3.0SC to 3.5litre with CIS - What CIS mods required?

[mikedsilva]

I have a project in mind.. well, it's sorta aready happening albeit slowly.

3.0SC "big port" engine being rebuilt with a 3.6 crank and 98mm Pistons to get 3.45litres (or a 3.5 as some refer to it).

My experience and understanding of CIS is limited however I want to try to use it to run this motor.
Compression will be approx 10.2 and cams will be 964ish or 993SS ish...

Can the stock CIS adequately supply enough fuel?
Or does the fuel distributor need to be modified to supply more fuel?

I've spoken briefly to someone who refurbs the FD and WUR and he says he can rebuid them to suppply more fuel but that it would be helpful to know if I am looking for 10%, 15% etc...

Why am I going down this road?
Because itbs and aftermarket efi coupled with dyno tuning, linkages, fittings etc can be quite costly and it would be good to be able to offer an alternative that's relatively "affordable" to the average owner.

[Bill Douglas]

Sounds like a great build Mike.

What year is the CIS and is it a ROW Engine?

[Porchdog]

In on this.

I'm unexpectedly refreshing my 3.0. (Broken head studs). I'm definitely changing pistons and cams and toying with increasing displacement.

EFI/ITBs are tempting, but in addition to the cost, they seem to be endless projects as you fiddle with the tuning to get them running properly and keep them there.....

[mepstein]

Wouldn't using a 3.2 Moronic injection be affordable and easy(er).

[Tom_in_NH]

To stay with the CIS, you'll, at minimum, need the capability to adjust the warm-up control pressure regulator. There are a number of approaches to accomplish this. This one looks very interesting. Google "CIS Warm Up Regulator Digital"...

[mikedsilva]

Originally Posted by mepstein

Wouldn't using a 3.2 Moronic injection be affordable and easy(er).

No, I don't think so in this case.
You'd need intake manifolds, rails, afm, wiring harness, ecu, and way to mount the sensors on the 3.0 motor. Then you have a system that is still antiquated when compared to a typical modern standalone ecu and would still be marginal at supplying enough fuel for a 3.5 litre.

[mikedsilva]

Originally Posted by Tom_in_NH

To stay with the CIS, you'll, at minimum, need the capability to adjust the warm-up control pressure regulator. There are a number of approaches to accomplish this. This one looks very interesting. Google "CIS Warm Up Regulator Digital"...

Is that the Franken CIS? or something different?

My rudimentary understanding of WUR is that depending on the temp, it will vary how much control pressure is placed on the piston in the fuel distributor. Which in turn meters how much fuel is evenly distributed to the injectors.
The question is, if the WUR is adjusted so that less pressure is provided which would result in more fuel being delivered, can the fuel distributor actually keep up and be able to supply enough fuel ?

[mikedsilva]

Originally Posted by Bill Douglas

Sounds like a great build Mike.

What year is the CIS and is it a ROW Engine?

I'll have to check and come back to this...

[mepstein]

Originally Posted by mikedsilva

No, I don't think so in this case.
You'd need intake manifolds, rails, afm, wiring harness, ecu, and way to mount the sensors on the 3.0 motor. Then you have a system that is still antiquated when compared to a typical modern standalone ecu and would still be marginal at supplying enough fuel for a 3.5 litre.

I figure $2500 for the induction, ecu and harness. Larger injectors are easily available but even stock injectors run a 3.4 the system is antiquated but it still allows for a custom chip to be made to work the new displacement. It was just a thought. It’s your project to handle as you wish.

[Tom_in_NH]

I have never found a flow chart for CIS fuel distributors. But, lets say a heathy 3.5 liter should make 300 HP. At a BSFC of .5, that 300 Hp would require 150 lbs of fuel per hour. Thats roughly 25 gallons per hour. If the CIS in question is still together as a unit, flow test it. All 6 injectors into a bottle for a minute, and then weigh it. 2.5 lbs or more would be a favorable indication.

[PeteKz]

IME, the SC CIS is capable of delivering much more fuel than the 3.0 engine can use, or my 3.2 can use. How much more?

Tom in NH offered a good preliminary test.

After that test, I recommend putting the CIS back on the engine and then driving it. If you have an AFR gauge, and it doesn’t go lean at full throttle and 6500 RPM, it works.

