michaelscain

Hi,

Hope you don't mind, I have a question regarding the Porsche 3.4L engine installed in the 991 Base and 981S. Just wondered if anyone can help shed light on this?

The Base 991 has 350bhp and the 981S has between 315bhp and 325bhp for Boxster S and Cayman S.

Q1. Is the 3.4L engine really exactly the same in both the 981S and the 991 base car?

Q2. Did Porsche mass produce the 3.4L engine for the 991 base, Cayman S and the Boxster S to save money. For example did Porsche just remap the ECU in the 981S so not to hurt 991 sales? Is the ECU mapping the only difference?

Q3. Is it possible to remap the ECU in the 981S to safely release the same 350BHP as the base 991 car and also not stress/reduce life of the 981S engine?

Please Advise?

Michael

Voyager6

The answer is yes and no.

There are wiring harness and oil manifold differences between the two engines. As far as performance, yes, the mapping is the primary reason that the HP is less.

Although the mid-engine bay in the 981 runs hotter and some more conservatism may be warranted.

V6

mcomet

I've never heard of wiring or manifold differences tho I suppose it might make sense due to different placement of the engine. As far as I know the primary difference is just the ECU tune. There was also some discussion if the plenum/TB is different as well but I can't remember if that was found out to be the case.

Put it this way like you say there is 10hp between Boxster and Cayman S...that is just ECU tune. The Cayman GTS I believe is 345hp. Again just ECU tune. These are all the same engines, but Porsche puts them in their place to make the cars different and organize their sales. There are now several after market tuners out there that will happily sell you Stage 1 or beyond tunes to get your car to make what it can make.

As for whether it is safe, that is a good Q but since the engines make more on the other cars I don't personally know what would be wrong. I would be happy if my 981 CS made what a 981 GTS made and don't see that there would be any issue. Adding a 3rd radiator would be nice but I don't think it'd be required unless I was going to track and wanted to keep temps down. Cobb, TPC, FVD all offer tunes. There's been a fair amount of discussion on Planet 9 forums about these tunes and peoples results with them. My personal plan is to potentially get a Cobb stock tune, then maybe headers and then a pro-tune. Over time..once my warranty is up.

Voyager6

The oil filter points up to the rear deck on a 991 and point down to the ground and is accessed from underneath on a 981. The manifold difference is minor, but must be changed when swapping a 991 engine into a 981.

The wiring difference is solely the orientation of the engine and ECU between models that necessitate different wire lengths.

V6

DBH

The 3.4L engine varies in HP - 315 (BS), 325 (CS), 330 (BGTS), 340 (CGTS) in 981's and 350 in the 991. This is accomplished mainly in three ways: intake and exhaust routing and ECU tuning. I imagine that if you would address each of these items, you could bring any of these engines up to or above 350 HP.

JCtx

It was reported that the ECU tuning consists on solely not opening the throttle body completely. In other words, it's probably open 100% on the 991, and less on Caymans, to restrict airflow. Who knows, but sounds about right to me, since every iteration of the 3.4L would only require one certification. If you alter any other parameters, I think it has to be recertified. Maybe an expert can chime in to set the record straight. And finally, any tampering of the ECU can render the powertrain warranty void (and it's irreversible since the electronic seal cannot be restored, regardless what a tuner says), so not a smart move under warranty, but to each his own.

Mrg02D

Sounds like Lexus. They dumb down the engine for reliability sake. Never able to over work the engine.

Might the Boxster reliability be where it's at due to this fact? If it's capable of 350hp, but limited to 315hp, you really have a lot of room in there.