Just measured my stock air box and it's 86mm, same size as 3.6 which is right as 3.6 and 3.8 share same air box.

It's a big difference, I am going to data log my car with X51 fitted and email to Scott at softronic, hopefully he can alter my tune file to give additional fueling, otherwise I need to get a custom map or get the Porsche X51 map.

Yes the 3.6 / 3.8 air box have a grid in them but it's before the inlet tube where max is, so should not be of concern.

Just in the X51 air box the volume of air is greater at same maf speeds causing this lean condition. It's obvious a lot of people have fitted the X51 Airbox and no engines have died yet, so though they are running lean it's not fatal, but could be reducing engine life, scoring bores and of cause with the right AFR car will run even better, make more power and engine life will not be reduced.

 

Without sounding dumb, does that mean 12% more air? So as a quick fix could fueling say be increased by say 12% and say 6% passed 6500rpm as the fueling improved around 7000rpm simply as Porsche map throws more fuel in at the top-end for safety.

 

Good luck Gibbo, let's hope Scott/Softronic will fix you up with a new map file.

That would also be great news for others who've fitted the X51 airbox so fair play to you.

You're spot on about bigger MAF tube area causing lower MAF reading for same air mass flow, and hence 'fooling' the DME map into fuelling less.

However it should only cause seriously lean running at WOT: under pretty much any other conditions the DME will compensate by adjusting the fuelling to maintain lambda~1 (as long as all four O2 sensors and both main catalytic converters are working properly).

I'm no expert on the Bosch Motronic system, but I believe there is a fixed input parameter in there that defines the MAF tube area, it's used by the DME program in conjunction with air temperature (also taken from the MAF sensor assembly) to calculate air mass flow from the MAF sensor's output voltage.

I'm sure Softronic have a solution.

 

Yes the dyno operator did say partial throttle was ok, WOT was the issue with lean running.

 

Keep us posted, as I would like the updated Softronic tune as well. Hopefully a no cost fix.

 

Scott charges for custom maps, which is fair enough it takes a lot of talent and time.
I am working with Scott on a solution and hoping to be heading back to dyno this weekend with a new custom tune.

Getting the car Fuelling right will improve response and power too, particular in 2000-6000rpm range.

 

Tested new map which Scott has done for me which is an X51 map then customised to my car. To drive it's just better everywhere, more responsive, more eager and pulls harder, in short much better. Big kudos to Scott for putting up with me emails and working over the weekend.

Shall hit dyno next week and see what power is and what Fuelling is like, fingers crossed.

 

Mind sharing the cost? My comment on the no cost option was that I already purchased the softronic tune that is supposed to be taylored to my mods. Through you research it seems like it isn't, therefore I don't think it should be on me to purchase another tune.

Did you already have the softronic tune?

 

Yes already had softronic, but softronic is an adapting tune so for most bolt-ons it is fine. It's an off the shelf package,

What Scott has done for me is now more custom mapping, he's done me a good deal and car seems to drive great, if the Fuelling is right I am sure he can sort you guys out too whether your customer or not, it's not free but reasonable.

 

Would you mind shooting him the link to this thread.

 

Why not contact him directly?

 

Wasn't sure if he was a personal contact.

 

are you saying regardless of a x51 intake if you enlarge your ipd and throttle body you will not see any results and in fact lose power unless you get a custom tune?

i was wondering if the 997.2 gt3 airbox would fit our cars.. if offers the same function but much cheaper i bet

 

IPD and throttle body is fine. It is when you change to an intake with a different aperture size where the maf sits, you then need a custom tune.

 

Hi there

Got my AFR data from the dyno last week:-
1500 - 6000rpm @ 14.7 AFR at WOT
6000 - 7400rpm @ 13.4 AFR at WOT

So above 6000rpm things are OK as for best power you want around 13 AFR I believe on an NA car, but below 6000rpm it's quite lean which will rob power, response and things will run hotter.

I shall try to remember to post up the graph later/tomorrow. Am heading back to dyno this Friday to re-check AFR and power run.