.
Old 04-27-2007, 08:55 AM
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Swapping stock SC headers for SSI or early headers will not give you 15-20 HP...no matter what muffler you use. This has been beaten to death before with folks claiming butt-dyno gains that can't be scientifically quantified or rather..... verified.

I wouldn't bet more than a corner cart hot dog meal that the gains are more than 10 HP. Engine tune and age will vary the result.

There is a reason why exhaust manufacturers don't always lead their advertising with dyno numbers. Some don't even bother to dyno test....it's all about sound unless they can provide a scientific test of gains. Most of the gain is in the buyer's head (no offense to those who have spent $$$$). How else can someone justify all that money for such a small gain in power? If you gain 10 HP and spent $1000 (low number), you just paid $100 per HP.

Last edited by MotoSook; 04-27-2007 at 09:01 AM..
Old 04-27-2007, 08:57 AM
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Hi:

SSI's are made with 1.5" primary runners and they function just as well as 1.5" headers, depending on the engine's displacement and RPM range.

SSI's are ideal for 2.0 through 3.0 litre motors and work OK on stock 3.2's but anything beyond that really needs an 1 5/8" (or larger) solution.

On your CIS-injected 3.0SC, SSI's and headers perform the same (its a a big increase) but these motors will run cooler with headers due to improved airflow over the heads.
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Old 04-27-2007, 09:06 AM
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Timely post! I was shocked to find out this past weekend at POC that I can lose over 130 more lbs off my car and still be class legal. All the "easy," more obvious weight losses have been initiated, so we're getting into tougher stuff now. Out comes the hole saw!

Todd, I too would like to maintain passive heat, but don't need the blower. I may pick your brain about that later.

Down the line, I'm also considering headers in lieu of SSIs, as much for weight as any slight gain in performance. TRE have mentioned stepped headers as the next logical direction to go in for an actual performance gain and weight savings. I've searched on the subject and have found almost no information.

Does anyone have any pictures and additional reference on stepped headers?

The car is running a pretty hot 2.7RS motor into a 2in2out M&K, and I may at some point in the future ask Ben to build me a 2 into 1 collector straight pipe for the track only--no muffler at all.
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Old 04-27-2007, 10:57 AM
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Quote:
Originally posted by Souk
Swapping stock SC headers for SSI or early headers will not give you 15-20 HP...no matter what muffler you use. This has been beaten to death before with folks claiming butt-dyno gains that can't be scientifically quantified or rather..... verified.
Exactly! You need to add a cool collar to get those kind of performance numbers.
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Old 04-27-2007, 11:20 AM
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Quote:
Originally posted by 70SATMan
Exactly! You need to add a cool collar to get those kind of performance numbers.
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Old 04-27-2007, 11:34 AM
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It's tempting to mock the butt dyno gains of the SSIs on the 3.0 car, but the difference is nothing short of dramatic. I have never made a modification to any car I've owned where the difference was so immediately noticable. If I were advising a would-be buyer, I would say not to get bogged down in the numbers. It may actually be a 10-15 hp gain at the wheels, maybe 20 at the crank, but as someone said earlier, it could be a whole lot more and you wouldn't dispute it after driving the car before and after. Easily the best $2,000 I've invested into the car.
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Old 04-27-2007, 01:01 PM
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I am totally concur with 2002M3Drew. I recently migrated to SSI and a M&K 2in/1out and .... although I have not sorted the whole thing out > made the MOST dramatic difference to the 911 I have ever seen. power on/power off > rev-up/down throttle response.... world of difference.

I will get the final solution sorted out this weekend...

wrt BMW > most dramatic difference was migrating from single carp to DCOE40s... plus a Stahl header and answer? muffler ...love that carb instant-on throttle response ...

love the SSI..

Love the M&K..

Long live the 3.0

kgl
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Old 04-27-2007, 02:06 PM
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When I changed my C3 to ssi there was a noticeable increase in the rate that revs would build.

The engine will also run cooler because of the relocated oil line which no longer parallels the muffler
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Old 04-27-2007, 03:46 PM
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For the sake of the archives, the SSI's are clearly an equal length (approx.) header design, only encased in a stainless steel heat exchanger. They are an extremely similar design and/or improvement to the more mild steel factory offerings of ~1974. There is no fundamental difference b/w these and other "headers." Most of Porsche's exhaust designs, if not all, seem to be a header style, as opposed to a cast manifold. Below we see a 964 style heat exchanger, clearly not equal length, but a header none the less.

Steve W., among others, has in the past praised the values of a true set of race headers i.e. George's European race headers, which may indeed provide for greater power in an optimally tuned engine, but it seems that for anything 2.0-3.0 that sees any street duty, SSI's are a home run. Especially for Todd (nostatic), who said he liked having some heat (who doesn't?).

I believe credit for both photos goes to Bill V.


