slate blue

Hi Guys and Gals I was wondering if anybody knew whether 968 heads would fit on a 928 much in the same way 944 heads fit with some minor mods. I would also be using the 104 mm bore size. If Sterling is out there please feel free to chime in. Also does anybody know if the 968 camshaft profile is more aggressive than the 928GT profile. If it isn't there would be no point to do this conversion as I am aware that you can fit 968 valves and seats and this is not that an expensive mod to make. Also can you just fit the 968 cams into the head of a 928 4v. All the best and thanks in advance. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Steve J.

They bolt right on. See Sterling G.'s modifications -
<a href="http://www.928sg.com/heads.htm" target="_blank">http://www.928sg.com/heads.htm</a>

slate blue

From my understanding he used 928 heads and 928 cams (modified) and 968 valve covers, not 968 heads. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

Tom

968 or 944 cams won't work (different timimg!) and the vario cam system woud be difficult at best to retro engineer.

d richard

Great website sterling. Is the engine still running? any issues? Any dyno numbers?

slate blue

Thanks vey much Sterling, that has answered all my questions. I also would like to know what is the status with your car? <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

RedS2

I have a pair of S4 heads that are gorgeous and I need to part with them. Partly from reading Sterling's page and talking with him, I have a core set I rebuilt guides, surfacing, seals, bead blasting, washing, oil plugs, etc. This year (87-88) is a drop in on my 944S but the cooling passage at the fronthas to be drilled out for the 944. My heads use the same gasket as either the 944 Turbo or the 944S. Regarding the cam support, the heads are symmetrical left and right bank so you have one casting. BTW, I have a fine set of S4 cams and exhaust manifolds that need to go as well. Ellsworth Bros in Mountain View can easily add and has the cam support boss on each head. That is by far the big difference.

A 944 S2 enthusiast put S4 head on when his suffered the dreaded tensioner failure. He Devcon's the useless front passage up to the temp sensor.

The S4 cams are really weak; the lift is much much less than the 944 twin cam; I miked them and checked with Elgin it was so weak. You 928 guys have a lot of power to gain with better cams.

Note the 944S puts out 180 HP with a head identical to the S4 and much more lift on the cam. It does displace 2.5 liters, though. The S and S2 cams mike at about the same lift. I am getting 220 or a little more with my upcammed S2. Elgin offset ground the profile a touch.

I upcammed one of my S2's and it runs much more like a 968. Sterling's Variocam helps low end power but according to all my research, you can get the same top end from cam timing. His motor is just incredible and I am green with envy even with a very nice Turbo S in my garage. I think you 928 guys just need more cam and more displacement. The 968 head bolts to the same pattern as the S2 head which combustion chamber and valvewise just the same as the S head and S4 head when I last check with mike and gauges.

slate blue

Thanks red s2 that was really helpful and confirmed what I thought. I think what I would like to do is us the profile of the 968 cams as they were the last of the development from Porsche in respect to these engine families. If you extrapolate the 968 power into a 6.5 liter engine you in theory only would get 520 hp. The good thing about the 968 grind is that it is made for a six litre as apposed to the gt which was only a 5 litre. Also the bore stroke ratio is very similiar to the stroker motor. I think the variocam though would be a must.

If you have a look at the power curve of the 968 motor vs say Devek 6.5 (not being critical of their motors either) you will see that their torque drops off much earlier and the peak hp is produced a 1000 rpm lower. In theory anyway I think it would be possible to build a 6.5 litre that could produce about 575 hp and 485 foot pounds of torque. This should be quite streetable as the 968 came in tiptronic form. Thanks to all who responded.

Does anybody have more details on the variocam system. At what revs is it activated? Does it just advance all at once or progressivly? <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

RedS2

I must disagree about the Variocam. If you just want top end power, advance the cam timing. You will sacrifice torque and volumetric efficiency belown 3000 RPM (Yes, I know the Variocam turns on at 4K or you can use your own RPM actuated switch). Sterling just got the most bottom and top end possible out of that motor. The 944S with cams almost identical to the S2 puts out 180 HP from 2.5L. A stock S2 is about 208 HP. My upcammed S2 and a stock 968 put out about 230 HP from 3L. With all the low end you have with a big 928 motor, a 6.5L should have about the same HP/L as a 968 with the same camming. I expect about 500 HP from a very drivable 6.5L with similar streetability as a 968.

You 928 guys have weak cams for twice a 944 and the power is right there with little work. Re-welding a set of cams is about $350 per cam but you might find a little better price.

Steve Cattaneo

REDS2
Are you saying 944 turbo cams will bolt right on to 32 valve 928 heads and work? Do you have the lift and duration numbers of the 944-turbo cams? What do you mean by rewelding a set of cams?

How about 16 valve 944 cams? Do they have more lift and duration then my 16 valve euro 928 S2 cams? If so, will they bolt in and work on my 16 valve euro heads with no modifications

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

slate blue

Hi Steve, I must admit I was not thinking when I said can I just put in the 968 cams. The cams are not timed for the v8 motor. So the valves would open at the wrong time. Also you cannot put 944 camshaftd in your 928 heads, the reason is similar to the answer I gave to the above, but also the valve spacing is different so the lobes on the cams will not line up with the lifters.

Do not weld the cams is my experience, they tend to fail in street usage. In racing it has been found that welded cams fair better than in their respective street counterparts. Welded cams struggle with idling. Nothing is as good as a new billet preferably chill cast.

I was going to develop some affordable cams for the 928 based around the 944 profiles but I think demand wouldn't justify the time and effort. I have a 944 cam to get the specs from if needed. Also there is a page on the rennlist "Racer X" I think that details 944 cam profiles.

By the way my car is an auto so I will have to use variocam to produce big power outputs so that it remains driveable.

If anybody is interested in getting cams made I can put you in touch with people who can make them from top quality material and on a one off basis.

Jay Wellwood

I don't know about the 944 cams fitment on the 928 (haven't looked into this - yet). However, instead of the GT cams - the 85/86 cams can be fitted to S4 motors - and are nearly as hot as the GT cams based on the specs.

Minor modifications are required, but easily doable. The S4 cam is a pretty good cam, but as we all know the GT cams are the cake for the 928.

hth-

Steve Cattaneo

Greg,
Thank you for the clarification, I am always looking for less expensive (cheep) HP.
928s can benefit from aggressive cams, but new grinds are very expensive, unless you have souse.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

RedS2

944 cams will NOT fit on a 928; the ignition sequence is not correct and thus the valve timing is off. WebCams re-welds many cams starting with a decent core and Elgin does as well.

A good welding job with nitriding is as hard as the original billet.

Welded cranks (CCR or equivalent, Bay Area expertise) have to my knowledge stood up well to competition. Again, the skill of the craftsman is very important.

slate blue

Hi Steve I can get new cams made from a billet for approx $500.00 usd a cam. I also have euro cams that need a slight regrind and re-nitriding. These cams come from 80 to 83 model and have just worn through the hardening. If I reco them I would sell them for approx $750 USD. All the best Greg