Parts Catalog Accessories Catalog Tech Info Tech Forums
 
  Search our site:    
 Cart  | Project List | Order Status | Help    



Go Back   Pelican Parts Technical BBS > 1- Porsche Technical Forums > 911 / 930 Turbo & Super Charging Forum

Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
BlkBird's Avatar
 
Join Date: Feb 2002
Location: Atlanta, GA
Posts: 938
Compression ration question...

Fellow 930'ers,

No doubt documented somewhere, but what is the CR for a Turbo when it is on full boost?

For example, say your car is 8:1 CR off boost and you're running a 1 bar spring. Does that mean that at full boost you have doubled the atmospheric pressure and therefore doubled the CR to 16:1?

I'd imagine there would be some losses and you wouldn't really double the air pressure going into the motor but what's the final result going to be?

__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 11-20-2006, 09:04 AM
  Pelican Parts Technical Article Directory    Reply With Quote #1 (permalink)
Registered User
 
930turbo's Avatar
 
Join Date: Jul 2006
Location: Valrico Florida
Posts: 199
Try this link. It has a turbo compression calculator.
http://www.turbofast.com.au/TFcompB.html
__________________
'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 11-20-2006, 05:06 PM
  Pelican Parts Technical Article Directory    Reply With Quote #2 (permalink)
Registered User
 
BlkBird's Avatar
 
Join Date: Feb 2002
Location: Atlanta, GA
Posts: 938
Holy Toledo!

Anybody know these figures for a 3.3 930?

Bore: Cylinder diameter in inches.

Stroke: Engine stroke in inches.

Engine VE: Engine Volumetric Efficiency in percent. VE changes with engine RPM, a engine at wide open throttle at 3000rpm could have a VE of 90% and at 6000rpm 60%. This is a rough guide. At maximum RPM modified engines may have a better VE, eg: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%, four valves per cylinder 75% to 90%.

Standard Comp: The Compression Ratio of the engine.

Boost Pressure: Boost pressure in pounds per square inch.
__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 11-20-2006, 05:08 PM
  Pelican Parts Technical Article Directory    Reply With Quote #3 (permalink)
Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,163
Garage
97.0mm bore, 74.4mm stroke, stock boost pressure = 0.7bar or about 10psi
__________________
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 11-21-2006, 01:02 PM
  Pelican Parts Technical Article Directory    Reply With Quote #4 (permalink)
Registered User
 
BlkBird's Avatar
 
Join Date: Feb 2002
Location: Atlanta, GA
Posts: 938
So using Fred's figures and assuming a VE of 90% and a stock compression of 8:1 -> one bar (14.7psi) would yield a 13.6:1 compression ration when on full boost.

Assuming a VE of 80% and a stock compression of 8:1 -> one bar (14.7psi) would yield a 12.2:1 compression ration when on full boost.

Assuming a VE of 70% and a stock compression of 8:1 -> one bar (14.7psi) would yield a 10.8:1 compression ration when on full boost.

I'm not sure what the VE for a 930 is but I suspect we would fall under the category of "maximum RPM modified engines may have a better VE, eg: ... 65% to 80% " which is in line with the 12:1 compression ratio I've heard used when referring to our cars.

Sound about right?

__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 11-21-2006, 05:11 PM
  Pelican Parts Technical Article Directory    Reply With Quote #5 (permalink)
Registered User
 
930turbo's Avatar
 
Join Date: Jul 2006
Location: Valrico Florida
Posts: 199
I backed into a VE of approximately 78% for the 911.
__________________
'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 11-24-2006, 05:55 AM
  Pelican Parts Technical Article Directory    Reply With Quote #6 (permalink)
 
Now Available for Ordering:   101 Projects For Your BMW 3 Series 1982-2000  [more info]
Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,163
Garage
Stock compression for a 3.3 is 7.0 to 1.

You know what would be great is for a survey of a few users that have dynoed their cars and see if we could back into the efficiency ratings for each case to get a feeling for what it should be once we average all the results. This is just a guess for now without real data to back it up.

I had my completely stock 3.3 dynoed at 249 hp at the wheels at 5500rpm....
-------For example---------
1) doing the math yields: 249hp * 1/.88(12% loss at drivetrain)= 282hp at the crank.

2) using the chart on the site and assuming intercooler efficiency of 75% and a turbo efficiency of 60%yields:
ENGINE EFFICIENCY of 76%......not too bad.

Anyone else got some results to post?
Old 11-30-2006, 03:44 PM
  Pelican Parts Technical Article Directory    Reply With Quote #7 (permalink)
Registered User
 
BlkBird's Avatar
 
Join Date: Feb 2002
Location: Atlanta, GA
Posts: 938
Here's an interesting link showing dyno results for a number of Turbos, including my own. By the way, what does a stock 3.3 look like?

Turbo Guys Comment on this Dyno Sheet

__________________
C.H.
Boost Addiction - honestly, I have it under control
1989 911 Turbo Cabriolet
Mods include: Kokeln IC, GHL Headers, Hooligan muffler, Modified K27 7200, BL WUR, LC-1 & XD-16, Bilstein Sports (4), TRG sway bars, Oversize torsion bars, Strut brace
Old 11-30-2006, 05:55 PM
  Pelican Parts Technical Article Directory    Reply With Quote #8 (permalink)
Smart quod bastardus
 
fredmeister's Avatar
 
Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,163
Garage
A stock turbo is too fast to capture on film at rest.....needs a high speed camera, though I get your point.
-----
__________________
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 12-01-2006, 01:24 PM
  Pelican Parts Technical Article Directory    Reply With Quote #9 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 09:01 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2016 Pelican Parts - 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.