924Board.org

sarbirus · Joined: 16 Mar 2008 Posts: 13 Location: bournemouth, uk

Years ago, someone told me that a 924 makes extra power if the compression is raised a little and taking 1mm from the top of the block was about right for a euro 924 na engine.. is this true?
_________________
Sarbirus
England
92 964C2 - Thinking about converting to widebody
89 944 Turbo - Modified by JMG/9XX 400 BHP
83 944 Lux - staying standard for now
83 924 Lux - 9XX head - transformed performance!
81 924 turbo - staying standard... probably

Paul · Posted: Mon Mar 24, 2008 9:36 am Post subject:

Yes, but it will effect your valve timing.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

sarbirus · Joined: 16 Mar 2008 Posts: 13 Location: bournemouth, uk

That makes sense, so I would need a adjustable cam pulley, ok.

So what is the standard compression ratio of a euro engine (XJ) and what would it rise up to by taking 1mm off of the block?

Has anyone done this? what did they find it did to the power delivery of the car?
_________________
Sarbirus
England
92 964C2 - Thinking about converting to widebody
89 944 Turbo - Modified by JMG/9XX 400 BHP
83 944 Lux - staying standard for now
83 924 Lux - 9XX head - transformed performance!
81 924 turbo - staying standard... probably

Paul · Posted: Mon Mar 24, 2008 10:29 am Post subject:

The search button found this:

http://www.924board.org/viewtopic.php?t=21097&highlight=compression+ratio
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

1mm should give you around 10.1:1 with euro 9.3:1 pistons. it will retard your cam about 1.3°.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

Martijnus · Joined: 29 Dec 2006 Posts: 2019 Location: Netherlands

I've skimmed a mm off too, haven't put the engine back together, but my calculations gave me about 10:1 compression ratio... 2mm would give 11:1 but someone calculated this again a while ago and that differed from my calculations.

So I'm not sure about it... but 10:1 or 1mm would be safe... and valve timing changes indeed... that is quite easy to calculate too.
_________________
"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