That is retarded. Moving toward a higher number btdc or lower number atdc
is advancing the cam.
- Tony
At 01:04 AM 2/27/2005, Bill Babcock wrote:
> Ahead one, back two. I tried to tweak it a little closer, now it looks like
>I'm retarded about five degrees. My centerlines are now 113.5 atdc for the
>intake and 107 btdc for the exhaust. that's retarded, right? I probably want
>it either even or slightly advanced I would guess. I think I need a book on
>camshaft theory.
>
>I did make a little drawing, and that helped.
>
>-----Original Message-----
>From: owner-fot@autox.team.net
>To: Bill Babcock; 'fot@autox.team.net '
>Sent: 2/26/2005 6:46 PM
>Subject: RE: Yikes and cam problem:: HELP!!!
>
>Bill, the specs on the cam I'm running indicate that the cam should be
>installed with 3 degrees of advance, and that with this advance the
>centerlines are Intake 106 degrees ATDC and Exhaust 112 degrees BTDC.
>At
>20 thou checking clearance (I know this would normally be 50 thou but
>not
>on this cam) Intake opens 37 degrees BTDC, closes 69 degrees ABDC;
>Exhaust
>opens 75 degrees BBDC, closes 31 degrees ATDC. This is 286 degrees
>duration at 20 thou.
>
>Make whatever sense of this you can. I'm not an expert on this, but
>thought these would be helpful.
>
>I suspect that your original installation specs were pretty close...
>
>- Tony Drews
>
>At 07:37 PM 2/26/2005, Bill Babcock wrote:
> > I think you're having a lot more fun than me. I'm struggling with cam
> >timing on my motor and I need a sanity check.
> >
> >Here's the problem. I've got a kind of unknown cam in Peyote--the guy
>who
> >could give me some hints on the specs is incommunicado for a few weeks.
>I'm
> >compounding my problem by installing a vernier cam wheel, so there's no
> >marks to start from. I set up a degree wheel and dial indicator, and
>started
> >measuring. I assumed that the timing should be set with .050" lift, and
> >since I'm coming straight from the cam follower and assume a 1.4 rocker
> >ratio, I'm using .036" lift.
> >
> >I tried setting it up with 50 degree BTDC inlet open and got some very
> >screwy numbers. So I checked the centerline of the intake and exhaust
>cam
> >lobes and decided to start with 110 degrees ATDC. After a bit of
>fiddling I
> >measure:
> >Intake opens 33 degree btdc
> >centerline 112 degrees ATDC
> >Intake closes 65 degress ABDC
> >
> >which gave me
> >exhaust open 72 degrees BBDC
> >Exhaust CL 115 degrees BTDC
> >Exhaust closes 25 degrees ATDC
> >
> >and that calculates to:
> >Overlap 58 degrees
> >Intake duration 278
> >Exhaust duration 277
> >calculated centerline intake: 106 ATDC
> >Calculated exhaust CL: 113.5 BTDC
> >
> >Weird. there's no way the exhaust should close that early and the
>intake
> >opening is about good for a street engine.
> >
> >So I tried again, setting the centerline of the intake cam to 100
>degrees
> >
> >I got:
> >Intake
> >open 37 degres BTDC
> >CL 98 degrees ATDC
> >closes 57 degrees BBDC
> >
> >exhaust
> >opens 79 degrees BBDC
> >CL 120 degrees
> >closes 17 degrees ATDC
> >
> >which calculates to
> >Overlap 54 degrees
> >Intake dur 274
> >exhaust dur 276
> >Inlet cl 100 ATDC
> >exhause cl 121 BTDC
> >
> >I'm flummoxed. Can't figure out what I'm doing wrong. Any ideas?
|