I remember that post. They are pretty small in terms of volume. I'm not an engineer or an expert in fluid dynamics, so I have no clue whats necessary, but in my redneck mind, more is betterer.

so i have a tap removal tool coming (don't listen to the internet kids, a 5mm hole is really too tight for an m6 tap, 5.5mm is much better), but even if I can't get that out, there are 2 other mounting holes nearby and a hold down plate will serve my purposes fine if it comes to that.


A word about drilling. The aluminum is soft and drills easily. The holes are roughly 15mm deep and the bolts extend about 12.8mm into the head, so drill accordingly. A piece of tape on the drill is sufficient to mark depth.

The drill block works fine but makes it hard to find your center punch divot, so there were 1 or 2 misstarts. Call it weight savings ;) To prevent further issue, I have done the following:

line up aluminum plenum with the ports
Use a 6mm drill bit with a sharp point as a punch. This fits very tightly in the mounting bosses of the plenum so you can accurately center. It works way better than trying to use a marker or paint.
Then I enlarge hole with center punch. Check and recheck alignment here.
Then I free drill a divot in that spot. Check alignment again

Then comes full drilling.

Drilling must be fairly accurate, but at the end of the day, the plenum aluminum is soft, so you can hog out the hole a bit to perfect your alignment, so if your hole is a little off center, no big deal.

hope this helps.

Great info!

Cant wait to see the finished project

few pics just for the hell of it
http://986forum.com/forums/uploads02...1548774647.jpg
http://986forum.com/forums/uploads02...1548774743.jpg
http://986forum.com/forums/uploads02...1548774873.jpg
http://986forum.com/forums/uploads02...1548774938.jpg

Great pictures.....thought there would be more room to withdraw / install air boxes though...without lowering the engine temporarily. I never have the time , facilities, or inclination to hack away at plastic from above.

It looks like the top surface of the plenum will be at the lip of the engine bay with the addition of the metal bases.....fingers are crossed. Others have done it so...

Just hope you don’t have to take a shapping hammer and English wheel to the cover

If the height becomes an issue, i will lower the motor to get clearance but would prefer not to exceed .5"

Probably sick of my posts by now, but drilled 4th hole on drivers side. 90 degree drill made it easy but youll need a buddy to hold the drill block. I free drilled and it turned out fine.

Not in the slightest. I'm watching this thread intently!

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Tap extractor worked, hole and threads are fine. Got my gaskets so hopefully some progress on sunday

No way man ...Keep the pictures and posts coming

Quick update.

1. I have 7 holes. You will need to remove alternator and aos to drill pass. Side but thats easy with everything out. Unintended benefit is that woth 996 setup, its easier to get to everything by taking off upper plenum only. So no fuel lines, aos lines or similar.

2. Although im marking well, my drilling has not been brilliant. The holes are straight but frankly off the mark. This i think is partly due to not being able to see your marks when using the drill block. If i was doing it again, i would likely go freehand.

I have managed to get everything together by enlarging directionally the holes in the lower plenum. Im not proud of it but drilling in situ, its somewhat unavoidable in my head. The ports in the head are bigger than the intake so you have some margin for error. As long as there is no protruding lip at the connection, you should be ok.

3. God the center portion gets gunked up. What a mess. Im not gonna make it perfect.

4. Im not sure the extent of this work will be worth the effort, but we'll see. Not too many power adding options that are cheap so the sweat equity is the cost

I was thinking of something similar to this tool for the job.....but there may end up being too little room to set it down.

Yeah that might work on the center holes. No chance on the outside ones.

gents, If i'm honest, the juice here isn't worth the squeeze (i can't imagine). This was an awful lot of work and I'm not even done yet.

If your 3.2 is on a stand, go for it. otherwise, unless you have time to kill, i'd skip it.

anyways, my current status and my fuel rail solution. Before you ask, its rock solid, the angle to the port is excellent and I only had to cut off 3 tabs.http://986forum.com/forums/uploads02...1549319664.jpg
http://986forum.com/forums/uploads02...1549319800.jpg

just to follow up. The AOS hose that runs from side to side is an epic POS and broke in 3 spots. Right into the trash with that. I will run an-12 braided hose to the factory end fittings with an internal spring to prevent vacuum collapse in its place.

I'm not sure how people don't lower the motor, but in my case, the passenger side plenum is right up against the top lip of the front firewall. I purchased .5" spacers and longer studs to lower the motor a bit.

Lastly, when reinstalling the fuel rail, make sure you have the harness above and to the outside of the rail. Found that one out the hard way.

