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Old 08-23-2004, 03:44 AM   #1
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Post Rx-8 And Vacuum Lines

POWER PAGES display until 02/17/04
1993 MAZDA RX-7.
Prior to testing any of the products, we performed a routine maintenance on the rotary, changing the oil and the spark plugs. We recommend changing the spark plugs every 15,000 miles on a rotary. Routine checks of the oil level on a rotary engine should also be performed. Even though the oil was changed only 2,000 miles ago, the oil level was already reading one quart low. Instead of adding oil we decided to change it. With the vehicle strapped to the dyno we performed a baseline run. The 7 was oly able to muster 201.4 hp and 199.2 lb-ft of torque to the wheels. Even with a 15-percent loss to the wheels, the car should be making around 217 hp. The Mazda was down nearly 16 hp. Instead of proceeding with the bolt-ons, we decided to investigate. Fortunately for us, our dyno shop, XS Engineering, is a rotary performance specialist. After talking to Koji Arai and Pete Yeung of XS, we were informed that bnroken vacuum hoses were a common occurrence in the third-generation RX-7. The heat generated by the engine causes the rubber hoses to dry out permaturely, making them very brittle and prone to cracking. If there is a leak in the vacuum lines performance figures would be affected. We performed a pressure test on the entire engine to locate any possible leakage. Immediately after pressurizing the system, we notived several leaks in the spider web of vacuum lines dirctly under the intake manifold. In order to replace the vacuum lines, it would require us to remove the upper half of the manifold. Instead of finding another RX-7 for testing, we proceeded with the work. Pete "Fei Low" has workedc on hundreds of RX-7s, and is capable of performing the modification with his eyes closed. He removed the upper intake manifold and started replcing the factoru rubber hoses with silicone hoses. When we asked why not use regular rubber hoses, he pointed out that hte silicone hoses are more durable than the rubber hoses and are less likely to get hard brittle. He was also quict to note that any performance enthusiast planing to increase the boost presure on the Mazda needs to have this modification done. Without the modification, the hoses can easily break off or be blown apart under boost. Besides replacing the lines with silicone units. Pete also added a tounh of super glue to further secure the line onto the intended portal to prevent any possible blow-offs at higher boost levels.
With the Mazda all buttoned up, it pulled a:
BASELINE POWER-201.4(SHOULD BE 217+)___HP+N/A___TQ LEVEL-199.2___TQ+N/A
MAINTENANCE-230.5___HP+29.1___TQ LEVEL-203.1___TQ-3.9
A'PEXI INTAKE-238.5___HP+8.0___TQ LEVEL-215.4___TQ-12.3
A'PEXI N1 EXHAUST-242.6___HP+4.1___TQ LEVEL-233.9___TQ+18.5
FINAL___HP LEVEL-242.6___ HP+41.2___TQ LEVEL-233.9___ TQ+34.7

Ok so after all that my question is... Do we need to worry about this vacuum line/hose problem with the RX-8?
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Old 08-23-2004, 07:12 AM   #2
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I wouldn't believe so, the so called "rat's nest" in the FD RX-7 was for the complicated sequential turbo system. The RX-8 shouldn't have anything close to this.
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Old 08-23-2004, 08:45 AM   #3
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The RX-8's vacuum system is FAR simpler than the 3rd gen RX-7's. I think the '8 has around 8 vacuum lines, whereas the 3rd gen 7 had around 70-some-odd.

The 3rd gen RX-7 had an EXTREMELY hot engine bay as well, being rather cramped with two turbos under the hood. All the rubber would quickly vulcanize and get ROCK hard. The '8 has a much more roomy engine bay, and from all reports I've seen doesn't run near as hot.

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Old 08-23-2004, 05:24 PM   #4
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My RX-7 3rd gen uses vacuum lines to control or read a lot of stuff. The RX-8 uses -electric- motors and sensors to control the intake system. No comparison. Only reason to mess with the hoses in an RX-8 is for looks.
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Old 08-23-2004, 07:51 PM   #5
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OK this is good to know. So based on this. Do you think the 8 is less "routine maintenance" then the 7?...
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Old 08-23-2004, 07:51 PM
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2004, 2007, engine, intake, leak, line, lines, mazda, pressure, routing, rx, rx8, test, vaccum, vacuum

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