Cam timing...

[bpu699]

Long story. Getting ready to set cam timing. Prior owner said cams in the 87 930 were sc cams, web cams ran them on their cam doctor said they are stock 930 cams...

Getting ready to do timing tomorrow...

Stock 930 cam timing is .9-1.1, correct? Can someone verify please... dougherty’s Website says 0.8???

SC is 1.8...

Huge difference...

So before I set the timing, any last ditch method to verify the cams are truly stock 930, not SC? I want to believe WEB cam, but this motor was quite modified. I tend to believe the P.O. changed the cams too...

Would it be as simple as just checking max lift?? Sc cam and stock 930 lift are very different...

http://www.drcamshafts.com/

Any hard to timing incorrectly? I assume it will just run poorly...

Thanks...

[dannobee]

0.65mm to 0.80mm if they're stock 930 cams. 0.80mm is a good setting for a little better low end.

Stock turbo cams have less than 0.400" lift on the intake. SC cams have .450" on the intake.

[Ollies930]

You do not need a cam doctor to measure your cams, just a degree wheel and a dial indicator. Set timing around 1.5mm and see what the duration is at .040" and .050". Adjust cam timing accordingly and done.

[bpu699]

Originally Posted by Ollies930

You do not need a cam doctor to measure your cams, just a degree wheel and a dial indicator. Set timing around 1.5mm and see what the duration is at .040" and .050". Adjust cam timing accordingly and done.

Not sure I know what that means... see duration at .04?

[bpu699]

Originally Posted by dannobee

0.65mm to 0.80mm if they're stock 930 cams. 0.80mm is a good setting for a little better low end.

Stock turbo cams have less than 0.400" lift on the intake. SC cams have .450" on the intake.

Seems that might be a good starting point maybe...

[Ollies930]

Turn the engine over until you have .040" valve lift, mark the crankshaft degree, then rotate crankshaft past maximum lift and back down to .040" lift, check the crankshaft degree and calculate your duration.

[dannobee]

Check the duration just like Ollie said, but most of the cams use 0.050" for "effective" duration. The factory turbo grind and the factory SC grinds are pretty different, duration-wise.

IIRC, factory turbo cam is 3degATDC, 37degABDC, 27degBBDC and 5degBTDC, set range 0.65mm-0.80mm, preferred 0.80mm.

Factory SC cam is 4deg ATDC, 50degABDC, 46degBBDC, and TDC. set range 1.1mm-1.4mm, preferred 1.25mm.

These are for factory, unmolested, not reground cams. YMMV. If it was previously rebuilt, I'd trust the cam doctor, especially if the rest of the engine was modified.

[bpu699]

Thanks guys, so here is what I found this weekend. Not sure if I did this right so comments appreciated.

1) Cam lift. St the gap for .004. Dial indicator on the spring retainer. Lift was .360. Per Dougherty racing cams lift is supposed to be 0.368 for 930, .450 for SC. So, much closer to 930 specs. Didn't hit .368 but cam was reground, perhaps that effected lift? Does this sound correct?

2) Duration. I think I did this wrong. I set the GAP for .05 with a feeler. Then check duration on the #1 intake. It was 205. Per specs from what I can tell 930 cams are 208, SC are 228.

So based on this info seems it is in fact 930 cams, correct? Set timing for 0.7-0.8 mm, correct?

[dannobee]

Yup!

And that little variance in your lift from spec is likely due variances in the machining of the rocker arm pad, causing the ratio to be a tad off.

[Walt Fricke]

The variance in lift measured with a standard Z block at the valve spring retainer is due to the fact that the Z block indicator hole is at a different angle to the plane of the valve cover surface than the valve stem itself is. The Z block hole is perpendicular to that surface, while the valve stem travel is not. Any time you measure an up and down motion with an indicator or other tool which is not co-axial, your measured motion will be less than the actual motion.

In essence you are measuring the adjacent side of a right triangle, while the valve is moving along the hypotenuse. Easy to see why what you measure has to be less than the actual movement. It is a cosine angle effect, which you can compensate for with some trig if you want. I think it is about a 2 degree difference, but I've not measured that yet, and it can vary with the heads (think 2.8 RSR heads).

This is insignificant when setting valve lash with indicators, and when setting cam timing. But, as you found, shows up when measuring total lift.

So yes, 930 cams.

Unless you are running a turbo (or a blower?), you don't want those cams. Sure, the engine will run. But at reduced performance over a stock 3.0. Now's the time to take them out and put in a 3.0 or 3.2 cam (they are the same, though all the 3.2s have the bolt end for the cam gear, while the early 3.0s had the traditional big 46mm nut).

