Stock Nismo and TT?

[ihiryu]

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

[Hotrodz]

Originally Posted by ihiryu

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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[OptionZero]

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

Like buying a high end suit but slapping on crappy shoes

[Jayhovah]

Originally Posted by ihiryu

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

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.

[ihiryu]

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.

[Jayhovah]

Originally Posted by ihiryu

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

Shortly followed by

[ihiryu]

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.

[Jayhovah]

Originally Posted by ihiryu

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!

[ihiryu]

Originally Posted by Jayhovah

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!

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

[phunk]

Originally Posted by ihiryu

Lol. Well the problem that I have is the sheer fact that 1/2 throttle and WOT feels basically the same in power.

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.

[phunk]

Originally Posted by phunk

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.

[BOLIO 671]

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?

[BOLIO 671]

Originally Posted by BOLIO 671

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?

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

[Hotrodz]

Originally Posted by BOLIO 671

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

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.

[Jayhovah]

Originally Posted by Hotrodz

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.