OK since all the wonderful things on the g35x are kinda new to me as I am from a non computer, non sensor, carburetor and V8 background...so here are my questions. forgive me if this has all been covered somewhere...

So it seems that from what I have read a z tube will give you a little more high end/rev HP at the cost of some low end torque. So is it also true that exhaust mods such as coupe mid and or a cat back system will have an opposite effect on performance as in little more low end at the expense of high end/rev? If that is true is best to do both so that the engine will stay balanced so to speak ie more air in more exhaust out so the benefits will be the same small low end and high end gain???

unless the sedan is a lot different than the coupe the z-tube isnt going to give you anything except change in tone from deletion of the resonator box

Long story short, any intake modifications on our motors are essentially for looks and more intake noise. A minimal power gain at best. A coupe mid pipe will be the same principle but maybe a little more midrange power.

That's good to know and interesting so no "real" gains from z tube or mid pipe a swap . So I gueS it's the same for a cat back system or is ruts different in the "gains" department? So where do the bolt on gains come from a spacer or something more involved?

The problem with the 3.5L in the G35 is that it's pretty much maxed out N/A from the factory. Nissan really engineered these motors to have as much HP as possible from the factory. As a result, trying to increase the HP using aftermarket components without using a form of power adder can be difficult and quite expensive.

Best N/A mod you can do is an intake spacer, but short of that you will spend a lot of money for small gains. Cams, throttle bodies, tunes, etc.

They really aren't like a V8 engine where a head swap or cam swap can be done cheap and give you 50HP (depending on the engine).

If you really want bang for the buck power gains, look into a power adder.

^^^ This

Get a 5/16" plenum spacer (motordyne) maybe a 05'-06' Rev-Up air box (built in velocity stack), change exhaust if you want (I put on an HKS "axle back" muffler and I love it). If you want to make real power, you really need to think about FI. Vortech or some sort of Twin Turbo set up. I lean toward the Vortech as it's power delivery is not as violent on the motor (power builds with RPM) as a TT set up.

My understanding (and others more knowledgeable will correct me, thankyouverymuch) is that the one area of design weakness was that the the OEM plenum design constricted air flow. The spacer opens it up and adds about 15 HP. The flaw was fixed in the second gen (hence the reason they are rated 15 HP more than first gen) and why adding a spacer to second gen doesn't provide the same boost.

very interesting Thanks for the great and honest information!!
so intake and most exhaust are smoke and mirrors on these little motors. Some benefit but more sight and sound than anything else and Forced induction is the only way to make any true significant changes...
So for the 5/16 spacer is it worth the effort? What kind improvements are we talking about just numbers or something you can actually feel in the way it drives?

You can add intake (spacer, CAI) and exhaust (headers, low restriction exhaust), cams mods, but without a tune, you will never reap the full benefits of them. I think that the most I have seen from "bolt on" gains is abut 25 hp.

Others will have to speak to the butt dyno effect. I don't yet have a spacer. I have an Infiniti Elite extended warranty and I'm not touching anything but cosmetic mods until that baby is done. No way am I giving them an angle to deny a claim. But when it expires, I will get a spacer; I've heard enough positive here to conclude it is worth it.

It more or less fixes a slight design flaw.

On the 3.5L the stock plenum choked out the front cylinders because it was angled down rear to front. The spacer just lifts the plenum up slightly to allow for better airflow to these cylinders.

So the intake spacer's "gain" is really just correcting this issue.


My G35x is pretty much 99.99% stock, but the 1 mod i'd consider is a spacer. However, at 153K miles not sure it's worth it at this point. I should have done it at 10K miles.

R u SRS? Get one used upper spacer only for $100 you!

wow great information!

So the plenum spacer is the biggest bang for the buck so to speak....ill have to look into that a little more...

+1 on the 5/16th plenum spacer. This will net you a lot of usable power, not just only in the high end range.
Also changing the cats to either HFC's or TP's will yield some decent gains. Depends on which route you go with as well for this as it's a matter of Standard Test Pipes vs HFC vs ART Pipes (Basically better test pipes).

That 5/16 is the best gain. Another good gain as you been reading is HFC/TP. I say look in to Fast Intention exhaust. It will give you the back pressure in your engine to give you more power.