new to moding my '04 G35x Sedan and have a few questions after scouring threads.

i am adding a ztube and also have a k/n drop in. Looking for a touch better peformance/mpg's and deeper engine/exhaust not (NOT RICEY!!) I have heard alot about the following

1. What is a plenum spacer (lower vs upper??) and what does it do if you swap it out? Increased performance/mpg? Altered sound? Is it hard to install and how much do they cost?
2. Any reconmmendations on exhausts? (not CAT systems, just muffler)? I am looking at swapping out the midpipe with a coupe/FX.

Trying to keep it on a very lean budget as this is just a minor hobby

Thanks!

 

motordyneengineering.com will give you info on the spacer or just look around on the forum and search.
as for exhausts, for na personally i dont think theres any other route to go for gains w/o going with a catback. stillen is pretty cheap sounds great not ricey

 

That's a good start, if you want to increase the power a bit and make use of that k & n filter, buy a used rev up air box, with the bigger velocity stack. and replace it with yours.

the plenum spacer is exactly what it sounds like, it's a spacer between the top of the intake plenum and the lower plenum. Popular ones are the motordyne 5/16 or 1/2 iso thermal spacers.

the lower thing you've read about is. the MREV2 lower plenum. which is an entire piece that is connected to the engine that is replaced.

for your engine, i would only recommend getting a plenum spacer, as the mrev2 isn't as beneficial and isn't a great $/power ratio.

when you swap it out, the exhaust tone is deeper and the engine will growl a bit more, you will gain more power, and it does seem like it's an increase throughout most of the powerband.



as for the muffler, that's subjective,

 

Don't expect higher mpgs with performance mods, chances are you'll be pushing the car even harder, giving you lower mpg.

The plenum spacer goes in between the upper and lower plenums increasing the amount of air going in. It's one of the best mods you can do to a G35, and it's relatively cheap. It'll increase the performance and give your car a mean growl under load. Just do a search and you'll see how everyone likes it.

I don't know much about different mufflers, but hyperlite21 is right, don't expect any gains if you only change the muffler. If you're local, I'm selling my 07 coupe midpipe .

Believe me, it only starts as a minor hobby .

 

thanks for the input and keep it coming. How hard is it to install the plenum? Avg cost?

 

do it yourself, first time will take about an hour

 

Thanks for the info. Looking at either a 3/8th or 1/2th plenum. Maybe an axle back system as well.

Edit: after reading the motordyne install instructions, I am weary about performing the install. I can swap out a ztube no problem, but dont trust myself to perform the plenum swap. Has anyone ever had a mechanic (i.e. Carx/Meinke, etc) do this form them????

 

It's really not that hard. If you can change the Z tube, you can do this. The only thing you will need for sure is a torque wrench calibrated in inch/lbs. You can borrow one from a friend or an auto-parts store or you can buy one at Harbor Freight or some other discount tool store for about $20. It is a must to get the proper torque on the plenum bolts. I installed the MREV2 (not for your car) and a 5/16" spacer myself, it took about an hour and a half.

 

And I wont have to cut the coolant hose and reseal, correct?

 

Correct. When I did mine I even left the Trottle body electrical hooked up. I undid the bolts and then lifted up the upper plenum and TB together and hung it by the hood with a bungie cord. That way you don't have to worry about recalibrating it if you happen to turn it on with it disconnected.