Greetings,

Yes, I've looked at the mega compilation of Sedan Exhausts thread. While it did make me cry, it didn't exactly help in this situation.

I've searched here, and most of the threads I've found are either super old and I don't wanna necro, or they don't ask quite the same question I have.

But I'm sure you've heard it all before, so here goes. (expect a little bit of hand-holding, please)

I can't afford a cat back system. The cheapest "reputable" system (meaning one I've seen recommended on here multiple times and that isn't some cheap Chinese rip-off from eBay) is a Megan cat back system MR-CBS-IG034D-M+MR-CBS-IG034D-R. Unfortunately I can't afford the $396 + installation. I thought about trying the classifieds here, but the ads are very old and outdated. Plus I gather shipping costs will be a nightmare.

So I'm now looking at axle-back setups. From what I ascertain, this would just include the muffler and exhaust tips. Some mufflers include exhaust tips, which simplifies things, and some don't. Also, I'm considering the single tip vs the dual tip which is what I have now (Stock exhaust on a 2003 G35 Sedan - think it's the Sport edition if that matters).

So if you can bear with me, I do have a few questions I haven't been able to answer satisfactorily through searching.

1) Does an axle-back system help with horsepower or torque, at all?
2) Is an exhaust mod (axle-back) made more effective with intake mods? (I've got a drop-in K&N, Stillen Z-tube, throttle body spacer, and Motordyne 5/16" plenum spacer) Silly question probably but I'm asking if the two system affect each other and in what way?
3) I've heard about rasp and drone. Considering I'm not doing a full cat-back, is it likely to get either rasp or drone with just an axle-back setup?
4) I've heard about potentially losing HP and/or torque. In what circumstances does this happen? Can this happen if I just throw on any old muffler/exhaust tips? Or is it more to do with cat-back and resonator delete type setups?
5) Being that the rest of the exhaust setup is stock, how do I actually pick a muffler/exhaust tips? What are the important aspects? Can I pick any old size and shape? What role does length play? What should I pick for Inlet/Outlet sizes?
6) Is there any harm going from a two-tip to a one tip exhaust?
7) Must I choose a muffler/exhaust that is specific to the G35? Is it bad to choose a 'universal' setup?
8) If I were to post a few examples of what I'm looking at, could you possibly help me narrow it down?
9) Is it possible to replace in steps? I.E. muffler/exhaust tips this year, resonator next year, y pipe year after that?

I know that's a lot of questions, and pardon me if they've been asked a million times before...I'm really trying to learn and I've read quite a few threads on this site on this topic (and quite a few flame wars lol).

Here's what I think I know right now: I'd be replacing the red and orange parts; and the muffler has the inlet(?) on the right hand side, so I should probably choose a replacement muffler with the inlet in the same place.

Magnaflow cat back

G35 sedan exhaust diagram

Thanks for reading! I'm sorry I don't know how to make the images smaller...

 

1. No, catalytic converter is by FAR the most restrictive point in the entire system.
2. No, pipe diameter becomes an issue and the 2.25 in diameter stock pipe is fairly restrictive by nature, hence why dual exhaust setups make more power.
3. More of a rasp issue if swapping just the axle back, noise = rasp and a well tuned system is finding the balance between the two.
4. No, unless you somehow chose a more restrictive muffler, but the most congested part of the entire system is the catalytic converter so almost always, no.
5. No comment
6. No, a dual tip setup is typically used because it doesn't protrude any LOWER on the vehicle, entering and exiting parking lots will rub the tip on a large diameter single exit.
7. No, but you will need a muffler shop to do the installarion
8. Sure
9. Yes, but each time you replace components you have the risk of unwanted drone/rasp and will require more exhaust tuning to "fix" the issue.

Here's what I suggest, since you apparently want to make both MORE POWER and SOUND BETTER I think you should replace the OEM midpipe with the coupe mid-pipe, this adds a lot of good exhaust note to the sedan. Next replace the factory catalytic converters with HFC, this frees up the most restricted point of the entire exhaust system as well as adding more volume to the exhaust. You will be sourcing a used coupe midpipe which if you can find it locally should only be about $75 and is an easy bolt on you can do yourself, try to find a pick-n-pull wrecking yard to yank one from. The HFC you can also source used and will probably find for around $350 shipped, this is another easy to do mod, if you do have to pay a muffler shop to do these mods for you they will both be cheap since they are 100% bolt-on components that don't require any other work.

