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low compression / high boost or vice-versa?

 
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-nick  



Joined: 16 Nov 2002
Posts: 2700
Location: Cambridge, MA

PostPosted: Tue Mar 11, 2003 2:49 pm    Post subject: low compression / high boost or vice-versa? Reply with quote

more turbo newbie questions... which is more desirable? i would think you could make more power with low comp / more boost but driveability will suffer?

for instance why not just crank up the boost with the 7.5:1 931 pistons versus less boost with 8.5:1? looking at the power stats it seems porsche didn't lower the boost with 8.5:1 which confuses my basic understanding. i would think owners with 7.5:1 motors could safely crank up the boost more than 8.5:1 motors and get more power out.

my copy of maximum boost is coming in the mail so i won't keep asking these general questions.

thanks,
-nick
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Peter_in_AU  



Joined: 29 Jul 2001
Posts: 2740
Location: Sydney, Australia

PostPosted: Tue Mar 11, 2003 4:49 pm    Post subject: Reply with quote

with real engine management, knock sensors and intercooler, 8.5:1 is probably a good start point for a turbo. Unfortunately the 931 has none of those things.

For something that's driven everyday high-compression low-boost. Take a look at the 996 Turbo - 9.4:1 compression.
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1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you
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924RACR  



Joined: 29 Jul 2001
Posts: 8118
Location: Royal Oak, MI, USA

PostPosted: Wed Mar 12, 2003 12:46 am    Post subject: Reply with quote

Don't forget that octane is just as much a factor (remember Rick's rants on Toluene?) and the gas in the US was crap at the time, unleaded with low octane, hadn't figured out properly how to replace the lead.

Now, with the current gas prices, I'm a bit glad my turbo's not demanding premium! 89 is quite sufficient for me!
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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sandgroper  



Joined: 07 Dec 2002
Posts: 95
Location: in limbo

PostPosted: Thu Mar 20, 2003 4:02 am    Post subject: Reply with quote

i,m with Aussie Pete,baramundi dude,ahh wanted to check out my ROW 931avatar.
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Lizard  



Joined: 03 Nov 2002
Posts: 9379
Location: Abbotsford BC. Canada

PostPosted: Thu Mar 20, 2003 4:40 am    Post subject: Reply with quote

how hard is it to install a knock senser on the 931, and all it does is retart the spark correct
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924RACR  



Joined: 29 Jul 2001
Posts: 8118
Location: Royal Oak, MI, USA

PostPosted: Thu Mar 20, 2003 6:13 am    Post subject: Reply with quote

Depends on your engine management!!!

I think there's something in the tech section on this, using the SAAB engine controller...
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Vaughan Scott
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'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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