3.0l CIS upgrades?

[911SauCy]

sell 3.0 for down payment on 3.6 vram swap...

[MichaelSJackson]

The biggest problem with CIS is that it requires a less aggressive cam. Any exhaust gases escaping out though the intake, pushes the big plate of the air-flow meter to move backwards, limiting fuel delivery. So no aggressive cams. The stock cam really restricts the engine.

Only real solution is to replace the induction so you can upgrade the cams.

However, if you want to keep the CIS and you have a US car, you'll get a significant bump by replacing the terrible exhaust with headers or SSIs (if you want heaters). Just a bolt-on change. You'll want to do this no matter what else you have planned. So first things first.

Another bolt-on I like is changing to an MSD-6AL with a matching coil. Lets you open the gap of your plugs. Not a big bump, but some and idles smoother.

Next, decide if you want to go further and replace the induction. If you do, here is where I'd pause and attempt to set your goals. Every change becomes dependent on the others. You'll get advise on lots of different and wonderful setups, but are their goals inline with what you desire from 911 ownership?

I'd like to point out that CIS cars can benefit from a weight loss program. Also, the suspension components are tired and could be renewed and/or upgraded.

Have fun!

[jac1976]

Originally Posted by MichaelSJackson

The biggest problem with CIS is that it requires a less aggressive cam. Any exhaust gases escaping out though the intake, pushes the big plate of the air-flow meter to move backwards, limiting fuel delivery. So no aggressive cams. The stock cam really restricts the engine.

Only real solution is to replace the induction so you can upgrade the cams.

However, if you want to keep the CIS and you have a US car, you'll get a significant bump by replacing the terrible exhaust with headers or SSIs (if you want heaters). Just a bolt-on change. You'll want to do this no matter what else you have planned. So first things first.

Another bolt-on I like is changing to an MSD-6AL with a matching coil. Lets you open the gap of your plugs. Not a big bump, but some and idles smoother.

Next, decide if you want to go further and replace the induction. If you do, here is where I'd pause and attempt to set your goals. Every change becomes dependent on the others. You'll get advise on lots of different and wonderful setups, but are their goals inline with what you desire from 911 ownership?

I'd like to point out that CIS cars can benefit from a weight loss program. Also, the suspension components are tired and could be renewed and/or upgraded.

Have fun!

“Aggressive” is subjective. A 964 grind and the Webcam 20/21 along with the SSI have been proven to help the SC even with CIS. No doubt, changing the induction opens up more power...along with your wallet.

[Rawknees'Turbo]

Originally Posted by juanbenae

OK pnutz, that one made me laugh out loud....

Ha ha, same here, C2 - really funny!

[MichaelSJackson]

Originally Posted by jac1976

“Aggressive” is subjective. A 964 grind and the Webcam 20/21 along with the SSI have been proven to help the SC even with CIS. No doubt, changing the induction opens up more power...along with your wallet.

jac1976,

You're right "Aggressive" is soft term. I have no idea of the performance goals desired. I'm just trying to provide a new CIS owner with some background for future decisions, without going into a multi-page description of all the possible paths forward.

And I've heard of many people bumping the cam a bit (ie. 964). But I don't get spending the money for new cams and the effort of opening the top end for that increase? Install a set of PMOs and have more freedom choosing a cam? Once you cross the line of replacing the induction, so many more paths are open to you.

My CIS had remained basically trouble free and adding SSIs made a nice Porsche so much better. I'm not pushing anyone to ditch their CIS, but it creates a performance ceiling.

Everything I just said is subjective.

[Coastr]

Is the advice to get carbs going out of date compared with ITB and EFI? Seems a few people are getting very good results from 3.0 with various ITB solutions and a bit of exhaust. Better economy and driveability, and just as much if not more power? Cost is constantly falling as kits are available. I know that if I was ditching cis carbs would be my last choice after simple Efi (old cis manifold), Efi w/3.2 intake, Efi w ITB and Efi w/turbo. For a street car carbs is a compromise.

[David Inc.]

I'm considering ITBs myself right now and I wouldn't consider carbs for a minute. Nearly the same cost except poor reliability, economy and not quite the same power as EFI? Not a good sell.

