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Old 11-06-2018, 09:18 AM   #1
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3.4l 996 intake manifold on 3.2S motor

Gang,
looking to install a 3.4 intake manifold in my 3.2 equipped boxster.

I have the 987 airbox and maf, 996 throttle body, and customer intake tube already, so I'd like to put on the 3.4 manifolds. Also have 987 engine cover for more clearance.

I think I understand the necessary steps, but correct me if I'm wrong:

1. Aluminum lower runners required
2. Plastic upper plenums
3. Fuel rail from a 996. Is this correct?

install:

1. Drill and tap holes in heads
2. run shifter cables under plenums
3. ??????

Any other tips or parts necessary?

thanks.
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Old 11-06-2018, 09:58 AM   #2
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i looked into this and i *think* that you may have to fabricate a braze-on or somesuch out of JB weld to create a place to drill and tap for one of the spots required to attach the lower runners to the head.

and yes, fuel rail has to change - mounting points are different. you could fabricate new tabs on the rail if you are ballsy enough to weld a fuel line, but note that you have to be bang-on as it is only the two fuel rail fasteners per side that keep the injectors in.
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Old 11-06-2018, 10:25 AM   #3
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thanks. I don't mind getting new fuel rails from a 996. I'm assuming they just bolt on in reverse?

never heard the jb weld sitch on one of the intake runners though.
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Old 11-06-2018, 11:28 AM   #4
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well, the fuel lines run over the transmission end in a 996, and if you put a 996 intake on a 986 you have to reverse the whole intake (to get the TB over the transmission end) so the fuel lines will be in the right place when all is said and done. you'll have to figure out how to adapt the 986 fuel lines to the 996 rails - porsche looks to use 1-time barbed fittings, but i've read that with heat you can get them off with no damage and then just hose clamp them when reinstalling (perhaps with some fuel-rated thread sealant?). you'll also have to extend your brake booster vacuum line to the other end of the engine.

you'll have to take a hard look at your head; here's a good pic of a 996 manifold; i think you'll find that there is no spot on the head to drill and tap in at least one of the required locations:


https://www.ebay.com/itm/99-05-PORSCHE-911-996-CARRERA-LOWER-INTAKE-MANIFOLD-ADAPTER-PLENUM-9961101017R-/291880861094
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Old 11-07-2018, 03:55 AM   #5
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I've put a 3.4 intake on a 3.2. I believe all I had to do was drill and tap the heads. I used the 3.4 fuel system but had to use the 3.2 boxster wire harness. I went over it on my build thread.
Woody's build thread
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Old 11-07-2018, 05:49 AM   #6
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i stand corrected! post 243.
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Old 11-07-2018, 10:09 AM   #7
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woody, awesome, thanks. how did you run the shifter cables and were there any issues getting everything to fit?

thanks.
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Old 11-07-2018, 12:11 PM   #8
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Would Cayman 3.4 runners be more easily adapted?
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Old 11-07-2018, 05:50 PM   #9
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Originally Posted by Quadcammer View Post
woody, awesome, thanks. how did you run the shifter cables and were there any issues getting everything to fit?

thanks.
I trimmed a little bit of the upper engine cover area in the back so the intake tube wouldn't rub and a little in the front to clear the intake. Other people said they didn't have to do any trimming but did have to drop the motor an inch or so. I tried to run the cables under the intake but that didn't work for me. I can't remember why. I have them going over the top now with no real problems. I wish I had gotten the 3.2 dyno'd with that 996 intake, custom exhaust and 996 ROW tune. I bet it would be putting out the same HP as the 3.4 I have in it now.
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Old 11-08-2018, 04:07 AM   #10
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I also have the cables over the top of the intake but on a 3.4L. I currently have a hard top on but it’s coming out off soon when my suspension shows up I can grab pictures of the routing if needed. This is a 3.4 swap like woodys.
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Old 11-08-2018, 04:42 AM   #11
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sounds like over the top it is. If I have to lower the motor a bit, that should not be an issue when combined with the 987 engine cover.

thanks guys.
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Old 11-08-2018, 06:04 AM   #12
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Can you guys discuss what modifications were necessary to the fuel system and or 996 fuel rail to make this work?

thanks.
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Old 11-12-2018, 04:57 PM   #13
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Very interesting! Does anyone have power numbers or Dyno charts showing gains from using the 996 manifold on the 3.2? I'm really interested to see just how much power could be made with our 3.2. Given that the 2.0 in the 1967 911R & 904 made 220, why can't we get 350 from the 986 S motor?
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Old 11-13-2018, 09:33 AM   #14
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Originally Posted by j.fro View Post
Very interesting! Does anyone have power numbers or Dyno charts showing gains from using the 996 manifold on the 3.2? I'm really interested to see just how much power could be made with our 3.2. Given that the 2.0 in the 1967 911R & 904 made 220, why can't we get 350 from the 986 S motor?
My guess is the 3.2 heads won't flow enough to get it.....so intake, exhaust and significant head work are required. Porting, camshafts, valves / springs, cam timing. This restriction was of course put in place by design. I believe one can approach 300 with bolt ons but I have not heard of any being able to break through

Woody posted some surprisingly good dyno results from bolt ons and ECU tunning. I would link it if I could find it.

