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Old August 4th, 2019, 11:29 AM   #1
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Question Turbos, VCM and Tuning on J35Z2

I've read up alot in posts around here and followed the long thread from NVA-AV6 about a 7th gen turbocharged accord v6 build project a while ago.

Owning a 2010 Sedan 3.5L V6 with the J35Z2(Auto) VCM Engine, I'm having a hard time finding actual tested information about this motor as very few/none have actually shared details about actually modding and dyno-testing this engine, besides general pointers.

1. Why does nobody tune the J35Z2 for a turbo build? Let's say hypothetically I procure a custom turbo manifold for a single turbo setup, acquire all parts required. I know people keep saying VCM is a hindrance. But where Exactly does VCM stall me in terms of tuning?

As I understand, VCM engages only on very light throttle, which is not enough to spool the turbo. As I go WOT/heavy foot, VCM immediately disengages, so I don't see how it interferes with forced induction.

Reading up more on it, the cam lobes on J35Z2's camshaft for VCM-deactivating cylinders are just circles, so the valves for those remain shut in VCM mode.

I just don't see how VCM can mechanically affect tuning.

Of course I am just getting started with knowledge and hands-on experience with all this and might be completely wrong or missing a major point here.

People mention that maybe the OEM ECU triggering a secondary map under VCM mode interferes with the primary map. But all this information seems to be speculative most of the time and I haven't yet come across any tested results.

Has anyone ever actually turbocharged the J35Z2 successfully while preserving VCM (maximum fuel economy under part throttle, even if the difference in gas mileage with/without VCM is about 2 mpg)?

2. Seeing that KTuner has the ability to disable VCM and tune AF ratios/timing, etc. on the J35Z2, can KTuner be used to tune a turbocharged J35Z2 setup?

Also with the above questions, I also am ignoring the weaker automatic tranny's ability to handle any significant power (340 whp+).

I'm also ignoring the fact that the Accord handles like a boat stock and is a FWD not ideal for such power (Wheelspin/A family sedan).

I'm also not taking into account the general hate for VCM due to part failure/design issues, as I personally like having the extra 2 mpg and haven't yet come across any fouled spark plugs/worn engine mounts/noticeable vibrations on a properly maintained 10+ years old car (Maybe I got lucky).

I'm strictly speaking about just tuning this particular VCM engine.

What I can't wrap my head around is if people have poured down money for built FWD inline 4 turbo civics with 800hp+ (which indicates sometimes money isn't really the issue), why are built turbo J35Z2/Z3 so rare/non-existent?
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Old September 4th, 2019, 02:33 AM   #2
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Bump. Anyone?
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Old October 7th, 2019, 09:57 AM   #3
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Couldnt agree more
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Old November 3rd, 2019, 04:59 PM   #4
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The cam lobes for VCM deactivated cylinders are NOT just circles. When VCM activates, it triggers a solenoid that stops the cam follower from pushing the rocker arm, so the rocker arm can't open the valves. Not that this answers your question, I just figured it was good to clear it up.

It is definitely possible to turbo an 8th gen. My biggest fear is that it will force the auto trans to give out sooner than its already short life expectancy.
There are plenty of things that you can be afraid of, but if you are willing to risk it, I don't see why you can't.

The one thing I don't understand is why you would bother to keep VCM enabled. Even on low boost you are going to be throwing way more fuel at the cylinders, way more than you will be saving with VCM. Could you keep VCM on? Maybe, but why risk something going wrong when you could totally eliminate the risk by turning it off?
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Old November 9th, 2019, 08:11 PM   #5
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I have an 04 accord coupe j30a4 stock internals boosted which has been riding good since 2017. Havent had any main issues.....can only use the hondata flashpro with the jseries motors
7th generation
03 accord coupe
HFP lip kit
Spec stage 4 clutch
Modified siemens injectors 560cc
Hondata Flashpro
6speed tranny
60mm borg warner
9 pounds
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