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Old 11-16-2019, 05:41 PM   #1
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74mm 996 throttle body on a 2.5l engine?

I have a 1999 2.5L Boxster with the (68mm?) cable throttle body. We all hear about the easy gains of HP and torque a larger, 74mm plenum such as IPD can give to the 2.7 and 3.2 engines. I was wondering why IPD has never made a Y plenum for the 2.5? I 'think' it's because the 2.7 and 3.2 have the e-gas throttle vs the older, cable throttle.

So I'm wondering, has anyone ever installed a 996 c2 74mm cable throttle body onto a 2.5 and then installed the 74mm IPD plenum? Keep the stock MAF housing for the computer readings? I have NO idea if this can even be done!
(This is just a cold, Saturday afternoon's musings)

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Old 11-16-2019, 11:44 PM   #2
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Just use the plenum and throttle body from the 996 3.4 for simplicity. It bolts straight on. Make up your intake from silicone tubing.
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Old 11-17-2019, 08:52 AM   #3
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Dont think the 2.5 needs the bigger tb
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Old 11-17-2019, 09:11 AM   #4
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I have the 74mm cable throttle body on my 2.5. I'm using the 2.5 plenum, it bolts right up. The 68mm throttle body is only smaller on the inside, the body itself is the same size. If you have them sitting side by side it is easy to see. Performance gains? Maybe a little at high RPM's. Maybe a little quicker throttle response. It does change the intake sound for sure. I'm still running stock exhaust, maybe with headers and high flow cats it would make a bigger difference. I paid less than a hundred bucks for it on Ebay, so for that price I think it's worth it. Would I pay $1000 to see if the IDP plenum would make it better? No.
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Old 11-17-2019, 09:34 AM   #5
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Thanks everyone for the responses and simplifying everything!

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