Originally Posted by JCviggen

Except that with exhaust mods you're not moving more air so much as reducing pumping losses. How does an ECU measure pumping loss? I'll wait.

Also, our car do not have air flow sensors. They calculate air flow from the MAP plus stuff like Pbaro, IAT, engine speed and fixed values that were based on the stock car's characteristics. It works fine with a modified exhaust because the airflow into the engine actually changes very little. But the ECU can be effectively slightly "wrong" about the amount of air it ingests if you change anything that is necessarily defined by a fixed value. The slight correction required is taken care of by the wideband o2 sensors in the exhaust, but it's a very small correction that is easily within the tolerance allowed.

With less backpressure he ECU will have an easier time running more timing (it cannot distinguish the mods from good fuel in this case) but most of the power is simply "made" by not losing it to shoving the exhaust gases out through a straw.

There are certainly ways that different cars with different configurations that would have an easier time catching on but that's not really the point in this case.

Originally Posted by JCR-Porsche

1. Logging AIT’s or at least being aware of them should be very simple in that case, is that something that was considered or measured?

2. Consistency (no side air intake fans) between the before & after tests doesn’t take away the issue mentioned above. It will definitely impact results because you’re introducing a factor which you will not encounter in the real world unless you almost entirely blocked the side vents.

3. Comparing a header back exhaust to a rear silencer replacement on a different car, 9 months ago really bares no relevance at all. No bashing here, just presenting factors that can lead to skewed results, I’m trying to help.

4. 100-200kph acceleration data is the test to use to compare before after but again these really need to be completed on the same piece of road (we use track) and with conditions as close as possible too. 0-60mph is way more to do with the launch than anything else.

5. If our rear silencer ‘loses’ power then we certainly wouldn’t be posting the times that we are, we’re actually quite a long way ahead and we have data from our race manifolds / OPF delete with stock rear and race manifolds / OPF delete with JCR rear and there is a very distinct gain in performance.

5.1. In regards to stock vs rear box only 100-200kph data this is something that I will be able to gather in the next few weeks with the next willing customer car we have in, no issues, I’ll share on this thread ASAP.

6. Again, I was trying to be polite, very happy that you’re successful and earning lots of money. I think you’re getting the wrong end of the stick with a number of responses on this thread. You have to be reasonably open to criticism when presenting this kind of information in this way.

JC

Originally Posted by Archimedes

Simple solution to this OP. Find someone local with a stock car to run them back to back on the dyno on the same day, being careful to match fuel, pressures, etc. Porsche tolerances are very tight on their motors, so the stock baselines should be similar.

Originally Posted by 4lflat6

AIT matched the ambient temp by a couple of decimal points. I look forward to seeing the 100-200kph data. Contrary to what you are saying, I am pretty happy about the different suggestions/explanations that I got here. There are for sure some people who comment without reading the post or just come here to troll but that is internet for you some people are passionate about JCR and I get it. Like I mentioned these are my numbers, my reality, my facts. People are free to draw their own conclusions. This is a data point that I wish I had before I purchased the exhaust, hence I am sharing it here for the next person who may want to make the same purchase.

Originally Posted by JCR-Porsche

I really doubt that logged / PIWIS measured AIT's matched ambient temp within a couple of decimal points, thats almost impossible, especially with no fans by the side air intakes.

Very much appreciate you're telling your story but I think you're on your own with the results that you have gathered.
As part of the dyno test we will also log AIT's and run with and without fans to demonstrate the point that im making above.

Originally Posted by JCR-Porsche

Planning to be able to get this test completed on 20th of this month, everything within one day. It's a little more difficult as im not prepared to run / publish 100-200kph testing on the road. Tests mean nothing without accompanying video of the run so we will be completing the runs on track at Donington Park.

JC

Originally Posted by 4lflat6

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).

Originally Posted by JCR-Porsche

I really doubt that logged / PIWIS measured AIT's matched ambient temp within a couple of decimal points, thats almost impossible, especially with no fans by the side air intakes.

Very much appreciate you're telling your story but I think you're on your own with the results that you have gathered.

We have a customer who is willing to help with the data gathering so we will be completing the back to back dyno at an independent dyno shop with proper testing techniques and logs and will follow up / back up each result with 100-200kph runs. 100% stock 718 GT4 with only our rear silencer replacement and approx 5000 miles.

As part of the dyno test we will also log AIT's and run with and without fans to demonstrate the point that im making above.

Planning to be able to get this test completed on 20th of this month, everything within one day. It's a little more difficult as im not prepared to run / publish 100-200kph testing on the road. Tests mean nothing without accompanying video of the run so we will be completing the runs on track at Donington Park.

JC

Originally Posted by kitwetzler

It always amazes me that people think dyno results are "scientific" without actually being scientific about it. Without airflow into the side vents, the car will produce much less power than with, and be much more sensitive to conditions within the dyno cell. You end up testing a situation where the car will never be. The DME we have is very sensitive to air temperature and the only way to do testing is to make sure conditions are identical and controlled as best as possible - fans simulating the car moving are the first step.

Originally Posted by JCviggen

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.

Originally Posted by 4lflat6

Seems like the rev limiter will only kick in at 8100RPM so hitting 8000RPM should not be an issue without an ECU tune. See article here.

Originally Posted by rahtid

I haven't received my non-silenced race exhaust yet but this is why I chose JCR, the extensive track testing they do for their products. Dundon is also good but JCR have easy bolt ons and sounds better imo.