You've added a breathing mod. Don't know if you've replaced your cats as well, but the exhaust is less restrictive.

I would say a tune is in order either way.

 

No, I didn't replace the cats. Only the cat-back HKS exhaust. Other than this newly installed exhaust, my car is stock.

 

Maybe the reason it's been sold twice?

I can't speak for this car but for most cars, exhaust systems decrease back-pressure. Since the car is not FI, certain exhaust systems can cause you to lose power. NA cars need back pressure. I would think that with the G being kinda slow in the low end (STOCK) that an exhaust would further accent that. However, you should see an increase in the mid/high end. That sucks if you do mostly city driving.

I think more people experience these loses then they let on because it "sounds great". I think the import scene has taken the exhaust thing and exploited it. Remember, the basis is supposed to be that IF a car is being strangled by the factory for whatever regulation, that an aftermarket exhaust, intake, header, etc is supposed to unleash power by allowing it to breathe better. But the G37 engine? It's pretty much a maxed out, highly tuned VQ engine.

As far as tuning... I've never heard of tuning a NA car until I got on this forum so I can't really speak to that. Perhaps it will help? It still won't help you regain all of your back pressure.

 

Yeah, I would say that I noticed something similar, but not as drastic. That makes sense, as I have noticed better power through the mid and higher RPMs as expected. Coming from Twin Turbo 300zx (that made 400hp/tq to the wheels) I never expected this to do that much, as with any NA vehicle. Maybe I didn't see too much difference as I have an intake installed as well.

I will admit that I bought my HKS for the sound and looks.

 

Thanks everyone for your responses. Learning from someone that has "upgraded" their exhaust helps the most. I bought the exhaust mostly for the sound, never thought it'd impact the vehicle's performance so negatively. Well,I drove the car for less than 2 hours before I dropped it off at the body shop, so I'll check things out after I pick it up this Friday.

Mattster, I noticed you also have an aftermarket exhaust, is it a catback? If so, did you experience what I did? And did the tune you recommended me fix it?

Wyldfyer, I'm with you on the absence of back pressure causing sluggish take offs, do you think there's such a drop of backpressure even with this catback exhaust? The only difference against the OEM is the fact that it doesn't merge the dual exhaust into one pipe right after the cats. Is that where the backpressure is originated?

Malex2326, you didn't notice such a drastic impact in performance after you installed your HKS, which makes me think that there is something else wrong with either the exhaust or the install. While we were swapping the h-pipe, we noticed it didn't come with a gasket for the end that faces the canisters; since the seller had shipped the exhaust with most of the required hardware (we were only missing 2 bolts), we assumed it just never came with one from factory. Maybe there is a huge leak there, causing all the trouble?

All speculations on my part, until I get my car back and actually check again.

Malex, does your intake really make a difference? I fully understand that it won't add 40 or 50 HP LOL, but will it make up for that lost low end power coming from the exhaust?

One thing that may help you guys see how bad the issue is... Before, I barely needed to bring the engine up to 1,000-1,200 rpms for a nice slow take off on first gear, but with the new exhaust, it felt like I was about to stall the engine and had to hit 1,400 and above to obtain similar results (even after the ECU reset). Since the exhaust is nice and louder, people can hear me struggling during take offs at red lights, and it's embarassing lol.

 

The intake I have came with the car. You definitely need exhaust gaskets between every "joint" / connection point.

BTW - how did you get around the fitment issues with the 4WAS?

 

I figured as much. The guy that sold me it is trying to see if he can find that gasket for me. I've been asking around to see if anyone sells them, even as a complete hardware kit. Unfortunately HKS isn't doing business in the US anymore, so I can't contact them. I wonder if that company that makes the HKS replica sells them?

For the 4WAS fitment, I was going to post pics once I get my car back from the body shop tomorrow

 

You should be able to pick up exhaust gaskets from any exhaust shop I would think. Didn't think there was anything special about the one's i received, except that they may have larger diameter holes.

 

Thanks Malex, I'll do that and just replace all the gaskets just to be safe. Car wasn't ready today, they want to make sure they paint is dry before the put the fogs lights back on.

 

Get it back yet? Wondering how you cleared the 4WAS system.

 

Yes I did. I've had it back for about a week, but haven't taken pics yet. I just bought all new exhaust gaskets and will replace them next week sometime. I'll take pics once the car is up on the lift, so that you guys can have a better visual. But it is doable and with no adverse effects in performance or sound.

 

Good to hear.

 

So I ended up having to replace my clutch and flywheel. All was done yesterday, so while the car was up on the lift. Updated the first post with a picture, unfortunately the lighting wasn't too great and all I had on me was my phone. I'll take more pictures from the back showing both tail pipes lined up.

As I said before, there is no change in exhaust tone or performance whatsoever, and the pipe does not hit the 4WAS components at all. Nothing else was modified to make it fit, so if someone out there has 4WAS and really likes the HKS system, go for it!