[SOS-cars] Re: stock aan and 7a cams

[M Pederson]

That’s a great idea, but 
. What exactly is a “good” cam for a turbo motor?

 

High rpm power?  Low rpm torque?  

Overlap, to do or not, & if so by how much?

 

At least with the 7A and all the other 20v NA 86.4mm stroke by 144mm rod
engines,

One would be dealing with the same piston accelerations and speed.  

 

My impression is that “aggressive cams” whatever aggressive means, isn’t
necessarily “good” in a turbocharger application.  But I’m certainly willing
to listen to arguments to the contrary.

 

I believe the Bentley publishes figures, and they’ve recently been posted
either here or on the S-Car list, for acceptable compression test numbers
and maximum cylinder to cylinder variation.  I think a compression test psi
reading will vary with (a) altitude; (b) condition of your starter and
battery; (c) throttle open or closed (its supposed to be open); oil temp and
viscosity.  

 

As I recall, one key “killer” variable (i.e. what you DON’T want to see) is
a great cylinder to cylinder variation.

 

Ah-ha, Bentley C 15-7

   Compression pressures:      9.0 – 13.0 bar    (131 – 189 psi)

            Wear Limit:                7.0 bar             (102 psi)

   Max permissible difference between cylinders

                                             3.0 bar             (44 psi)

 

How to Check (Bentley C 15-6)   

-          Engine Warm – coolant temp gauge @ 80 C°  (176° F)

-          Turn quick fasteners (arrows) on connector cover on rear of
engine compart bulkhead 90° to left & remove

-          Mark and separate connectors -5 & -6 (to ignition coils)

-          Remove cover with coils on cylinder head

-          Unscrew all sparkplugs

-          Check compression with VAG 1381 and adapter 1381/1

-          Throttle valve fully open

-          Operate starter until no further pressure increase is indicated
by tester

 

HTH

mike

 

  _____  

From: audibusdriver [mailto:audibusdriver at yahoo.com] 
Sent: Wednesday, February 11, 2004 1:25 PM
To: SOS-cars at yahoogroups.com
Subject: [SOS-cars] Re: stock aan and 7a cams

 

I was looking at getting very aggressive cams with more lift and 
duration. I found a supplier but I was looking at finding out what 
stock is and go form there. I currently have a 7a exhaust cam and 
it's nothing special. I want something to wake up the motor & 
turbo.....
BTW does anyone know what the stock compression reading(psi) is with 
the 9.3-1 comression ratio. I know mine is a little low and am going 
to do a overhaul very soon, so that is why i'm looking at cams!