slate blue

That's really interesting, that would be great too! I have both GT and 86.5 cams, I have them packed up at the moment, but if somebody else out there would measure them that would be helpful.

martin D

The valves would close because the Tappets/lifters are hydraulic & would compress the extra 1 mm when installed (same p/n '85-'86 , '87>).
Interesting though as the extra 1mm material on the lobes would allow a greater range of regrinds

mark kibort

wow, this is getting complicated!!!
mk

6.0-928S

I was told by Mark at 928Intl that the base circle must be machined down the extra 1mm.

BC

Hmmm.

Mark A? Are you listening?

Kibort - can you put a *page* on your title so he sees us down here?

slate blue

and the base cirle is indentical. The lifts are also identical, now my question is which set to use, MarK K does your power taper off after the GTs does? The Gt produces max hp @ 6200 I wont to produce max power @ 6800. Has your heads been modified at all Mark. If not you are doing quite well. I think I may hit 350 - 375 with fully flowed heads and 40 mm intakes, and a bigger reground cam. Starting to sound feasible to me.

I think I'm going to go with the 86.5 cams, later closing, wider lobe separation angle which should allow a better idle, read still can use air cond.
Mark could you please post a dyno run, that will probably seal me decision.

mark kibort

Ok folks, in hand, i also have an S4 cam and GT cam. Greg is right, the base circle of the two years of cams are close to identical. I measured 33.9mm vs 33.8mm. Lift on the two cams are 42.85 and 43.85mm for the 85-86 and 41.85 and 42.85 for the S4. the bearing diameters are identical .

so,where did this information come from that the S4 and 86 cams have a different base circle?? clearly is incorrect. However, there is a 1/10mm difference, but that could be just measurin error (.003"-004") not a factor.

So, it looks as though the 85 cams just needed to be cut on the ends, and they are the same. the driver side exhaust cam is left to be compared. If it has some differences, that may be the area where the modifying needs to occur

I compared my dyno run with Ron G from 928 international. we both were puttin down 320hp. my curve looked a little broader at the 6000rpm range, and there were some slightly differnent torque peaks in the 4500 or 3500rpm range. but, those differences were small. i dont have the MAF screens, and he still does, and that could be the subtle difference. (plus, a million other areas, along with me having the the racing headers from devek Level II as well as a suspect 1 tooth error on the cam belt, which is now fixed. comparing to my original dyno runs, 335 at the wheels gave just 15more hp and torque .

Im willing to bet my 1 tooth error after my waterpump and timing belt re-adjustment was worth the 15hp.

I dont think you will get anywhere over 350hp, as flowing heads and larger valves will probably be worth only about 15-20 max hp. Anderson didnt see any big gains when he did some of some the intake mods and he has the 6.4 liter engine.

I wonder why Anderson was quoted as knowing about the re-grinding of the 85 as i dont think he was aware of the differences in cams between 85 to S4. so far, (but speak up if you do) I dont think anyone knows.

So, you have my measurements. 85 cams seem to be the same lift and base circle as the S4.

MK



MK

QUOTE=Greg Gray]and the base cirle is indentical. The lifts are also identical, now my question is which set to use, MarK K does your power taper off after the GTs does? The Gt produces max hp @ 6200 I wont to produce max power @ 6800. Has your heads been modified at all Mark. If not you are doing quite well. I think I may hit 350 - 375 with fully flowed heads and 40 mm intakes, and a bigger reground cam. Starting to sound feasible to me.

I think I'm going to go with the 86.5 cams, later closing, wider lobe separation angle which should allow a better idle, read still can use air cond.
Mark could you please post a dyno run, that will probably seal me decision.[/QUOTE]

Lagavulin

That's interesting as I ran the 85-86 intakes for months; evidently, the valves do close since the car ran well. But according to your post, the car should not have even started up after the install.

So the question is, where did you get your information?

Mark Anderson

"I was told by Mark at 928Intl that the base circle must be machined down the extra 1mm."

I think there is some miscommunication here as I do not believe the above statement. I do believe that the spec on the 85/86 are similar to the GT cams and I did look into installing them once. The 2 exahst cams are easy as you just need to cut off the last bearing journal. The 2 driven cams are another story. I sent a sample to Web cam and they did not have a simple solution.

Lagavulin

Hi Mark,

It is the 2 intake cams which are easy to do by just lopping off the ends, as well as the intake on the passenger side.

Only the exhaust cam on the driver side needs the additional machine work as described earlier in the thread.

Tim Murphy

I believe Todd has figured out a solution. He machined the intake cams and installed some sort of collar at the bearing location. Next time I'm over there I'll see if I can get a picture.

BC

My cams should be here today - can i send them over tim?

mark kibort

as Mark said, (and he ment the intake cams) the intake cams dont seem to need anything, as the bearing journals look idential, spacing is the same all the way to where the cam pulley mounts. It would be interesting to see what the mods to the intake cams would have to be. Unless, of course, that the post regarding the intake cam mods, is really about the exhaust cams. (which are the driven cams)

I havent done a close comparison of the exhaust cams, but i sure would like to know the differences.

So, do we have 100% agreement that the intake cams only need to have the ends cut off to be identical to the S4 cams in fit? where did that 1mm bearing circle differnce come from? who is the author, " 928-6.0 " ? credible??

Murf, you mean "Exhaust cams" dont you ? (and not the intake cams as your post said. ) com'mon guys your confusing me!!


Mk

Vilhuer

Is this really needed? Isn't there readily machined bearing surface for longer cams with normally plugged in oil feed and all? Maybe all it takes is one exhaust cam mod.

mark kibort

seems like that is just a hack saw mod. doesnt have to be pretty, but there is not really anything in the S4 heads to accomadate the extra bearing, so i dont think you would want the extra length cam area in there on a re-fit.

Im wondering about the exhaust cam. ill have to compare this evening

mk