This has been a long drawn out project but once I get the braided hose, I should be able to finish up in an hour or so as I have all the vacuum lines run and all of the harness plugged in.

I’m looking forward to seeing your results. I have a motor arriving soon and I have all the 996 parts from my recent teardown. The job that you are completing would certainly be easier with the engine on a stand. It will be fun to see what effect this has on performance. Are you using the 996 maf and tune?

I have a softronic tune and the stock maf in a 987 maf sampling tube.

Keep it up man....we all appreciate your hard work! This stuff takes a lot of time.

Yes, I can recall wanting to build a scaffold so I could lie over top of the car to do this kind of work. Inake work is a drag on this engine.

One thing I don't understand is the difficultly surrounding the fuel rails. Why cant the Boxster ones be used?

Will this level of assembly allow the airbox to come in and out with a reasonable amount of work?

Airbox should come out easily at this stage.

The boxster fuel rail tabs are just in the wrong spot. You cut them off and buy $3 worth of clamps rubber line clamps at home depot. They get tweaked and shortened a bit. Then you put a long m6 bolt through with one clamp ear above the intake and one below. Then put a nut below. That looks the fuel rail in solid. It took a bit of thinking but the actual doing it was fast and easy

So, how is it coming along? I´m really curious of this mod.. I have thought of all kinds of mods but you all know the cost/hp is really high. The usual "breathing improvement" with plenum, tb, airbox, headers, race cats.. Seem to give a slight improvement, but not that much really.. Could it be that a 996-intake is the ticket to real improvement? :dance:

sad to say its been a waiting game for parts.

So, as anyone who has dealt with the long AOS tubes, its a fragile pain in the ass. I initially ordered some an12 braided hose to replace it, but seems that was too small, so I have an16 hose arriving today. I lowered the motor .5" with some readily available spacers. Once the hose is in, it should be quick work. I should be done by saturday.

If you had all the parts ahead of time, this wouldn't be so bad. I'm working on it in little pieces, which is making it feel much longer.

Recommend you replace the "air breather" at the front of the driver side head where that hose will connect too.

did that when I swapped the motor in last year.

doing that is a real pain with the motor in the car.

Don´t mean to destroy the thread, but do "we" believe that the 996-manifold is the ticket to more power (in relation to the usual breathing-mods)? If I understand Woody:s posts correctly it sure seems that way.. I´ve always thought that the "next level" needs to be very expensive: turbo/compressor/larger displacement. But if we can get close to 300hp with the 996 manifold, that would be really great value for money

I´m also curious about how the lowering of the engine is done, what spacers? Pics?

I think the theory is that the 3.2L in the boxster makes 258bhp and the 3.4L in the early 996 makes 300bhp. Partly the differences are due to the airbox, which is truly pathetic in the 986, as well as exhaust.

With a 3.2L with a 996 throttle body, full exhaust, 987 airbox, pullies, and the plenum, it should produce as much or more than a stock 996 given the very small displacement difference.


As to lowering the motor.

The stock setup is some M10 by 83mm studs.

I purchased M10 by 100mm studs along with 4 M10 .5" spacers.

so you basically support motor, remove stock nuts and studs

Lower motor by .5" or more

slide in spacer, thread in stud, and tighten nut and you're done.

Took maybe an hour. I didn't lower the tranny as I believe the .5" difference should not cause any weirdness with drivetrain angles.

Its done, car runs pretty damn good. More details tomorrow

Damn, very cool!!! Looking forward to more reports!!

Thanks for a good answer! The "problem" I have in general is that I have seen any conclusive dyno figures on air-mods, many reports of "seat of the pants", and then on the dyno there isn´t much. Will be really interesting to find out how yours run when you have had the chance to evaluate.

Well, congratulations to you for your perseverance and thanks for keeping us in the loop! :cheers:
I will re-read this thread and consider doing this with the 3.6 intake manifolds, tb and fuel rails, etc that I already have from my 996 engine teardown. Since I already have the airbox in place and the headers and high flow cats, it may be worth the time and trouble.
And, of course, my engine will be on a stand! :)

Thanks for this any pictures of this set up? This arrangement sounds like the rear mounts which would lower the transmission would it not? I can't recall the exact configuration up front but would have thought that there would be no facility to lower there......I will have to did up my old mount and have a look

ok here goes. Might be a bit rambly.

