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Larry_Ratcliff 02-03-2007 12:20 PM

Advantage of 3.2 intake over 3.3 turbo intake?
I searched through this forum for carrera intake conversion trying to find out what the advantage is. The reason that I was looking is that I was thinking that there would not be a significant advantage of the 3.2 intake over a 3.3 intake with injector bosses under the iintake runners.

Is it for the longer intake runners?

Larry Ratcliff

RarlyL8 02-03-2007 12:46 PM

The Carrera intake is popular for EFI conversions. The stock flat "pancake" 930 intake is not an optimal design when it comes to flow.
The intake port sizes are different on a Carrera vs 930 so you would need to address that issue.
Many have done EFI conversions using the Carrera manifold, someone will chime in with their personal experiences. Do a search using the 911 forum, a ton of info should come up for you.

Porschefile 02-03-2007 01:02 PM

I'm no expert but, the basics are that the 930 intake is designed for torque and the 3.2 intake is designed more for horsepower. Some obvious differences is the 3.2 Carrera intake has a significantly larger plenum area. The Carrera intake does appear to have longer runners but, hopefully someone that knows for sure can chime in to verify this. For forced induction applications, larger plenums are more desirable for creating horsepower as they are less of an intake airflow restriction. With the Carrera intake you will probably see a bit less peak mid range torque, and you will be able to maintain torque/hp higher in the rpm without quite as much of a drop off on the top-end. For forced induction, IMO it's worth it.

Larry_Ratcliff 02-03-2007 02:06 PM

Based on what I am hearing. It sounds like the carrera intake would cause more of a lag than the stock intake. I would take low end torque over high end HP any day for drivability. It would be very interesting to see a comparison between the two intakes on the same engine ... both torque and HP curves.

NathanUK 02-03-2007 02:44 PM

The carrera will flow more than the 930. Iirc the 930 manifold is only good for 500bhp at the crank, after that it is losing you max power.

Porschefile 02-03-2007 03:58 PM

The thing is though, there won't be any significant or detrimental decrease in low-end torque. The Carrera intake isn't exactly a short runner manifold like you'd find aftermarket for a Honda or anything that would completely kill the low-end. It's just that the 930 manifold is so restrictive. Just remember, torque at higher rpm equals more hp, which gets more work done. Stump pulling torque at 2-3k rpm doesn't necessarily make your car faster if your hp/tq is practically plumetting off the face of the earth on the top-end. ;)

Jim2 02-03-2007 04:26 PM

From what I recall in my younger days of tuning, a shorter intake runner lends to pulse tuning at high rpm, longer intake runner is required for low rpm. On the other hand exhaust headers are the opposite. I have a book on manifold and header design which I could reference.

The 930 intake manifold shape and size appears to be a space compromise as result of the amount of other "stuff" needed in the engine compartment: air plumbing to/from the turbo, intercooler, air metering box, priority valve, air filter housing, etc.


BoxxerSix 02-03-2007 10:44 PM


Originally posted by Jim2

The 930 intake manifold shape and size appears to be a space compromise as result of the amount of other "stuff" needed in the engine compartment: air plumbing to/from the turbo, intercooler, air metering box, priority valve, air filter housing, etc.


Yes that is correct due to the size and space occupation of the CIS assembly atop the manifold. Hence the reason the 3.2 manifold is a good excuse for an EFI conversion.

If I had kept my 965, this would have been my next mod as the Tec3 sitting next to me needed a home and was calling to my car. Still needs a home, but one is coming soon.....

Craig 930 RS 02-04-2007 08:04 AM

The Turbo manifold absolutely sucks for even air distribution.
Uneven air distribution = uneven AFRs from cylinder to cylinder, etc etc

The world is waiting for a miracle manifold for CIS users.....

RarlyL8 02-04-2007 11:45 AM

The only way you can accurately compare a Carrera intake to a stock 930 intake is by doing an EFI conversion using a stock 930 intake - both on the same engine. I have never seen that done on the same engine.

What you choose depends greatly on what your goals and budget are. Carrera manifolds go for around $250-500 depending upon condition and EFI equipment.
The 930 manifold will support 500HP so it isn't a horrific piece.
The Carrera manifold might better lend itself to a 400+HP application where head work is going to be done (you must do something to address the difference in port size from stock 930 heads and stock Carrera manifold).
The Carrera intake makes an EFI conversion easier if you plan to use the Motronic system of the 3.2L engine.

Craig 930 RS 02-04-2007 12:05 PM

Good point. I have.

A local guy had a MOTEC EFI conversion done......with the stock manifold. He was disappointed in the results. 420 RWHP I believe was the max which is right about 500 FWHP. I don't recall the head work/porting etc that was done.

