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Nytsky's Engine Build

NYTSKY

By NYTSKY,
in Engines & Forced Induction

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NYTSKY
NYTSKY
SimonR32
SimonR32

Unless you have a GTR

NYTSKY
NYTSKY

Testing out the tyres.

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MBS206 Grand Master

MBS206

Posted
Posted

Restriction found...

Why would you run a 3" pipe, at the point where the gasses are their hottest, and most turbulent (IE, when they need the biggest area to flow)?

Drop the dump, and I bet power climbs. Or are you still on the screamer?

MBS206 Grand Master

MBS206

Posted
Posted
Adam told me the dump is fine for 400+. But that will be one of the things ill be changing.

Most of the dumps I've seen for 400+ have been 3.5" - 4"

And the outlet may be 3", but take a look at the big power builds, they all mouth out nearly instantly

Primordial Grand Master

Primordial

Posted
Posted

Increasing the diameter of the exhaust at any point isnt the magic bullet unfortunately. As soon as you exceed the the most efficient diameter you start to detriment the system. 'The most efficient diameter' is the $64m question though, and obviously pretty variable.

Hot gas is less dense, so the engine doesnt have to work as hard to 'push' it out. Increasing exhaust diameter makes the gas expand quickly, cool quickly, and become dense. Obviously dense air at the beginning of the exhaust process is bad news.. it equals resistance. Think about the reasons for heat-wrapping exhaust headers - it's definitely not meant to protect intake temps.. the hotter the temperature of the exhaust gas, the 'easier' it's expelled. Increasing exhaust diameter too far decreases temperature, and therefore is inefficient.

What you've seen in real life Matt, is probably a system which is close to the most efficient diameter for the dump pipe - but I guess it depends on whether they've tested it side by side with a dump with a smaller diameter (or matching) outlet size to the turbo too! :cool:

Someone correct me if I'm talking shit, this is just my understanding :blink:

Ryno Experienced

Ryno

Posted
Posted
Increasing the diameter of the exhaust at any point isnt the magic bullet unfortunately. As soon as you exceed the the most efficient diameter you start to detriment the system. 'The most efficient diameter' is the $64m question though, and obviously pretty variable.

Hot gas is less dense, so the engine doesnt have to work as hard to 'push' it out. Increasing exhaust diameter makes the gas expand quickly, cool quickly, and become dense. Obviously dense air at the beginning of the exhaust process is bad news.. it equals resistance. Think about the reasons for heat-wrapping exhaust headers - it's definitely not meant to protect intake temps.. the hotter the temperature of the exhaust gas, the 'easier' it's expelled. Increasing exhaust diameter too far decreases temperature, and therefore is inefficient.

What you've seen in real life Matt, is probably a system which is close to the most efficient diameter for the dump pipe - but I guess it depends on whether they've tested it side by side with a dump with a smaller diameter (or matching) outlet size to the turbo too! :cool:

Someone correct me if I'm talking shit, this is just my understanding :blink:

You're sort of on the right track, but you also have to consider Bernoulli's theorem, which roughly states that as velocity increases, pressure decreases. (this is the basis behind the lift equation in aircraft etc). The same works in reverse, so if the velocity of the exhaust gasses decreases (due to a sudden increase in pipe diameter) the pressure will increase and impede exhaust flow.

The trick in making a perfect exhaust would be to have the pipe diameter increasing at the same rate as the exhaust is cooling, to keep the flow the same, and hence no pressure change.

Just a thought, heat wrapping your 3 inch dump may be a "band aid" fix to the problem, as you would be retaining more heat in the exhaust, which would keep the flow faster in that section. But the Ideal solution would probably be a nice transition from the 3 inch output of your turbo, to a dump that matches the rest of your exhaust.

MBS206 Grand Master

MBS206

Posted
Posted

The easiest test to find out if the dump/exhaust is being a restriction, is quite simply to drop it.

But can anyone find a car make 400RWKW with a 3" dump? Most I know of from experience run 3.5" - 4" dumps, and then a 3.5" system.

While you're say going to a smaller pipe increases speed, decreases pressure. You also have to know for a fact, that whilst you go really small, the speed of the gas might be super quick, and low pressure in that section, but the section before has been restricted down basically, and it now has a huge pressure build up.

Run too small of a dump, the pressure in the turbo / exhaust manifold starts to build up, and counteract the pressure going INTO the motor.

It's not like I said go and put a 6" dump as from experience, everyone knows that it will become detrimental to the exhaust flow.

Whilst the hotter gas is less dense, it also takes up more area. And that's the big problem, as it's exitting the turbo, exhaust gas can be as hot as 850degrees, by the time it reaches that tail pipe, a mere 200 - 400 degrees.

Half the temperature, half the density... So you need half the area for the cooler gas...

I agree, there is an art to building exhausts, bigger is not always better, but experience tells me, for 400KW, a 3" dump is too small.

DCIEVE Mentor

DCIEVE

Posted
Posted (edited)
no...

simply no, you are wrong

From his list, the only differences to my pos are the 3" dump (3.5), 76mm china cooler (100mm) and obv the 26 head. I'm not sure about simmo but most of the guys I know making over 400rwkw are running 3.5 or 4" drain pipes.

Edited by DCIEVE
SimonR32 Grand Master

SimonR32

Posted
Posted

i made 430rwkw with a 3" dump

brockas just made nearly 440rwkw with a 3" dump

rr84wa made about 420rwkw with a 3" dump

nattalotto made nearly 470rwkw with a 3" dump

thats a quick list off the top of my head...

dont forgot a shit load of exhaust flow is going through the gate at high rpm!!!

TiTAN Grand Master

TiTAN

Posted
Posted
i made 430rwkw with a 3" dump

brockas just made nearly 440rwkw with a 3" dump

rr84wa made about 420rwkw with a 3" dump

nattalotto made nearly 470rwkw with a 3" dump

thats a quick list off the top of my head...

dont forgot a shit load of exhaust flow is going through the gate at high rpm!!!

all running screamers?

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