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Old 06-12-2019, 01:07 AM   #1
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2.7 swap for 2.5? (Blown motor)

I blew my motor a couple weeks ago on the track and need a replacement. The S motor is going to require too much work but an early 2.7 might be a good fit. I have an early 97 2.5 with a non-programmable ecu. Can I use my 2.5 ecu with the 2.7? Iím assuming the transmission can handle the 15 extra HP. Anything else I need to be concerned about?




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Old 06-12-2019, 05:07 AM   #2
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I'm not sure a 2.7 will be much if any less work than a 3.2. you still need to active the resonance tube, you still need to convert back to the cable throttle body, and you might run into issues with the ecu.

If you're thinking about a 2.7, I'd just find another 2.5. The difference in power is negligible.

I'm so happy that I went with the bigger engine, really ups the fun factor.
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Old 06-13-2019, 02:17 AM   #3
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Did you go from a 2.5 to a 3.2? What transmission did you use?
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Old 06-13-2019, 05:16 AM   #4
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yes, 2.5 to 3.2

Stock 5 speed tranny (which i recently grenaded, but that seems common even on spbs).

Pretty easy swap.

Adjust wiring in dme, reuse old harness, get 3.4 996 cable throttle body, and fabricate intake tube. I also used a 987 airbox.
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Old 07-02-2019, 02:57 AM   #5
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So I pulled the trigger on a 2.7, its the best option for me because I can add ballast and stay in my class. An S motor would have required a class change. I'm having trouble figured out what all I'll need to do, does anyone know if the ECU needs to be swapped? Are there any wiring changes that need to be made
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Old 07-02-2019, 03:53 AM   #6
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You can probably bolt up the 2.5 intake to that and make it a direct swap although you will likely lose a bit of power.

If you keep 2.7 intake you will need a custom intake tube, and to repin the ecu for the resonance valve
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Old 07-02-2019, 09:50 AM   #7
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You can probably bolt up the 2.5 intake to that and make it a direct swap although you will likely lose a bit of power.

If you keep 2.7 intake you will need a custom intake tube, and to repin the ecu for the resonance valve
Thanks, re-pin the ECU for the resonance valve? Do you know if thereís a write up on this? Re-pinning the ECU doesnít sound like an easy one.
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Old 07-02-2019, 10:35 AM   #8
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here's the important info from the pelican engine swap article:

- These cars ran the Bosch Motronic 5.2.2 system, which uses a cable-driven throttle body, similar to nearly all earlier Porsches. When installing an engine into one of these early cars, you need to use a cable-driven throttle body and corresponding crossover tube that matches that engine. (I.E. use the cable-driven throttle body from a 1999 996 Carrera when installing a 3.4 engine: the standard 2.5L throttle body is too small). The Boxster cable attaches directly to the 996 throttle body with no modifications necessary.

- Very early 1997 cars had non-programmable DMEs. If you have one of these cars, you might need to purchase a new DME and matching immobilizer to go along with it. Immobilizer codes for these early cars are not stored in the Porsche dealer information system, so there's no way of linking the existing immobilizer to a new DME. Don't buy a 1997 if you are definitely planning on doing an upgrade as you might get stuck with one of these non-programmable DMEs.

- Boxster engines from 2000-02 and all 996 engines have an extra crossover tube with a variable resonance flap that is controlled by the DME. When you reflash your 5.2.2 DME to control the new engine, you also need to add some wires to the DME harness. The resonance flap is controlled by a solenoid switch that then applies vacuum to the flapper. You wire this solenoid by running one wire to a 12V source and the other wire to pin 59 on the DME (the DME controls the valve with a switchable ground).

so, you may be able to just bolt on your entire 2.5 intake, otherwise you will have to address the resonance flap issue (or replace it with a straight tube, or use an rpm-driven window switch) as well as the throttle body issue (2.7 has a larger throttle body than a 2.5 so you can't reuse your 2.5 tb without replacing the plenum as well and not sure how it will mate to the rest of the 2.7 intake runners, etc. - soln is a 996 tb which requires the 996/997 plenum). and there is the non-programmable ecu issue. i don't think you want to get into a dme swap (unless perhaps the new 2.7 is coming with the required electronics?) so i think you are going to have to cross fingers and hope the 2.5 ecu can adapt to the larger displacement of the 2.7 (i know raby would run their 3.6 builds with a 3.2 tune ...). of course this means no re-pinning the ecu to drive the resonance flap.

