Rick Carter

I'm trying to get a better understanding of our cams.

The 85/86 32v cams lift; intake .393, exhaust .353. Is this lobe or valve lift? I'm guessing lobe. Duration intake 253, exhaust 236. Are lift and duration measured at 50/1000? Are the lobes center line symmetrical? What are the rocker arm ratios?

I also have questions about the opening and closing.
I saw a chart that had intake opening at 6 after TDC and closing 54 after BDC. Is this correct, or does it open before TDC? The same chart had exhaust opening 43 before BDC and closing 4 before TDC. Is this correct or does it close after TDC?

Thanks,

Lizard928

Rich,

The duration numbers you state above are total duration.
Duration @ .050" is 211 intake and 200 exhaust.
The lift is lobe lift from base circle OD.
The 928 uses no rockers, the cam is a direct drive so no rocker arm ratio there.

As well the lobes centerline is not symmetrical.

Rick Carter

Thanks! I spaced on the rocker. Since it's not symmetrical what is it? Any info on the valve opening an closing?

ptuomov

The workshop manual has the opening and closing events.

Jim Morton has the digitized S3 and S4 lobe profile data, you might want to pm him if you need really precise info.

Rick Carter

I think I have enough info, I was passing it along to an engine builder friend of mine. I think the opening and closing info I have is from the workshop manuals. Don't most intake cams open before TDC and most exhaust cams close after TDC? Unless I misread, and its possible I'll look again, the 85/86 32 v intake opens after TDC and exhaust closes before TDC.

ptuomov

From memory, those are events at 1mm lift. The valve "cracks" open earlier. That's why it's helpful to actually know the cam profile. It's also useful to know how the lifter works in the head to figure out the actual valve lift.

Lizard928

at 1mm of lift (.040") the S3/GT 216/206 in/ex