[bpu699]

Originally Posted by Walt Fricke

The variance in lift measured with a standard Z block at the valve spring retainer is due to the fact that the Z block indicator hole is at a different angle to the plane of the valve cover surface than the valve stem itself is. The Z block hole is perpendicular to that surface, while the valve stem travel is not. Any time you measure an up and down motion with an indicator or other tool which is not co-axial, your measured motion will be less than the actual motion.

In essence you are measuring the adjacent side of a right triangle, while the valve is moving along the hypotenuse. Easy to see why what you measure has to be less than the actual movement. It is a cosine angle effect, which you can compensate for with some trig if you want. I think it is about a 2 degree difference, but I've not measured that yet, and it can vary with the heads (think 2.8 RSR heads).

This is insignificant when setting valve lash with indicators, and when setting cam timing. But, as you found, shows up when measuring total lift.

So yes, 930 cams.

Unless you are running a turbo (or a blower?), you don't want those cams. Sure, the engine will run. But at reduced performance over a stock 3.0. Now's the time to take them out and put in a 3.0 or 3.2 cam (they are the same, though all the 3.2s have the bolt end for the cam gear, while the early 3.0s had the traditional big 46mm nut).

It’s a 930 with a turbo...

I am shocked I have stock cams. I tracked this car and everyone commented on how linear the throttle was... it definitely didn’t feel like an on/off switch. Car ran great, so will leave it be...

Thanks all for your help.

[bpu699]

Originally Posted by dannobee

Check the duration just like Ollie said, but most of the cams use 0.050" for "effective" duration. The factory turbo grind and the factory SC grinds are pretty different, duration-wise.

IIRC, factory turbo cam is 3degATDC, 37degABDC, 27degBBDC and 5degBTDC, set range 0.65mm-0.80mm, preferred 0.80mm.

Factory SC cam is 4deg ATDC, 50degABDC, 46degBBDC, and TDC. set range 1.1mm-1.4mm, preferred 1.25mm.

These are for factory, unmolested, not reground cams. YMMV. If it was previously rebuilt, I'd trust the cam doctor, especially if the rest of the engine was modified.

Alright, just spent the day doing this...

Still trying to figure this out, I see lots of quoted values for the correct setting, from .8mm, to .6-.8mm, to .65-.8mm...

I tensioned it with c clamps... set both sides for 0.7mm, or .028 inches. Went great, much easier than I thought... figured middle of the range is good? Checked several times, same results.

Went then and took the tensioner, squeezed with a vice which purged them of oil, and placed a pin. Verbatim from Wayne’s book. Replaced c-clamp with tensioner. The tensioner now has “give” whereas before it didn’t when full of oil...

Being silly, I rechecked timing again. Now, with tensioners, it’s .024 or 0.6mm on both sides...

Leave it??? Or retime with the tensioners in? Not sure which reading to go with, c-clamps or tensioners?

Also, is there a big world difference between 0.6 or so and 0.8?

As on odd follow up question, at one point the c-clamp popped off, the chain skipped a tooth, but I didn’t realize it. Tried turn the crank, gently as always, and it hit valves at part of the rotation. Caught the mistake, realigned the cam and started over. I was pretty surprised that skipping one tooth causes valve interference?!?! Most cars you need to skip 2-3 teeth before that happens. Is that normal?

[dannobee]

Most people would probably never notice the difference. The more you advance a cam, the sooner it "comes on." If you leave it at 0.6mm, theoretically it'll have more top end. Personally, I'd reset them to 0.8mm, but that's me.

Yes, 1 tooth off is enough to bend valves. The pistons have no valve reliefs. Other manufacturers make the valve reliefs big enough to account for a chain breaking. Porsche does not.

[bpu699]

Originally Posted by dannobee

Most people would probably never notice the difference. The more you advance a cam, the sooner it "comes on." If you leave it at 0.6mm, theoretically it'll have more top end. Personally, I'd reset them to 0.8mm, but that's me.

Yes, 1 tooth off is enough to bend valves. The pistons have no valve reliefs. Other manufacturers make the valve reliefs big enough to account for a chain breaking. Porsche does not.

So should I go with the reading with the tensioner in? Or with the chain held by the c-clamp?

It’s 0.6 with the tensioner, 0.7 with the c-clamp. It’s not like I aped the c-clamp on, I actually used one of the linear clamps, hard to over tension those. Once the tensioner refills with oil on start up, will the timing goto 0.7?

There was another thread on here where folks were posting that chain tensioning while setting the timing has a significant effect on timing...