After you add the HFC if you do have a little drone (resonated HFC probably won't have this problem but are harder to find, see if you can find the Fast Intentions RHFC) then you can add a Vibrant resonator which will eliminate the problem.

This setup will give you a good clean exhaust note that will NOT be raspy and have no drone, it can be pieced together as you can afford it and has proven results in sound quality.

If you want performance from your sedan the number 1 thing you need is an intake plenum spacer, then the OEM airbox from a rev-up, then the high flow cats, then the tune. Swap out the rear differential for the 3.5 geared VLSD from a 6MT coupe or sedan. I also strongly recommend the TransGo shift kit for the transmission. These mods all work very well together and make for a VERY fun sport sedan. If you can find the 3.5 VLSD for a good price you should bump it to the front of the list since it's a pretty substantial improvement in acceleration.

 

However if you want to make POWER then you're best off with the Vortech V3 supercharger kit.

$200 plenum spacer = 10whp
$500 HFC = 15whp
$1200 full cat back =10whp
$700 tune (cable/license/etc) =15whp
$400 3.5VLSD = 0.3 sec improvement 1/4 mile, doesn't actually generate POWER
$250 Transgo = 0.1 sec improvement 1/4mile, doesn't actually generate POWER

$5000 Vortech supercharger = 100 whp

Pretty cost effective power upgrade for the Vortech.

 

This message is completely out of my budget. But informative, nonetheless. I will reply in detail to your other, longer message.

Thank you!

 

Thank you for such a quick response and so much information. I was unaware the cats were the most restrictive part. Unfortunately I live in California and we have stupid CARB... so I haven't wanted to mess with the cats at all because I need to pass emissions testing. I will look into high-flow catalytic converters, but I'm guessing they are out of my price range.

I do have the 5/16" plenum spacer and that was a fun and easy mod. I have a drop-in K&N filter as well. Didn't know about the rev-up air box... I'll look into it. But yeah, that's about the range I can afford to invest you know? I'm not looking to make this thing a nuclear rocket, just a little bit more power and sound. If the axle-back does nothing but looks and sound... I may put the whole thing off until/unless I have to replace other parts of the system due to corrosion/leaks. Mine's 16 years old at this point. Another thing I may do is to Frankenstein it, and basically do a cat-back system, a piece at a time, until the the cats fail and at that point I would replace them with high flow ones (I could more easily justify the expense at that point -- especially to the wife and cats!)

Perhaps a stupid question, but the coupe's midpipe... where is this/does this go in relation to the schematic I posted above? It is behind (closer to the rear of the car) the resonator?

 

Yeah the resonator is in the midpipe.

 

So I've been looking online at catalytic converters... some seem to good to be true. Can one go with these "universal" converters (I've seen as low as $100)? How does one know what is considered a high-flow? Is anything other than factory oem an improvement? Or is there something specific to look for?

Thanks again for entertaining my questions.

 

Since you are looking for a budget option I would try to find a set of used HFC. As for the actual flow of them, it's a two-part answer. Firstly they typically have a larger inlet/outlet diameter thus allowing more air to pass. Secondly they have a more porous media and a good set of HFC's will be made for an exact application that allows them to filter JUST BARELY ENOUGH to not cause the check engine light to go off, this also increases airflow and thus you have the potential for more power.

Not all vehicles respond the same to modifications, Honda Civics made huge gains from just an intake because the stock intake was very restrictive, The G35 typically sees no gains from an intake pipe because that's not a restrictive point, however our catalytic converters ARE a very restrictive point (compared to other aspects of the engine, this was a very well designed platform from a performance standpoint so gains will be minimal regardless). Generally speaking you will want to avoid generic HFC and definitely stay away from brand new ones that are in the $100 range. They're probably just going to melt quickly.

Now for passing emissions inspections... If you are in California you're pretty much **** out of luck, there is no such thing as a CARB legal HFC. If you are NOT in California then you just need to pass a smog check which involves a visual inspection and passing an OBD2 scan to make sure there are no diagnostic trouble codes.

