Trying to understand the cumulative effect of breathing mods

KingJoseph

OK, so I understand that with an aftermarket exhaust on the Nismo, you sacrifice some of your low and mid range power for power in the higher rev band. Conversely, with the M370 intake manifold mod from Motordyne, it seems you gain in the low to mid range and lose a little top end.

Something tells me the two mods together don't necessarily offset the losses in a simple arithmetic type of way for an overall gain. Can anybody explain what to expect from the combination of two mods of this type either from a seat of the pants perspective or with dyno charts?

Further, I have high flow cats. At what point does this car have too LITTLE backpressure? If ever?

Thanks in advance.

Megan370z

saying it short and simple.


it all come down to optimizing the airflow capabilities of your mods.

bigger doesnt always mean better ,
doesnt mean its big and it will result in less restriction,

an exemple for this is your exhaust ,,,
too big of an exhaust, your airflow will slow down considerably before it leave the tailpipe. this also create backpressure
which you want to avoid as much as possible if you are staying N/A and want the most power in the higher powerband.

once you have a good flowing exhaust you have to find where is the bottle-neck. which will surely be on your intake side.

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TeamARK

Note that you simply cannot put one and one together with mods. It comes down to how compatible each parts are with each other. Sometimes its hard to measure this because of how gases are released. They blow out in pulses not a constant streams of air fuel and gas.

In order to make your mods work at its optimal level, a good tune is necessary.

jcosta79

You don't want back pressure. What you want (and what most people mistake back pressure for) is velocity. In broad, general terms, the smaller the piping diameter, the faster the exhaust gasses will flow.

Think of blowing air out of your mouth with your mouth wide open, versus blowing out of a straw. Not much velocity to the air coming out of a wide open mouth, but from the straw it's quite different.

So what happens when you slap on a larger diameter exhaust system is that you lose velocity (and with it, low to mid-range torque) until the engine is moving enough air to properly use the larger diameter piping.

Tuning an exhaust system properly is quite difficult. Just look at how many updates F1 teams make to their exhausts. Bigger is usually NOT better, especially if you are not adding some sort of forced induction.

What you typically want to look for in an aftermarket exhaust is smooth bends and transitions, as well as smooth welds on the inside of the piping. Anything on the inside of the piping that can cause turbulence will hurt performance because air running through a tube travels along the walls, not the "empty space" on the inside.

As a (very) general rule of thumb, smaller diameter piping (and long header primaries) will help improve low to mid range torque, while larger diameter piping (and short header primaries) will help improve top end power. Unless you are drag racing, you want a system that favors low to mid-range torque because that's where you are spending the majority of your time. As much as we would like to think that we are speed demons that drive everywhere at WOT, very little time is actually spent at redline.

Hope that helps somewhat.

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2012 PW NISMO #0559 - GT Spec Brace Kit - Swift Springs - ARK TP & Invidia CBE K&N Intake - UpRev Tune - 15mm Z1 Spacers & Studs - StopTech Slotted Rotors & SS Lines - ZSpeed CMAK with Stage 2 Clutch and Lightweight Flywheel

SS_Firehawk

Jcosta79 did a great job explaining it. Regarding that M370 intake manifold, the reason why it improves low, mid, and mid high rpm's is because the intake runners are longer, this improves torque. The shorter runners on the stock manifold benefit high in the rpm range. Even at our engines power band, the shorter runners don't have much benefit in high rpm power over the longer intake runners when both are properly tuned. The concept is very similar to headers.

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Coon-azz

I agree here.

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tylerk

So are you saying that for a DD, you would recommend keeping the stock exhaust (non-nismo touring sport) as apposed to upgrading to say a Fast Intentions CBE?

I'm not disagreeing with your post, just curious why everyone raves on performance gains from this particular product. Maybe it's the aesthetics that everyone likes with this mod?

SS_Firehawk

What Jcosta was eluding to was being naturally aspirated, 2.5" is the best size for the car. 3" is best for forced induction applications making 650+ bhp.

Example: Our car's stock exhaust is a coffee straw. 2.5" exhaust is a regular straw, and a 3" exhaust is a water hose. Blow through the coffee straw and sure you get velocity, but there is a lot of back pressure. Blow through the regular straw and we still have very good velocity, but we also have much less back pressure. Blow through a water hose, the size of the hose is so large, there is very little velocity and no back pressure. It's too big to be efficient for the application.

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jcosta79

I'm not sure what diameter piping FI uses for their CBE, but if it's 3" it's likely too large for N/A applications. I had 3" exhaust piping on my 517 RWHP Corvette, so it's a good bet that on a 370Z it's way overkill.

The power gain you are going to get by replacing the stock exhaust is in the muffler section. OE mufflers tend to be very restrictive because they have multiple baffles inside slowing down and quieting the exhaust. Aftermarket mufflers are typically less restrictive and offer a more "straight through" exhaust flow.

Hope that helps.

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2012 PW NISMO #0559 - GT Spec Brace Kit - Swift Springs - ARK TP & Invidia CBE K&N Intake - UpRev Tune - 15mm Z1 Spacers & Studs - StopTech Slotted Rotors & SS Lines - ZSpeed CMAK with Stage 2 Clutch and Lightweight Flywheel

SS_Firehawk

F.I. makes 2.5" standard and 3" nonresonated turbo exhaust.

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TeamARK

Unless your going FI, 3" exhaust system is not unnecessary. I know that there are 2.75" in the market but thats pushing it. Bigger is not always better.

chknhawk

The Greddy application (TI-C) is 2.75. That coupled with a test pipe or HFC should be ok for NA I think... Based on everything said here so far. I feel like I get a little more power to the wheels through the power band and not just high end. That is just seat of the pants and not so much tune/dyno. I do howerver know this. Once my Z realized that I was not taking the aftermarket bolt ons off it is over correcting the A/F mix and now the car idles at 1000 rather than the 6or700 it was at without the CEL. (Also CAI on the intake side for a little less congested airflow).

I like my setup and I think it works pretty good for this little car. Without spending 8000 - 10000 on a FI kit I have a little bit more HP and I can at least keep up with the NISMOs out there>

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