Is there a definitive answer on what kind of torque curve changes we can expect to see with a GPF delete OAP alone (keeping the factory headers, muffler, etc.)?

Plenty of people report the car "feels" more powerful, but it's pretty well-known that loudness can affect your perception of power. I saw a dyno test in another thread where someone had removed the filter element from the factory OAP (leaving a big empty cavity in the pipe) and actually measured lower torque values below 5000 RPM or so.

Has anyone actually done a before/after dyno test with just an aftermarket OAP, e.g. Akra, Soul, etc.?

 

I would love to be proven wrong, but without an ecu tune, I don't see power increases being a big factor in aftermarket exhaust decisions. I'm always skeptical of reported power gains and would love to see Dyno results taken immediately following the upgrade and then a few months later. I would let sound and weight be the determining factors until we get an ecu tuning option that can take advantage of the free flowing exhaust.

Caveat - this is from my experience with modern 911s so again, happy to be wrong on the 718 GT4/Spyder platform.

 

JCR did so a while back.

 

The prior thread done by a Rennlister is about as good as it gets in terms of a comparison. He did immediate before and after dyno runs on the same dyno with the filter in and then with it removed. And he showed zero gains. And he had no axe to grind either way.

There's no way a different pipe in the same place covering the same ground is going to make much of any difference. I wouldn't accept anything a tuner puts out without someone independently verifying it similar to what that gentleman did.

 

As far as I remember he actually had a loss of few HP. Or maybe that was the one who gutted stock one

 

reduced back pressure... might need some time for the ECU to relearn, if in fact that is something that it is able to dynamically account for...

 

Could be

 

Great question! Like playing cards in the spokes of your bicycle when you were a kid.......of course you were faster!
It would be great for a vendor/manufacturer to post iterative examples of torque and power gains and/or losses associated with:
1. Just an OAP replacement pipe.
2. Just a rear muffler.
3. Just headers.

 

If pipe A and pipe B are both straight through but with different bends or similar then yes, but in this case the delete pipe is just that, a pipe, and the original is a pipe with a massive obstruction in it. Maybe the cat is snuffing out all the velocity upstream and another flow restricting item down the chain doesn't matter at that point?

I'm admittedly not an exhaust engineer, but on the surface it seems difficult to think that removing the OPF matrix isn't going to have some measurable performance gains.

 

This.

Ron

 

I’m guessing the area of the void of the OPF is probably the same as the area of the pipe connected to it; thus, no increase in flow rate, no power. Although you probably have turbulence.

Also, when I had my 991.2 GTS, I felt I lost some power with headers but after 100 miles or so, I gained power up top. With Sport cats I also felt more power after a few more miles. So the ecu does need to adapt.

 

Only way to tell if there are real power gains is for independent before and after runs to be performed on the same car, same dyno, same day. The only thing we know for sure at this point is that gutting the OEM OPF nets you nothing, and maybe costs you a few ft. lbs. or torque. All the rest is speculation and I wouldn't buy anything a manufacturer said that hasn't been independently verified. And the most inaccurate measure of all is the butt dyno.

 

Agree on all counts above based on initial findings... but how much does what Larry Cable said factor in, being: "might need some time for the ECU to relearn, if in fact that is something that it is able to dynamically account for...". Or if the current onboard software can't grapple with, then what a 3rd party tune might bring to the table in synergy with this hardware change? Different levels of owner commitment would factor in of course as perhaps someone who wants to keep stock mapping may in fact never get any appreciable gain out of the hardware change, but could it be that someone who wants to maximize their tune with an outside contribution may get a desirable gain from swapping out the GPF section?

 

HI Everyone
I am the president of Fabspeed Motorsport and I picked up a 718 GT4 way back in April 2020 for long term system development and I'm also a Porsche nut like you guys and 30 year PCA member.
Removing the GPF left and right pipes saves significant weight and adds about 5 ponies. There are no significant dyno proven gains BUT she sounds alot better and pops snarls on over-run when you jump off the throttle.

We tried multiple dimensions of exhaust tubing and different collectors and the final design made the most bang for the buck. If you do a full Fabspeed system we have recorded 35+HP and she runs and runs. Feel free to cruise by FABSPEED Motorsport weather permitting you can test out my car and see how its made. Everything is made 100% inhouse.

 

Well that's a pretty honest offer. The geography doesn't really permit me but cheers to that kind of transparency