As for rebuilding a FD to “deliver more fuel”, I remain skeptical. I’ve opened those things up to clean them, and the only adjustment i know of is the screws/springs for balancing delivery to each injector. You can make that adjustment yourself without opening up the FD.

[Old H2S]

If you do the ICARP FD conversion your self it is cheap and easy. The flow restriction will be the steel fuel lines running to the injectors. If you use old style plastic lines they are larger on the ID. Then the pump will be the limiting factor but bigger pumps are easy to get. You must have a stand alone AFR gauge and a fuel pressure gauge to see when you're at.
Manual control on CIS works great. I bought all new stuff so..
Rebuilt FD 1000 from Curt, expensive but he's anal about perfection. I would go with Brian this time..
Injectors 200
AFR 250
FP gauge. 200
Aeromotive FPR 200
Tubing- McMaster-Carr. 50
compression connectors 50



So this is the control knob you must put somewhere inside the car so you can twist it up or down to get the AFR you want. You need both gauges too, I only use the FP gauge to start the car when cold by lowering the pressure, I have started the car at 20F so far with no problems. The FD only needs 2 lines changed to run ICARP CIS, you are running it just like stock but you are the WUR so you just saved a bunch of time, money, and headaches to get that to run right let alone jack up the gas for more HP. All the stock CIS crap still is hooked up and running so you do not need to change all the junk you fixed. The 2 hard plastic lines run to your new regulator. Need a richer mixture for your hotrod .. turn up the pressure and down goes the AFR.
OR
Go Holley single carb for cheap in any size up to 1500 HP. I have a quick change set up and jump to ICARP CIS in the winter and the Holley carb in the summer when I'm being an jerk and beating on my Blue Mule.

[911MANN]

Hey, Mike: Sharing some thoughts here. I spent a long time determining my best route re: my 3.2SS project, and I read A LOT before making my final decision. BTW, I have been quite distracted in the last 6 months, but it's time for an update on my 'Prodified 3.2SS' thread, and I will do that before long. Here are some things I remember reading on your topic- hopefully, they will give you a bit of a short-cut to your destination.

I understand the intake air is the limiting factor, even in the larger 3.0L ROW CIS intake runners.

Brian of RarlyL8 in these forums has noted several times over the years his ability to modify FD and WUR for increased fuel delivery in racing applications.

Look up old Pelican Forums from 20 years ago, and you will find some information on topic. A member of that era going by rdane had great contributions based upon his project to blow-out his 911SC CIS engine to maximum displacement. One of the threads was called "CIS with a 3.2 or 3.4. Is it worth it?" I see several Pelican threads along those lines from 2004, 2005 and 2006. I suggest chasing them down and reading their thoughts and projects. If I recall, rdane really liked his 3.4L version. I recall rdane did or participated in a long thread back then describing his journey in that project.

I am interested to hear about your project's developments. Please keep us posted- and good luck!

[mikedsilva]

Originally Posted by 911MANN

Hey, Mike: Sharing some thoughts here. I spent a long time determining my best route re: my 3.2SS project, and I read A LOT before making my final decision. BTW, I have been quite distracted in the last 6 months, but it's time for an update on my 'Prodified 3.2SS' thread, and I will do that before long. Here are some things I remember reading on your topic- hopefully, they will give you a bit of a short-cut to your destination.

I understand the intake air is the limiting factor, even in the larger 3.0L ROW CIS intake runners.

Brian of RarlyL8 in these forums has noted several times over the years his ability to modify FD and WUR for increased fuel delivery in racing applications.

Look up old Pelican Forums from 20 years ago, and you will find some information on topic. A member of that era going by rdane had great contributions based upon his project to blow-out his 911SC CIS engine to maximum displacement. One of the threads was called "CIS with a 3.2 or 3.4. Is it worth it?" I see several Pelican threads along those lines from 2004, 2005 and 2006. I suggest chasing them down and reading their thoughts and projects. If I recall, rdane really liked his 3.4L version. I recall rdane did or participated in a long thread back then describing his journey in that project.

I am interested to hear about your project's developments. Please keep us posted- and good luck!

hi and thanks for chiming in.
Yes I think I read a couple of those threads and noted how old them were. Suggesting that since it isn't often done, perhaps is isn't that successful.
Will try to find some of Rarly's old threads for reference... cheers

[Bill Douglas]

There was a 911 Turbo with CIS. The spec's of that may be worth looking into as fuel requirements may be similar.

