Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Oct 2008
Posts: 55
compression ?

What is the normal and bad compression of the cylinders of 930 ?

Regards
Max
Old 02-07-2009, 05:51 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
After the next project
 
x98boardwell's Avatar
 
Join Date: Sep 2006
Location: Central Valley, CA
Posts: 1,522
Garage
around

7:1 or 7.1:1. I may be slightly off but that is close
Old 02-07-2009, 06:25 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Wer bremst verliert
 
JohnJL's Avatar
 
Join Date: Jan 2005
Location: Toronto, Ontario
Posts: 4,729
If you mean for compression testing the figures are in psi...I'm note sure on a 930 but others will chime in.
__________________
2007 911 Turbo - Not a toy
1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 02-07-2009, 06:50 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Oct 2008
Posts: 55
Quote:
Originally Posted by JohnJL View Post
If you mean for compression testing the figures are in psi...I'm note sure on a 930 but others will chime in.

yes psi compression testing
Old 02-07-2009, 07:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Driver
 
Noah930's Avatar
 
Join Date: May 2005
Location: Los Angeles
Posts: 14,286
Garage
Funny. We all look for these numbers in a PPI, but I've never seen anyone really publish what the factory would consider "good" numbers.

I wonder if that's partially due to the fact that not all mechanics really know how to do a proper compression check (motor should be warm, for example). Temp will alter the values.

I've heard mechanics/shops say that numbers in the 90s-120s are OK. But, again, this seems to be more hearsay than actual figures someone looked up in a shop manual. Obviously, the values that you would get in a normally-aspirated motor (somewhere in the 160-180 range will be much higher than what you would expect in a turbo motor, with it's lower static compression. Everyone also seems to agree that the clustering of the numbers is important (most important?). As long as all 6 cylinders are within a few psi from each other, most likely the motor will be healthy.

If someone actually has seen officially published compression values for a 930 motor, I'd like to see them.
__________________
1987 Venetian Blue (really looks like grey) 930 Coupe
Old 02-08-2009, 05:51 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
beancounter
 
jwasbury's Avatar
 
Join Date: Jan 2008
Location: Weehawken, NJ
Posts: 3,549
I checked mine (1979 3.3 liter) and found all cylinders were around 135, except #6 which came in at about 120. Still a good number, but I'm keeping an eye on that one. This was with a warm engine, throttle plate open.
__________________
Jacob
Current: 1983 911 GT4 Race Car / 1999 Spec Miata / 2000 MB SL500 / 1998 MB E300TD / 1998 BMW R1100RT / 2016 KTM Duke 690
Past: 2009 997 Turbo Cab / 1979 930
Old 02-08-2009, 07:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Wo ist die Rennstrecke?
 
DonE's Avatar
 
Join Date: Mar 2004
Location: Brooks, GA
Posts: 1,211
Compression tests are really meant to look at compression across cylinders, not compared to other motors. For example, I had a tired OEM starter when I ran a test just after a rebuild. The numbers were in the low 120's. Then the starter went out and I replaced it with a high torque unit. Being paranoid about my engine, I ran another compression test about 3000 miles later and found I had numbers in the high 130's, and consistent across all cylinders. Nothing but the starter had been changed. If you want to get an idea of the true state of the cylinder you have to perform a leak down test.
Old 02-08-2009, 08:02 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,233
Garage
I figure shouldn't the values be roughly compression ratio times 14.7psi plus 1 times 14.7psi.
For example at 7 to 1 compression 7x14.7 = 102.9 plus 14.7 or 117.6psi.
This assume 100% VE or Volumetric efficiency. In reality it must be less because 100%VE is not attainable at low rpm speeds especially with our manifold design.
This is alot lower number than 120 or 130psi that most guys are quoting. Just theoretically what I suspect to be the case.
Someone else chime in please.....sanity check needed.
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 02-08-2009, 04:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Oct 2008
Posts: 55
Quote:
Originally Posted by fredmeister View Post
I figure shouldn't the values be roughly compression ratio times 14.7psi plus 1 times 14.7psi.
For example at 7 to 1 compression 7x14.7 = 102.9 plus 14.7 or 117.6psi.
This assume 100% VE or Volumetric efficiency. In reality it must be less because 100%VE is not attainable at low rpm speeds especially with our manifold design.
This is alot lower number than 120 or 130psi that most guys are quoting. Just theoretically what I suspect to be the case.
Someone else chime in please.....sanity check needed.

