Overhead Cams

[vennard]

How do you get away with all that engine and using a non c/w crank shaft? I would have thought it would be one of the first things you did. Damn cool though I remember the magazine feature on it.

[Wally]

Speaking on OHC type 4 engines, has anybody ever heard of the 'Overfly' engine that Rolf Holzapfel developed for the Kaefer Cup?
Alex maybe?


It was a new development in 1995 from Holzapfel in which he also used the Porsche 964 cylinder heads AND the 100mm cylinders and pistons. He also used those with a 86mm stroke SCAT crank to give exactly 2,7 ltr.
He used a cam housing that his tuning workshop made themselves.
The test engine with 10,4 compression and self developed Melcher cams produced 247 (DIN) hp at 6250 rpm and 294 Nm at 5500 rpm! The engine used twin spark (from the dual spark 964 heads) and 51mm Weber carbs.

Personally I don't understand how you can use the stock 100mm cylinders which ran with 76,4 mm stroke in the 964 engine for 86mm stroke, but the picture in the german mag 'Gute Fahrt' showed all these parts indeed together!

Unfortunately these never did make it into the Kaefer Cup due to the 2 liter restriction the following year(s).

As you would supect, everything has been done already by some one.

Greetings,
Walter

[BOBTAIL]

During the design stage we came across that article from Gute Fahrt.
I got the impression that Dr Gerolds car was powered by "that" type of engine ,By "that" I mean cast cam boxes( that was the bit that nearly made us give up!)
For the amount of machining, it was much more economical to do the job the way we did.
We also noticed that they cut out the barrel registers and welded in new peices to change the stud spacing.We just redrilled the heads and cambox to accommodate the difference.
Its funny seeing all the different 911 headed motors and we all seem to use the same belt setup.

Crank......Seems that too many people throw away too many stock parts to replace them with parts of an inferior quality.

[SuperRSi]

Bobtail,

Very nice work. Do you think any of you would be willing to share drawings of what you welded or machined so we could build something on this side of the pond? I can weld and machine in house, so in my spare time I could probably build one up in oh say four years.... It would be interesting to do it piece by piece as one had time and money for parts. It also would help to learn from the mistakes ya'll (from Texas) made. So whip up some plans and sell them to me.

Thanks,

Randy

[BOBTAIL]

Originally Posted by SuperRSi

Bobtail,

Very nice work. Do you think any of you would be willing to share drawings of what you welded or machined so we could build something on this side of the pond? I can weld and machine in house, so in my spare time I could probably build one up in oh say four years.... It would be interesting to do it piece by piece as one had time and money for parts. It also would help to learn from the mistakes ya'll (from Texas) made. So whip up some plans and sell them to me.

Thanks,

Randy

Drawings? you realise we write with a tig torch

Really its quite simple to work out what goes where and what needs modding, No, honestly Ive been trying since we got it running to convince folks its doable for not very much cost.

We kept the stud spacing as T4 and modded the heads and camboxes.
The head oil returns go into the deep sump.

You're lucky in that you can get the bits together and mail me, we didn't have that luxury.

The crank drive was machined to adapt the T4 taper which went to 2 polo crank sprockets, just a simple top hat design.
We had to buy the bits and make them fit together ,not knowing it would work.

Just go buy your carrera 2 twin plug heads and 2 cam boxes, with cams and take some measurements.
Ill always be here for advice.

[SuperRSi]

Writing with the big blue arc, I understand. I have been writing with plasma as I can use a smaller font, and use the blue arc to edit. Let me work up some courage (and cash) and then start looking for the heads and bits.

And I will be asking lots of questions.

Thanks,
Randy

[Wally]

Originally Posted by BOBTAIL

Just go buy your carrera 2 twin plug heads and 2 cam boxes, with cams and take some measurements.
Ill always be here for advice.

Cool!, but how would you use the cams of the Carrera? I mean you cant just saw of the remaining cylinder at each end: a six cylinder has a very different cam timing. You would be out by 30 degrees or something...?
Did you have new cams made (for a 4-cylinder)??

On another note of OHC aircooled engines: did all of you know that the Citroen GSA had a 4-cylinder OHC aircooled engine? It was only 1300 cc, but still, it has been made in quite some numbers (at least in Europe) in the late seventies/ early eighties(?).
I should have got one from the salvage yard then
alter
Greetings,
W

[BOBTAIL]

Originally Posted by Wally

Cool!, but how would you use the cams of the Carrera? I mean you cant just saw of the remaining cylinder at each end: a six cylinder has a very different cam timing. You would be out by 30 degrees or something...?
Did you have new cams made (for a 4-cylinder)??

On another note of OHC aircooled engines: did all of you know that the Citroen GSA had a 4-cylinder OHC aircooled engine? It was only 1300 cc, but still, it has been made in quite some numbers (at least in Europe) in the late seventies/ early eighties(?).
I should have got one from the salvage yard then
alter
Greetings,
W

Oh yes you cut the 2 middle lobes out of the cam and I think you turn it ...I cant remember but you turn the 2 parts so many degrees and pin the parts together, to make a 4 cyl cam.
We did have Piper make some cams but they seemed not as good as the pinned stock cams.