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xpernet
Joined: 07 Apr 2004 Posts: 414 Location: Kitchener, Ontario Canada
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Posted: Sun Feb 22, 2009 4:35 am Post subject: Normal Vacuum Reading at Idle? |
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Im getting ~45KPa at 800rpm, ive heard that it has to be less than that. Whats my target reading? _________________ 1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body
"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche |
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ideola
Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI
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Posted: Sun Feb 22, 2009 5:29 am Post subject: |
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At idle, vacuum should be in the range of 17-20 HG on a healthy, no-vac-leak, fully warmed-up NA car. If I'm doing the conversion correctly, at 45 kPa, you're only pulling 13 HG, which is too low, and indicates that the idle is either too low, the ignition is retarded too much, or most likely that you have a vac leak somewhere. _________________ erstwhile owner of just about every 924 variant ever made |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Sun Feb 22, 2009 6:18 am Post subject: |
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Could also be crappy oil, worn rings.
Great vacuum gauge guide RIGHT HERE. _________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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RC
Joined: 25 Mar 2007 Posts: 2636 Location: Australia
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Posted: Sun Feb 22, 2009 3:27 pm Post subject: Re: Normal Vacuum Reading at Idle? |
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xpernet wrote: | Im getting ~45KPa at 800rpm, ive heard that it has to be less than that. Whats my target reading? |
Na. Thats about right.
Consider idle is now down to 800RPM Vs stock 950 and being a 77 most likely have the low comp, small valve, poor cam, 95Hp engine.
You can run 20° ignition advance at idle safely, even up to 100Kpa MAP. That should lower idle MAP slightly and give quicker acceleration. Probably wont get it much lower than 40Kpa anyway by increasing/decreasing VE bins by 1 or 2 units at a time. Arrange bins so that idle falls right in centre, ie. 800RPM @ 45 or say 40 Kpa, whatever. Compromise between smooth idle, low MAP, and AFR. Should be able to run 14:1 at idle and even up to 14.7 if accurate. Each engine is different though and individual tunes will vary, whatever gives you the best compromise for your case.
BTW 45Kpa is nearly 17"Hg, so dont worry. |
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Smoothie
Joined: 01 Jan 2003 Posts: 8032 Location: DE (the one near MD, PA, NJ)
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Posted: Sun Feb 22, 2009 10:07 pm Post subject: |
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? I get 45kPa = roughly 13"hg. _________________ "..it's made in Germany. You know the Germans always make good stuff."
'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox |
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ideola
Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI
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Posted: Sun Feb 22, 2009 10:17 pm Post subject: |
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Smoothie wrote: | ? I get 45kPa = roughly 13"hg. |
So do I, using a calculator program on my Palm...
13 HG is low, even at 800 RPM, at least on a CIS car. _________________ erstwhile owner of just about every 924 variant ever made |
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xpernet
Joined: 07 Apr 2004 Posts: 414 Location: Kitchener, Ontario Canada
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Posted: Mon Feb 23, 2009 12:51 am Post subject: |
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my bad guys, i meant 65Kpa ... So if im not mistaken, i should be around 17-20HG @ 950RPM... that means i got some tweaking to do after im done my midterms lol
Yeah i have the 95hp engine... so i can run 20° advance eh? Good to know _________________ 1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body
"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche |
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Martijnus
Joined: 29 Dec 2006 Posts: 2019 Location: Netherlands
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Posted: Mon Feb 23, 2009 1:34 am Post subject: |
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I'm reading about 50-55 kpa at idle with ITB's.
My afr at idle is around 13 though... at that it runs best but to be honest I haven't tried to go to 14.7 yet. _________________ "Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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Raceboy
Joined: 01 Mar 2004 Posts: 2326 Location: Estonia, Europe
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Posted: Mon Feb 23, 2009 1:53 am Post subject: |
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40-45 kPA is normal for 924 engine. I have installed VEMS on three 924-s and all of them had about the same vacuum readings at idle. All of them were Euro 125hp engines. _________________ '83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche |
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Martijnus
Joined: 29 Dec 2006 Posts: 2019 Location: Netherlands
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Posted: Mon Feb 23, 2009 1:59 am Post subject: |
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I'm quite interested in the correlation between TPS and MAP during driving on a stock 924 engine (with EFI...doesn't matter..at least no intake mods)...
would be a great base to see how that corresponds to readings with ITB's (mostly for ignition purposes) _________________ "Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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RC
Joined: 25 Mar 2007 Posts: 2636 Location: Australia
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Posted: Mon Feb 23, 2009 2:27 am Post subject: |
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ideola wrote: | Smoothie wrote: | ? I get 45kPa = roughly 13"hg. |
So do I, using a calculator program on my Palm...
13 HG is low, even at 800 RPM, at least on a CIS car. |
Ha ha, can see you both fell in the same trap guys.
Pressure calculators are useful tools but they dont think for you if you are unsure of the units or application.
We are not measuring pressure but vacuum here. 45 Kpa is absolute which is around 13" Hg absolute. However since vacuum gauges are calibrated to measure vacuum (negative pressure) the 0 baseline is atmospheric pressure at sea level. Although it varies due to prevailing atmospheric conditions it is generally accepted at 101.295 Kpa. and in absolute terms this equates to 29.9213 inches mercury.
No pressure, ie. 0Kpa will read 29.9 (practically 30) on a vacuum gauge. 30 - 13 = 17
So for all automotive applications 45Kpa is actually 16.63"Hg.
Anyway, 65 Kpa is a different matter. It is too high, or low if we are talking vacuum.
May need some more tuning and a good check for leaks. Try the advance too, will also help low end power and acceleration. |
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