Strosek Ultra

Tuomo, you are right as always. Consulting the data I have, the conclusion is Porsche has used the same profile for both S4 intake and GT exhaust cams. My handmade chart is showing the timing of 1987 928S4 cams in the engine. Note the 1987 cams are marked differently but are the same compared to later models. As you say Tuomo, these cams are way too small for a serious NA engine performance build.
On the chart note the non-existing opening ramps which make the hydraulic grind impossible to run on solid lifters.
Åke

Rob Edwards

Finally got the bits and pieces needed to measure some of Anderson's cam collection. Practicing on the stock S4 cams, I get 7.98 mm of lift on the S4 exhaust , which is spot on vs. the factory quote. Will start by degreeing the stock ones just to make sure I can replicate Ake's curve on the S4 cams, then will go to town on the collection.

It is worth mentioning that any time the lobe is depressing the lifter at all, even though the dial indicator tip is on the base circle, the cam deflects upwards 0.3 mm. I set up the valves with only an inner valve spring to minimize the spring tension, maybe I need to splurge for a pair of Comp cams' valve check springs:

http://www.jegs.com/i/Proform/778/66...FQmNaQodomkF_g

Doesn't really matter since it won't affect the lift measurements any.

Strosek Ultra

Rob, from the pictures I see you have the dial indicator pointing directly onto the cam lobe. I am sure you know you cannot measure the cam profile this way, only the cam lift. You have to have the dial indicator onto the lifter in a right angle which is physically impossible depending on the size of the shaft and the lobe. That is why I made the measuring setup as viewed in post #19. Do remember there is always measurements errors and tolerances to take into account. For example the nominal lift of the S4 exhaust lobe is 8mm. You have measured 7.98mm, I have measured 7.95mm. This is a very small difference, smaller than the thickness of a hair which is 0.05mm. If you measure the lift on all the lobes of one camshaft you will find some deviations, especially if the cam has been run (wear). I cannot see a deflection of 0.3mm (do you mean 0.03mm?) on the camshaft when depressing the lifter. The cam bearing play will allow for a certain deflection but not very much, this is a very rigid setup contrary to a pushrod engine. When the lobe is moving across the lifter, the lifter will slightly rock in the bore which is another source of measurement error.
If you like to measure the lobe profile the way you do I think one way is to turn the head over and point the dial indicator directly to the valve head. You need a solid lifter which can be turned from a piece of steel as the hydraulic lifter is not rigid enough.
Åke

Strosek Ultra

Rob, I have measured most of the factory 928 cam profiles. All of them except the GTS INTAKE have been found to be in good according with the factory specs. I have got the lift (9.5mm)of the GTS intake to be the same as the factory specs but the duration differ. My measurement is 212.5 degrees @ 1.0mm of lift, the factory spec is 228 degrees @ 1.0mm of lift. It would be nice if you can verify the factory duration figure is incorrect.
Åke

Strosek Ultra

My handmade GTS lift diagram.
Åke

ptuomov

Very interesting, Ake. It would make some sense for the GTS intake camshaft duration to be there around 212 degrees @ 1amm if the factory follows the following design logic: First, pick the valve events. Second, use specified acceleration limits to lift the valve. Then let the lift be whatever the lift ends up being. This design logic would lead the 212 degree @1mm intake to have a lift somewhere between the S4 and GT cams' 9mm and 10mm, and perhaps not coincidentally GTS's lift is right there in between the two at 9.5mm.

Strosek Ultra

Do remember my measurment method is not extremely accurate. It is all made by hand and even if the quite large degree wheel I have is more accurate than a small degree wheel you have to calculate with up to a couple of degrees of measurement errors. I agree basic logic tells us the correct GTS intake duration probably is 212 degrees @ 1.0mm. The maximum lift velocity for all factory profiles I have checked is pretty much the same about 0.125mm per degree crankshaft.

