4lflat6

First of all, let me be clear, I LOVE JCR! In fact so much so that I spent $7,000USD of my hard earned money on their Non-Silenced Race Pipes. That being said, I wanted to share *my* experience with the broader community. Treat this as one data point in addition to other data points you may have to find when it comes to your decision on choosing an exhaust system for your 718 GT4/GTS.

Why I bought the JCR Exhaust:

• Sounds amazing (higher pitch vs. the deeper sounding steel exhausts out there)
• Good customer service (Jonny has been very responsive here on Rennlist)
• Light weight (Saves around 10kg)
• Improves Power and Torque

Out of the reasons above, all hold valid except for the last point. There are a few factors involved in that. First of all, I did not install the JCR exhaust until after the 1K Miles breakin period was over. Throughout the breakin I ensured the revs stay below 4K, drove the car on longer journeys and after the breakin did an oil change (again at 1K miles). Once the breakin period was over, I drove the car hard for about a week, helping (in my mind) the ECU to map the power outputs of the higher rev range. All that done, I went in at JoTech and did my first baseline test. The test includes 3 dyno runs. Video of the dyno runs posted below. Here's the output from the baseline run (all 3 runs)



With the baseline test out of the way, I went ahead and installed the JCR exhaust a few days after ( ). I drove the car hard for about a week to make sure the ECU has enough time to adapt to the new airflow. Lots of chatter around whether or not performance gains from exhaust stick or is reverted by ECU (check this thread here). Two weeks after the baseline test, I take the car back for AFTER dyno with JCR exhaust now installed.

FACTS about second dyno test with JCR Exhaust:

• Identical fan setup to baseline (no direct fan input to side air intakes)
• Same tank of fuel as baseline (Shell 93)
• Ambient/air intake temperature was higher by 1 degree in second test (JCR exhaust)
• Humidity was up from 45% to 55% in second test (JCR exhaust)
• Same technician, same dyno machine

The results were shocking. I gained 3HP at the very top of the rev range but LOST 10 HP throughout the rev range (where it actually matters). So not only I didn't gain 13HP as JCR claimed, but I lost 10HP from the factory output throughout the rev range. I discussed the results with Kenny from Jotech. Kenny is the owner and Jotech is a well respected performance shot here in Dallas. They do 1500HP stage 3 R8s, GTRs, Mclarens (very respectable performance shop) and he said the change in humidity could potentially reduce output buy 3-4HP but no 20HP (which is the delta between what JCR claims and what I got in dyno).

Here's the Dyno output of the second run with JCR exhaust with all parameters:



Here is the same dyno results, showing a point of rev range where I lost 10HP with JCR exhaust compared to stock factory exhaust:



I shared this feedback with Jonny from JCR and he basically said it has to do with the dyno runs being two weeks apart before just ignoring my follow up correspondence. I pressed him to share additional data points on their claim of 13hp gain and they one and only proof that was provided was the dyno run from a Spyder ( ).

In my opinion there are only two ways of explaining this:

1) JCR Exhaust does not improve your HP/TQ: If you look at the Spyder's dyno results, the baseline is 355 and JCR exhaust output is 369. In my case, the baseline was 365 and JCR exhaust output is 369. Oddly, both cars have identical outputs after JCR exhaust installation. That makes me wonder if the Spyder's baseline test was in fact inaccurate.

2) JCR Exhaust does improve your HP/TQ: but as Janko said in the references rennlist article above, the ECU eliminates the gain by revamping the parameters.

I have captured some videos of the dyno runs and my scattered thoughts about all of this in this video here:

rp2000r

To really compare results got to do runs same day I would think but thanks for sharing your info and results.

jmartpr

We got to eliminate from RL Janko's comment about the ECU adjusting maps thus canceling any HP/TQ improvements/gains when modding a vehicle...this is basically nonsense, the ECU doesn't know how much power it's making or should make. It just needs to hit a set of parameters on the maps via sensor inputs.

On your Dyno results.....there's good evidence that replacing the rear muffler does add power but it also depends on the design on that muffler system.
Jotech tested the Soul race system and almost got 30 whp..of course that one also eliminates the GPF but that's a lot of power from a catback, so there's got to be tangible restrictions on the OEM muffler.
Do you plan to test again the JCR? How about adding OAP?

JCviggen

What we're seeing here is probably down to variance. Not exactly the same atmospheric conditions, the car may have been strapped down with more force, the tire pressure a bit lower... the airflow slightly different with warmer air going into the side intakes... it's difficult to detect a 10 HP delta reliably on a dynojet in different sessions. Probably the initial 16 HP claim is best case scenario as well, a delta between a really good run with the exhaust and not the best ever run on the stock exhaust. It's a first party result so assume that +16 is about the highest you'll ever see and about half that is more likely.

The ECU doesn't compensate downwards. My GT4 with a full exhaust on it is still putting in really strong trap speeds on the racetrack, they haven't gone down at all.

