How restrictive is the original exhaust?

[flywheel]

I'm wondering how restrictive the original exhaust is? For instance, how much will I gain if I remove the cats but keep my original catback, or buy an aftermarket catback system? Or say I buy freeflow cats, but keep the original catback?

[MrHarris]

If you want the most gains, replace the mid section or x-pipe. 20whp and 20wtq is very possible with a good design. As for the rear section, from all the dynos I've seen, only RPi's rear section has any real gains.

[dogears]

Why do you RPI fans/guys spread mistruths about the exhausts? There have been numerous dynos posted of Eisenmann, Vorsteiner, AA, Dinan, etc etc etc, all showing modest gains from cat back systems.

The RPI dyno was full exhaust-no cats. We went over this in another thread on here recently.

There is no way in hell that RPI is making significant rear section gains that are elusive to the other manufacturers. Instead, I believe it is the continuing use of full exhaust dyno in error.

I have seen pretty consistant 20-25HP gains when swapping full exhausts. Maybe up to 6-12HP or so on the rear section. Maybe a tad more on the full if optimized with an ECU tune.

No offense....

Originally Posted by MrHarris

If you want the most gains, replace the mid section or x-pipe. 20whp and 20wtq is very possible with a good design. As for the rear section, from all the dynos I've seen, only RPi's rear section has any real gains.

[MrHarris]

Originally Posted by dogears

Why do you guys spread mistruths about exhausts? There have been numerous dynos posted of Eisenmann, Vorsteiner, AA, Dinan, etc etc etc, all showing modest gains from cat back systems.

The RPI dyno was full exhaust-no cats. We went over this in another thread on here recently.

There is no way in hell that RPI is making significant rear section gains that are elusive to the other manufacturers. Instead, I believe it is the continuing use of full exhaust dyno in error.

No offense....

Go look at tightie's review of the RPi. Like 5 or 6 pages back there's a dyno on the dyno dynamics with just the axle back with some pretty serious gains. Looked almost like the full system.

[dogears]

As for the dyno chart, I say BS. Gains are too large. We'll need to see at least one more dyno to corroborate otherwise I think we could be comparing the worst of several stock runs against the best of several RPI exhaust runs. There is not that much power to be had in just the rear section. With all due respect

There is no way that the axle back produces gains so similar to full exhaust unless the numbers were intentionally skewed due to lack of averaging the runs or other manipulation.

Originally Posted by MrHarris

Go look at tightie's review of the RPi. Like 5 or 6 pages back there's a dyno on the dyno dynamics with just the axle back with some pretty serious gains. Looked almost like the full system.

[dogears]

Something is fishy! Is this a comparison of the best/worst runs? With no methodology divulged this dyno test is worthless to me as it may be misleading. Read Pencil Geek's great article on dyno methodology. Notice the run numbers in the first dyno. Run #7 is compared to run #18. Where are the other 16 runs?


Just rear section - 21hp



Full Exhaust

[flywheel]

So, it is possible to get a few hp from a rear-section but basically it's the middle-section that really counts and is worthwhile changing? I'm not going to put serious money into the car right now, and was looking at the Kelleners sport engine kit:

http://www.kelleners-sport.de/english/index_d.htm

It says ECU upgrade and cat removal but I'm not sure I want to remove the cats. Possibly just have freeflow cats and keep the rest of the exhaust stock, unless of course the stock exhaust is too restrictive to actually gain anything significant from the ECU upgrade.

[RPIpower]

We dyno them SEVERAL times and in different conditions. We never do a "best of each run". The runs are as it and we dont post gains unless the numbers are backup with consecutive runs. We welcome people to come watch our R&D during our testing sessions. Sometimes only single graphs are posted. Thats why we post with several runs like on the second dyno graph. Most of the dyno sheets posted are captures of what the customers ask us to print out. In some cases, they want the graphs with the most gain...I guess for bragging rights? Peak power is the same all all the stock runs though.

[RPIpower]

Originally Posted by MrHarris

If you want the most gains, replace the mid section or x-pipe. 20whp and 20wtq is very possible with a good design. As for the rear section, from all the dynos I've seen, only RPi's rear section has any real gains.

Are you sure about this? Lets make a bet JJ. Lets bet lunch.

[dogears]

Eloy, I am sure you make a fine product. You and I both know that there is only so much to gain from axle back. The fact is that choosing the runs the way you did can change things from a 14hp gain to a 21hp gain, for instance. Bragging rights, maybe.... But there are plenty of other systems dynoed at similar gains in the mid teens. I have never seen over 20hp with just mufflers though. If I was in CA, I would come by. Maybe even use your products. However, I have to be skeptical and although you post good numbers, I need to see the other plots and another 3rd party dyno session if I am to believe your gains are 40-50% better than everyone elses. Especially considering removing the cats only yields 5-10hp more according to the other RPI dynos.

Please post a graph of all the runs so we can see how the other plots looked....

Originally Posted by RPIpower

We dyno them SEVERAL times and in different conditions. We never do a "best of each run". The runs are as it and we dont post gains unless the numbers are backup with consecutive runs. We welcome people to come watch our R&D during our testing sessions. Sometimes only single graphs are posted. Thats why we post with several runs like on the second dyno graph. Most of the dyno sheets posted are captures of what the customers ask us to print out. In some cases, they want the graphs with the most gain...I guess for bragging rights? Peak power is the same all all the stock runs though.

[vegastrashed]

Max stock = 324 rwhp
RPi Axle back = 341 rwhp
--------------------------------
17 rwhp gain

RPM was changed to MPH for a M5board member's request.

BTW, the next graph *.010 was 322 rwhp. From *.011 - *.018, it was with the GT Axle back exhaust.

[RPIpower]

Originally Posted by dogears

Eloy, I am sure you make a fine product. You and I both know that there is only so much to gain from axle back. The fact is that choosing the runs the way you did can change things from a 14hp gain to a 21hp gain, for instance. Bragging rights, maybe.... But there are plenty of other systems dynoed at similar gains in the mid teens. I have never seen over 20hp with just mufflers though. If I was in CA, I would come by. Maybe even use your products. However, I have to be skeptical and although you post good numbers, I need to see the other plots and another 3rd party dyno session if I am to believe your gains are 40-50% better than everyone elses. Especially considering removing the cats only yields 5-10hp more according to the other RPI dynos.

Please post a graph of all the runs so we can see how the other plots looked....

The thing is that we dont/didnt just dyno it once. We dynoed the car several times in different days. Above is the highest stock dyno we have for the same car. Also, I understand that our numbers are pretty different than others. We dont do things the same way as others. Who else goes smaller than stock piping? I can tell you not many people.

[dogears]

My bad.... The tiny graph looked like over 20hp gain to me. 17hp is more in line, especially considering the 1-2% variations in testing.

Carry on!