new pistons & cylinders CR
 

I am thinking about replacing my pistons and cylinders using LN eng. cylinders(nickies) and twin plugging what is a good CR if I am using 964 cams and CIS with SSI/Dansk dual in/out? I have been looking at ways to twin plug also. I am reading the electromotive but I think the dizzy looks better any thoughts?

Re: new pistons & cylinders CR
 

Need some more info here in order for the board to give you a better answer. I am assuming a 3.0L SC is your starting point and by your cam choice you will be sticking with CIS? Bore diameter chosen and octane availability (i.e. pump or race gas) are two variables (and there are others as well) that will weigh heavily.:)

Ralph

If you are already replacing your pistons, you might consider JEs or another design that gives you more options in the future for different cam profiles. As I understand it, you only need twin-plugging over CRs of about 10, so if you are going that way, you probably also need to consider valve clearances.

Others here have forgotten more than I know...

yes My starting point is a 1983 SC with 80,000 that I pulled off the heads to do a top end job.

I would like to get the most displacement possible and the highest CR and still run pump gas with twin plugs and keeping CIS

Buy Dane's engine.

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/226319-fs-3-4-twin-plug.html

Well, to be brutally honest, if this is your goal I would consider the 3.6L transplant. With your 3.0L CIS motor as the basis and running on pump gas, I wouldn't build a large bore street motor over 10:1, even with twin-plugs. Better to err on the conservative side, as there are no knock sensors to retard the timing in the event that detonation is detected. You can always blend race gas to provide some extra safety margin, but that gets expensive and old real quick.

Your 3.0L motor can be made all the way to a 3.7L using 102mm Mahle pistons/cylinders, 74.4mm Carrera crank and Carillo rods. Andial sells this kit. The above parts are not cheap and by the time you combine that with twin-plugging, machine work and normal rebuild replacement parts, you will be up and over the cost of a 3.6L transplant with only comparable power and perhaps less reliability. I would guesstimate that you are looking at around $12K just in parts/machine work.

But, just like if you were doing a 3.6L transplant, your stock 3.0L oil cooling will not be up to par with a larger motor so the trombone cooler will have to be ditched in favor of dual Carrera coolers in the fenderwells or a large, front mounted cooler. Figure in those costs as well, as I did not with the dollar figure quoted above.

3.2L guys already have the longer stroke crank and rods necessary to easily build 3.4L or 3.5L motors and get somewhere near 3.6L power levels for less cost than doing a 3.6L transplant, but the 3.0L guys not only have to spend serious money for the larger 98mm or 100mm pistons/cylinders, but also purchase the Carrera crank and rods as well just to get in the large displacement game. 3.0/3.2 to 3.6/3.7 conversions were somewhat popular in the late '80's/early '90's, but times have changed and unless you really want to be different, you are better served going the transplant route.

IMO (and take it FWIW), I would either do your rebuild using 98mm Mahle's for a short-stroke 3.2L retaining your CIS with the aftermarket smog cam of your choice and SSI/stainless muffler exhaust (and pocketing the extra money or spending it on a different part of the car) or go with the 3.6L transplant if your budget is over $10K.

You mention the LN Engineering cylinders, unfortunately I don't personally know of anyone using these and therefore can't speculate, although the proprietor does post on this board. I think Jeremy964 is building a 3.2L to 3.4L motor using these as the building block so you might want to get into contact with him to get his take.

Ralph