GT3 82.5mm Throttle Body!

[Yellow986S]

Hey guys,

Would a GT3 82.5mm Throttle Body fit on a 2000 Boxster S?
I know that I will need a larger plenum to compliment the larger TB, is there anything else?

Will this larger 82.5mm throttle body create better performance numbers compared to the 997 76mm TB?

The IPD plenums are too expensive for just a plenum so I would rather go with a OEM larger TB and plenum for cheaper.

[JAAY]

Ipd is great if you can buy one.

[Shehadehd]

Originally Posted by Yellow986S

Hey guys,



Would a GT3 82.5mm Throttle Body fit on a 2000 Boxster S?

I know that I will need a larger plenum to compliment the larger TB, is there anything else?



Will this larger 82.5mm throttle body create better performance numbers compared to the 997 76mm TB?



The IPD plenums are too expensive for just a plenum so I would rather go with a OEM larger TB and plenum for cheaper.

I'm working on a similar conversion. I opted for the 75mm throttle body because the MAF tube has a 75mm inner diameter. If you decide to go with a bigger throttle body, be aware that the MAF housing will restrict the airflow anyways.

Also, if you get a 83.5mm throttle body you will need to pair it with a similarly sized plenum. Reducing it to fit into your intake manifold will most likely require some reducers.

Lastly, running the 83.5 throttle body/ plenum with the 75mm maf housing will cause air velocity to decrease because 3 inches of air will need to fill 83.5mm of space. This can cut low end torque and reduce air pressure at the cylinder heads.

I think to really benefit from the 83.5mm throttle body over the 75mm, you will want a larger MAF housing. Keep in mind, this will most likely require a fuel/maf remap. running with almost 1" more air might push your injectors to their rich limits, in which case you might run lean with the added airflow you get at high rpm and speed.

With all that being said, if you find a way to do it, go for it. I would love to be proven wrong because then I can follow with the larger setup

Someone else might also want to check my info as this was just a kick of the tires explanation.

[The Radium King]

from what I understand, the oem gt3 plenum is different that the m96 plenums and won't mate to your intake manifolds. the largest plenum you can get that will fit is the 997, and it won't mate to the gt3 tb. so, if you want to use the oem gt3 tb you have to get the ipd plenum.

an option may be to bore out your assembly - pedro offers this service.

otherwise, note that the oem intake design on the m96 is a reducing diameter style (on 986s: airbox to 75mm maf housing to 68mm tb; 997: 83mm maf housing to 76mm tb) this is to accelerate the air via venturi effect as it travels down the intake; the accelerated air facilitates engine breathing at lower rpm and increases torque. at higher rpm the reducing diameter can introduce resistance to airflow, so cars designed to spend extended time at max rpm (ie, track cars, gt3) just use the biggest tube possible. if you look at ipd dynos, cars with this product installed actually have less torque at low rpms but more hp at higher rpms.

so, as posted earlier, I think you might be wasting money and effort making your tb bigger than your upstream maf housing. you will kill low rpm torque without the high rpm hp benefits as you are still doing work to accelerate and then decelerate the air as it passes through the maf housing. you will probably get modified throttle response, however (similar to a sprint booster) where the power comes on earlier in the throttle pedal travel.

I don't think fuel delivery is an issue. I've never read of a 10 hp increase overwhelming the injectors, fuel pump, etc.

[The Radium King]

still going ...

if you want to go the ipd/gt3 route and increase your maf housing diameter, the cayman/987 is a match. further, the cayman/987 airbox is a HUGE improvement over the one that came with your 986. so, put in a 987 airbox and maf housing (the 986 and cayman/987 use the same maf) and you are now 83mm throughout. as already posted, this will f-up your cars tune, as the ecu uses the area of the maf housing to calculate airflow. this means:

1) hope the computer can adapt (if you search on this forum there is at least one person who has done such on track cars and had no issues);
2) expensive custom tune (Pedro is probably your best and least expensive option here); or
3) try to use an ecu map for a 996 3.4 e-throttle pre-variocam+. this map is designed for the larger maf housing diameter and *should* work on your car. cost would be the amount of time it takes your mechanic to push it with a piwis or pst2 (3 minutes). I eventually want to test this out but would love someone else to prove the concept ...

