With my '04.5 G35 sedan, I've done: RevUp intake box, Z-tube, 5/16" spacer, Magnaflow resonator, removed internal muffler valve, and Kinetix hiflow cats. Just did a hypertech 'tune' (lol). 174k miles on the clock.
IMO The VQ's are pretty tuned up. IMO the 5/16" plenum spacer is the only mod that made a noticeable difference. The hi flow cats made a small difference, but my OE cats were a little bit clogged, however my cat-back is still mostly stock. The HFC's make the car A LOT louder. Every 'cold air' intake I've seen intake just changes/increases the sound the engine makes, or makes the car run worse b/c hot air lol. I have not seen one header dyno for a DE that shows any gains below 4k rpm. For daily driving, the stock headers are just fine.

One thing that I think might be noteworthy, is the earlier cars (all '03 and early-'04 cars) don't have wide band O2 sensors. This may be why some owners feel zero difference with mods, as the ECU gets far less of an idea of where the AFR is actually running.

I picked up a used Hypertech tuner #62005 locally off of craigslist, as I'm still saving for a proper UpRev tune.
It seems to increase the throttle responsiveness quite well, and both Hypertechs dyno and one of the dyno sheets I found online showed that it corrected the AFR from running too lean in higher RPM's, which is one of my concerns with switching to HFC's. It has options for the Stillen intake and Takada intake, I tried the option for the Takada, and it made it run really, really rich. I've worked on dirt bike carburetors a number of times, and the smell was all too familiar. Needless, I switched it back to the 'stock' intake option and it ran better LOL.
Overall it seems to work, but I'm not convinced its a go-to. Everyone I've talked to thats had an UpRev say that its really worth it.

 

HFC's/cat back and the lightweight flywheel were by far the two biggest mods for "feels like it's going faster" imo. Especially that flywheel, going from a 28# to a 14# flywheel was literally night and day difference.

 

How when they come stock at 270-293 HP?

 

Probably talking wheel HP.

From the factory the rev-up engine was rated at 290ish at the crank, but you can expect ~15% frictional loss getting that power to the wheels, so most dynos read ~240 HP at the wheels. Full bolt-ons and a tune usually only net 40 WHP. YMMV.

 

Yep, two different motors came in the G35 (not counting the 2007+ HR motor), most came with the normal VQ35DE rated at 270 BRAKE hp, the 2005-2007 6MT coupe and 2005-2006 6MT sedan came with the "rev-up" version of the engine which also has exhaust cam timing and was rated 293 BRAKE hp.

Actual wheel horsepower is quite a bit lower than the BHP ratings.

 

Hey guys new to the forum But I live in AZ Mesa area just got my first G 06 coupe so far I’ve done z1 with plenum spacer , K&N typhoon with AEM dry flow , new plugs coils , z1y + 2.75pipe + 4”res, to dual exit exhaust , mishi moto radiator ,thermostat, bleeder valve , and z1plenum spacer does the car need to be tuned badly I’ve heard the car takes learning time up to a week maybe longer sometimes is this true ? And where around here is a good spot to street tune I’m working with 300-500 $?

That’s old girl there

 

When they're talking about "ECM learning" they're really talking about Long Term Fuel Trim. Basically every engine requires a little more or less fuel based on things like vacuum leaks over time, differences in fuel pressure, injector clogging due to age, machine tolerances delivering more/less fuel, etc. The ECM can make a broad adjustment +/- up to like 25% for each bank of the engine to compensate for all that stuff.

That's all it does, when you do an "ECM reset" all you're doing is resetting the LTFT to zero then it adapts, it's CONSTANTLY adapting though, you should reset anytime you make an engine modification, including things like replacing engine sensors or fixing vacuum leaks, just speeds up the process.

The car will not run any different though (this doesn't affect the vehicles base fuel/timing map), it runs almost entirely off the Short Term Fuel Trim which is updated several times per second in some cases. LTFT is in many ways just a diagnostic tool to see if you are developing any mechanical issues that need to be fixed.

As for the tune, Uprev is your main option for the G35, look for a local Uprev tuner and get a price quote. There are also reputable e-tuners, I'm not sure you'll find what you're looking for with that budget though. Send a pm to @seymore4 if you're interested in e-tuning.

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The ECU does "learn" to some extent, however that's within a very limited range and meant to adapt to different climates/ elevations/ etc with all OEM equipment. If you modify stuff and change how the engine breathes its going to run differently. Also the targets that it is trying to learn to are in no way ideal from a performance standpoint. Lots of fun to be had with a proper tune. Biggest thing you'll notice is a more responsive peppy car from fixing the factory throttle restriction.