Proving Grounds
Description
Having gone down the all-motor, bolt-on, power-adder path with our recently retired '06 Infiniti G35 Coupe project car, we're quite familiar with the limitations of the VQ35 in normally aspirated form. Despite throwing a full complement of bolt-ons at the engine, we only bumped at-the-wheel output from 221 whp to 258 whp on U2Ndyno.com's Dynapack when it was all said and done. That's a decent gain and it helped bring the car to life quite a bit, but we got nowhere near our 300-whp NA goal, which should really be a lot easier to attain with a 3.5-liter V-6.
Of course, now that we've retired our G, an all-motor power-maker appears on the market that would've undoubtedly helped us move much closer to that elusive 300-whp mark. SG-Motorsport has been hard at work developing its new longtube headers, true race-quality pieces that have been tested and tuned on the company's Grand Am 350Z race car (you've probably already read the "I Wanna Go Fast!" story about SG's recent racing adventure on page 50).
One of the big bottlenecks when trying to make more normally aspirated power from a VQ35 is the factory exhaust manifolds. In the quest to reduce emissions, Nissan equipped the VQ with very short headers so the catalytic converters can be placed as close to the heads as possible for faster light-up time (where the cats achieve the required temperature to work their emissions-killing magic). As a result, the headers' primary runners are cut prematurely short and this forces a less efficient collector design because the primaries must come together abruptly to make space for the cats.
Hand-crafted from stainless steel tubing and featuring stepped primaries, SG's longtube he
To overcome the design limitations of the OE headers and uncork the VQ on the exhaust side, SG-Motorsport has replaced the factory headers and catalytic converters with its race-tuned longtube headers. Beautifully TIG-welded from stainless steel and using true racing merge collectors, the SG longtube headers make zero compromises in their design. These headers are optimized for both low-end torque and high-end horsepower, the stepped primary tubes improve low-rpm engine response while the primary lengths have been tuned for optimum high-rpm output. As an added bonus, SG headers also feature slip fit merge collectors, helping reduce install time by as much as 75 percent.
Results
To test SG's longtube headers, we borrowed the company's low-mileage '06 350Z Roadster. Equipped with a stock RevUp engine, a custom 3-inch diameter cold-air intake and a custom 3-inch diameter single-exit exhaust, we started by baselining the car with the OE headers. During this process we tuned the factory ECU for maximum output using an UpRev Osiris reflash that optimized fueling, ignition timing and cam timing. Strapped to U2Ndyno.com's conservative-reading Dynapack, we got a best reading of 257 whp and 239 wtq. That's some very impressive jam from an internally stock RevUp with just an intake, after-cat exhaust and an ECU reflash.
After letting the engine and stock headers cool down, we threw the Roadster on a hoist and swapped on the SG longtube headers. This job took us about four hours, less than half the time it took us to swap Stillen headers onto Project G35.
The time savings were a result of the SG longtubes having an individual tube for each cylinder that slip fits into the merge collector, allowing them to be installed without having to remove the steering shaft, lifting the engine up or doing any other hard labor often required when installing one-piece headers.
Once the SG longtubes were bolted up, the Z Roadster was loaded onto the Dynapack and the fun really began. Some intake and exhaust cam timing adjustments using our UpRev Osiris tuner were required because of the additional flow through the exhaust (and therefore through the heads), but the ignition timing and air/fuel-ratio targets stayed the same. After a few pulls, the power started to nose over and it was time to compare our gains.