[Nux]

Originally Posted by Coastr

Is the advice to get carbs going out of date compared with ITB and EFI? Seems a few people are getting very good results from 3.0 with various ITB solutions and a bit of exhaust. Better economy and driveability, and just as much if not more power? Cost is constantly falling as kits are available. I know that if I was ditching cis carbs would be my last choice after simple Efi (old cis manifold), Efi w/3.2 intake, Efi w ITB and Efi w/turbo. For a street car carbs is a compromise.

This is a 3.0 with EFI/ITB setup in the very first stage of tuning. Look at the torque curve. We like. A Lot.

[emcon5]

Originally Posted by Nux

This is a 3.0 with EFI/ITB setup in the very first stage of tuning. Look at the torque curve. We like. A Lot.

What cam? 295 NM is about 218 ft lbs, which is quite respectable.

[Nux]

Originally Posted by emcon5

What cam? 295 NM is about 218 ft lbs, which is quite respectable.

I'm cheating a little here. It's a 10.5CR twin plugged 3.0 with DC24/21 grind cam.

I'm confident that we can get this baby to +310nm with a little fine tuning of the ignition. Top end should be better with a different muffler.

[MichaelSJackson]

Carbs vs. EFI:

Carbs are simple and they overcome the CIS limitations on cams. EFI can do all that and more, but the learning curve is steeper. At least for an old school'er like me.

I chose EFI because I wanted to learn about EFI. My original goal was to hot-rod my 3.0 and be period correct. I tried to imagine what Porsche would have done in 1978 if not forced to try and address emission standards, with the technology of the time. That would have been Webers, free flowing exhaust and an appropriate street cam? Today that means PMOs, SSIs and 993s?

Another reason EFI is more complicated is simply choosing which path to take. With carbs you just choose PMOs, unless you have to have Webers.

'78 SC w/BITZ

[Bob Kontak]

Originally Posted by Jack Stands

Have you seen Bruce Anderson’s book? I think that other than changing to 964 cams or increasing displacement, your options are limited with the CIS injection.

The bummer is the incremental benefit of each upgrade is small and the price is high.

If I remember Bruce said exhaust, SS 3.2's, cams and shorter gears is a very nice combination.

What's that gonna set you back?

[emcon5]

I have said this many times, but it is worth repeating. If you need to replace your pistons/cylinders anyway, it is silly not to go to 98mm pistons and cylinders. The cost difference is minimal, it will work with your stock induction system. It is a ~6.5% displacement increase, and the increase in power than comes with it, for a couple hundred bucks, which just doesn't happen with a Porsche engine. They just didn't leave that much on the table.

Look at it this way, in the late 70s-early 80s they were getting ~180 HP (210 HP for the euro SC) from an 2 valve N/A 3 liter engine with fairly mild cams. For comparison, the Corvette of the time made 190 HP, but it did it with damn near twice the displacement, 5.7 Liters (and got worse fuel economy, 15 vs 17 MPG). The V8 Mustang in the early 80s only put out 120 or 160 HP depending on which engine you got.

Look at it this way, if the Corvette was making a similar power level for the displacement as the 911 SC, it would have been putting out ~380 HP.

Originally Posted by MichaelSJackson

I tried to imagine what Porsche would have done in 1978 if not forced to try and address emission standards, with the technology of the time. That would have been Webers, free flowing exhaust and an appropriate street cam?

This seems unlikely. They abandoned carburetors in the late 60s, clearly because they thought fuel injection was better. If emissions were not a factor, I expect they would have stuck with Mechanical fuel injection, either an evolution of the Bosch they already used (to 1975 in places where emissions were not a problem), or the Kugelfischer found on 935 and the SCRS, at least until Bosch came up with an better (electronic) fuel injection system.

[MichaelSJackson]

emcon5,

No argument from me, about Porsche using MFI over carbs. Likewise, I feel the SCs are already a very nice car and I have no desire to attempt to make it into much more than it already is. One of the reasons I use the term "hot rod". If I need to replace something, I look at the upgrade options and pick what is appropriate for me.

I'd dismissed MFI so quickly, so long ago, that I just didn't even think to mention it as an option in what Porsche would have done if...

Thanks for filling in that detail.