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Join Date: Dec 2006
Location: Pretoria, South Africa
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Please show me your custom intake manifold!

Hello all,

I would like to replace the CIS on my 79 SC. Replacing it with ITB is well documented. What I would like to know is the pro vs. cons of ITB vs. a custom intake manifold.

What should I take into consideration? Recommended lengths, shapes, size of injectors etc. etc.

I will be running standalone management and ignition coils.

If you have pictures and specs it will be greatly appreciated!

Many thanks in advance,

F.

P.S. Engine internals are stock and I would like to keep it that way.
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1979 Porsche 911 SC

Last edited by FrancoisJoubert; 01-06-2007 at 06:55 AM..
Old 01-06-2007, 01:24 AM
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Stock Porsche manifolds are very hard (if not close to impossible) to beat. If you want something better than an SC manifold, get a Carrera 3.2 manifold. If you want something better than the Carrera manifold get the 964 manifold. Etc.
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Old 01-06-2007, 07:00 AM
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Unfortunately they are not that easy to locate around here :-( That is why Im looking for alternatives...

Has anyone attemted this?
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Old 01-06-2007, 09:57 AM
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Francois,
Shipping isn't as bad as you think. I believe there is one or two for sale on eBay so you may want to ask about shipping to France. There is usually at least one available and sometimes some Carrera fuel injectors as well.
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Old 01-06-2007, 02:10 PM
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I shipped a 914-6 oil tank to France for about $30.00, with the US Postal Service, 5-8 day service. The box was approximately 18X18X6 inches, and weighed 10 lbs. In metric, I'd guess 50cmX50cmX13cm, and 4.5 kilos.
I have no idea how many Euros.
Old 01-06-2007, 09:23 PM
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Shipping to South Africa will be atleast $100.

Also, I dont like all the plastic, cables etc. on the Porsche manifolds. I love the look of the ITB, nice and clean... That is another reason Im thinking to build the custom intakes, to clean up the engine bay...
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Old 01-06-2007, 10:04 PM
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How about a Carrera 3.2 aluminum intake. You could polish it.

I talked to a guy that did a lot of work and spent a lot of money trying to better the Carrera intake and he couldn't. If you're going for looks that fine, but I wouldn't expect to gain power from a custom intake.
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Old 01-07-2007, 06:06 AM
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I found this in another thread, I think it was from a 3.8 RSR. Im considering building something similar. It should provide a really wide flat torque curve seeing its a fairly long path for the air to travel.

One question I have around this intake is how does the air get to the connecting pipe closest to us, the one connecting the two halves so to speak?!?!?!

Do you think it could work? I like experimenting
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1979 Porsche 911 SC
Old 01-07-2007, 08:00 AM
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Hi there,

If you are going to make up your own intake, why not consider going the ITB route. The consensus thus far in this thread is that you would not be able to improve on the 3.2 Porsche manifold.

The ITB option is costly, especially for those of us in RSA, but there are other options.

You will need a lot of design time to get the benefit of the pulsing in the plenum. This is much easier with the ITB option. You only need to worry about the pulses in the individual intakes.

Here is a pic of the setup that I have been using in some or other form for the last two years. All parts are available locally, and it has been fun.



I am busy making up a new setup for my car, which will be ready by about March. This will operate with the new ECU.

I hope this helps.
Old 01-07-2007, 08:19 AM
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WOW, that looks really nice! :-)

Please can you elaborate on your spec, cost involved as well as who did the work...

Also, how is your 911 used? Road/Track etc.

Many thanks!
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Old 01-07-2007, 08:36 AM
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Hi Francois,
The car has evolved from a standard 911 SC to a 3.2, 300 HP monster. I currently race in the Porsche Challenge series.

The car is very streetable, with the exception of no fast idle on cold start. When starting in cold weather, it will idle at about 500 rpm for a few minutes, and then it's fine.

I did all the work myself. I used the base of the SC manifolds and merged them to the existing manifold, the the throttle bodies cam with. The throttle bodies cam off a Toyota RSI.

The throttles are 45 mm diameter.

The trumpets and the air filters with the Madonna style injection was also manufactured.

