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Old 01-09-2021, 05:29 AM   #1
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2.7 swap

I have the opportunity to ďstealĒ a complete powertrain from an 02 Boxster harness and all trans, mounts, computers. Everything but the tip for the trans. I can get it all for less money and time than rebuilding my basket case 99 with 5 speed and Iíll have a spare trans for my other 99. Question is what problems could I run in to? I already know that I have to deal with a vac line problem if Iím to bolt up the 5 speed to the engine that was previously an auto. Looking for any advise available.

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Old 01-09-2021, 08:09 AM   #2
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It has been done, but it's not a direct swap engine for engine.
Keep everything from the 2.5 in case you decide to use it on the 2.7.

The biggest differences will be in the computer/wiring harness and the intake. The harness from a 2.7L engine does not have the same connector for the computer as the 2.5L and the two can not just be interchanged without doing some modifications.

The throttle on the 2.7L engines is electronic and the 2.5L engines uses a physical throttle cable. The 2.7L engines have a 'resonance flapper' on the intake to improve airflow across the RPM range. In 2002 the fuel system changed and no longer used a vacuum controlled fuel pressure regulator on the fuel rail.

Look at some of these posts. 'Chi-town' and 'truegearhead' have done similar swaps to what you want to do.:
1999 Porsche Boxster Engine Swap Questions.......
2.7 swap for 2.5? (Blown motor)
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Old 01-09-2021, 02:27 PM   #3
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It has been done, but it's not a direct swap engine for engine.
Keep everything from the 2.5 in case you decide to use it on the 2.7.

The biggest differences will be in the computer/wiring harness and the intake. The harness from a 2.7L engine does not have the same connector for the computer as the 2.5L and the two can not just be interchanged without doing some modifications.

The throttle on the 2.7L engines is electronic and the 2.5L engines uses a physical throttle cable. The 2.7L engines have a 'resonance flapper' on the intake to improve airflow across the RPM range. In 2002 the fuel system changed and no longer used a vacuum controlled fuel pressure regulator on the fuel rail.

Look at some of these posts. 'Chi-town' and 'truegearhead' have done similar swaps to what you want to do.:
1999 Porsche Boxster Engine Swap Questions.......
2.7 swap for 2.5? (Blown motor)

Deal included DME for the 2.7, theft module, key and cylinder. I was just going to use the 2.7 DME. Looks like Iíll need a pedal though. I scanned through the thread you sent thanks. Iíll more closely read it when I have some car time tonight.
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Old 01-10-2021, 07:30 AM   #4
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Made the deal on the 2.7. Then I realized that engine is a fly by wire (no throttle cable) and a return less fuel system. Good news is the seller threw in the entire fuel system tank and all. Here is what I have from the donor car 2002 Boxster
2.7 l engine with harness
Auto trans
Complete fuel system
DME
Keys
Cylinder
Theft module

The receiving car 1999 Boxster
2.5l engine with harness
5-SPEED transmission

I would like to keep it as a 5-speed so that I would not have to change over cluster, linkages etc but not sure which module would work.

Looking for most economical solution
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Old 01-12-2021, 04:47 PM   #5
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Thanks for reaching out over IM. As you know I put a 2.7l in my 2.5l car. You need to use the 2.7 intake manifold, and the 2.5l crossover and throttle body and the 2.5l wiring harness. The vacuum port for the second cross over can just be blocked. I used the factory 2.5l ecu. It dyno’ed at more power to the wheels then a 2.7 is supposed to make at the crank and ran great. If you need anymore help let me know, happy to help

Edit: I also used fuel rail and return system from the 2.5
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Old 01-12-2021, 04:57 PM   #6
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This is what the hybrid manifold setup looks like all said and done. 2.7L runners, 2.5L throttle body cross over and 2.5L mechanical cable throttle body. Oddly the 2.5L throttle body and cross over is much larger than the 2.7L one which may be why this setup made so much more power than a standard 2.7

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Old 01-12-2021, 05:56 PM   #7
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Thanks for reaching out over IM. As you know I put a 2.7l in my 2.5l car. You need to use the 2.7 intake manifold, and the 2.5l crossover and throttle body and the 2.5l wiring harness. The vacuum port for the second cross over can just be blocked. I used the factory 2.5l ecu. It dynoíed at more power to the wheels then a 2.7 is supposed to make at the crank and ran great. If you need anymore help let me know, happy to help

