996 4s - diy 3.9 x51, reworked heads, schrick etc

Hi all, Thought I'd share some photos of my recently completed 996 3.9 4s engine project. I'm using westwood wet liners, mahle motorsport 100mm pistons, ARP hardware, have done a good amount of porting work on the heads, schrick 12mm inl cams, x51 intake manifolds and runners, 83mm tb, custom 997.2 airbox w/k&n filters and modded decklid with 2 intakes. I've renewed pretty much everything while in there inc all the chains, guides, shells, the oil pump relief valve for the uprated 997 one. It's got a LN dual row upgraded IMS. I'm using 997 S injectors and oil cooler, some unknown brand manifolds, 200 cell cats and gundo hacked 997 exhausts. I've flashed the x51 map on to use as the base map, the dme tuning so far has been relatively basic at sorting krkte to match 997 3.8 injectors (running same value as 997 s), changes to the dk maps to suit the larger TB, and a slight tweak to MAF calibration to suit the slightly different pipe diameter. I've still to do some datalogging and general sorting out, I don't currently own a wideband and am undecided on whether I'll bother going that route and doing some mapping on the road or to finish it on the rollers. Next project is to shed some weight, and I'm contemplating going rwd, all while keeping it road friendly... Cheers Tim

Nice, like the sound of this.

Lovely job Tim. MC

You've basically built my ideal engine! Good work, will be interested to see how your project develops.

As above, great work and I look forward to the updates :thumb:

Nice work, looking forward to hearing how it runs compared to your old engine

Good work, would like to see the numbers when mapped!!

Wow awesome Tim, keep us updated :thumbs:

How have you got access to the dme? Would love to be able to see what's going on in the engines brain! I've been toying with a standalone ECU recently, any reason you're not going for that?

Thanks guys for the comments. It's quite interesting, feels strong on part throttle at low rpms but on full load its character has changed and is a bit flat until 3/3.5k rpm or so at which point it really seems to rocket! I'm still running in (on 300 miles ish) so will get a better feel once its run in further and I can use it in anger, that and when the map is more dialled in. I changed so much at once it's a bit of a shame as it's hard to know what to attribute to its behaviour. I imagine the x51 inlet has pushed the powerband up quite a bit judging by the runner length/dia, perhaps it's also when the 'ventilhub' switches onto the big lobe at lower rpm with the spikier cam. Me too! Will be a while yet as I try to find time to sort out niggles and get some miles on it. I've an intermittent cam error on bank 1 I need to resolve, when I've datalogged on my driveway just revving the engine the cams both seem to be advancing/retarding as they should and the deviation looks ok, I need to test on the road, and may just swap out the actuator anyway. Reading the flash off these is pretty easy as with any me7.x.I just use my usual chinese knock off tool for this (as it does checksum correction and only takes about 30s to read/write) but have a few tools that will read it off. I'm fortunate that the x51 software I updated to matches a damos I have perfectly unlike the dme's original software so this saves me a lot of time figuring things out. I've used standalone ecus before and tbh it never really even crossed my mind for this car which is a road car. Standalones take ages to map well for transients and part load and are hard to get to drive as nicely as a factory ecu for every day use, even if you get loads of extra functionality. You've a pretty similar car history to me, I used to have an e36 m3 evo (saloon) and an e46 m3!

Interesting, I knew there was additional work when it comes to mapping a standalone ECU but I didn't know it was that hard to get a decent daily driver map on it. Clearly I understand that Porsche will have put the miles in when it comes to developing the car, I just hoped that the technology had come on enough that the ECUs were able to self map to some extent. I'm happy to tinker but I'd want to get it feeling OEM. Eventual plan would be to fit BMW throttle bodies - I'm a design engineer so making and designing the parts is no problem but I want to get a good understanding of the electronics first before I tear everything down. I've been interested in engine control systems for a long time and not being able to tell what's happening inside the DME is killing me. I noticed that I was getting some stiction at 0-1% throttle and my throttle return screw had worked loose slightly (a previous owner had played with it for some reason) and tweaking that back to the standard setting (~700rpm idle) feels like it's released about 30 horsepower! The ECU must have been adding or pulling timing to get the idle where it wants it and I'd not noticed the change in power as it was so gradual. If I could interrogate the ECU I would be able to see something was up, but it's a black box to me at the moment... I've got an early car so I'm on 5.2.2 which is a much simpler ECU I understand. Clearly a man of taste and sophistication!

Great project, thanks for sharing. What did you have to do to get the airbox to fit?

I've gone syvecs on my turbo, the benefit being I can remap the PSM as it would get overcome with the additional torque and shut the throttle valve. However, I also get to remap the variocam. For some reason Porsche didn't map it for full power and huge gains can be had by getting control, 120hp on the turbo (non standard car). Not sure what variocam system they use in the carrera though, might be worth looking in to?

It was a lot of faff to be frank and I'm not sure whether I'd bother with it again. Although it fundamentally just about fits the chassis, it won't line up to the tb and fouls all over the place so needed some surgery. Some smaller ancillary stuff was needed like moving the air pump over (I cut and re-welded the existing bracket and tucked it right in the corner), altering the oil filler tube etc., not to mention that with the maf tube I used the dme needed a slight tweak to the maf calibration curve (it would be the same using the original tube). I'm very happy with it now that it's done - I had in mind the 997 x51 when looking at what to do with the engine and with two cone filters and the two large air intakes not to mention using the larger TB the 997.2 box seemed like a good option to get as much cold air drawn in as possible and to maximise filter area. Thanks, interesting on the turbo. I've only ever mapped one 996TT (which I fitted a few parts such as gt2rs ICs and forge actuators etc, tubi exhaust w/sports cats), I tuned on the road and admittedly I didn't spend much time looking at the variocam+ but I'm not very experienced in tuning cam timing in turbo engines. Do you know where the gains were to be found? The m96.03 uses variocam+ on the inl cams the same as in the TT and I can alter the maps. On full load the cam is basically at max advance until 5k rpm and then starts to retard - with the larger capacity and longer duration inl cam there may be some tuning that can be done, I'd need to test on the rolling road I think.

John wrote the original thread here: https://rennlist.com/forums/996-tur...p-torque-gains-with-no-increase-in-boost.html Basically, the Variocam+ advances 30 deg at 1500rpm on a stock car Remapped, it's: 0-1500 off 1500-4000 advance 4000+ off Here's the table in SCal: MAP / RPM and valve angle