General steps:

1. Drain pressure from fuel lines, remove battery cables, remove stock intake plenums, all associated vacuum lines, harness connections, and fuel rails. Be super careful with the AOS hose if you plan to reuse. Its a biatch to get in or out and if you flex it, it will crack.
2. Remove SAI pump if you haven't already done so to get plenums out.
3. Remove AOS
4. Remove Alternator and loosen a/ compressor.
5. Clean and vacuum areas in question, making sure to stuff towels or similar in intake ports
6. Mark, drill (5.5mm) and tap (m6x1x15mm depth) your holes. My holes were not perfectly located so I had to hog out aluminum intake risers. Not perfect, but good enough.
7. bolt down lowers with new steel gasket (make sure to slot gasket holes if you had to widen intake holes). Retighten a/c compressor and reinstall alternator
8. I used a 3/4" hose with hose spring to prevent collapse to replace that dreaded AOS hose. That will slot through the holes in the aluminum riser. I ended up using the 45 degree angle AOS connector from the upper AOS hose to make the angle better on the lower AOS fitting, but I don't think its necessary.
9. cut tabs off stock fuel rail, use rubber clamps with longer m6 bolt and nut to hold rail in place. On my model year, the regulator side rails is bigger than the other side oddly enough. Could not tell you why, but clamps will need to be sized accordingly (i used 3/4" clamps and slotted and shortened them as necessary.
10. bolt down fuel rail being cautious about how fuel lines are run.
11. Lower the motor by at least 1.25" using spacers. I ended up using some thick washers along with my spacers to make a more solid lowering arrangement. Any less than this and the damn passenger side plenum hits the body. At 1.25", its close, but it clears. I lowered the tranny about .25" by using spacers above the triangle brackets that hold the tranny. This is only possible with aftermarket mounts.
12. Cut the vacuum hose on the drivers side with the slide on connection. Run 5/8" hose with hose spring from the remaining line to the slide on connector piece to make a splice. The hose spring is necessary to prevent the hose from collapsing. Clamp with regular hose clamps, but don't go nuts
13. Route all your vacuum lines as necessary. You have the one from the fuel pressure regulator and one from the SAI (with check valve (blow in it to confirm which side goes where)) that go into the crossover boots so be mindful there.
14.Remember to hook up your crossover flap vac lines and electrical connector
15. Bolt on your upper plenums with new gaskets. 7.5 foot lbs on all intake bolts. Don't torque these yet, leave them in but loose.
15. squeeze in the crossover tubes. much easier with upper plenums installed but not bolted down hard
16. Install all remaining ancillaries, tighten all clamps, secure plenums, zip tie or otherwise secure wiring harnesses, etc etc.
17. I had to shorten my custom intake tube to make the angle better. Maybe 1" cut off did the trick.

Honestly, the hard part and long part was waiting for parts and trying to do stuff without removing nearby things that just made life harder.

Pro-tip, if you think it might be easier to do something with something else removed, just do it. wasting time trying to sort it out with the thing in the way will just frustrate

Pro-tip 2: Don't tighten much of anything until you have everything in place (does not apply to aluminum risers). Basically the upper plenums, hose clamps on the crossover, etc should stay loose till you're ready for final tightening.

Pro-tip 3: Upon start up, check for vacuum leaks and particularly fuel leaks. Have fire extinguisher handy. Luckily I had none of either.

Tools: drill, metric drill set with 5.5mm bit, m6x1 tap, drill block (optional, i probably would not use again), 90 degree drill bit holder the accepts round bits, variety of hand tools, maybe a dremel, utility knife

The car runs fine and power felt good, but its been a little while since I've driven. Real test will come when I get out to the track and can measure vmax at end of straights.

No pics right now as I was in a rush to finish, but since I still have to play around with a few things, I'll take some.

Wow! Great write up.
I’m worried about clearance with 1.25” lowered engine, 1.25” lowered car, and 2 litre deep sump.

I have the car lowered by like 1.5", with 2qt deep sump and its certainly low, but its not hateful. High manhole covers and the like need to be avoided.

Soo, how is it running now, have you had time to evaluate the performance?

So the car performs well. I would say that power is up across the board, but 10hp is not super easy to feel. Im way faster at lime rock then i was but the weather was more conducive also.

All in all, id say its a worthwhile mod if you get the parts cheap and can do the work yourself.

True data will come at lightning or tbolt as thats the best comparison

Nice write up! I love the fearlessness exhibited, too! Haha. A man after my own heart.

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I built a skid plate for mine and it has protected the motor quite a few times. It has rash marks all over it.

So, what is the general impression after the summer? Still happy? I'm considering wether to try this mod during the upcoming winter.

While I do believe it added a bit of top end power, I'm not sure its worth the trouble as the lower ground clearance and work involved. If you want the absolute last hp, do it, otherwise I'm not convinced.

Thanks, then I might settle for the easier mods, exhaust, airbox, maf, throttle body, plenum and tune!