993RS

My car is having the LWF and the short gear ratios installed at the moment. As long as the engine is out, am going to have the valve timing checked. My mechanic recommended doing this, since, in some cases, the allowed tolerance by the factory can be up to 10%, resulting in 20-30 hp loss from the average quoted by Porsche.

Interesting is that to do accurate measurements, they temporarily install mechanical lifters on two of the valves.

If the measured output is not OK, some components will have to be replaced (quote: $300 for the test, if measurement not satisfactory: $1000 for correction).

viperbob

Wow. I'll stay away from commenting on this procedure.

The reason that you use a mechanical lifter is due to the fact that the engine is not running and there is not pressure in the hydraulic lifters. So you use a mechanical for the test and then measure when the valve opens compared to the orientation of the crankshaft.

So are you getting a dyno run for the before and after? The results should be interesting. Maybe the initial run will show that your car is fine and no need to undergo an expensive procedure.

chris walrod

Not sure why you would be charged $1k to reset the valve timing? The chain wheels or sprockets are held in place with friction, rather than the traditional 4mm dowel pin. Either way, its just an adjustment, about 95% labor a a few dollars for gaskets.

If I ever have my engine out, I will be checking my valve timing as well. Please post what you find..

993RS

Viperbob,
My feeling is that the car is running well. My reference point is my previous RS project car, that really did run very well. Just want to do the test to be sure. Will inform as to how it went..

Jim Morton

Phil:

FWIW, I have been there and done the valve timing check and adjustment. The results with back to back dyno test can be quick and exciting. When I was doing a 3.6 engine transplant into and earlier P-Car back a few years ago, I had a chance to to this exact work on an engine dyno. As I recall, we found the timing between the left and right hand cam banks to be off 7 total crank degrees. The timing correction resulted in almost 18 lb-ft of additional peak torque and about 12HP. This said, it brought our corrected dyno numbers more in the range of the published Porsche power output specs, nothing greater.

As far as setting the cam timing, I would recommend three pieces of advice.

1.) Getting the usable/verifed timing specs for the 993 cams is somehwat difficult. I tried to resolve the published 993 cam specs from Porsche with a well known cam designer/grinder and we found that the published data did not close to a complete cam profile. We ended up degree-ing a loose cam to get the specs. If I still had the "delta" dyno data from that work, I would happily post it. Unfortunately, that project was many cars ago and long since sold...

2.) If you have good specs, you do not need to replace the hydraulic lifter as you can measure the crank degrees at the point of maximum lift, even with the hydraulic lifter in place. The issue here is that you need to know how to decipher cam timing and lift specs and apply this knowledge to the setup in the engine. If your mechanic does not know the specifications to this level of knowledge, I would be worried that the setting could be made worse, not better.

3.) If you get good, confident results, consider drilling and pinning the cam timing wheels as Chis already mentioned.

Well, thats my $0.02

Best of luck. If you proceed and do the dyno runs, please post your results.

Regards

FlyYellow

Interesting data. so how much work is it to check the valve timing? couldn't the timing be adjusted with an adjustable cam gear? i would think this would allow you to pin point the max. hp / torque position on the motor.

also as i recall if you adjust the timing you may give up low end torque in favor of high end power?

am i totally off base here?

Cheers,
Boris

993RS

Jim,
Thanks for the information.
Boris,
I recall something similar about a better (flatter) torque curve.

BTW: an addtional piece of information which I would appreciate your thoughts on, is that they told me that it is especially with the C4S cars that often the valve timing has been shown not to be good... Can't figure out why...

chris walrod

With my poopy gear ratios (G50-20), I have given some thought to advancing the camshaft(s) to gain some more bottom end, hopefully to help me with the current ratios.

Jim, I loosely assumed these cam timing specs would be readily available? Thanks for the heads-up with this. HHMMMM... Wonder if I would send a 993 camshaft to a camshaft grinder to get accurate profile specs. I am sure any grinder would have CMM profile measuring abilities.. Think this would be worthwhile?

