924Board.org

[davke]

Hi,
i am going to shave the N/A (euro) block 1.4mm in these days. Who knows is it safety?

[ideola]

Why are you planning to shave it, and why 1.4mm? It will probably affect your ability to properly set up the valve and ignition timing due to limits in the movement of the timing belt tension roller.
_________________
erstwhile owner of just about every 924 variant ever made

[Rich H]

You will need a variable cam pulley and a bigger tensionner. A bigger tensionner can be had off various Audi's and the golf variable cam gear will fit.

1.4mm should be OK but I have no practical experience of this.

It will increase your CR from 9.3:1 to around 10.8:1 or so. 1mm~1CR on an N/A I assume this is why you want to do it. It's also going to be worth checking valve to piston clearance.

Rich
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[davke]

1.4mm to get 11 CR. I cant check valve/piston clearence at this moment so thats why i am asking. Variable cam pulley and a bigger tensionner are secondary problems.

[leadfoot]

calculate stock cam lift. i.e 11.9mm ~.427"
Stock head is flat. valves flush with head
Gasket adds 1 / 1.5mm compressed
Stock pistons are approximately 5mm from top of bore with valve reliefs cut into them approximately 3mm

so 11.9 - 1.5 - 5 - 3 = very close already.
The N/A is non-interference so according to these figures it's damn close and you want to take it another 1.4mm closer.

Now that's in respect to mechanicals, you still would have to address fuel quality and timing.
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Rich H]

I was sure it was more than 5mm from piston top to top of bore, I'm sure it was 8-10mm??

Anyone got an engine in bits to check?
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[RC]

Personally would have guessed 6 or 7mm. However thats irrelevant really. Should be measured/calculated on every individual engine allowing for various cams, pistons, prior head work, previous decking, line boring, crank grinding, rods,..........

Will second Leadfoot`s statement. It is indeed close already. Recall when building my ROW 9.5:1 that I only really decked the block 0.5mm (0.020") so would still have only the same 0.5mm valve to piston (non synchronized) clearance. Milling the deck 1.4mm will definitely make this an interference engine without other mods.

[Raceboy]

I've milled down NA block 2mm's with stock Euro 9.3:1 pistons, first used this block with NA head, then switched to 931 head. It didn't detonate on maximum power on 98 octane pump gas on neither heads, but using 931 head could benefit even more CR.

It makes engine an interference type and requires to machine new groove to the cam pulley (I'm not very keen of variable pulleys excluding tuning). With 2mm's off the block, tensioner was at it's limit. Anything more and you'll aither need bigger tensioner or shorter belt.
_________________
'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

[Martijnus]

With 1mm off my block my crompression should be just over 10:1. My engine is an interference engine now, the valves will surely hit the pistons when my cam belt dies.

My tensioner didn't do the trick anymore...it was at its end, I moved the hole instead of using a different roller/belt.
I made my cam gear variable, which is necessary.

Did you think about the cam timing being different? If so, did you come up with a plan to time it (exactly) back with variable cam gear?

I wanted to go to 11:1 CR, but due to the design of the head I decided just over 10 was the limit for daily use..

but as raceboy says, it can be done... I didn't want to take the risk.
_________________
"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

[davke]

Thanks for answers