AirSpeed VW Community Forums

Technical => Engine Tech Forum => Topic started by: flat4 on July 25, 2006, 12:59:08 PM

Title: Cam Timing
Post by: flat4 on July 25, 2006, 12:59:08 PM

I've read that by advancing the timing on the cam, you gain top end power, but bottom end torque suffers, and the opposite is true if you retard the timing, you gain bottom end but lose up top.  Has anyone experimented/implemented either of these strategies?

Title: Cam Timing
Post by: jim martin on July 25, 2006, 02:51:27 PM

yes i have tried all 3 positions on the same motor with the same cam.
what are you trying to accomplish

Title: Cam Timing
Post by: flat4 on July 25, 2006, 04:01:33 PM

The car is primarily going to be used at the strip, with the occasional drive on the streets, so fastest ET I suppose.

Title: Cam Timing
Post by: flat4 on July 25, 2006, 10:01:20 PM

???

Title: Cam Timing
Post by: jim martin on July 25, 2006, 11:19:24 PM

got your pm sorry my friend got tied up.
without knowing anything about your motor/car / trans ,giving advise is limited
first i'm assuming you have checked your cam timing correctly against the supplied card as you will most likely find many are actualy ground 4 deg advanced.
you need to have i rod and barrle  on so you can find actual top dead centre and not what your pulley reads.
there are alot of things that change by retarding or advancing your camshaft which is a whole book in itself and i don't feel like typing all night.
here is some good info that may help you.
you need to know your final gearing and rpm you expect at the end of the quarter.
then you pick a camshaft that will give you that rpm plus/minus 500 rpm
of course there is alot of things that can change that such as displacement /heads/vehicle weight etc.
and if you then find you need a bit more or less rpm you could change the cam timing,i don't recomend you play with it and set it as per the timing card as if its a new combo it is a unproven so you need to base results from somepoint and straight up is the best starting point.
bumped up some info that may help see other post
 

Title: Cam Timing
Post by: flat4 on July 26, 2006, 03:36:34 PM

Thanks for posting/reposting all the good info...it makes sense.  What does a guy use to attach the dial gauge to the head when measuring?  If I'm reading into this correctly, I should assemble one half of the engine (piston/sleeve, head, valves, rocker arms, pushrod) and take my measurement, adj. the cam if necessary, then reassemble everthing.

Title: Cam Timing
Post by: jim martin on July 26, 2006, 05:44:39 PM

the most important part of any engine build up is taking your time and go 1 step at a time ,you should have your motor bock apart and together in various staged at a min 6 times
go to members rides and find the build up of my car and the last section was assemble of my latest motor.
i can't remember where i left off ,but i do have all the photos up to the completed long block.if setting cam photos are not there let me know

Title: Cam Timing
Post by: flat4 on August 01, 2006, 01:14:36 AM

I've been playing around with the cam in my new engine, and it seems as though the cam is out about 10 degrees on the intake lobes alone, but the lobe centers are out only 4 degrees.  If I were to match the lobe centers to the cam tag by retarding the timing 4 degrees, will this be acceptable?  As it turns out, my duration also appears to be .274 instead of .260 at .050 lift.

Ideas?  Suggestions?

Title: Cam Timing
Post by: John W. Kelly on August 01, 2006, 08:14:54 AM

Advancing will add low end while retarding will move the power band higher. When I degree a camshaft, I rarely get the exact numbers that is on the card. This is no problem unless its way off. Remember, most cams have ground in advance.