3.3 SS Induction questions........

[fred cook]

I am gathering bits and pieces to build a 3.3L SS engine based on a 3.0L block. I have the 100mm Mahle pistons, KN cylinders, ported twin plug Carrera heads and a set of 964 cams. The existing 3.0L engine that this will be built from already has the SSI exhaust conversion which will be retained. Ignition will be by way of XDI direct fire system. That covers pretty much everything except the intake system. As I see it, I have the options of keeping the CIS system or changing over to 46mm PMOs. The PMO ITB option is not being considered at this point due to costs. If I keep the CIS system, would it be worthwhile to change out to a digital WUR? Also, what modifications might I need to consider to the CIS hardware to maximize the potential performance? Compared to the cost of a set of PMO carbs, I could spend a reasonable amount on mods and still come out ahead $$$ wise. Also, If, I can get decent performance from the CIS system, I believe that it would provide somewhat better fuel mileage than the carbs. It seems that I have read of CIS engines being built up to 3.5 or 3.7L displacement, so adding 10% should be "doable".

Thanks for all input and suggestions.

[JJ 911SC]

Look like a fun project.

BTW, I just notice that all your Haulers use "Title Case" except for the "wife hauler"... Just a typo?

[boba]

Since you have your pistons, this will be a critical factor.

What piston dome do you have and what is the CR?

[fred cook]

The Mahle pistons that I have are rated at 10.3/1 compression. However due to a little extra volume in the heads from the twin plugging, it should actually come in at 10.1/1 or thereabouts.

[boba]

Next is the piston dome, is it a CIS piston. If it is a high dome top you would do better with an individual throttle such as PMO/MFI/EFI ITB.

Then cam profile. You do not want overlap with a common plenum. A 964 cam will work with common plenum, you could use up to something like a 964 super sprint or cup grind.

[fred cook]

These are domed pistons, not CIS style. And, yes I agree that with ITBs a much more aggressive cam could be used. However, with the 964s and the CIS, I should be able to get good power up to 6500 rpms or so and still have very good mid range torque. Since this engine is going into a mostly street car with the possibility of an occasional autocross or DE day, I am hoping to keep some good bottom end and midrange pull. I guess the main question at this point is, what mods might the CIS need in order to work at it's best with the larger displacement? Since the heads are Carreras and have also been ported (originally built by Ollie's and most recently freshened up by Xtreme Cylinder Heads in Fla.) I am considering changing to the early larger port runners which will make it easier to match the intake ports. That leaves the fuel distributor and air intake plate mods to consider? Also, as I said in my first note, am also considering a digital WUR or perhaps the modification to make the original WUR adjustable.

[boba]

I am not sure how significant the impact would be with the CIS common plenum setup but with individual throttles larger dia tends to move the power band up the RPM range giving more top end while a smaller dia will tend to improve mid range and torque. If you have the smaller dia runners now I would start with that as you describe your desired result.