cam timing question for 964 cam on SS 3.2
 

I am using the top from a '78 SC,
the bottom from an '82 SC, (With enlarged intake bores and 98mm P/C's)
the cams will be 964 profile.
For cam timing, should it be the specs for an '82 SC, or should it be cam timing for a 964?
Is the camshaft the determining factor, or is the bottom with 98mm P/C's what you go by?
Thanks for your help. SmileWavy

Porsche timing specs for the 964 cams 1.26mm.

Some folks who use these cams in a 3.0 like to time them a bit higher (2.0mm) for added bottom end. You mentioned you are using 98mm p/c's. I'm gusiing you are building a SS 3.2, in which case the added displacement will give you a torquier bottom end and you'd probably like to rev the SS a bit higher. I'd use the Porsche specs of ~1.25mm. Make sure once timing is set, you check the p/v clearance......this is your determining factor!!

hey Charlie, Gunter, my engine rebuilder used the 964 spec for my 3.2 ss. One question i have that slightly relates to the 3.2ss topic is that the 78/79 engine was spec'ed for a W8dc plug and the higher compression SC went to a colder plug, W5dc. I just pulled the W8DC's fr with less then 5K on them and the rebuild {they didn't look great} and replaced them with the W5DC's. I actually think I'm getting a cleaner burn..my start up smoking is going away. Any thoughts on this?

In the 3.2 I time them right at 1.26(or as close as I can) I just finished a 3.0 and delivered it today that I had timed at 1.35 with 964 cams. Car had good bottom end and pulled great. Really made a nice improvement on that car. Mild gain, but nice.

The cam is the factor in setting the timing. (for the most part). However the SC timing spec changed a few times over the production run and the grind stayed the same....... That said, the 3.2 uses the same cam and the timing spec never changed and it is still very similar to the 964 spec. Both cams have the same lobe center I think, don't have the specs in front of me though to confirm that.

Cheers, Jeff

Thanks guys: I am a long way from getting it done but want to get all the details ready. JW E-mailed me back recommending 1.4mm, so, it must be somewhere between 1.25 and 1.4.
The JE Pistons are a work of art and they were special made to fit the 98.05mm Mahle pistons.
Ron: Your MO arrived but is only good in the US. I am going for a long run with the WA gang near Seattle starting tomorrow and will try to cash it there.

Gunter, let me know if you have any issues with the MO.

Gunter,
Looking forward to hearing of your progress.

Yeah, 3 steps forward and 1 back.
Ron: The CDI is coming your way; USPS last Friday.

The JE's have deep valve cuts not sure your piston to valve clearance will be that much of an issue. What compression? Probably your cam provider can provide you with what you'll need but I have heard of both the 1.25 and 1.4 for the 964 grind.

Thanks, Jeremy.
Compression is 9.8 : 1 and, yes, the valve pockets are deep on the JE's.
JW says he doesn't like regrinding SC cams because of the adjusters having to be set too deep, so, it makes sense to me to look for a pair of 964 cams.
They should fit into a 3.0 liter engine after the "pump end" is cut off on the left 964-cam. :confused:

JE's: Did you CC them to make sure they are actually 9.8:1? The last two sets of "9.8:1" 98mm JE's (for a 3.2SS) CC'd out to 10.5:1. I had to machine them to get the right compression.

964 cam: Yes, you can cut the end off the 964 cam and use it.
-Chris

I did and got pretty close to that (although I have to admit it was a little difficult with my flame ringed heads and cylinders)- I planned on also doing the cylinder volume test too once I got everything together...

Grinding the SC cams to 964 specs only removes .030" off of the base circle. Which is .015" per side. Defenitly not going to set the adjusters too deep.
The cam setting follows the cam profile. 1.26mm is Porsche specified for the 964 cam. Going to 1.4 or 1.6mm slightly advances the camshaft for bottom end power.

Thanks John, that helps.
Jeremy and Chris: I wouldn't know how to do a volume-test.
Can you not determine the CR by checking the deck height?
Is there a formula for deck height vs. CR?

not really - you have to "cc the heads" -- that's what the volume test is. It is not real hard - you need a burette (Chem. supplies store) a plexiglass plate and some ATF (it's colored and easy to read). How to Hotrod VW Engines is the book I learned from - dunno if its in BA's book or not.