Last edited by The Radium King; 07-02-2019 at 10:47 AM.
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Old 07-02-2019, 11:01 AM   #9
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Quote:
Originally Posted by The Radium King View Post
here's the important info from the pelican engine swap article:

- These cars ran the Bosch Motronic 5.2.2 system, which uses a cable-driven throttle body, similar to nearly all earlier Porsches. When installing an engine into one of these early cars, you need to use a cable-driven throttle body and corresponding crossover tube that matches that engine. (I.E. use the cable-driven throttle body from a 1999 996 Carrera when installing a 3.4 engine: the standard 2.5L throttle body is too small). The Boxster cable attaches directly to the 996 throttle body with no modifications necessary.

- Very early 1997 cars had non-programmable DMEs. If you have one of these cars, you might need to purchase a new DME and matching immobilizer to go along with it. Immobilizer codes for these early cars are not stored in the Porsche dealer information system, so there's no way of linking the existing immobilizer to a new DME. Don't buy a 1997 if you are definitely planning on doing an upgrade as you might get stuck with one of these non-programmable DMEs.

- Boxster engines from 2000-02 and all 996 engines have an extra crossover tube with a variable resonance flap that is controlled by the DME. When you reflash your 5.2.2 DME to control the new engine, you also need to add some wires to the DME harness. The resonance flap is controlled by a solenoid switch that then applies vacuum to the flapper. You wire this solenoid by running one wire to a 12V source and the other wire to pin 59 on the DME (the DME controls the valve with a switchable ground).

so, you may be able to just bolt on your entire 2.5 intake, otherwise you will have to address the resonance flap issue (or replace it with a straight tube, or use an rpm-driven window switch) as well as the throttle body issue (2.7 has a larger throttle body than a 2.5 so you can't reuse your 2.5 tb without replacing the plenum as well and not sure how it will mate to the rest of the 2.7 intake runners, etc. - soln is a 996 tb which requires the 996/997 plenum). and there is the non-programmable ecu issue. i don't think you want to get into a dme swap (unless perhaps the new 2.7 is coming with the required electronics?) so i think you are going to have to cross fingers and hope the 2.5 ecu can adapt to the larger displacement of the 2.7 (i know raby would run their 3.6 builds with a 3.2 tune ...). of course this means no re-pinning the ecu to drive the resonance flap.
Thanks! I saw that info as well. I wonder if I could bolt on a 3.4L cable throttle intake. I donít believe those have the flap. I also donít understand why canít just delete the flap.
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Old 07-02-2019, 11:18 AM   #10
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I'm in the middle of putting a '97 2.5 into a 2001 base, sort of the opposite swap. In my case, I swapped over all of the 2.7L intake, fuel, harness, and vacuum stuff to the 2.5. The only real creativity involved was making a template and re-drilling some of the mounting holes in the intake a few mm over from where they were.


There's a big difference in the 2.7L intake and the 2.5L intake. By my HF calipers the intake port on the 2.7L engine is 54mm vs 43mm on the 2.5L. Between that and the resonance tube, I'd want to keep the 2.7L intact and look at swapping the DME and adding some wiring and pedal for e-gas.