Edit: I also question the RPM scale being accurate for the second run. The baseline run ends about where you usually see on a dynojet - well short of 8K RPM - but the second run actually goes past 8000 which is impossible without an ECU tune. It appears to me like the second plot is shifted to the right by a few hundred RPM.

4lflat6

I may do another dyno run in 6 months (entertaining swapping JCR with Akropovic). As for OPF removal/OAP, I know several people who ended up selling their JCR Non-silenced Race Pipes because of the excessive droning with OAP. I will consider OAP after I switch from JCR to Akropovic or Soul.

Thank you. I understand the reason why everyone says the dyno runs should be in the same day is mostly to keep the external parameters the same, In my case all external parameters are identical with exception of humidity which should not have that big of impact when it comes to dyno results. Think about multi-stage performance mods done over the course of several months. They are very much progressive and cumulative in power build up. I would understand being off by 3-5HP but not 20HP.

4lflat6

We are really talking about 24HP delta. JCR claims gains of 13 HP, in my dyno I lost 11 HP (which makes delta 24HP). In my opinion that's sizable enough to raise concern. Also note, each dyno session included 3 pulls. What you see there is the average of the 3 pulls (all yielding very similar, but slightly different results). Interesting observation about 8k mark, I will investigate that but even if we shift over everything by 200-300 RPM, the best case scenario we will have near identical results to factory which makes the addition of JCR exhaust, unimpactful to the overall performance.

JCviggen

Well, we can argue over what it ought to be, but I will keep pointing at the unreliable measurement being by far the most likely issue. Second to a worse batch of fuel from the gas station or whatever...

An exhaust like this is not a complicated thing. All these aftermarket exhausts are 2.5 inches from where they attach to the OAP to the end tips, with a crossover pipe in the middle. The valves open path has the same basic layout, length and diameter as a Soul, Kline or Cargraphic except there is no real muffler on the small path with valves closed. The JCR rear section must have about the same power gain as everyone else because there's no area of the design of the 718 rear section where it could make a big difference for power gained (or lost). Increasing the diameter of the undersized stock piping is what makes most of the power.

Real world performance has seen cars with aftermarket exhausts including JCR picking up considerable straight line speed gains that are well documented, it takes more than a fairly primitive dynojet setup (I'm not a fan of the strapping or the visible cooling fans) to disprove those...

Alpha Ice

What gear did you perform the tests in? I can see the additional humidity affecting the results some. Did you have any issues with lights on the dash? A lot of info has been provided before about running the car on a 4 wheel dyno vs just running the 1 axle. So those are also variables that could be causing problems (engine slowing down timing if it finds that the wheels are running weird). Just my .02, but I can't say I have a ton of experience, just what I've gathered around the forums.

RoadrunnerGTS

I doubt any rear section would give any power gain. 13HP (4%) loss on a dyno could be due to a number of factors such as tyre pressure, strap down, weather, fuel etc.

FYI, Janko theory on ECU changing parameters is a joke. Not possible. ECU's power/torque calcs are theoretical. The ECU is blind to actual power increases derived from bolt-ons. Most ECU's have a torque limiter to protect drivetrain, but this is way higher than you would get from bolt-ons.

horns

There's just about 100% chance the ECU/control system Porsche uses has an estimation of the power/torque being made. In fact, it is common in current production cars for torque/driveforce to be targeted by the control. The ECU "knows" more than you're thinking it does.

Whether or not Porsche has set up the control to limit torque when the engine is breathing better than stock is a different discussion.

Alan C.

This is why I’ve used Dundon exclusively on my 991.1 GT3, 991.2 GT3 and 981 GT4. Have an issue you can send it back. However, I’ve never had an issue with anything from Dundon.

jmartpr

You are assuming that right? Because using the PIWIS I haven't seen anything like that....even on the file dump you download when working on warranty requests.
Yes...a GT4 ECU today do know a lot of what's going on but not that much.....so not a 100% chance.
Anyway, we are diverting from the issue here which is the ECU capping power if you do mods which is totally nonsense on this car...there's enough evidence around from owners and sellers.

jmartpr

Dundon is good but there are a couple other that are also good...I also like Cargraphic products a lot.

horns

There are 1000s of parameters that are either read or calculated in modern ECUs. Torque is a calculated parameter for more than one OEM. That I can tell you with 100% certainty. I don't have direct experience with PIWIS, so I don't know what it shows and what it doesn't. However, knowing that other makes not only calculate torque in the ECU, but it is used as a very critical control parameter, I would be utterly shocked if the ECU in our cars didn't have a calculation for it.

That doesn't mean the ECU is adjusting to modifications to limit torque, but the capability exists if OEMs want to do so. I would argue if Porsche's control was adjusting to limit torque as a result of improving airflow as some have suggested, it would do so much quicker than two months down the road unless the car wasn't driven in that time frame.

jmartpr

On that I have to agree......the File Dump you get from the PIWIS 3 is a huge data file that that Porsche request when doing a warranty. As you mentioned, the list of parameters and detail is huge...but I have never seen a reading or calculation of Power/Torque, unless it's hidden on the ECU and not readable, which from a warranty approval perspective would be strange..