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Old 06-15-2015, 10:46 AM   #1
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What can you tell me about the 74mm TB?

I am working on my 996 turbo.

I realize the 986 and 996t share the same throttle body, 68mm
part number 986 605 115 01

Then I saw a 74mm throttle body from a 2.7 boxster, but all my part references show the same number for all 986 boxsters.

So does the 74mm come on the 987?

If so, are they interchangeable?

Thanks!
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Old 06-15-2015, 11:30 AM   #2
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my understanding is that 996, 997, and cayman/3.4 987 boxster tbs are all interchangeable and 74mm ID. tt runs a smaller tb because the air is compressed and you don't want to uncompress it by increasing the pipe/tb diameter.
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Old 06-15-2015, 01:09 PM   #3
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interesting... it seems if you buy an IPD plenum they say you need to use the 74mm TB, but I'm wondering if the 74mm TB is a direct bolt on.

My 996 is running 1.55 bar on bigger turbos, so I'm not worried about de-compressing.
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Old 06-15-2015, 02:34 PM   #4
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Welcome, it's a popular mod discussed quite frequently here for rather cheap. About 20 or so hp by adding the 74mm TB+ 997 Distribution-T and 987 Air intake box. I'm about to embark on that mod myself.
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Old 06-15-2015, 02:42 PM   #5
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I realize that. I'm not working on a 986 so I'm trying to understand if the 74mm TV will work with my oem plenum.


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Old 06-15-2015, 03:01 PM   #6
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Quote:
Originally Posted by Lapister View Post
Welcome, it's a popular mod discussed quite frequently here for rather cheap. About 20 or so hp by adding the 74mm TB+ 997 Distribution-T and 987 Air intake box. I'm about to embark on that mod myself.
Is there dyno data available to support that?
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Old 06-15-2015, 05:35 PM   #7
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What can you tell me about the 74mm TB?

Seems that I have found my answer. The 74mm TB which is a 997 part number does not work on the 996 turbo oem plenum.

Sort of sad since the cost of the 986 part number is almost triple that of the 997.

As JFP said... Even in the highly modded 996t world I haven't seen convincing enough data to drop that much money into buying the nearly 1000 plenum to make it work on my car.

I make 700 to wheels with the small 68mm TB. I just figured if it was cheaper to get the 74mm is give it a shot since I have to replace the TB anyway.

Last question, in the 986 community, do you guys find TB failure common?





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Old 06-15-2015, 05:55 PM   #8
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Originally Posted by stilov View Post
I make 700 to wheels with the small 68mm TB.
Could you elaborate a bit more, Please..?
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Old 06-15-2015, 05:56 PM   #9
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On my 996 turbo not a boxster.


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Old 06-16-2015, 12:02 AM   #10
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Originally Posted by JFP in PA View Post
Is there dyno data available to support that?
I have dyno'd my last S before and after the 74mm throttle body, 996 plenum and larger MAF to tb intake. It gave a little over 5bhp.
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Old 06-16-2015, 02:28 AM   #11
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I have dyno'd my last S before and after the 74mm throttle body, 996 plenum and larger MAF to tb intake. It gave a little over 5bhp.
That is more inline with what I would expect.
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Old 06-16-2015, 02:59 AM   #12
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I don't have a previous dyno number to compare my added hp from the mod Lapister listed, but it's way more then 5 hp. EDC didn't list the mod Lapister listed, it's 20 HP on my car at the least.
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Old 06-16-2015, 03:07 AM   #13
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If you add in exhaust system, remap then the total increase was 20-25bhp but the throttle body and plenum alone was just over 5bhp. All with before and after on dyno. The butt dyno always felt stronger to me too but the reality is it's not as much as you feel.
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Old 06-16-2015, 03:31 AM   #14
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Originally Posted by edc View Post
If you add in exhaust system, remap then the total increase was 20-25bhp but the throttle body and plenum alone was just over 5bhp. All with before and after on dyno. The butt dyno always felt stronger to me too but the reality is it's not as much as you feel.
He didn't just list a TB and plenum change he also listed the 987 air box. You changed to a larger MAF housing, even with a tune I believe that's a mistake. It's way more then 5 hp.
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Old 06-16-2015, 03:49 AM   #15
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He didn't just list a TB and plenum change he also listed the 987 air box. You changed to a larger MAF housing, even with a tune I believe that's a mistake. It's way more then 5 hp.
I think you keep confusing my cars and listing things which I haven't done! I have had 2 Boxsters both modded, but both different. One is a 550 with the standard 987 airbox and the other an early S.

