Stock Nismo and TT?
 

Has anyone done the stock Nismo catback with twins? I was wondering what kind of power it would be restricting?

If you are going to TT your Z why would you not upgrade your exhaust? The loss of power would be significant...as much or than 50whp imho.

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Especially when the OEM cat is a main restriction for a STOCK ENGINE

Like buying a high end suit but slapping on crappy shoes

You'll be giving up spool speed... Could maybe make up some of that with a boost controller, but you really want to open up the exhaust to keep your turbos moving. Also keep in mind that TT'ing your car can be an exercise in heat management and restricting your exhaust will allow a greater buildup of heat that would otherwise blow out the tailpipes.

Now, depending on your setup there can be two sides to the coin. IIRC, you are going with GTR turbos, no? Do they have internal wastegates? I am running an Invidia Gemini catback, which is relatively small (dual 2.36") compared to what a lot of TT guys are running (dual 3"). Because my kit is internally gated, and the internal gates in my kit are so small..even with my relatively restrictive exhaust I start to get a little boost creep at the top of gears 3+.

If you are doing GTR turbos - are they journal bearing? That may slow the spool as well.. so there are multiple tradeoffs and compromises depending on how your TT setup is configured.

For the guys that are running ball bearing turbos and fat external wastegates - you'll see most of them have dual 3" exhausts for good reason. =) They are maxing out the spool and don't have to worry about creep.

All of that being said, a plain nismo exhaust is going to be more restrictive than you want for pretty much any setup. Upgrade for sure.

I haven't started my thread yet on it, but the kit is actually on. Even with the stock exhaust I see about 6 psi at 3300 RPM's.

If you're happy with it, then I say :driving:

Shortly followed by :pics:

Lol. Well the problem that I have is the sheer fact that 1/2 throttle and WOT feels basically the same in power. Husam is graciously sending over his dumped Y-pipe for me to test, so I can do back to back logs and check the difference.

Sounds good! I am sure you know this, but make sure you get your tune adjusted for the dumped pipe before you start testing... you are going to flow a a lot more air through the system and that won't really be reflected via boost pressure. Good luck and be sure to report your findings!

Sori to thread jack... But since we’re on the topic is there a significant difference in using a 2.5” Exhaust over a 3”? Will 1/2 an inch make that much difference on the spool?

I'm lucky in that respect, since I tune my own cars lol

This is normal with forced induction. When you are building boost at part throttle, airflow is already bypassing the throttle plates and building up in the plenum rather than behind the throttles. Regardless if you change the exhaust or not, 6psi part throttle and 6psi full throttle are going to always feel pretty much indistinguishable in engine torque.

Although this was written as if the 370z didnt have VVEL. Exclusive to the 370z, there is probably some more power in full throttle versus part throttle due to the VVEL position. That is mostly off topic but couldnt let it slide that I ignored VVEL in my post here talking about throttle plates.

Well with that being said, phunk, do you have any experience with the stock exhaust? I haven't played with my VVEL tables with the exception at WOT.

The exhaust was the first thing changed on my car. I would put it on the dyno and tune it out and see where you are at. If you are going to keep the car at just 6psi or so, it might already be making plenty of power.

Sorry all, been really busy. Went to the dyno and did a very quick tune on it, and was not happy with the results.

I'm making a smidge under 400 right now, and I am positive this is an issue with the stock exhaust. With that being said, I've ordered a cheapo ebay exhaust for testing. I plan to cut this exhaust up if it's too loud to ad resonators lol.

Also, this was only ignition timing and fuel done, I think if I spent more time with the VVEL and VTC, I'd definitely would pick up power. I did run after run with only breaks from flashing the maps on it lol.

Some news! Husam and I have been chatting, and I moved to an ebay exhaust, and turned up the boost. I turned it up the boost from 8 to 10 psi, and lets just say I did a pull, and was pleasantly surprised! I was soooo surprised that that I had thought it was a lot more than two. Then I saw my datalog and it showed another 2 psi!

Currently I'm at 12 psi, on my street tune, and it feels way stronger, but my injector duty cycle is at 80%, so I'm scrambling to finalize my water meth system.

Anybody able to chime in on this ^^^^^

Only 2psi, but opening the exhaust allowed for a lot more overall flow. You would have made a good bit more power without even turning up the boost! :)

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The difference is the 2.5" will spool faster and torque will come on strong due to the back pressure in the 2.5" exhaust. With the 3" you will see higher whp numbers and your tuner should be able to control the torque better which allows for the increase in top end. Spool not really a factor unless you are using a large turbo from what I can tell on our cars.

I disagree with this. There is no benefit to downsizing the exhaust for scavenging on a turbo motor, and it will only harm spool speed. You want to maximize the pressure differential across the the turbo to speed up the spool.. back pressure behind the turbo will only reduce spool, flow, and require more boost to make power.

For the 2.5" vs 3" exhaust question, its really just a question of diminishing returns.... It doesn't appear to me (and I haven't really looked at it with much scrutiny so I could certainly be wrong) that the 3" is going to do a whole lot more for you in a modest 500whp type of build.

I don't disagree with what you are saying as I think we are saying the same thing but you provided the long and more detailed answer. Ultimately the 3" will out perform the 2.5" due to scavenging and the reasons you pointed out, however I have not seen much difference on power, spool or any other performance points on a non-built motor. The 2.5" will produce good numbers up until about 635whp or so before the tq becomes to much and as you stated it will be a question of diminishing returns on a 2.5" if you want big power. As far my comment on spooling faster or more aggressively, that is due to back pressure if I am mistaken then I have been edumicated!:p

6 psi isn't enough to gain much power even after a tune. I had the same thing with my first Z until i put it at 9 psi but even then, 9 psi isn't THAT much in the grand scheme of things. As for the exhaust, your stock nismo exhaust is sitting relatively close to 2.5" so if you dont use the catalytic converters and put on some muffler deletes, i feel you would render about the same results as getting a full exhaust.

With that being said, i would recommend 3" of pleasure to your fun meter. You can hear the turbo's (especially on cold start), sounds better and you will gain a little more from it v.s. a 2.5" exhaust but do not expect anything drastic.

The Nismo dual exhaust (piping) will outflow a single 3" exhaust by about 15% due to greater cross sectional area. A single 3" exhaust will support 600whp.

However, it is not just the pipe diameter that you guys need to consider. The rear muffle is more than likely baffled a fair bit in order to generate a certain tone, and flow which was purposefully engineered by Nissan

There is mention of scavenging, which does not apply in this case at all. Scavenging refers to one exhaust pulse pulling exhaust gasses from the next combustions cycle chamber. This can only be achieved with the use of OEM, or aftermarket equal length headers.

With turbo applications it is a very simple rule, as the principal of operations is primarily based on pressure differentials. The turbo will spool faster if the pressure differential between inlet and outlet is greater, hence the benefit of a larger downpipe. The pre turbine pressure (depending on the kit/turbo/turbine) can easily be double the boost pressure. So if you are at 12 psi boost, your pre turbine exhaust pressure could be 25psi. If you exhaust (post turbine) builds up a resistance of 5 psi, that is a loss of efficiency.

So with a turbo system, bigger exhaust is ALWAYS better.

Hey all, just wanted to update,I haven't been ablet o make it to the dyno yet. I've gotten most of my parts for the methanol, just need time to get it all together. My plans are to get it on the dyno and to leave it as is, and see what my pre-meth numbers are. Hoping to get on the rollers this weekend.