Easiest way to do it and be back on the track would be a direct swap of all the intake, throttle, engine harness, vacuum, and injector stuff from the 2.5 onto the 2.7 - the reverse of what I did. To re-drill the intake mount, just make a template, knock out the steel spacers, (fill the old holes if you want quality) and drill holes in the replacement intake.
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Last edited by 78F350; 07-02-2019 at 03:51 PM. Reason: A little bit of re-grammaring
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Old 07-02-2019, 05:10 PM   #11
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I just realized there may be a problem putting the 2.5L intake runners on the 2.7L engine: The rubber seals may not contact the intake ports on the head due to the smaller diameter.
Solution? ...Fabricate a bolt-thru adapter plate to fit the 2.5L seals and cover the excess port.
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Old 07-02-2019, 05:21 PM   #12
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I'm in the middle of putting a '97 2.5 into a 2001 base, sort of the opposite swap. In my case, I swapped over all of the 2.7L intake, fuel, harness, and vacuum stuff to the 2.5. The only real creativity involved was making a template and re-drilling some of the mounting holes in the intake a few mm over from where they were.


There's a big difference in the 2.7L intake and the 2.5L intake. By my HF calipers the intake port on the 2.7L engine is 54mm vs 43mm on the 2.5L. Between that and the resonance tube, I'd want to keep the 2.7L intact and look at swapping the DME and adding some wiring and pedal for e-gas.
I will be following this swap with great interest!! I would imagine there would be a dramatic loss in low end torque going to that large an intake on a 2.5. Intake velocity should take a major loss. It will be interesting to hear your impression. Of course if it works out then Porsche really did put the hurt to these engines!
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Old 07-02-2019, 05:37 PM   #13
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I still don’t understand why a 3.4L 996 manifold wouldn’t work. If you don’t have this problem on a 3.4 than why can’t you just use the 3.4 manifolds
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Old 07-02-2019, 10:04 PM   #14
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I still donít understand why a 3.4L 996 manifold wouldnít work. If you donít have this problem on a 3.4 than why canít you just use the 3.4 manifolds
Take a look at a 996 3.4 manifold. The one's I've seen are much more differenter than the 2.7L. They still have the resonance flap and also have a 2 piece runner on each side where the injectors mount to the lower, aluminum part. Looks like a bigger can of worms to open rather than an easier solution.

Body and cross-tubes:


Lower intake where the injectors mount:
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Old 07-03-2019, 04:17 AM   #15
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So what would happen if you used the 2.7L manifold and simply removed the valve or blocked off the crossover tube altogether?
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Old 07-03-2019, 08:25 AM   #16
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My guess is that to a casual driver the difference having it open or blocked off wouldn't be noticeable. To you on the track, you could choose which way is more advantageous.

Normal function is closed below 3k rpm, open up to 5k, then closed again; so, best low and high end power = closed, best mid-range = open.
Check this old post. The .PDF link in it is dead now, but I had quoted the important part: What's the function of this valve?

Running with the 1997 DME could also be an important factor. Probably closed (less high velocity air) will be best.

I have a 2001 2.7L DME/Immo/Key set boxed up. I could send it on loan if you want to experiment. I should have an e-gas pedal too and could dig it up along with the connector and some of the wire to the DME.

The other variable might be injectors. I noticed that the injectors I swapped from the 2.7L were a different color than the ones that came off the 2.5L. They may be different pressure and factor if you are running too lean or rich. I don't know the specs....

So... quick and simplest configuration to try: block the second tube and adapt your cable throttle body to work and use your 2.5L engine harness. If that isn't good, it's a starting point to work from.
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Old 07-03-2019, 09:58 AM   #17
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ok, here is your best bet.

Use the 2.7 intake. Leave the resonance flap unhooked. Squeeze your 2.5 crossover tube into the 2.7 plenums. Fabricate custom intake tube. Use 2.5 or 3.4 cable throttle, not sure the bigger one is needed.
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Old 07-03-2019, 03:29 PM   #18
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ok, here is your best bet.

Use the 2.7 intake. Leave the resonance flap unhooked. Squeeze your 2.5 crossover tube into the 2.7 plenums. Fabricate custom intake tube. Use 2.5 or 3.4 cable throttle, not sure the bigger one is needed.
Sold! Iíll give this a try. Thanks for everyoneís help. One more question can the 2.5L tune handle the change in displacement or will I need to reflash it? Iíll grt it dynoíed and the air fuel mixture checked immediately.

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