[Schulisco]

Originally Posted by Bill Douglas

There was a 911 Turbo with CIS. The spec's of that may be worth looking into as fuel requirements may be similar.

All 3.0 and 3.3l Turbos (930 & even 964 turbo 3.3)were equipped with CIS. They run uber rich to prevent knocking and to keep the combustion temperatures within limits because of the lack of a knocking surveillance. Supercharged engines tend to start knocking due to high intake temperatures, too lean mixture, too aggressive ignition timing, hot engine and high ambient temperatures, etc. Supercharged cars (even old and modern ones) can be identified due to much soot around the exhaust..

I cannot imagine that a natural aspirated 3.5l engine may need/consume that much fuel as a 930 did, even on WOT...I suppose that the original 3,0l CIS may be still sufficient enough to supply a 3.5l engine, probably with a slight increase in mixture setting of the idle mixture screw. 3.5l is only a 16% increase from a 3.0l displacement, this value should a 3,0 CIS be able to deliver too. The 3.0l throttle valve will be more limiting in this case...
And before I start to mix up parts from other cars like the 930 I would definitely add a lambda gauge and if in the case of running lean I would add a push button to operate the cold start valve to give extra fuel shots when I notice lean running. Depending how often this extra fuel is required and if the idle mixture screw / CO screw is maxed out, I would start adding parts from a 930. But only then. Or - my way - I would develop a microcontroller to activate the cold start valve automatically instead of the manual push button. Or in a simpler way - by simply adding a microswitch to the throttle.
It goes without saying that such a heavy tuned engine must be optimized down step by step and very carefully...this is not an easy DIY job.

Thomas

[RarlyL8]

Yes CIS can be used effectively on a larger displacement engine. One caveat is cam profile; CIS air meter plate does not like higher lift/duration idle pulsing.
The challenge will be to keep the costs/modifications to a minimum. As posted, there are many ways to skin this cat. Without getting too far into the weeds, there are several choke points on your current system. IF your current CIS is the '78/9 with larger runners and the -031 fuel distributor you have a much better starting point. Unfortunately the displacement increase and other mods are going to outpace the 10% flow increase limitation of the SC fuel distributor. Other fuel distributors can be used, or the current FD highly modified, but now you are getting into system balancing and rebuild/modification costs which would also include the WUR.
Possibly the least expensive and invasive route would be to employ a throttle switch 7th injector. The SC CIS runners are equal length and fuel compatible. The cold start injector could be used for this purpose as it has been (although rather crudely) on turbocharged applications. The challenge would be metering the fuel during WOT as the RPMs climb. Some sort of raising rate regulator or frequency valve could be used, optimally based on AFR. This is not IMO the best way to add fuel but could be a viable less expensive option.
Another option (bear with me on this) is TBI systems such as the Holley Sniper. All of the choke points are eliminated. The only mod needed is a small sheet metal base plate that replaces the CIS air box and uses the OE intake runners. One of my customers did this with great success. Cleans up the engine bay, is very simple, and adaptable.

[mikedsilva]

Originally Posted by RarlyL8

Another option (bear with me on this) is TBI systems such as the Holley Sniper. All of the choke points are eliminated. The only mod needed is a small sheet metal base plate that replaces the CIS air box and uses the OE intake runners. One of my customers did this with great success. Cleans up the engine bay, is very simple, and adaptable.

hi
yes, a Holley Sniper is a candidate for sure. I picked up a second hand 2 barrel sniper and have an aluminium collector box ready to go. But I'm still going to try CIS first.

[jrwilson]

Originally Posted by RarlyL8

Another option (bear with me on this) is TBI systems such as the Holley Sniper. All of the choke points are eliminated. The only mod needed is a small sheet metal base plate that replaces the CIS air box and uses the OE intake runners.

I'd like to hear more about this option!

[RarlyL8]

If the focus is to remain on increasing the CIS capacity to fuel the added displacement we would first look at the fuel distributor. Let me know the part number and we will see if it is doable using that unit. The next potential restriction might be the throttle body. Need to know which CIS system you have to identify the choke points. If you have the '78/9 setup it's a better starting place.

I like the Sniper setup personally. It is very clean, simple, and it works. I've got pictures of it somewhere and will post if I can find them. Looks a lot like the carburetor picture posted earlier, just a TBI unit sitting on a custom plenum box. Eliminates all of the CIS clutter and complexity.