[Subscribe to Daily Digest] |
Members do not see ads below this line. - Help Keep This Site Online - Signup
I’m sorry this is really long. If you like puzzles, then read on and please share your insight! :-)
PART I – Cam Timing
I’m having trouble with cams: engine is a B212 bottom end with a B204 head and a TE05 in an '86 900. The engine has nearly 8k miles on it now, using a B204 exhaust cam and '89 900T intake cam.
Recently, I read an old post by 900 Aero that said the B2x4 heads are 0.036-inches thinner than B2x2, and so the B2x4 cams are advanced 10* to compensate (it’s my understanding that the thinner head would retard cams from a B2x2 by the same amount). So I pulled the 900T intake cam and put in the original B204i intake cam (all B204 cams, turbo or not, are the same, according to EPC). Thus, the original cams in the original head should now both be timed properly WRT to the crank, yes?
Well, the car now goes like a scalded cat at low revs; in fact, there is about, oh, *zero* lag, and I get 3 or 4 psi off the line before the clutch is out, and this is without driving hard. It seems too advanced to me. (BTW, new chain was used in the rebuild; cam gears are unworn.)
When I put the B204 intake cam in, I messed up and had to start from square one: flywheel at TDC, 16 chain links from notch to notch on the sprockets, lined up the notches on the camshafts with the notches on the caps, and put the cam notches just slightly "uphill" of the cap notches, per Saab tech advice, rotated the whole thing a few times to ensure the timing was right, then buttoned it all up. But not before triple-checking everything. Presumably, then, the install is correct??
So my question is, even though the B204 intake cam is timed more like a B2x2 N/A intake cam, should the car be *so* responsive at low revs? The 89 900T intake cam should’ve been closing at 56-degrees ATDC *plus* ten-degrees due to the thinner head, for a total of 66-degrees ATDC, yes? By comparison, the B204 intake cam, in the proper B2x4 head, closes at 46-degrees.
PART II – Ignition Timing
Here’s where it starts to get weird. For the entire time I’ve been running the engine with the B204 exhaust and 89 900T intake cams, I would often get knock at 3-5 PSI, but have no problems at higher boost. I ruled out fueling with a wideband, BTW.
So, fed up, I kept testing/retarding/testing/retarding until I’m at ***4 degrees BTDC*** (I've been running at 14-degrees BTDC). Remember how I said the car goes like a scalded cat? Well, this is at 4 degrees!! Except for the extremely good low-end response, the car runs normally – exhaust isn’t too hot, etc.
So...is the *cam* timing proper but the notch in the exhaust cam off by 10-degrees such that I need to reel in the ignition timing to compensate?? This just doesn’t make sense to me that the car runs pretty darned well at this ignition timing.
When I built this motor, I guess I didn't think things through well enough; live & learn, I guess...
THANKS!
posted by 67.183.141...
, Wed, 4 May 2005 15:19:42
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