I did the most work and dyno runs with the S. Mods as in my sig and posted previously ie no MAF change or 987 airbox and it totalled 20-25bhp.

As I mentioned, the TB with intake in isolation gave about 5bhp.
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Old 06-16-2015, 04:13 AM   #16
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Originally Posted by edc View Post
I think you keep confusing my cars and listing things which I haven't done! I have had 2 Boxsters both modded, but both different. One is a 550 with the standard 987 airbox and the other an early S.

I did the most work and dyno runs with the S. Mods as in my sig and posted previously ie no MAF change or 987 airbox and it totalled 20-25bhp.

As I mentioned, the TB with intake in isolation gave about 5bhp.
You don't have the same mod as Lapister posted. You can not compare what you did to what I did, they are not the same. I misinterpreted what JFP quoted you on, you listed larger MAF to TB pipe.

I'll stick by this mod gave the car way more then 5 hp gain. Even the 2004 550 Spyder had a 6 hp gain with just the 987 air box.

I've run a 2010 style Camaro SS and there was nowhere the Camaro could pull away from my Boxster. A 2010 Camaro SS has a ptwr of 0.1091983556 and in order to set with that, a 986 Boxster would need a 25 hp gain. My intake upgrade was done meticulously, not just thrown together.
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Old 06-16-2015, 04:56 AM   #17
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Of course the mods are not exactly the same as the other poster but given that nobody else seems willing to post up before and after dyno's or simply hasn't done it then I put my data up as a point of interest for comparison. It's not the be all and end all but at the end of the day I am not making these numbers up or telling you how it feels. I am just showing what those mods mean. My dyno plots show 5bhp or thereabouts for the intake, plenum and throttle body.

Nobody is questioning your intake. I'm sure every home DIY'er has got largely the same thing just made a slightly different way. Mine was just simple aluminium tubing and 4 ply silicone hose. I'm sure yours like mine is not using some fancy engineering computer program to test for optimum flow etc.

I wouldn't read too much in to the power and weight of other cars because if you go that far then you might as well consider diff ratios and gearing etc.
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Old 06-16-2015, 05:34 AM   #18
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I wouldn't doubt your numbers, you didn't really do anything to help the car breath better using the stock 986 air box. You're probably lucky it gave you any hp increase.
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Old 06-16-2015, 05:48 AM   #19
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Originally Posted by JFP in PA View Post
That is more inline with what I would expect.
This is what I would expect as well. I don't see the stock intake, TB, and plenum as a significant restriction with stock displacement. Unless you add 3.4L the result will just be a narrowing of the torque curve. Maybe a few Dyno ponies above 6k rpm but overall slower lap times on a race track. Less than ideal results.
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Old 06-16-2015, 05:57 AM   #20
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This is what I would expect as well. I don't see the stock intake, TB, and plenum as a significant restriction with stock displacement. Unless you add 3.4L the result will just be a narrowing of the torque curve. Maybe a few Dyno ponies above 6k rpm but overall slower lap times on a race track. Less than ideal results.
I'll have to disagree with that. The 3.2l will benefit from this mod. I have first hand experience with the mod, the cars pulls strong throughout the rpm range. If anything his dyno shows the results of when you don't fully execute the modification.

Last edited by KRAM36; 06-16-2015 at 10:00 AM.
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