Realize that this by itself is not a damnation nor approval of a stock manifold, but rather a potential showing of the limitations that a stock manifold will produce - when this engine was compared to a nearly identical engine with a Carrera manifold.

I believe the Carrera manifolded engine had another 40hp.
YMMV, take this for what it is.

SCHNELE 02-05-2007 05:34 PM

The longer runners bode well for more low end torque, you guys, think volumetric efficiency on a blown car. The Carrera intake will outflow the restrictive 930 intake.

hobieboy 02-06-2007 05:14 AM

I'm not trying to argue that 930 intake is superior, but Brian has a good point - Anyone who uses the Carrera intake needs to do something about the port size.

And I bet 99.999% of them ended up enlarging the port on the head. The engine becomes a much better air pump; hence more power (assuming everything else is the same).

But now its a much more costly route...

JimCulp 02-06-2007 05:23 AM


Originally posted by SCHNELE
The longer runners bode well for more low end torque, you guys, think volumetric efficiency on a blown car. The Carrera intake will outflow the restrictive 930 intake.
I was under the impression that shorter runners were better for low rpm torque and longer runners produced better high rpm HP hence the design of Varioram.

Garen 02-06-2007 06:02 AM

Waiting for experts to chime in, but I do believe that longer runners are good for torque, while shorter runners aid in high RPM HP. That is why most systems out there, varioram included, will effectively cut the length of the runners as the RPM's go up. I think that the main reason for using the Carrera intake is the simplicity of running the fuel rails (you can just buy existing, proven 3.2 rails and lines), coupled with the better flow characteristics and port sizes, and also, because it has become the norm. It's kinda like the engine equivalent of a ducktail spoiler for an early car! Plus, the basic runner/plenum design is very similar to later manifolds, like the 964/993 cars.

The design of the 3.3 manifold seems to have been compromised more for packaging issues than for sheer flow. It was the only way they could get the CIS hardwar, the IC, A/C, smog pump, etc under the lid. They probably figured that the positive manifold pressure would compensate for the intake's shortcommings.

An interesting test would be to run a non-turbo motor with an EFI/3.3 manifold, vs the 3.2 Carrera. You would really see the differences then.

On another note, it is intersting that the TPC 993 supercharger package uses the basic 3.3 pancake manifold design as well. Packagin needs, I suppose.

JimCulp 02-06-2007 06:14 AM

Actually Garen and SCHNELE I think you are right- I had it backwards.

Craig 930 RS 02-06-2007 07:09 AM

It's two things:

Balance between runners
CFM capacity

WERK I 02-06-2007 08:56 AM


Originally posted by JimCulp
Actually Garen and SCHNELE I think you are right- I had it backwards.
Nope, Jim, you were right. Long runners shift the Volumetric Efficiency of the engine towards the higher end of the RPM range. Look at it from an inertia perspective; a column of air at rest, tends to stay at rest. A column of air in motion, tends to stay in motion. Longer runners increase the cylinder filling efficiency at high RPM's......kind of a ram effect. If you look at the Can-Am cars of an earlier era, you would find the normally aspirated engines were tuned to the track they were running. High speed tracks like Road America, the engines had high stacks. But on shorter tracks, where exit speed made all the difference, short runner tubes were used.

Rob 930 02-06-2007 09:27 AM

If anyone has any interest in the flow numbers from Carrera manifolds, here's a link to an old thread I started when I was building my engine:

It doesn't compare 930 with Carrera manifolds, it only compares Carrera manifolds before and after Extrude Honing.

Jim2 02-06-2007 09:50 AM

F1 car 19,000 rpm: 2.5" intake runners

Buick V6 FWD automatic 2500 rpm: 17" intake runners

Porsche V-ram and non V-ram have the same peak HP, but he V-ram has more mid range torque resulting from Porsche adding intake runner length as seen on the top of the intake manifold.

Overview: Exceeding 100% volumetric efficiency on a reciprocating internal combustion engine requires "pulse" tuning, among othere things. This "pulse" occurs when the moving column of intake charge is stopped by the intake valve upon it's closing, the moving charge column bounces off the back side of the intake valve and reverts the othere direction up the intake runner leaving a region of low pressure behind itself. At an optimal intake runner length the reversion wave goes right out the end of the velocity stack, at which point the differential pressure drives new charge back down the velocity stack. If the intake valve is open when the reversion wave arrives theree is an opportunity to impact the cylinder with charge exceeding atmospheric pressure. There is really lots of stuff going on, more than meets the eye. A 930 intake would be suited for an RPM well beyond the engines mechanical limit, except that there IS NO PLENUM eithere...

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