I've known a few Cali folks that have successfully worked the CARB system by taking factory cats, hollowing them out (removing the media) which basically turns them into a sort of resonator, then installing them with a double set of non-foulers on the O2 sensors. It's illegal, it works, I don't recommend it unless you can afford the ticket, you will need a very lean custom tune to pass the emissions inspection otherwise they're going to smell the exhaust and know you're not running with cats installed.

A better option is to KEEP the OEM cats and swap them back onto the vehicle for your inspections. Run HFC's so the guy sitting next to you in traffic doesn't report you because your exhaust is burning his sensitive eyes

You should be able to pick up a used set of HFC's for a good price, it's one of those things you just need to keep your eyes open for and set some money aside so you can jump on them when the price is right. Facebook marketplace, craigslist, etc. Get yourself a cheap borescope for a smartphone so you can actually LOOK at the inlet and outlet of the media to inspect for melted spots. You don't want to waste money on somebodies ****ed up parts and you can't really see the inlet media on the G35 due to the bend in the pipe.

 

I'm using the Fast Intentions resonated HFC. They make both a resonated and non-resonated one, I strongly recommend FI if you can find them for a good price, if I had to pick just ONE mod for my coupe it would definitely be the RHFC's. Sound is deeper than stock, no rasp, no drone, feels better when I press the right side pedal.

 

I am in California =( no high flow cats for me are CARB legal? I can't afford the ticket and I don't know enough to do the illegal method. Damn.

Other than the intake mods I've already done, and the Supercharger option which is way beyond my means... what else can I do to eek a tiny bit of hp/torque and maybe sound out of this my baby? Still go with the coupe midpipes? Bother changing the Y pipe? Bother changing the muffler and exhaust tips?

Thank you again very much for your input.

 

Start with the cheap options, look for a coupe midpipe and an HR y-pipe. You should be able to find them each for around $75 or less and it will make an '03 sedan sound like a completely different animal. Don't touch the muffler or tips until you're in a position to go for a full cat-back system.

Next look for a 3.5 VLSD differential from a 6MT equipped coupe or sedan, it will give a MUCH quicker 1/4 mile time than HFCs, tune, etc. It's the best go-fast mod you can do to the naturally aspirated 5AT equipped platforms (you do have an automatic transmission yes?) and you can pick them up for under $500 usually. It's a very straightforward installation too, unbolt the axles, unbolt the propeller shaft, unbolt the wheel speed sensors, unbolt the differential. Installation is in reverse, all the torque specs are listed in section RSU - Rear Suspension of the FSM.

https://www.nicoclub.com/archives/in...e-manuals.html

Look up how to count the revolutions on a differential to determine the gear ratio, use match marks on the input and axle shafts, rotate the input shaft EXACTLY 3.5 turns and the wheels shafts will turn exactly once. Easy to see if it's a VLSD as well, grab each of the axle shafts and try to turn them in opposite directions, it will be VERY stiff (but you can do it) if it's a viscous limited slip differential.

 

Also, if you haven't already, see if there's a G or Z club in your area. The best deals will always be from friends.

Let me just repeat that in caps to make sure it's fully understood.

IF YOU HAVEN'T ALREADY, SEE IF THERE'S A G OR Z CLUB IN YOUR AREA.

THE BEST DEALS WILL ALWAYS BE FROM FRIENDS.

 

I built my first 400whp camaro almost entirely on the generosity of others, I was dirt poor at the time but I had a lot of FRIENDS.

 

I have the FSM, but I'm hardly qualified to do the work... I have an apartment and not much experience working on cars (nor tools). I actually have the 6 Speed Manual, so I'm assuming I already have that VLSD correct? Not to appear dense, but what is the HR part of an HR y-pipe? Lastly, if I do get in place the two pieces you're talking about, the HR y-pipe and the coupe midpipe/resonator... isn't the muffler/exhaust tips the last step then I would basically have done a Frankenstein cat back system?

 

LOL good advice. But I don't do facebook or social media so I'm not quite sure where I would look. I guess I'll start looking for San Diego G35 owners...

Thanks again!