Rob Edwards

Hi Åke-

Yes, understood on measuring lift vs. actually degreeing the cam. I was playing around with the various dial indicator tips and extensions and was just measuring max lift on the S4 cam. I have an angled tip and extension that I think will work on the lifter for degreeing. Learned all about 4-48 threads while finding the combination of bits that would work.

Will do the GTS cams next and report back on what I get as far as a profile.

Strosek Ultra

Rob, I do not know if using an angled tip will work well. The tip must not touch the lifter bore edge. Think the best method is to have the dial indicator at the valve in the combustion chamber. You need a solid lifter though, the hydraulic lifter is not solid enough, it will get partly compressed.
If you like I can make you a couple of solid lifters and send in the mail. The height of the lifter is not very important. The valve does not need to be seated when measuring but no valve lash is allowed.
Åke

Rob Edwards

That's a very kind (and tempting!) offer, I'd love to have a pair of solid lifters for this purpose but hate to bother you - I could also just buy a pair of 35 mm solid lifters but am not sure which of the solids have a long enough foot to be plug 'n play with the standard install height without a bunch of shims.

This one wouldn't work, obviously:

http://techtonicstuning.com/main/ind...oducts_id=1890

I think I could piece together something workable from this list:

http://www.eurospecsport.com/product...rformance.html

I need to measure a stock hydraulic lifter to get a sense of what would work.

Strosek Ultra

Rob I have sent you an email.
Åke

ptuomov

Has anyone actually measured the GTS lobe separation angle? Is that suspect, too?

Strosek Ultra

I have not had the opportunity to measure the GTS lobe separation angle which has to be done on an assembled engine. The specs say 118.5 degrees which is more than for the other 928 engines but I cannot say it is suspect. The cams are installed/timed 5.5 degrees retarded which is very close to the other cams and make sense for a very mild cam. Overlap is in practise non existing. Long duration much overlap racing camshafts are almost always run in an advanced (around five degrees) setting.
Åke

Rob Edwards

Åke very generously made and sent me some solid 35 mm lifters to help with the cam degreeing that I'd like to do-




I finally got around to playing with them this afternoon- here's the setup:

Comp cams 4902 mount with pointer, mounts in any M6x1 hole.
Comp cams 4758 checking springs- coil bind is closer to 17 mm vs. ~ 15 mm for stock inner springs but without a lower spring perch or shims they should be ok.
VW387 holder for dial indicator, against the valve face.

Åke very correctly points out the most accurate way to measure is by measuring valve lift, so I flipped the head on its side

Setup for degree wheel:



Setup for dial indicator:



Since I have a couple sets of cams to measure I figured it would be worth getting some sort of program to graph all the lift measurements, so I got the basic version of Cam Analyzer.

To make sure I have some confidence I'm measuring correctly, I installed a stock pair of S4 cams in this driver's side head, with valves/test springs/solid lifters in cylinder 7. Åke's solid lifter is a little thicker than stock, so the valve doesn't actually close all the way, but one gets a nice stable transition off the base circle. The max lift of the intake lobe is where I set TDC, for lack of a better reference.

Graph of lift vs. camshaft degrees (confusing, I need to figure out how to get it to display in crank degrees....)



Table of calculated durations at various lifts. The published values for S4 intake and exhaust duration at 1 mm lift in crank degrees are 205 and 195 degrees. Multiplying the numbers by 2 to get from cam degrees to crank degrees, I measured 202.2 and 196.6, so I'm off by a little, but not much.

Published max lifts for S4 cams are 9 and 8 mm, I measured 8.95 and 8.00 mm, so perhaps this intake lobe is worn a bit. But the measurements are in the ballpark.

Published LSA is 106.5 degrees, my numbers calculate 105.7. FWIW.

Next step is to do my set of GTS cams, then the various race cams. It's probably 45-60 minutes per set to mount them in the heads and pull the values.

BC

This is great stuff Rob. Love the interaction with the software.

You also have a few sets of S3, right?