CAlexio

Cats are part of headers...

neanicu

Of course! I totally messed that up! I have seen the headers in the other thread before they were shipped out to you,but I totally spaced out when writing the above post.

BGB Motorsports

I like this recipe! I agree with a lot of what is stated above except i want to add that the flywheel drivability isn't affected. ChrisF is having his installed right now along with the Guard LSD and will be able to chime in with feedback. Great writeup though...i like that path and i think it's a good one!

Please see below...these however are all valid concerns. My answer below is an attempt to ease that worry but at the same time, if you guys have any concerns and don't really want to even be considered out of spec on the warranty, we are ready for you when it expires!

This is actually a great story or a perfect example of how most places work. You had a warranty issue and wanted to take advantage of the labor to share expenses and were billed for aftermarket parts installation. If these parts create a CEL, there will be a reason for it and the manufacturer will have to fix it for it or give you your money back. If you modify your car and get a CEL for something else and are trying to get the factory to pay for it, you're going to have a hard sell once they see the aftermarket mods. These guys are very sharp though and if you say "fix it and tell me how much it costs" they're going to spend 2 hours on it at $130 per hour and $260 later you are on the hook for the reason it failed. I think that that's the sacrifice. Here's a good example...if for some reason your MAP sensor fails down the road (and i have no reason to believe it will) then yes you're not going to get free labor to diagnose it if you have an IPD plenum or a big throttle body on because they're going to want it back to stock before they deem that the stock configuration was without issue.

Both the BMC and K&N are plug n play. The K&N filters are $105 for the pair and $215 for the BMC. I have yet to dyno test the both back to back. We started selling K&N because of the price, availability and because we figured you're talking about 1 HP difference MAYBE?

I think you might have bad information. The exhaust manifold on the GT4 and essentially every DFI Porsche 997.2/987.2/981/991 has the cat built into it. You cannot remove them...you could cut them open and hollow them out for off-road purposes but we don't really recommend that. We tried it early on when manifolds didn't exist in late 2009 and had to be ready for testing at Daytona but now that there are parts you don't have to.

I think that 1 - 2 hp is a conservative number and that's one that i like to go with. I tell people that they increase throttle response slightly, help fuel mileage and add a hint more of sound but are best used when spending money on throttle bodies, plenums or manifolds.

neanicu

Absolutely! I totally got that wrong!

Regarding air filters,I think we agree,that for best results you really need to get more air into the engine and high flow filters are just a part of the pkg. Do the throttle body,manifold and a tune for real gains.

BGB Motorsports

As one of my mentors used to tell me, a motor is just a big air pump. The more air you can get in there, the more power you can produce. Since it's DFI, injectors and fuel rail pressure has more than enough fuel on tap for anything we do. You just need to feed her more air.

cox1974

i dynoed my gt4 with and without the bmc filters in the same day.... ZERO gains.....

neanicu

Yep,just a big lung.

BGB Motorsports

This doesn't shock me given that we are talking about something that is estimated to produce 1 - 2 hp and you see runs differing by 3 - 4 hp from one to the next. Furthermore heat soak plays a role and at the end of the day, intake testing gains are sometimes never even proven on the dyno given the lack of air flow. This is why i tell people 1 - 2.

neanicu

It makes sense if you think about it : the filters are part of the air box. The air box feeds into the throttle body. Let's say that aftermarket filters allow more air past them,that extra air will still end up against the restricted throttle plate. Now if you change the throttle body as well to a larger one,then you will benefit from the extra air that gets passed the high flow filters,because it will allow it to be fed into the manifold at a higher rate and volume. The engine will also benefit from an intake manifold that fills up the cylinders faster and with more air. I also think that the computer needs to be aware of the extra air(tune) in order to make more power.
Then of course,you will need a higher flow exhaust.

I see all these components going hand in hand if you want real gains. Of course this is just my opinion FWIW...

cox1974

Beantown Kman

John, are the gains from intake and exhaust modifications on the GT4 engine any different than those same modifications would be on the 987 3.4 DFI engine? Is there anything about the 3.8 engine in the GT4 that makes it more receptive to those "breathing" improvements? Is the software any more of a factor on one of those engines over the other?

GAZZ

This is true, but in the old days of pre DFI (987s') there was no throttle restriction software so the gains were better with an after market air filter, but only slightly. 4-5HP max.

d00d

Replacement high flow air filters do so by having bigger pores, so they don't do as good a job at filtering out crap.
Depending on where you drive, this crap can be silica dust that causes cylinder scoring.
Oiled ones can leak onto MAF sensors causing premature failure, the GT4 doesn't appear to have one though.
The best way of getting better flow through the filters is to build a bigger air box and use a filter that filters out the same micron size particles as stock.
Looking at the GT4 Technik shows that the dual filters are of a generous size to not interfere with what the stock or 991 throttle body can pass, so just keep them.

Mvez

it's pretty obvious the biggest restriction from the factory isn't the headers, or exhaust....it's the throttle body.

If I was to do ANYTHING, it would first be the IPD 82mm plenum and matching 991 throttle body. There is a big reason why it exists, and Porsche uses it.

We already know the exhaust isn't very restrictive, it's already pretty loud. Headers have "GT" less restrictive cats, not regular model versions. The stock airbox should provide more than enough flow for the larger throttle body.

Assuming this fits without issue, this will be your best bang for buck mod, that won't require any additional software, and shouldn't throw a CEL. More importantly, it should help "wake up" the car below 5500 and everywhere for that matter, IMO

IPD 82mm Competition Plenum & 82mm 3.8L 991 Throttle Body
http://ipdplenums.com/products/plenu...-dfi-carrera-s

jmartpr

I think you need to re-think your modifications plan.......the headers on the GT4 have the same cats all other 981 have, so not sure where you get the info on a less restrictive exhaust system. I do have to agree the PSE exhaust system is pretty good from the factory but headers (even with Cats) will provide a boost in torque and HP specially in the mid rpm range. They are essential and the first building block for any build. IMO are the 1st mod anyone should do and the only one that will not throw a CEL if equip with cats.


The TB and Plenum are on the other side of the engine equation and should complement pretty well any exhaust upgrade, but.....you will get CEL problems so a new ECU or a COBB is mandatory for this mod. We still haven't seen a lot of testing data on this mod so a lot of people are waiting to see the final results of bolting this mod on top of the others. Headers and exhaust on the other hand have a bit more info on the forums with solid results.