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Greek55's Avatar
 
Join Date: Nov 2006
Location: Columbia, S.C.
Posts: 310
If getting more air out do you need more air in?

I put SSI's on my car about a year ago. Huge difference, but what I have found is it runs stronger up to 5000 RPMs then it is seems flatten out. I know that the choke on the air is the exhaust, but with SSI's I have eliminated some of the outging air restriction. Is there a way to get more air in, without adding turbo or a supercharger and keeping the CIS system?

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Smoke
1982 911SC Rosewood
SCWDP # 0097
Old 10-29-2007, 11:05 AM
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Tyson Schmidt's Avatar
 
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,580
You may need to reset the fuel mixture. Many CIS cars are on the lean side to begin with. Then if you free up the exhaust, it gets worse.
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'69 911E coupe' RSR clone-in-progress (retired 911-Spec racer)
'72 911T Targa MFI 2.4E spec(Formerly "Scruffy")
2004 GT3
Old 10-29-2007, 12:01 PM
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DW SD's Avatar
 
Join Date: May 2004
Location: Encinitas (San Diego CA)
Posts: 4,495
Yes, you need more system throughput to make more power. Your engine is an air pump. It all works together:
1. intake manifold, throttle plate(s), head port design, valve cross sectional area, combustion chamber, cam timing and lift and exhaust manifold and muffler.
2. It seems that Porsche didn't leave a lot of power on the table in any of these given areas.
3. You might pick up 1% to 5% with some changes like you are talking about, but to generate big changes, you really need to made broad changes to the system.
4. prices are effected accordingly.

Doug
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Old 10-29-2007, 12:04 PM
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Join Date: Jun 2004
Location: Rio Rancho, New Mexico
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Greek55,
The '81 through '83 SC's intake ports are 34mm. This compares to the earlier SC's '78 through '80 which were 39mm. My stock '76 2.7 liter is 35mm.
The SC exhaust ports are all 35mm.
Porsche racing engines designed for high rpm's all ran larger intake ports. As big as 43mm, unless turbo-charged.
The choke point for air flow with your '82 SC is the small intake port size.
If you want high rpm performance you'll need to open up the intake ports.

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DOUG
'76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's.
'85 911 Carrera, stock, just painted, Orient Red
Old 10-29-2007, 12:15 PM
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