mark kibort

I know we went over this before, but im willing to bet my cams in the holbert car are some how, modified 85-86 cams, at least the lift is the same, and thus the same as a GT with some duration differences.
what does it take to fit the 85-86 cams in an S4 head? i remember the discussion but cant seem to find it. i Know we have to lap off the end of the cam as there is not a final bearing cap, but what else should i have to do to make them work. how critical are the bearing dimensions? they must be pretty critical, if the current bearing caps have serial and order numbers to them.
anyone with some real life experience here, that could offer some info, would be appreciated!!

OR, can my missing teeth cams be reworked to welt on new teeth to the sprockets that are missing one tooth?

Mark

BC

There is some lopping-off, but I think that one or two cams don't need changes at all. There is some more material needed in a certain place, and that is the difficult part I believe.

My opinion after several months of research was that the acquisition costs of the cams PLUS the welding, etc, would add up to the cost of GT cams.

Jeff F

Mark:

I had my 968 cams repaired for the same issue--only I was missing more teeth than you (five on both total if I remember). The only way to repair these is to have entirely new sprockets put on your cams. If you have even one broken tooth, the rest are compromised and will fail eventually. Check the wear patterns. The single roller design is a weak spot, and once the chain wears and gets longer (it does not stretch, it wears slightly at each joint), and starts to ride up out of the saddles and closer to the top of the teeth, eventually snapping them off after wearing them where they were not designed for the stress.

Partswerks is the ONLY company that does this fix. New cams was the only other alternative. They charged me about $1,400. plus shipping. Cheaper than new as my lobes were ok. You could probablly find used cams easier than I could for the 968. New ones may be cheaper as well. I was looking at 2k for new. Good luck!

Jeff

'87 5-spd. (some extra stuff)
'86 951 2.8 (lots of extra stuff)
'92 968 Cab. (mostly stock and staying that way)

Vilhuer

AFAIK cam bearing caps are numbered because they were drilled when in place and would not fit to any other place than their named position. Cams themselves have some fixed tolerance that will naturally have to be in the range but I think '85-86 has same size range as all later cams. If I recall right '85-86 exhaust cams have narrower bearing surface at front surface meaning they would need to be widened to fit S4 heads or heads changed to older measurements. S4 heads have normally unused surface at rear bearing cap and I think it's not needed to do any major modifications there. There is oil feed all ready for longer cams bearing surface lubrication. Hope more knowledgable correct me if this is totally wrong.

Stan.Shaw@Excell.Net

i have both sets of cams and heads ('86 & S4), and intend to bring them in to a machine shop in the next couple of months to find what it will take. Any useful information is appreciated.

Lagavulin

Other than cutting off the ends which is easy, the only 85-86 camshaft that needs modification to fit in an S4 head is the driver-side exhaust.

The collar on the front bearing journal on the cam needs to be ground down flush with the rest of the cam's bearing journal since that bearing surface on the S4 head and cam was lengthened. In other words, the collar on the 85-86 cam is in the way of the S4 head's front exhaust bearing cap.

Now for the tricky part. Once the collar is removed, a new collar of some sort will need to be welded back onto the cam to prevent the cam from 'walking' out the front of the head.

As someone already mentioned, scoring a set of GT cams for $1000 would be the way to go.

goliver

What type of gain will using the 85-86 cams in an S4 make HP wise?

Regards,

BC

Well Lag, I think I just bought some cams. So that 1000 dollar GT camset got really far away as the 85 cams I have are 160 bucks so far.

Is there any goodness in mixing amd matching cams S4/S3?

Any info?

Tim Murphy

brendan, hang tight with those 85-86 cams. We are experimenting now with the modifications for fitting them into the S4 heads. You may have to send them to me to have modified but it doesn't look like it will be that big of a deal. We should know very soon as to the fit but it will be a while before we can give results of any gains.

BC

Thanks Tim. I'd think gains wouldn't be very big without headers and port matched intake at least on NA. I'm not sure how gains would be realized on boost, unless there would be some sort of increase equal to NA and adjusted for the increased efficiency? I'm thinking again about bigger intake valves to go with these. Don't really know.

Tim Murphy

If you are going to put boost into the intake forget about larger intake valves. Put your money into exhaust.

BC

I already have an MSDS (Or as devek calls them - Level I) set. I will do a X-over into dual 2.5s straights into one or two Spintechs or Hooker Maxflows. If I do the maxflows, I will need some muzzling upstream, but that cools and slows the exhaust pulses, which sometimes removes the effectiveness of the X-over, so I don't know.

My aim in design is to control sound as much as I can withouyt impeding flow, but hvae a very tight grip on resonance. The sound that gets inside your inner ear is my pet peave.

mark kibort

If you look at the S4 vs the GT , the only difference was the cams and that was good for about 15+hp. rev limit change didnt change max hp numbers. the rest is the same. im almost certainl the ole holbert car has the 85 cams, and that could be why my curves are slightly different than some equally prepared GTs , but with the actual GT cams and computers at the exact same hp at the wheels. (ie ron gottshock's GT racer vs the Holbert car. both 320ish at the wheels)

mk

6.0-928S

The base circle on the 86 cam is 1mm. larger than the 87 cam. If you just bolt it in the valves won't close. A cam grinding shop must reduce the base circle by 1mm.

BC

Are you positive?