If we get into the heads and start doing it, how is the 3.2's propensity for head cracking mitigated? One could asks this for a total engine build as well.

I feel your frustration ......I remember track days where I just couldn't shake old 993 on my tail...
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Old 11-13-2018, 09:52 AM   #15
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well, the size of runners on the 996 plenum doesn't seem to be bigger than that on the 3.2, i think the difference is length - the 996 units are longer, so you will see more of a venturi effect and better cylinder fill at lower rpms. they may actually reduce max hp a bit as the increased length would be seen as a restriction at wot, but raise the overall torque curve up a bit. and more area under the curve is the goal, not necessarily the max number.

if you think about it from a porsche design point of view, the only reason the boxster runners are shorter is so they could fit the engine in the car.
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Old 11-13-2018, 02:33 PM   #16
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Quote:
Originally Posted by jaykay View Post
My guess is the 3.2 heads won't flow enough to get it.....so intake, exhaust and significant head work are required. Porting, camshafts, valves / springs, cam timing. This restriction was of course put in place by design. I believe one can approach 300 with bolt ons but I have not heard of any being able to break through

Woody posted some surprisingly good dyno results from bolt ons and ECU tunning. I would link it if I could find it.

If we get into the heads and start doing it, how is the 3.2's propensity for head cracking mitigated? One could asks this for a total engine build as well.

I feel your frustration ......I remember track days where I just couldn't shake old 993 on my tail...
These heads do,
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Old 11-13-2018, 08:31 PM   #17
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Quote:
Originally Posted by j.fro View Post
Very interesting! Does anyone have power numbers or Dyno charts showing gains from using the 996 manifold on the 3.2? I'm really interested to see just how much power could be made with our 3.2. Given that the 2.0 in the 1967 911R & 904 made 220, why can't we get 350 from the 986 S motor?
Back in 1967 the HP numbers were gross, not net. The difference is that they could measure the output with no accessories attached, open exhaust, no air cleaners, etc, in whatever temperature and conditions the maker wanted. Now the numbers are far more accurate, because the conditions of the measurement are standardized, and all the accessories are attached and functional.

Your 220 HP in 1967 would probably measure under 200 HP using the SAE net ratings.

You can read up about it here - https://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/
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Old 11-14-2018, 03:25 AM   #18
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Don't quote me on this but I'm pretty positive the difference between the 3.2 and 3.4 are the case and pistons when it comes to the long block. The heads are mostly the same but the 3.2 has slightly less compression. The only real difference between the two is the intake, tune and exhaust systems. I didn't feel much of a difference when I went from a 3.4, to a 3.2 with the 996 intake, fuel, and custom exhaust made with the same diameter tubing as a 996.
The seals inside the valve adjusters were going bad in my 3.4. I put the 3.2 in while i fixed the 3.4. I almost considered leaving the 3.2 in but I had lots of $$$ invested in the 3.4, so I reinstalled the 3.4. My box made 279hp at the wheels with the 3.4 and my friend mad 249hp at the wheels with his 3.2. Here's the thread Two modified boxsters on the dyno I contribute the difference in power between us to the length of the intake runners, mileage, tune and maybe the exhaust. I have a customer who owns a shop in Dallas. He claims to have made 300hp at the wheels with a 3.2. I tend to believe him as he works on some amazing vehicles and worked for Ruf at one time.
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Old 11-15-2018, 08:28 AM   #19
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These heads do,
Nice...good flow and no cracking? Details? Fitment on which engines?
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Old 11-15-2018, 08:54 AM   #20
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These heads do,
Indeed. Care to share specs? Bigger valves? where in the heads was the porting done, and how much larger are the runners now?

I've got the 74mm TB & a splitter in the intake (Pedros Garage). the rest of my intake is 3.2, but I know the TB made a difference. I wonder what an 82mm TB (GT3) would do. I've put this out there before, but my car made 244RWHP with all of the bolt-ons.
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