Edit: I also used fuel rail and return system from the 2.5
Injectors from the 2.5 or 2.7 or are they the same?
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Old 01-13-2021, 04:26 AM   #8
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Injectors from the 2.5 or 2.7 or are they the same?
I donít know, I used the 2.5 injectors. With such a small displacement increase the computer will just adjust the injector duty cycle to make it work.
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Old 01-14-2021, 06:08 PM   #9
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Do you remember how much larger the intake cross over tubes are ?? Thanks Frank
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Old 01-15-2021, 10:21 AM   #10
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Do you remember how much larger the intake cross over tubes are ?? Thanks Frank
Take a look at the photo below, you can see the rubber hose itís stretched from the smaller diameter 2.7 to the larger 2.5 cross over. The ID of the 2.5 is the same size as the 2.7 OD
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Old 01-18-2021, 03:56 PM   #11
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Do you remember how much larger the intake cross over tubes are ?? Thanks Frank
Iíll measure mine when I assemble them.
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Old 01-24-2021, 12:07 PM   #12
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I was able to put in a few hours this weekend. Removed intake and fuel injectors. In the process of cleaning up the 2.5L harness. Removed exhaust had to drill out 5 of 6 bolts. Quite a PITA. Removed Auto trans (tip). Took 3 hours as nose of converter was stuck and I didnít want to pry too hard and break anything. Now I am having trouble with the flex plate. Rusted on. As the name implies it wants to flex too much when trying to pop it off. Any tips or tricks to this?
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Old 01-24-2021, 12:10 PM   #13
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Originally Posted by truegearhead View Post
Thanks for reaching out over IM. As you know I put a 2.7l in my 2.5l car. You need to use the 2.7 intake manifold, and the 2.5l crossover and throttle body and the 2.5l wiring harness. The vacuum port for the second cross over can just be blocked. I used the factory 2.5l ecu. It dynoíed at more power to the wheels then a 2.7 is supposed to make at the crank and ran great. If you need anymore help let me know, happy to help

Edit: I also used fuel rail and return system from the 2.5
Did you only use the crossover with the throttle body or both crossovers?
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Old 01-24-2021, 12:15 PM   #14
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Did you only use the crossover with the throttle body or both crossovers?
I used both, the non-throttle body cross over has a flapper in it that the 2.5l ecu canít handle so I just blocked the vacuum line that controls it.
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Old 01-25-2021, 10:25 AM   #15
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Iíll measure mine when I assemble them.
The Ď02 was 87mm
The Ď99 was 97mm
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Old 01-25-2021, 10:29 AM   #16
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I used both, the non-throttle body cross over has a flapper in it that the 2.5l ecu canít handle so I just blocked the vacuum line that controls it.
I apologize for what I now see was a not so smart question. I did not realize the Ď99 only has the one crossover.
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Old 01-25-2021, 03:17 PM   #17
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Do you remember how much larger the intake cross over tubes are ?? Thanks Frank
Ď99 is 97mm
Ď02 is 87mm

Rookie mistake. I replied to myself. Iím going to buy some silicone reducers 3.75 to 3.5 and try them.

Last edited by Dllrd23; 01-25-2021 at 03:24 PM. Reason: More info
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Old 01-26-2021, 09:11 AM   #18
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@truegearhead - I'm much in the same boat here. Looking to swap out my 2.5. From what I'm gathering you used the 2.7 engine, swapped the fuel rail, the crossover and the throttle body form the 2.5, the 2.5 harness and blocked off the crossover valve?

Everything else pretty much plug and play?

@DLLRD23 - Keep us up to date, I'm watching this one with a lot of interest.
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Old 01-26-2021, 02:52 PM   #19
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Originally Posted by Aanic View Post
@truegearhead - I'm much in the same boat here. Looking to swap out my 2.5. From what I'm gathering you used the 2.7 engine, swapped the fuel rail, the crossover and the throttle body form the 2.5, the 2.5 harness and blocked off the crossover valve?

Everything else pretty much plug and play?

@DLLRD23 - Keep us up to date, I'm watching this one with a lot of interest.
Yep thatís it!
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Old 01-26-2021, 03:30 PM   #20
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@truegearhead - I'm much in the same boat here. Looking to swap out my 2.5. From what I'm gathering you used the 2.7 engine, swapped the fuel rail, the crossover and the throttle body form the 2.5, the 2.5 harness and blocked off the crossover valve?

Everything else pretty much plug and play?

@DLLRD23 - Keep us up to date, I'm watching this one with a lot of interest.
I just bought some silicone reducers for the crossover from Intercooler Pipe Fabrication they were 3.75Ē to 3.5Ē. Iíll let you know how they work. Next order of business is figuring out which exhaust to use. The 2.5 would be plug and play but when I went to get it yesterday, I stood it up on end and a bunch of oil ran out meaning the converter (I think only one side as this was a blown head gasket issue) would be full of oil and likely ruined. The exhaust on the 2.7 has the o2s in the wrong location for the harness which isnít a huge deal but will require some wiring. I just got some mesh loom to update the harness and some cloth electrical tape from amazon today to freshen up the look of the harness. It was fairly inexpensive (200í of tape 25í of 1/4Ē loom and 25í of 1/2Ē loom for $40). Researching which IMS bearing to go with right now. That is next after the harness then all should go quick after that.


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