SSI:


964:
Old 04-27-2007, 04:50 PM
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Quote:
Originally posted by 2002M3Drew
It's tempting to mock the butt dyno gains of the SSIs on the 3.0 car, but the difference is nothing short of dramatic. I have never made a modification to any car I've owned where the difference was so immediately noticable. If I were advising a would-be buyer, I would say not to get bogged down in the numbers. It may actually be a 10-15 hp gain at the wheels, maybe 20 at the crank, but as someone said earlier, it could be a whole lot more and you wouldn't dispute it after driving the car before and after. Easily the best $2,000 I've invested into the car.
"nothing short of dramatic" +1
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Old 04-27-2007, 05:04 PM
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I've asked a couple of times before and never got a reply: Does the 993 exhaust look similar to this, i.e. not equal length?


[/B][/QUOTE]
Old 04-27-2007, 05:35 PM
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Mine is not quite the setup you mention, but I ran several tests stock versus SSI/dual out Dansk install. This is on a 79SC.

Performance Test done - SSI vs Stock SC

Also, I had my car dynoed by Imagine Auto following the install and was very surprised that the numbers were as large as they were. Two runs; 189 HP and 190 HP at the wheels. I'm not sure what this means as far as engine HP but if the wheel HP exceeds the stock HP at the crank, I'd say there is a real improvement with installing the balanced SSI headers. I've run up against some newer Porsches and either pulled on them or stayed side by side. My cars weight is 2820 lbs with a full tank of gas.
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Old 04-27-2007, 05:59 PM
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Quote:
Originally posted by milt
I've asked a couple of times before and never got a reply: Does the 993 exhaust look similar to this, i.e. not equal length?
no, the 993 looks nothing like the '75-'94 exhausts

993, near equal length, there is a lateral expansion chamber in the cat, not the worst design but not the best either


A cat bypass using separated x-overs is a better solution


964(similar to '75-89 911), very inefficient because of the long path x-over from the right side & which causes interference between the sides at the merge at certain points of the rev range. A cat by pass here merely reduces restriction at the cat, but doesn't solve the x-over issue.


The advantages of equal length are overblown as long as stock smog cams w/ close to zero overlap are used.
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Old 04-27-2007, 06:18 PM
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Quote:
Originally posted by Souk
Swapping stock SC headers for SSI or early headers will not give you 15-20 HP...no matter what muffler you use. This has been beaten to death before with folks claiming butt-dyno gains that can't be scientifically quantified or rather..... verified.

I wouldn't bet more than a corner cart hot dog meal that the gains are more than 10 HP. Engine tune and age will vary the result.

There is a reason why exhaust manufacturers don't always lead their advertising with dyno numbers. Some don't even bother to dyno test....it's all about sound unless they can provide a scientific test of gains. Most of the gain is in the buyer's head (no offense to those who have spent $$$$). How else can someone justify all that money for such a small gain in power? If you gain 10 HP and spent $1000 (low number), you just paid $100 per HP.
i can not speak for mr souk's data, but from my personal experience it was the best $2k ive spent on my otherwise stock 78 SC. if you've lived for any amount of time with a crossover/stock exhaust/cat & even the half way there cat by-pass and switched to the ssi's the results are unequaled. the motors mid range power and rev capes is not even close to what you've known. i can't quantify actual horse power numbers, but a very respected motor builder i speak with says 15-20 is a realistic gain. if they are only the 10 mentioned above, i would consider paying that for another 10 because when you've only got 180 stock, 10 is a bunch.

if you wanna go carbs or can afford some mid-west nonsmog upgrade i admire your salted roads all snowy winter. but for a california car needing to pass smog every two years and does not have the wong chip option it is the best bolt on/off horse power gain you can get.

i generally respect mr souk's knowledge and written word, however we part ways here.

T$

PS- i think the 15-20 was stated by a cat named bruce in some book he authored with a 911 on the cover.
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Old 04-27-2007, 09:41 PM
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Never been called Mr. Souk before...wait...a buddy's son does call me that...and now that I think about it, the kids I tutored way back when called me that


But I think that cat Bruce, said something like this:

"The early-style exhaust system -made by SSI-can be installed on any of the SC engines for a performance gain of 17-22 hp depending on the year of the engine and the dynometer used. I have no specific data on an SC engine, but we did get 13 HP on a Carrera 3.2 engine with the SSI heat exchangers and dual outlet muffler."

No specific data to support the 17-22 HP and only got 13 HP in the better 3.2 engine. Not sure where Bruce would have gotten the 17-22 numbers, but given the variability of dyno accuracy and with all due respect to Mr. Anderson, I still think $2000 for 10HP (even 13HP) is a bit excessive.

Having said that I do have used headers (early headers and European headers) that will be used on one or two of my engines. But they won't be called stock engines, and I haven't spent more than $500 for the two.

Mr. Toby I'm not saying the gain isn't there, just not on the order of magnitude that our butt dynos would lead us to believe. Now bolt on some carbs and maybe a little cam foolery and you will have a respectable engine. I did talk to a racer in Cali that has to run CIS...and they managed to play with their engine to get 230 or so....of course he didn't tell me how he got that with CIS on a 3.0

Last edited by MotoSook; 04-28-2007 at 04:57 AM..
Old 04-27-2007, 10:09 PM
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