3.3 SS w/CIS

[fred cook]

I will soon be building a 3.3L SS engine based on a 3.0L block.

I currently have:
100mm Mahle pistons 10.3:1 compr.
100mm LN Eng. cylinders
964 Cams
Carrera twin plug heads (ported)
XDi Direct Fire ignition

I would like to build this engine using the CIS injection system. I know that there will be some hp left on the table, but I really want to see just what can be done with this setup using CIS. So, knowing that I have big port heads, should I use the larger runners from an early CIS engine or simply port match the ones that are on the current 1980 engine? Also, are there any mods that can be done to the fuel distributor/air plate to help them flow more air and/or fuel? My goal here is to build an engine that will rev well but also have good midrange torque. Since most of my driving is on the street, max hp at high rpms is less important than power and torque in the mid ranges.

Any input will be appreciated!

[PFM]

Fred,

I am far from a CIS expert but I do hear replacing the CIS manifold is a real key to gaining HP in these engines stock, adding displacement will make a bad thing worse. Granted at low RPM no big deal but as the RPMs come up it will hurt. I do not have a CIS manifold or I would offer to put it on the flow bench to see what information that would shed on power.

[fred cook]

Actually, the CIS system on my 3.0 engine works quite well, pulling hard up to 7k. Since I am probably going to try to limit the new engine to around 6500 rpm, the air flow (volume) should be a wash. My main concern is that the heads that I have have been ported (some) and I see port matching as being an issue with the small runners now on the engine. Actually, this is kind of an experiment, using the CIS in a more high performance setting. If things don't work out as hoped, it will be realtively easy to pull the CIS and convert to PMOs. On the other hand, if I am satisfied with the performance, I have saved about $4 grand that can go into other mods (brakes, suspension, etc.).

[soren.911]

I have CIS on my RoW 3.2L and it has a lot of buttom and mid range torque. It is perfect for overtaking without shifting down.

Racing between my friends standard (exept SSI and Dansk) 1984 3.2 I am much faster under 4200Rpm.

Here is at little clip of mine: YouTube - ‪Porsche 911 3.2 CIS‬‏

[Steve@Rennsport]

Fred,

FWIW,..large-port SC heads support about 325BHP in stock form with Carrera heads doing a little better. Your CIS intake system and compatible cams are really the biggest obstacles for major power.

[fred cook]

Steve,

Thanks for the input. What kind of hp do you think this engine would make with
1) CIS and 964 cams
2) 46mm PMOs and 964 cams
3) 46mm PMOs and say maybe 911S cams?

[Steve@Rennsport]

Originally Posted by fred cook

Steve,

Thanks for the input. What kind of hp do you think this engine would make with
1) CIS and 964 cams
2) 46mm PMOs and 964 cams
3) 46mm PMOs and say maybe 911S cams?

Hi Fred,

Too many variables to guess at here,...

Compression ratio, exhaust system, ignition timing, fuel octane, cam timing, and how the engine is assembled all play big roles in its performance.

I will tell you that you should see something around 245 BHP if everything is right on 92 octane or better.

S cams will shift the RPM range up and require a good exhaust to take full advantage of your combination.

If you elect to install PMO's, you'll do lots better with a different ignition system,...

[fred cook]

The pistons that I have are 100mm Mahle 10.3:1, but with the cylinder head volume, should come in at 10.1:1 assuming standard clearances for deck height, piston to valve, etc. The exhaust will be SSIs with a 2 in 1 out muffler. The ignition will be via an XDi system w/dual plugs. Maximum advance should be somewhere around 24 degrees (initial, mid and top advance are individually adjustable). Right now I am planning on using 964 cams. The heads are Carrera w/dual plugs and stock size valves but with some porting done. They have had a multi angle valve job done and spring tension set by Xtreme Cylinder heads in Florida. Induction options are keeping the CIS or going to 46mm PMO carbs.

Thanks,

[Steve@Rennsport]

964 cams are pretty conservative at that displacement so this looks like a nice torque motor to me. Given the limitations imposed by the CIS, thats all you can practically do.

With PMO's or a good ITB system, you'd have the flexibility to use any cam you want (within the limits of piston-to-valve clearance) and thats the path to much better throttle response and more power.

It simply depends on what you want,....

[fred cook]

Group picture, cylinders, pistons, cams, ignition, etc.



Carrera twin plug combustion chamber



Intake port



100mm LN Cylinder and Mahle Piston



XDi twin plug direct fire ignition set



Still have to acquire plug wires, bearings, gasket sets, etc. At least the expensive stuff is already "on the shelf"!

[fred cook]

After much soul searching, web surfing and penny counting, I have decided to go with the 46mm PMO carbs. Given that I want an engine with strong midrange torque even if I have to give up some top end h/p, What cams should I be looking at? Right now I have a set of 964 cams and a set of stock SC cams. Probably want to keep the red line at about 7K. The engine will consist of the following bits and pieces:

Carrera twin plug ported heads
XDi direct fire ignition
100mm Mahle 10.3:1 pistons
100mm LN Engineering cylinders
46mm PMO carbs
SSI exhaust w/2 in 1 out muffler
???? Cams

[tadd]

Mod S would be nice, so would DC44s on 104 LC.

Glad to see your abandoning the tractor motor .

t

[Steve@Rennsport]

Mod S would work VERY well.

[fred cook]

Can my 964 cams be reground to Mod S specs?

[Steve@Rennsport]

Originally Posted by fred cook

Can my 964 cams be reground to Mod S specs?

They would need to be hard-welded for that profile.

[KTL]

Now that Fred has entered the carbureted territory, what effect does that have on his chosen ignition system? I see the comment about the Electromotive ignitions alot, and haven't been able to find out the answer after numerous hours of search button usage.

I know the older HPV-# systems have some issues with timing float, which should be confirmed with a timing light under load via the dyno- as noted on a few occasions by Mike Bruns I see. But I haven't gathered what are the other limitations with the Electromotive stuff. At face value it seems like simple, effective ignition. Almost seems too simple.

Thanks,
Kevin

[fred cook]

Well, I've got it, it's paid for so I guess we will find out if there are any issues or problems. Looks like I get to be a guinea pig!

[fred cook]

Talked to Richard Clewett at Clewett Engineering. He said that there are no problems/issues using the XDi ignition with the PMO carbs. He even offered some timing "starting points" for the 3 settings on the XDi system. I'd say we're good to go!

[KTL]

Didn't mean to imply that the Electromotive systems don't work properly with carbs. They do work well. I have single plug Electromotive HPV-1 on my 3.0L 9.8:1 with Weber 46s and a friend has twin plug HPX 3.3L 10.5:1 with 46s also. Just trying to find out what are the limitations (plug gaps? spark energy? reliability?) of the Electromotive stuff from the guys with years of experience with these.



The mech distributor with twin MSD 6AL and Blaster coils has been a choice for a lot of people building hot engines as well. I don't think they go with it just to be "period correct" since it has proven to be a very good setup for dialing in the timing and making great power. But from a simplicity and compact packaging standpoint, the Electromotive setup with bundled coils and crank pulley trigger seems like a tidier setup to fit into the engine bay?