[Johnny Danger]

To the best of my knowledge, no one has recommended using a TB any larger than a 76mm or 78mm with at the M96 engine. Also, keep in mind, ideally the ECU should be remapped in order to adapt to the significant increase in air/fuel ratios. You should check out Pedro's kit for the 986.

[epapp]

Originally Posted by Shehadehd

Someone else might also want to check my info as this was just a kick of the tires explanation.

Nah spot on mate



Sent from my iPhone using Tapatalk

[Yellow986S]

Originally Posted by Johnny Danger

To the best of my knowledge, no one has recommended using a TB any larger than a 76mm or 78mm with at the M96 engine. Also, keep in mind, ideally the ECU should be remapped in order to adapt to the significant increase in air/fuel ratios. You should check out Pedro's kit for the 986.

Yeah after I have installed all performance parts I will get a ECU remap from Pedro but that will be at the very end. Can he do a custom tune for exactly what performance parts I have even if they are not his brand?
Like Fabspeed race exhaust and underdrive pulley

[Yellow986S]

Originally Posted by The Radium King

still going ...

if you want to go the ipd/gt3 route and increase your maf housing diameter, the cayman/987 is a match. further, the cayman/987 airbox is a HUGE improvement over the one that came with your 986. so, put in a 987 airbox and maf housing (the 986 and cayman/987 use the same maf) and you are now 83mm throughout. as already posted, this will f-up your cars tune, as the ecu uses the area of the maf housing to calculate airflow. this means:

1) hope the computer can adapt (if you search on this forum there is at least one person who has done such on track cars and had no issues);
2) expensive custom tune (Pedro is probably your best and least expensive option here); or
3) try to use an ecu map for a 996 3.4 e-throttle pre-variocam+. this map is designed for the larger maf housing diameter and *should* work on your car. cost would be the amount of time it takes your mechanic to push it with a piwis or pst2 (3 minutes). I eventually want to test this out but would love someone else to prove the concept ...

Is the 987 airbox a direct bolt on that I can swap? if not what needs to be done to make it work.

I understand now that the GT3 TB is too large and will do more harm than good unless I change the MAF, which I don't plan to do.

Can I use the 76mm 997 TB, 987 airbox, and Techno Torque plenum?

Will this affect the MAF and will I see any performance gains with this setup?
Thanks

[Shehadehd]

Originally Posted by Yellow986S

Is the 987 airbox a direct bolt on that I can swap? if not what needs to be done to make it work.



I understand now that the GT3 TB is too large and will do more harm than good unless I change the MAF, which I don't plan to do.



Can I use the 76mm 997 TB, 987 airbox, and Techno Torque plenum?



Will this affect the MAF and will I see any performance gains with this setup?

Thanks

I think TheRadiumKing has a long thread the answers just about any question you might have on the issue.

I'm not sure about the 987 airbox but there's a thread on it called 987 vs 986 airbox or something like that. It looks like a tad more than a bolt on

[The Radium King]

that's what I have - 987 airbox, maf housing from my 986 airbox, cayman tb (same as 996 or 997) and 997 plenum (I didn't see the need to pay the extra $ for the pedro unit). I am very happy with the result.

there is a thread here on how to modify the airbox to work - there is a 'muffler' on the outlet that needs to be dremmeled off, and an opening (where the outlet pipe opened into the muffler) that needs to be plugged - I used a waste piece of the muffler plastic and a $20 plastic welding kit off ebay to get it done.

to use the 986 maf housing, just saw it off your old airbox (smooth the edge) and fasten it to the 987 airbox.

you'll need a variety of silicone elbows and reducers, etc. for example, the 997 tb, while 3" (76mm) on the inside, is 3.25" (83mm) on the outside (thick metal lip). the maf housing, however, is approximately 3" ID and OD (thin plastic). so, you'll need to reduce to mate the two.

further, you'll have to make a hard 90 degree turn coming off the tb, as the 997 plenum (or pedro unit, as he just modifies a 997 plenum) doesn't angle like your oem plenum. i accomplished both by using a silicone 90 degree reducing elbow that goes from 3" to 3.25".

to attach the maf housing to the airbox you have a number of options. the airbox outlet has a flange on the end - you can saw this off and use a 3.25" to 3" silicone straight reducer to join the two (pls confirm the 3.25" dimension, as I didn't do it this way). or, I found that the 3.25" end of the reducer will press fit inside the flange, which is what I did (I inserted a 3.25" ring sawn off an old aluminum coupler inside the reducer to keep it from collapsing).

