Custom exhaust design based on other after-market products.
01-11-07, 05:12 PM
#1
Custom exhaust design based on other after-market products.
I was all amp'ed up about the Borla exhaust, and ordered one. Unfortunately, it was pulled when they figured out it would not be street legal. It was the 1st exhaust that I thought was "worthy" of purchase due to the X-pipe design and removal of the secondary cats. I realize that many of you will have issues with my environmental views, but I don't really care about increasing my emissions by 10% to gain 3 HP. My guess is that removing the secondary cats probably just about makes the difference between a stock IS350 and a non-ULEV pickup truck. On top of that, I feel somewhat confidant that adding a turbo would have worse environmental consequenses.
Since there aren't any exhaust systems now that meet my criteria, I'm wanting to do a custom exhaust. I've been looking at the "manifold back" systems on the market (LMS and Megan), and I think they really missed the mark on design. I've also looked at Roro's custom dual exhaust, and I think it missed the mark as well. I don't knock Roro at all since I think he was being very innovative. I just think his approach wasn't very well concieved or scientific.
The modified quote below regarding the LMS exhaust is from this thread, and my comments are below that.
This exhaust seems to go far beyond all others regarding power increases on the dyno. I realize that the dyno testing methods are not really known, but at least they were done on the same machine. I strongly believe that 9 rwhp is very significant especially since the gains are across the board. The operator would have to have made a HUGE testing error to screw up that much.
The biggest problem I have with this design is that LMS used an H-pipe instead of an X-pipe. I imagine that a good quality X-pipe like one of these would have made a significant improvement. I also don't think the excessive sound level would have been necessary if they designed the mid-section better and used better mufflers. It may not even be a benefit at all to do "true dual" due to scavenging, so I feel like that might just be a marketting ploy. Megan's approach might be just as good or better (I haven't been able to find independant dyno info about Megan's exhaust...).
Below is a modified quote about Roro's custom exhaust from this thread.
Again I want to applaud Roro's efforts. However, I feel confident that he would have doubled his gains by doing SOMETHING to combine the cylinder banks somewhere with an X-pipe, H-pipe, or 2 Y-pipes. Based on his dyno plots, he didn't gain much more than people with axle-back exhausts.
Below is another picture from Roro's thread of the stock exhaust components that he removed. The front Y-pipe doesn't look all that different from the Burn's pipes (I got under my car to examine mine closely). However, the rear Y-pipe looks really poor.
Okay ... so my point to this thread is to get technical opinions about what might be the best of all these designs for a custom unit. It seems to me like the deficiencies above can be overcome. It also seems like a good off the shelf axle-back (possibly the HKS unit?) combined with an optimized mid-pipe will be better than anything else available. Considering the above designs, it seems the optimum mid-pipe would be to simply remove the cats since I think the "true dual" thing with an H-pipe and 2 crappy resonators isn't even as good as the stock Y-pipe and single resonator. What do you think?
Since there aren't any exhaust systems now that meet my criteria, I'm wanting to do a custom exhaust. I've been looking at the "manifold back" systems on the market (LMS and Megan), and I think they really missed the mark on design. I've also looked at Roro's custom dual exhaust, and I think it missed the mark as well. I don't knock Roro at all since I think he was being very innovative. I just think his approach wasn't very well concieved or scientific.
The modified quote below regarding the LMS exhaust is from this thread, and my comments are below that.
After a slight delay in the delivery, the exhaust has finally been installed. It’s a stainless steel, true dual, CATBACK exhaust system with H-pipe, polished stainless at the rear section only. It is not smog legal due to the removal of the 2 rear catalytic converters. The front cats are still retained. The exhaust comes with two resonators.
A baseline dyno was already impressive with horsepower readings of 254.6 (to the wheels) and torque of 223.6. Readings after the exhaust showed maximum horsepower of 263.7 and torque of 236.4. There were reported gains of 22 rwhp. This however was reported with a prototype. I know for a fact the resonators had to be redone (due to the fact that they were too loud), and I haven’t seen any other dyno sheets with the production model. Depending on many variables (different dyno machines, temperature/humidity, etc.), the results will vary.
A baseline dyno was already impressive with horsepower readings of 254.6 (to the wheels) and torque of 223.6. Readings after the exhaust showed maximum horsepower of 263.7 and torque of 236.4. There were reported gains of 22 rwhp. This however was reported with a prototype. I know for a fact the resonators had to be redone (due to the fact that they were too loud), and I haven’t seen any other dyno sheets with the production model. Depending on many variables (different dyno machines, temperature/humidity, etc.), the results will vary.
The biggest problem I have with this design is that LMS used an H-pipe instead of an X-pipe. I imagine that a good quality X-pipe like one of these would have made a significant improvement. I also don't think the excessive sound level would have been necessary if they designed the mid-section better and used better mufflers. It may not even be a benefit at all to do "true dual" due to scavenging, so I feel like that might just be a marketting ploy. Megan's approach might be just as good or better (I haven't been able to find independant dyno info about Megan's exhaust...).
Below is a modified quote about Roro's custom exhaust from this thread.
Again I want to applaud Roro's efforts. However, I feel confident that he would have doubled his gains by doing SOMETHING to combine the cylinder banks somewhere with an X-pipe, H-pipe, or 2 Y-pipes. Based on his dyno plots, he didn't gain much more than people with axle-back exhausts.
Below is another picture from Roro's thread of the stock exhaust components that he removed. The front Y-pipe doesn't look all that different from the Burn's pipes (I got under my car to examine mine closely). However, the rear Y-pipe looks really poor.
Okay ... so my point to this thread is to get technical opinions about what might be the best of all these designs for a custom unit. It seems to me like the deficiencies above can be overcome. It also seems like a good off the shelf axle-back (possibly the HKS unit?) combined with an optimized mid-pipe will be better than anything else available. Considering the above designs, it seems the optimum mid-pipe would be to simply remove the cats since I think the "true dual" thing with an H-pipe and 2 crappy resonators isn't even as good as the stock Y-pipe and single resonator. What do you think?
Last edited by Gernby; 01-11-07 at 05:23 PM.
01-11-07, 07:13 PM
#6
True dual exhausts don't benefit as much from scavenging. If someone were to design an exhaust system for the IS that had 6 totally individual pipes from the engine to the tips, it would suck *****!
Last edited by Gernby; 01-11-07 at 07:35 PM.
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01-11-07, 07:24 PM
#8
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Do you think we would gain any power going into a larger single pipe after the first set of cats instead of running two pipes? I had great success running a down pipe and single 5inch pipe back to a single muffler on my Supra.
01-11-07, 07:34 PM
#9
Again, I don't know nothin' about designin' no exhaust systems, but intuition tells me that there would be a significant difference in performance between the 2 X-pipes pictured below. The one on the left is Megan's X-pipe, and the one on the right is Burn's X-pipe. I would expect that any change in cross-sectional area will cause back pressure due to the change in velocity of the gases, and Megan's X-pipe looks like it will have FAR more of a change at both ends of the transition.
01-11-07, 07:41 PM
#10
I think a "perfectly designed" single exhaust would probably make more power than a "perfectly designed" dual exhaust, but it would look like hell on our car. However, I don't believe that larger is necessarily better due to the backpressure that might result from the change in diameter.
01-11-07, 08:41 PM
#13
Here is the close-up of the section that I'm leaning toward modifying. I think the best thing to do is to cut the secondary cats off (far left), and either replace them with straight pipes to the OEM Y-pipe, or replace them with a Burn's Y-pipe close to the left and go straight into the stock resonator.
