Carrera Intake for Megasquirt

[JohnJL]

I was planning on using my chopped-up airbox and refurbished intake runners from my 3.0 and mount the injectors tbitz-style in the runners. I also had my eye on that aluminum airbox another pelicanite had mocked up.

I was at my neighborhood shop this week and their tech was poo-pooing the CIS intake setup, even as modified for MS. I did point out that I extricated the cold-start plumbng. His points were:

1. The airbox volume was too small to create usable resonance.cylinder charging at any rpm

2. The port to the intake runners wasn't efficiently shaped. There was no "bell" to it.

3. The intake runners weren't tapered at all and any attempt to dremel out the inside of the intake runners where they meet the head was actually counter-productive as it was increasing the volume (and so slowing the air charge) at exactly where you want it to be at its max velocity. I actually agree with this one in theory.

He offered my a complete left-and-right side intake and throttle body (modified to accomodate a true TPS potentiometer) from a 3.2 for $300US. Sounds like a decent deal...

I also seem to recall I'd need different intake head studs?

So here's the question...can I hear from people who have tried a 3.2 intake as well as others with MS or any other EFI?

I am running standard 81 US 3.0 heads, DR20 cams and 9.5 JE Pistons...your info much appreciated.

[rfuerst911sc]

Maybe I am a dim bulb but I don't see the Carrera manifold being superior to the CIS runners. If you look at the CIS setup vs. the Carrera they look basically the same, you have 6 individual runners being fed by a single throttle plate. What am I missing? I am struggling with this decision myself as I want to EFI my setup this winter and am thinking the Tbitz setup that uses the CIS runners is the best approach for performance, cost and reliability.

[JohnJL]

I don't think you're a dim bulb, I'm asking the same question!

I do know the inner diameter of the runners on the 3.2 intake is larger (this is a ROW intake vs 80 USA 3.0).

Also there appears to be maybe 2X plenum volume with the 3.2 vs. 3.0 intake.

I would like to hear from people who have used them.

Back to Bathurst...

[randywebb]

I'm sure somebody has flow bench data - they may not want to share tho...

A lot depends on what rev range you will be at.

You can just look at them and get a rough idea...

Look at them both (from all angles) and repeat to yourself "fluids don't like to turn corners"...

[rfuerst911sc]

Correct me if I am wrong but the fluid is not making any bends in either setup, the fuel is being shot into the intake pretty straight in. It is the air that's making the bends. I can see where the Carrera intake and the 78-79 CIS runners because of their larger I.D. would flow more air at higher RPM's.

[Alan Cottrill]

Sometimes gases are fluid. I believe he is applying the term "fluid" to describe the action of air as it flows through the intake.

fluid describes the motion of either a gas or liquid.

liquid is a state of matter.

[randywebb]

Bingo.

both gases and liquids are fluids.

[randywebb]

oh yeh - I should add that once you have gas in the air stream you have other problems - the droplets can be deposited on the walls for example. But keep it simple for a first estimate.

[JohnJL]

Now we're getting somewhere...I suspect Noah's right about the mid-range torque all other things being equal, assuming that the 3.0 engine's torque is optimized with the CIS runners. Aside from straight-up velocity (which might be higher with the smaller-diameter runners), there mught also be beneficial wave/resonance from the larger and straighter plenum/intakes.

I am interested in hearing more about the "un-evenness" of the intakes to the different cylinders. I don't know a hell of a lot about the 3.2 engines...is there a consensus that some cylinders are starved/suffer knocking/overheating more than others?

[steand]

The 3.6 plastic intake is known to make a more even distribution off air into the cylinders. The 3.2 should have uneven cylinderfilling, that leads to uneven firing, since the teh petrol injected petrol is measured according to plenum vaccuum and rpm and temp; meaning that all 6 cylinder gets the same amount of fuel injected at a given situation, and that means to have even cumbustion in each cylinder, there must be sucked an even amount of air to make similar air/fuel miture in the cylinders.

Listen to a SC in idle, it deos'nt idle 100% steadily, the cylinders fires unevenly.

But remember the exhaust has also a influence on the cylinder filling.

I'm goin't to mount a 964 plastic intake to my SC next year, to convert to EFI.

[Asjac]

How much work is involved with chaning a 3.2 to the plastic 3.6 intake??

[mb911]

I am interested in this as well. I could make the aluminum boxes anyway we wanted even go with mandrel aluminum bends if that would maximize the intake . What about making them work much like a backwards header? Please keep this going I will be mocking up prototypes over the winter!

[steand]

The 3.6 intake has a 3 bolt pattern vs. the 3.2 2 stud mounting, so you need 6 adapters. Plus of course the intake system. Maybee you could run the 3.2 Motronic directly on the 3.6 intake, but to control the Vario Renonance chamber flapper, you need a more modern control unit, that has ekstra outputs.

I'm not sure about the difference from 3.2 to 3.6 but i think it was on http://www.rennsportsystems.com/2e.html i read about the differences or 9M racing in UK.

[David]

When I took the EFI101 class with Ben Strader he mentioned how good the Carrera intake was. He said he worked with a race team that tried unsuccessfully to build a better intake. I think that every Porsche intake flows better than the one before it and that we'd be hard pressed to improve on it, unless you go with ITB's or a slide valve.

[randywebb]

"I am interested in hearing more about the "un-evenness" of the intakes...:

- It is routine to use abrasive drilling mud to equalize the 3.2L intakes (aka "Extrude-Hone"). I agree the 3.6 ones will be lots better - assuming the dia.s are a match for what you want to do. But the thread started as a comparison of 3L with 3.2L - the 3.6 is another level of complexity. They are also a bit lighter BTW...

[randywebb]

"I am interested in hearing more about the "un-evenness" of the intakes...:

- It is routine to use abrasive drilling mud to equalize the 3.2L intakes (aka "Extrude-Hone"). I agree the 3.6 ones will be lots better - assuming the dia.s are a match for what you want to do. But the thread started as a comparison of 3L with 3.2L - the 3.6 is another level of complexity. They are also a bit lighter BTW...


re "every Porsche intake flows better than the one before it and that we'd be hard pressed to improve on it"
- I would say you are safe if you substitute "is better" for "flow" above - and almost as safe if you use "works better"
The factory is not trying to max. out flow or even hp -- or even achieve the best hp vs. mid-range torque curve... they ARE trying to optimize many many variables, including hp., mid-range torque, COST!, emissions, fuel economy, etc. etc.
So they don't have the same goals as the hotrodder, racer, or AutoXer ...

[JohnJL]

Anyone have empirical results on which cylinders are filled more/less with a 3.2 intake? Which cylinders are more prone to detonation on a 3.2?

[jpahemi]

My 3.2 intake flows (CFM) as follows:
(1) 290.3
(2) 298.4
(3) 297.7
(4) 294.6
(5) 300.6
(6) 297.1
From the #'s, I'd say cyl 1 get the least amount of air, thus runs richest.
These are Ex Hone #'s .
j.p.

[JohnJL]

Thanks JP.

Any others with pre-hone numbers? With experience with lots of a particular cylinder seeing detonation/wear consistently?

[KobaltBlau]

bump, pre-hone numbers would be really interesting. I wonder if this un-evenness is a wive's tale or not.