Maurice,
I would like to provide the answers to some of the questions you poised above and also clarify some of the (mis)information provided in an earlier post on this X-crossover string.
To get answers to your questions, I called Rhino mufflers technical information line and spoke to a knowledgeable gentlemen, Jay. Unfortunately, Jay was not immediately aware of any recent Hot Rod Magazine article concerning compariosns of a X-crossovers on a vehicle using their mufflers. After talking with him a few minutes, he did recall an installation done over a year ago on a 1970 Mercury Montego. Jay asked that we let him know what issue it was in so he could try to find it.
I then called The Muffler Man in Placentia, California to ask if they had information they could share with me about recent X-crossover comparison tests. I spoke to Tom, and like Rhinos technical representative, he was unaware of any recent articles. However, he did recall the Mercury Montego article and offered to send us copies of the magazine article after he retrieved it from his files.
I spoke to Tom about the X-crossover he sells and he said that when the hole sizes in the junction of their products are similar to other manufacturer's crossovers, he would expect ALL of them to act similar. Like our past experience, Tom found that too small of a transfer hole between sides reduces the power gain and too large of a hole increases the sound level. We also compared previous test data and I told him we generally saw increases of between about 6 and 15 horsepower over H-crossover systems and he said they usually expect to see from about 5 to 12 HP increases. Tom also said that they do work on 600 to 750 HP California drag race cars and said he uses the X-style crossover to reduce the sound level and pick up the power.
After acquiring the article, I found that the power gains mentioned in the post you questioned were in reference to a complete replacement of the original single exhaust system that used log manifolds and a single 2 ¼" pipe muffler system. Id like to share several quotes from the Hot Rod article: "Our mellow Merc still possessed the original exhaust system: 30 years in a Bay area garage had preserved it like a piece of beef jerky! While this meant factory levels of quiet in the cabin, it also meant severe exhaust-flow inefficiency- 1 5/8" manifold dumping into a single pinky-slim pipe". "We used equal length , long tube Hedman headers for our 150,000 mile 351C (1 5/8" primaries, 3" collector) and sent them to HPC in Utah, to get ceramic-coated inside and out." Hot Rod also used one of the Muffler Mans X-crossover and Rhino mufflers. The pipe diameter was increased from the original 2.25" (single) system to dual 2.5" exhaust pipes and tail pipes. The power thus gained from this complete exhaust system change was "22 HP and 11 ft-lb of torque at the wheels". Here is another direct quote from the Hot Rod article which was printed directly under a photo of the Muffler Man X crossover: "Instead of a typical H pipe, we opted for one of the The Muffler Mans X-style aluminized crossover pipes which was built in-house. The gentle bends of the X pipe help scavenging (no sharp corners to induce turbulence as in a traditional H-pipe system...), and the larger chamber at the center of the X deals more efficiently with exhaust pulses, which helps both scavenging and eliminating resonance. It also makes for a rich, rumbly exhaust note".
It should be noted that all X systems have a larger chamber at the junction due to the design.
Additioanlly, please note that Jim Hand commented on the expected power gain of similar X crossovers in his recent post on this subject, "In summary, the test results from Hot Rod tests clearly demonstrate that the Dr Gas X crossover, AND OTHER SIMILAR X SYSTEMS, do indeed meet the customers expectations of more power and therefore more performance."
So Maurice, to answer your questions, it was April 1999 Hot Rod, page 100, the "controlled test" article was about a 351C Mercury Montego with single exhaust that was changed to duals with headers, the power increase noted was gained by the complete exhaust installation, not just a specific crossover comparison, and the total power they found was a peak of 22 Hp and 11 ft-lb of torque.
I would expect the author that posted information regarding this test to answer your remaining questions. Please feel free to email me at
[email protected] if you would like additional information.
Tom Hand