In the chase for more HP, I will be improving on this design, which will also make a sleek, minimalist look in the engine bay. The new intake and ECU will be set up on the current motor, and once everything is working will install the 3.5l motor that is yet to be built.

I hope this gives you inspiration.
Old 01-07-2007, 08:50 AM
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Definitly

Im not as brave as you though, Im keeping the internals stock for now...however long "now" turns out to be, I dont know yet

A friend of mine suggested using M3 throttle bodies and injectors coupled with VR6 ignition coils, what do you think?

Apart for the RSi ITB, what other cars ITBs could be used?

Would it be possible for us to get together sometime, I can really do with the advice...
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Old 01-07-2007, 09:00 AM
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This is the high butterfly setup our shop is currently using for individual throttle bodies. The black intake stacks and adapters and linkage is of our own design.

We also use the factory 3.6 plastic intake with good results with EFI.

Rothsport Racing
Tualatin, Oregon

Old 01-07-2007, 09:38 AM
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Any idea of what hp/torque figures Im looking at with ITBs and standalone management on a engine with stock internals? Im trying to decide if it will be worth the expense and time...

Also, will I have enough flexibilty in the system if I decide to start working the internals? Too what extent will this be possible?
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Old 01-07-2007, 09:42 AM
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The individual throttle bodies are better suited for race applications than for street driven cars.

See the dyno sheet below for a stock internal 3.0 Euro engine with single throttle body, DTA EFI, and 3.6 plastic intake. It also has 1.5 inch headers with performance muffler.

Old 01-07-2007, 10:04 AM
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Thanks for the info RSScotty :-)

The vehicle would be for spirited road use and the occasional trackday. If possible I would like some flexibility to develop the internals further before having to do major upgrade to the EFI should I wish to develop it more for the track at a later stage.

Considering the dyno chart you just posted, would I be better of with something like the RSR intake manifold I posted earlier based on my needs above?
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Old 01-07-2007, 10:25 AM
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We have found that the RSR intake you posted a picture of is not suited for a 3.0 liter engine. It works best on big blocks (3.8) with large airflow capabilities.
The biggest bang for the buck is still with the 3.6 intake for a street and sometimes track car. With the resonance flap, it fills in the torque better in the 3800-5000 rpm range compared to an engine with individual throttle bodies.

If you are concerned with the appearance of the 3.6 intake, you can always paint it to a color of your choice...and remember it does not use the factory air flow meter when you go to EFI....you adapt a air filter like a K&N right off the OEM throttle body.

The other option is to use 6 indivdual throttle bodies ( these install in between the cyl. heads and the 3.6 intake) instead of the factory single tb. We still use the factory throttle body, we just delete the throttle plate. This makes for instant throttle response and gets along better with race type camshafts so you can make the engine idle.
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Here is the standard Jenvey set up, with their manifolds. Same throttles as RSScotty's shop uses but they have their own taller manifolds and much better linkage. With the standard Jenvey stuff you need to adapt their cable to the bellcrank on the transmission (not too big of a deal).





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Old 01-07-2007, 03:53 PM
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This is in my 914-6.



I have a full solids cad file on it if you want it.
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Old 01-08-2007, 09:56 AM
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I don't doubt that Porsche built a "good" intake. Fact, I'm probably going to use the 3.2 intake on my turbo for ease. BUT, Porsche kept improving and developing their intakes so even they weren't completely happy. They, though one of the best engineering firms, are under different restraints than an individual. There is going to be a trade off running an intake ideal for a 3.6 on a 3.2 though maybe a miniscule issue and to the performance stance possibly mute.

I'd use Porsche's research for runner length and plenum size. I'd also do a lot of research to determine best taper angles and modify length depending on the rpm YOU plan to use. You could improve on flow at the intersection of the runners to plenum. Many have argued that the stock TB and opening are restrictive.

Saying the above, I'm going with Jenveys for my NA since I still like the response of my MFI and ITB's. Fun over pure numbers for the street because if I just wanted fast I'd buy an EVO for the street.
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Old 01-08-2007, 03:07 PM
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