to join the whole assembly together I used a piece of the original ducting; inserted in the elbow at the tb end, and connected to the maf housing with a 3" silicone coupler at the other end. wrap in metal foil tape and done.

notes:

- airbox install is a ********************; I had to remove driver side intake manifold and bend up engine cover mounting tab to get it in.
- mounting points are the same for both airboxes, however, one point is a bolt on the 986 and a stud on the 987; I sawed the head of the 986 bolt, slotted it and made a stud out of it.
- you might have to jimmy your fuel tank vent line a bit.
- you can make fitting the elbow off the tb a little easier by sawing off the little flange on the engine compartment.
- may wish to incorporate an 'airflow smoother' to keep the maf readings stable - this is a honeycomb or mesh that sits in the airflow upstream of the maf. I got one off an old bmw maf pipe and fastened it to the end of the maf housing I had fabricated. does it do any good? no idea.

[Johnny Danger]

Originally Posted by Yellow986S

Yeah after I have installed all performance parts I will get a ECU remap from Pedro but that will be at the very end. Can he do a custom tune for exactly what performance parts I have even if they are not his brand?
Like Fabspeed race exhaust and underdrive pulley

I'm sure he can. Also, FVD/Brombach can create a custom file based on mods as well.

[Bigsmoothlee]

From what I understand the IPD plenum gives a lump of torque much earlier in the powerband due to its shape... I think 83mm is overkill for your typical boxster, with the 75mm throttle being just right.

As for the original poster, with a 3.2 you'd probably be better off installing a 996 intake manifold to go along with the cayman S airbox, since thats where the power is really restricted. There was a thread on Rennlist where a 996 owner installed a 3.2 in place of his blown 3.4 and didnt see a huge decrease in power...mostly because he used the 996 intake and exhaust.

[onaFLYer]

Originally Posted by Shehadehd

I think TheRadiumKing has a long thread the answers just about any question you might have on the issue.

I'm not sure about the 987 airbox but there's a thread on it called 987 vs 986 airbox or something like that. It looks like a tad more than a bolt on

I actually started that thread sooo long ago, two years maybe, and my car still has minor issues with the maf and low speed drivability. Make sure you really want to take time to sort things out before making changes like this.

[The Radium King]

odd. i've had no issues. when i first did the tb mod i hadnt swapped the airbox yet and was using a bmc airbox with an oiled filter which fouled my maf. once i got the airbox in every thing has been perfect, with a season of track days to confirm.

[onaFLYer]

It seems to be the larger maf housing from the 987 that causes my issue. I put a restrictor inside it to make inside diameter smaller, which helps some. Had two different softronic tunes, one works slightly better other not at all. I need to use the original maf housing from stock box and adapt it on there I guess. Just dont want to go that route until I can afford IPD and larger tb, Too many other hobbies....Just turned 10, 000 miles on engine in two years.

[The Radium King]

oh yeah, the larger maf housing confuses the computer - repurposing the oem maf housing fixes all that. meir is selling his larger tb setup for cheap - might be of interest to you. i also recall a post from jaykay where he talked with softronic and they cant (or have no interest in) revising the maf map that converts maf reading to airflow.

[Bfan]

Do you guys think one could wire up a adjustable resistor on the MAF signal wire (instructions can be found online) and tune the voltage with the aid of a "Air fuel ratio gauge", to make the OM tune work with with the bigger (996/Cayman) MAF housing? Just a thought

[Bigsmoothlee]

Originally Posted by Bfan

Do you guys think one could wire up a adjustable resistor on the MAF signal wire (instructions can be found online) and tune the voltage with the aid of a "Air fuel ratio gauge", to make the OM tune work with with the bigger (996/Cayman) MAF housing? Just a thought

Why not? People have been tuning jap cars since the mid 90's with a S-AFC which essentially modifies the MAF signal to the control unit. If you install a wideband A/F gauge to go along with it, you have a pretty good start on fine tuning.

[onaFLYer]

I've read posts on doing this, and I am considering it. Just bought a throttle body and plenum from Meir and plan on re-locating my maf housing with the original setup adapted to my 987 air box when it shows up. Hopefully this will cure some if not all of the nagging issues I've had. Plus add some hp with the larger tb & plenum.

Sorry for the post hi-jack OP.