3.2 CIS questions

[C3-R]

So I have 1974 911 hot rod with steel 930 flares, a dp front spoiler and rear bumper and a 3.2 CIS motor built by RUF when they were doing the original SCR cars back in the early 80’s. The motor recently dynoed at 193 at 5600 rpm and 205 tq at 4000 rpm at the wheels on a dynapack dyno. It has SSIs. I’ve been researching on the forum to see if there are any ways to potentially get a little more power out of the engine and understand that the cis is a limiting factor especially with going for hotter cams. I believe the compression ratio is 9:8 which is I believe higher than stock. And the motor hasn’t been apart under my ownership so i don’t know what cams or pistons are in it. Because the motor is healthy there’s no reason to disassemble other than to check what internals it has. All that being said I was thinking a modern fuel injection system would help but there’s a part of me that thinks PMO carbs would be a cool old school touch and feel. What gains could I realistically expect to achieve by going with either modern fuel injection or carbs? Thanks in advance.

[targa72e]

I went the opposite direction back in the day on my track car.. I started with a 3.0L big port SC motor 8.5 to 1 with SSI's. I had installed a 3.2 Carrera intake with programable FI on the motor for more power. I tuned this the best I could on the dyno and it did make more power. I then decided to back to stock class and reinstalled the factory CIS. The dyno below shows the difference.



You can see the CIS does a little better from 3.5K-4.5K RPM. From 4.5K up the 3.2 manifold is much better.

I eventually rebuilt the engine and installed later 9.3 to 1 pistons with the CIS and got much better power with a fresh engine and more compression. I would have liked to run the 3.2 manifold with the rebuilt engine but never did. Dyno below is my car and another in my class with same build specs. 3.0L big port, later 9.3 pistons, headers and good exhaust, advanced cam timing and good flowing muffler.



I would expect to get 20HP+ with a better intake system.

john

[Mixed76]

Nice comparisons John. Stock SC cam?

Sent from my Pixel 7 using Tapatalk

[C3-R]

Thanks John. Good stuff.

[mepstein]

Be careful with the new PMO’s. They aren’t what they used to be.

[Classic 911]

If this engine is an original RUF SCR and it was mine I would restore it to 100% originality.

It had 215 hp at the crank when new so to make 193 at the wheels. That’s approx 230hp and 327Nm torque at the crank. This is just mind-boggling numbers, even with SSI’s

You have a real great and healthy engine

Specs:
Power Output (DIN) 158 kW (215 bhp)
at Engine Speed 6,000 rpm
Specific Output 49.6 kW/L (67.5 bhp/L)
Displacement 3,185 cm3
Compression Ratio 9.8 : 1


https://en.m.wikipedia.org/wiki/Ruf_SCR

[C3-R]

Thanks Classic.

[911MANN]

C3-R:

If you continue down the path of refreshing your CIS for your high-performance 911, you might check out my Engine Rebuilding Forum thread entitled "The 'Prodified' 3.2SS". I am just finishing up this project and beginning to undergo real-world testing and evaluation of my higher-performance engine formula, which keeps CIS. I had hoped this final part of my project might be fairly uneventful, but we shall see......

[targa72e]

Originally Posted by Mixed76

Nice comparisons John. Stock SC cam?

Sent from my Pixel 7 using Tapatalk

Yes, stock SC cams.

John

[C3-R]

Thanks 911mann.