FlyYellow

Chris if you get a cam grinder to degree your cam, please let us know what the results are.

Also how easy/difficult (# hrs) to adjust the timing?

Cheers,
Boris

Jim Morton

Boris:

wrt your questions...

Yes, if you could find good quality adjustable cam timing sprockets (wheels) timing could be more easily set. However, Porsche used a simple clamping force design on the hydraulic lifer 3.6 aircooled street engines. So the cams likely lack the dowel hole for a simple back date. Also, good adjustable sprockets are not easily found. The sprockets need to be accurate and of the right metallurgy to be worth a darn. If you find anynthing, please post it !

As far as the results go, there are two basic aspects to making this adjustment.

1.) Getting the left and right banks timed the same. This makes the cylinders run consist to the same cam timing. From what I saw and have heard from others, this is usually the big culprit on the 3.6 from the factory.

2.) Advancing and retarding the whole cam profile for both banks from factory spec. This is the type of change that moves the positioning the torque curve relative to RPM. I would love to give you a simple rule of thumb for advancing or retarding the 993 cam profile to get a specific result torque result. However, as I never modelled or dyno'd the 993 engine with altered cam timing(s) as part of my previous project or my 3.8 build project, I do not have enough information to hazard a guess.

I do know that the NA 993 engine runs with a lots of cylinder pressure and has narrow lobe centers compared to other high output engines. This theme seem to be common to Porsche as part of the boxer layout engine. This suggests to me a narrower range of timing adjustabiliy, but I cannot guess much further than that. Anyone else know???

Also, as an additional data point, since the 993 is a single overhead cam design, we do not get to play with altering the overlap with the installation of adjustable timing gears, unlike the DOHC cars. That additional degree of cam Intake/Exhaust timing adjustment makes for some great fun on the engine dyno. Results with changing overlap and timing can be a lot of fun to "eek" out !!!

Have fun with this ! I think that valve event tuning is one of the most fun aspects of hot-ridding...

Regards

Jim Morton

Chris:

I did the cam profiling on a "Cam Doctor" rig. I know a lot of the cam guys / pro race teams have these. I am sure you'll find one easily down in LA-LA land. Getting good profile data is easy on the Cam Doctor as long as you use the correct follower style to match that of the engine, i.e. flat tappet, roller, curve tip rocker, etc. A warning, though, if used wrong, the Cam Doctor can lead you astray. Make sure the correct follow is used !!!

Also, the problem I had with the published Porsche spec was resolving out the cam entry/closing ramp vs. actually event timing. The spec lists actual event timing, but there is not enough info to correlate this what we found trying to degree the whole profile installed in the engine/car. Again, I think it might be the spec on the cam lobe itself which you cannot easily directly measure in the car, only at the valve. But that's just my guess. As you might recall, I bought my turbo instead of finishing my NA 3.8.

If I have time tomorrow, I will look and see if I can find the cam doctor sheet I did a while back. If I find it, I will post some specs.

Regards

chris walrod

Jim, I love this aspect of tuning as well. Although most of my experience is with small and big block Chebbies.. We could go as much as 4-5 degrees either direction. And yes, we have unintentionally bled-off a lot of cylinder pressure doing so I do recall rather large engine personality shifts which correlated with 1250' ET results. Back then, chassis dynos were not around, only the dragstrip

IIRC, one could backdate to the 964, dowelled cam sprockets, but I think a camshaft change was also required(?). I remember some talk about the 993RS cams were (are) this type. Steve Weiner would be the one to chime in on that..

Some time back, I remember an ad from Andial who offered a 2degree cam timing adjustment as an upgrade. Not sure of the details..

FlyYellow

chris,

yes andial has the 2 degree cam timing block. however, you can't use it if you have a chipped car (as i recall)?

Cheers,
Boris

FlyYellow

oh and this thread is dominated by speed yellow - what does that tell us?

993RS

Yikes! and initiated by an ex-Speed Yellow too. What does it tell us? That if you go for speed yellow, you are probably to a Rennlister what a Rennlister is to a non-Rennlister...