100 mm piston rebuild

[KlausMeine]

I was planning on dropping my 3.0 CIS engine (1979 SC) to repair the gearbox. While it's out I decided I want to do a full rebuild. My tentative plan so far:

-100 mm piston set 10.5:1 CR
-Twin-plug with dual coil ignition & Motec management
-SSI full exhaust
-964 cam regrind
-Weber 46 mm carbs
-May get heads ported

Questions:

1) Will the crank be ok pushing 100 mm pistons? Or does the stock crank have limit? Best estimate is around 275-300hp.

2) Will 46mm carbs flow enough to maximize power from the 100mm piston combustion? Or do I need to go with the 50 mm carbs?

Any suggestions & constructive criticism welcome.

[colingreene]

with that compression and piston size being run on carbs why would you hamstring yourself with 964 cams.
You can basically go anywhere you want on the cam.
Are you going to port the head.
Where do you plan on getting the piston and cyl from?

[winders]

Why would you use carbs when could use ITBs with MoTec??

[Jeff Alton]

Cam choice is waaaaay to mild for that combo.

Why carbs? possibly price and possibly nostalgia?

I agree with you though Scott, ITB's and modern ECU to get the most out of it, and far better behaviour at cold start etc.

We built a really sweet 3.2SS with PMO's a few months ago. It fit the elder gentleman's wishes perfectly. Went well with his Cortina in the garage. For him, ITB and EFI was a no go.

Different strokes for different folks as they say!

Cheers

[Zuffenwerker]

Originally Posted by Jeff Alton

Different strokes for different folks as they say!

I prefer the 66!


100mm p&c…mahle Motorsport making those or are you piecing a set together…refurbished cyls n new pistons?

Should be no worries functionally with the stock crank other than having the oiling modifications done when you have it apart.

Sounds like a cool sc build

[Jim Dorociak]

LN Engineering sells a 100mm piston & cylinder set, but very pricey. I am also considering a SS3.2 for my 914-6 as I have a 3.2 case already, but I was also considering using a 993 case I have but with 3.0 crank and thinking of using 100mm 993 cylinders and heads/cam towers to make a 3.3 engine just because I have most of the 993 parts laying around. Jim Dorociak

[Henry Schmidt]

Unless you choose to use machine-in 100s, I would opt for 98mm. No noticeable difference in performance and the thicker cylinders offer a more stable platform.
As Jeff said, cam choice is crazy mild.
If you are set on running the wide lobe center cam, the WEB 2021 would be my choice. If carbs are set in stone, think would about a DC 40 or 43-106.

http://www.drcamshafts.com/911profiles.htm

[Jeff Alton]

As Henry said, think different cams, if you can.

Will totally change the character and performance of the motor. Talk with John at www.DRCamshafts.com about your specific goals... He has made some specific cams for engines we have built, and I am sure he has done the same for Henry (likely more often).

Cheers

[Aircooled4evr]

Originally Posted by Jim Dorociak

LN Engineering sells a 100mm piston & cylinder set, but very pricey. I am also considering a SS3.2 for my 914-6 as I have a 3.2 case already, but I was also considering using a 993 case I have but with 3.0 crank and thinking of using 100mm 993 cylinders and heads/cam towers to make a 3.3 engine just because I have most of the 993 parts laying around. Jim Dorociak

Regarding your thoughts on a 3.3 engine. How did you intend to assemble this engine regarding the lack of stroke? with longer, special order connecting rods? Or some other way?

[PeteKz]

'79 SC engine heads have the larger intake ports. Unless you are building a serious race engine, don't spend money on porting the intakes. Just match the manifolds to the heads. That said, I'm sure someone here will insist that you fill in the notches were the fuel injectors squirt and then do a CNC porting job. It's always easy to spend someone else's money! ;-)

[PeteKz]

One other thing to consider: When I built my SC/3.2 engine, I had the exhaust ports coated with thermal barrier. Porsche did this in the 993 engines to cut down on heat absorption from the exhaust port. I haven't instrumented the before and after results, so I can't say for sure, but the engine does appear to me to run cooler than before. The normal operating temp is still the same, but on hot days and high power, it take longer for the oil to get hot. If that's true, then it's money well-spent. BTW, it was about $260 to get the 6 exhaust ports coated.