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February/March 2014 Question IT

Fixing what you broke

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Got a burning question or simply need some advice with problems you've encountered while wrenching on your current/future projects? Ask our automotive guru Eric Hsu anything-literally, he's going to answer every single question, as long as it's automotive related.

Got a tech question? Send it to questionit@importtuner.com

Newbie Build

I own a '06 350Z that spun a rod bearing in the No. 1 cylinder. I pulled the motor, which sat for three months. During that time I removed the crank and had it turned, along with new rod and main bearings. I removed the heads, knowing I had absolutely no engine-building experience but decided to build it myself in the kitchen following all the specs of the FSM and Haynes manual. Upon reinstallation, the car ran like a dream with the exception of a slightly high idle and intermittent stumbling that causes the engine to die. To address the idle issue, I removed the plenum, bank one and two cams and exhaust sensors, at which time I found the PCV hose on the back side of the secondary bank's valve cover was slightly loose. I also removed the valve cover off bank one just to take a peek and noticed it was contaminated with small bits of metal sticking to the sensors (bad, I know). I reinstalled everything, and to my dismay, the engine will not fire. I busted out the Fluke and tested the whole ignition system up to the coils. None of them are firing, although there is voltage all the way to the harness that plugs into the coils. If you could help me figure this out it would be a blessing.

-Raul, Odessa, TX

It's virtually impossible for me to diagnose something like this via email, but that generation of VQ35 engines has the occasional bad cam position sensor. The issue doesn't always show up as a check engine light either. It typically surfaces similar to your situation where the engine just doesn't start because neither the coils nor injectors fire. Since your ignition coils are getting power, it could be one of your intake cam sensors that is bad. To figure out which sensor is bad is the difficult part because they often check out OK electrically (i.e. sensor resistance), which is why the check engine light doesn't always come on immediately. If you have another buddy you can switch cam sensors with temporarily, that would be ideal. Otherwise you'll have to buy all four and try them out. Why they went bad when you were diagnosing I have no idea.

Subaru Swap?

I own '02 Subaru WRX (sedan) with about 176K miles. I was thinking about doing a whole STI swap (engine/tranny) down the road (I know it's going to be expensive). I like the style of the bug-eye Subaru, and the fact that it's light. Do you think that it would be worth the swap or would it be better to just buy an STI? And what STI engine/tranny should I get? I'm new to the car world, just got into it about two years ago, so I'm still learning but I'm not ashamed to ask dumb questions!

-Adrian Ramos, via importtuner.com

Whether or not the swap is worth it is a question you'll need to ask your wallet. Usually the math (read: cost of conversion) does the explaining for me. The best and easiest swap is going to be a JDM GDB EJ207 engine and transmission. You'll also need the rear end, as the transfer ratio is different between the STI and WRX. If you don't want to waste time on unnecessary BS, get yourself a complete swap: engine, turbo, intercooler, six-speed transmission, engine harness, ECU, flywheel, clutch, rear end, and driveshaft. You could also just get yourself a JDM GDB EJ207 engine, use it with your stock five-speed transmission, and modify your existing USDM EJ205 engine harness, but you will need the JDM GDB EJ207 ECU to control the AVCS inlet cams (the ECUs have the same connector). You could also go the ultralow buck way and get yourself a JDM GC8 STI (any generation) EJ20 engine and drop it in, but you'll need the matching engine harness and ECU. Some rewiring under the dashboard will be required too, which adds to the pain in the ass factor. Also remember that a GC8 engine is going to be old now and a high mileage turbo engine probably isn't an ideal swap. In the end it's all about what your budget is and how much time you want to put into the project. If you can afford it, the complete JDM EJ207 swap is probably the way to go.

Flywheel Decisions

I own a 350Z that's due for a new clutch. Apparently, these cars come with a dual mass flywheel, but upon searching the web, the only aftermarket replacements are single mass flywheels. I have heard that single mass flywheels give you better acceleration, but create more noise and can be a little stiffer. I don't mind the noise or stiffness, however I live in San Francisco and only take the car to the track about once a month or so, which leaves me spending most of my driving time in the city or surrounding areas. I was wondering if you could tell me which kind of flywheel would be best, single or dual? Could you suggest a proper one?

-Anonymous, via importtuner.com

It's not that the flywheels are single mass or dual mass, but it's their overall weight that allows an engine to accelerate slower or faster. Dual mass flywheels are named that way because there are literally two steel or iron sections (the dual masses) that are separated by rubber. The rubber section dampens drivetrain rattles and vibration, creating a smoother driving experience. The flip side is that dual mass flywheels have a service life and will need to be replaced because the rubber section deteriorates over time and sometimes they cannot be resurfaced when replacing the clutch.

Aftermarket performance flywheels are always going to be traditional (or "single mass"). With a solid, traditional flywheel you will definitely experience more noise and possibly some chatter (depends on your clutch) during engagement. However, San Francisco is a really hilly city and accelerating from a complete stop in the middle of a hill with an ultralight flywheel could be a severe pain the ass. An ultralight flywheel, aggressive clutch disc material, and light pressure plate would be the absolute worst combination that would cause massive chatter (I do mean massive) and would require you to heavily slip the clutch to get the car going. This would result in loud, clumsy, and unpredictable hill starts and short clutch and flywheel life. On the flip side, factory flywheels are typically very heavy and have plenty of inertia, making hill starts an easy affair.

Luckily the VQ35 has a lot of torque, but still going too light will make street driving in a hilly area more difficult in general. I would recommend a flywheel with only moderate weight reduction for the street. ACT's XACT Streetlite flywheel and HDSS HD/Perf Street Sprung clutch kit comes to mind for a great, street driveable combination. You did not mention your car's modifications, but the ACT HDSS 350Z clutch has a torque capacity of 455 lb-ft and only a moderate increase in clutch pedal stiffness. As another benefit, lighter flywheels also increase engine braking, which is a plus on the track.

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