Thanks ! .... good information !
Old 02-08-2009, 05:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Twins are more fun!
 
JMA-RUF's Avatar
 
Join Date: Dec 2005
Posts: 639
I was told around 115psi is around the norm for a 930 motor.
__________________
James
Carrera TT

(3.3, Protomotive MAP ECU, EFI, GT2 EVO CAMs, Twin Plugged, Twin Turbo's)
Old 02-09-2009, 12:44 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Oct 2008
Posts: 55
Quote:
Originally Posted by JMA-RUF View Post
I was told around 115psi is around the norm for a 930 motor.

Thanks JMA-RUF
Old 02-09-2009, 03:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered User
 
Join Date: Oct 2006
Location: Chas, SC
Posts: 1,028
Just as critical, if not more, that the numbers are all even, say within 10% of each other.
__________________
Tim
1986 930
Gone:71,2,4 914's, 70T, 71T(RS),77S
Old 02-09-2009, 04:39 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Porsche-Poor
 
bcoats's Avatar
 
Join Date: Feb 2005
Location: Seattle, WA
Posts: 463
Garage
I just had a leak down performed on my 3.3l motor, warm with 6K on rebuild, OEM P&C's and leak down results were 2%-3% and compression 115 across all cylinders (one was 120) if that helps. . .
__________________
1979 911 RS clone hotrod
1983 930 turbo-sold, will be missed
1992 964 C2 Coupe-regrettably sold
1980 911 SC Weissach-regrettably sold
1975 911S-sold but not forgotten
Old 02-09-2009, 09:28 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,233
Garage
Sounds pretty close to my theoretical calculation. Well within gage error.
As long as all are within 10-15% of each other is more important than the actual number.
Leak down is a better judge of engine condition too. Those numbers look really good.
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 02-09-2009, 09:31 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered User
 
930turbo's Avatar
 
Join Date: Jul 2006
Location: Valrico Florida
Posts: 200
10% or less is the key. Every tester will deliver a different number depending on the internal volume of the gauge & line, cranking speed, etc. 7:1 is a static measurement. Dynamic compression takes valve opening into consideration. Your actually measuring trapped stroke compression which can vary considerably based on valve timing. The achilles heel of these motors is the exhaust guides. They will wear to catastrophic failure while a compression - or even leak-down test will pass with flying colors. Listen to your valve train. If it still goes clickity clack after an accurate adjustment, beware. That's you exhaust valves rocking side-to-side in the void as it opens and closes. There's no where for the heat to go and they eventually snap off.
__________________
'77 930 turbo Garretson I/C 1 BAR spring, (2) '82 Triumph Bonneville Royal Wedding Edition
Past rides: '74 914 1.9 liter twin plugged track car, '83 928S, '87 924S, '75 911S w '78 ROW 3.0, '72 911T, '70 911T and various other insignificant domestic examples. Happiness is a grey tailpipe! Turbo lag......it's worth the wait!
Old 02-09-2009, 10:20 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
The duration and lift of cams installed and where they are timed changes where the intake valve closes at the beginning of the compression stroke so that affects compression at starter motor speeds too.

Mine has 964 cams timed around 1.26mm and compression is around 115-120psi with a cold motor.
If you test the motor hot and like burning fingers while doing it than by the time you get to the last cylinder it will have cooled alot compared to the first cylinder you did and that will throw the comparison off to some degree.

You should also hold the throttle wide open while cranking the starter motor for about 10 seconds on each cylinder.
Old 02-10-2009, 09:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 02:20 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.