Vilhuer

At todays euro/dollar exchange rate S3 cam mod was about $830 and maybe $750 for GT cam fix. US $ has gone down so much lately $800+ seems high. Few years ago it would have been under $500.

Unfortunatelly no, just 1mm numbers.

Jim Morton

Erkka:

Cool looking numbers. Looks like your grinder moved the lobe center on the intake cam to 112.

Also, if you do not mind sharing, what is the base circle diameter for both intake and exhaust cams after the regrind.

Vilhuer

Center should be same as before as tip of the lobe was not touched at all, just base lobe. If my numbers indicate change they are wrong. Cams come to 1mm lift point 5 degrees ealier than before and they return to 1mm lift also 5 degrees later than before.

Diameter is 0.5mm smaller than before as thats what was taken away from base lobe.

drnick

jim, do you know what numbers we should be using to dial in the elgin cams? im not there yet, still fitting a set of headers..

Jim Morton

Nick:

As we use a hydraulic lifter that installs first, you'll want to time the cams at their max lift point.

The trick for the 928 is establishing and knowing the lobe center angle of the intake cam to the exhaust timing belt wheel.

I plan to use three degree wheels for setting the event timing. One mounted in front of each timing belt wheel on each cylinder bank and the third on the crank.

I'll use the degree wheel on the timing belt wheel to set the lobe center angle of the intake cam relative to the exhaust cam, then set the overall timing (using max lift point) of the each intake to the crank. A many have posted, I would suggest advancing the lagging cam set by a few degrees to compensate for belt stretch.

Once all the timing is initially set, I'll verify the timing by turning the motor over by hand at least two full event cycles to let the timing belt do its thing on the various rollers, wheels, etc., then recheck.

To perform the above, you'll need to know which cores you had Elgin grind, S3 vs. GT. Assuming S3, your nominal timing points for max lift are 120.5 ATDC for the intake and 107.5 BTDC for the exhaust. How you shift for the .5 degrees, or more is a tuning choice. For the lag bank timing, many fellow Rennlisters have posted their opinions. Some may chime in here.

Feel free to e-mail / PM if you want to discuss this more.

mark kibort

I have a question. if we shave the base circle and the lifter is supposed to take up the slack, by how it pumps up, isnt there a chance that a car that has been sitting a long time, or if you replace the lifters with a new one, not fully full of oil, that the first adjustment of cam timing would be way off? Or, do the lifters push with at least the pressure of the valve springs (hard to imagine) so that they push down the valve slowley, even if they are not pumped up with oil?
Inquiring minds want to know.

mk

drnick

mark, i think this is why jim is suggesting timing at 'maximum' lift. this point should be the same regardless of how pumped the lifter is - im assuming its measured with a dial gauge on the back of the lifter.

jim, i do have the S3 cams and i think ive got what you posted in broad outline. ive not set cams up on the 928 before but i was under the impression that the exhaust cam has a fixed relationship with the intake determined by the number of chain links between them? is the lagging bank the right hand (usa drivers) side?

Jim Morton

Nick:

Yes, the relationship of intake to exhaust is fixed. Slight tweaking might be possible with adjustments made with the fixed cam to cam chain guide. I am anxious to play with this when we setup Dennis' engine. I expect to possibly shim up the guide as I think we will want to bring the lobe center angles closer together, or "narrow the lobe centers". I do not expect a lot of movement, maybe 1-2 degrees... maybe more.

Assuming that timing remains stock and on the OEM indicators depends on how well the nose of the cam remains in the same angular position to the stock timing marks after the cam regrind. FWIW, most cam grinders assume that you will degree in custom cams and not assume the stock timing marks still apply.

Hope this helps.

BC

Has anyone installed these modified cams as of yet?

John Speake

Anyone know how Euro S2 16v cam timing compare with S3 as per Erkka's table ?

drnick

john, ive read that the valve timing for a 4 valve can be a lot different than a two valve due to the valve sizing and air flow velocity.. you arent thinking of modifying the S2 are you?!

Vilhuer

These are all from WSM.

John Speake

Thanks Errka !

No Nick, I'm not thinking of modifying my S2, apart from a twin screw kit :-)