4-2-1? 4-1? Extractors broken down!

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Izso

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Izso

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I pretty much know what I want in my extractors. It has to be tuned length, ceramic coated, mandrel bent and I want a 4-2-1 setup. But I get asked "why?" so often I get tired of explaining.

So what I've done here is extracted Drexchan's entire explanation on how to choose an extractor based on what your preferences are.

Enjoy!

(Words and pictures courtesy of Drexchan and all are his intellectual property but edited for clarity)


Exhaust extractor FAQ: 4-2-1 or 4-1 better?

There isn't a simple answer. Asking the question is making the situation complicated already.

Lets go through two hypothetical graphs before I elaborate more.

GRAPH 1) Typical gain from a 4-2-1 and a 4-1 compared to standard.

**go google the relationship between power and torque

A typical 4-2-1 makes good gain from low-mid rev range to rev cut, without losing the low range.
A typical 4-1 makes huge gain from mid rev range to cut, but losing the low range slightly.

SO WHICH IS BETTER? This is a question you should ask yourself.

GRAPH 2) Typical revolution vs velocity relation for a 5-speed manual transmission

**revolution is RPM lah...
**velocity is speed lor....
**applicable for automatic transmission too


Now, check Graph 2, compare that to your driving style, see which rev range you use most (in normal driving, highway cruising, and sprint). Then compare that with Graph 1, see which type of extractor suits you.

Situation A:
You are doing a sprint, you will only use zone A (1k rpm to 3k rpm) once or twice and from 3rd gear on wards you will be using zone B (3k rpm to 6k rpm). So you want a 4-1 because it gains more in that range. Whatever gain in zone A (from a 4-2-1) is near to useless to you, and the gain in zone B from a typical 4-2-1 is lower than that from a typical 4-1. So a 4-1 is better for sprint.

Situation B:
You drive the car in town with traffic and you shift at 4k rpm max. You will need a 4-2-1 because you will be using the low to mid range most. The loss in zone A from a typical 4-1 will make your car more lethargic to drive at low speed with high gear ratios.

Situation C:
You are cruising on highway in 5th gear at 110km/h or slightly higher, and occasionally speed up to 140km/h to overtake some slow cars. You will be using zone B most of the time. So a typical 4-1 will be more suitable for you.

Situation D:
TOP SPEED? From the graphs, it has to be a 4-1 but since aerodynamic property of the entire car is more important at that speed, you won't experience much differences between the two. One may find the need to use 4th gear instead of 5th when a 4-2-1 is used, and it's easier in 5th with a 4-1.

So, it's all about the power band! Nothing to do with 4-2-1 or 4-1. It's also about how you use the power band, nothing to do with 4-2-1 or 4-1. CLEAR?

:biggrin:
 

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arrowhead

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arrowhead

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but there's the hybrid 4-2-2-1 headers that combines the best of both. i'd take that anyday!

great write up, gives a good insight on understanding one of the most asked question.
 

denyal

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denyal

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Situation A:
You are doing a sprint, you will only use zone A (1k rpm to 3k rpm) once or twice and from 3rd gear on wards you will be using zone B (3k rpm to 6k rpm). So you want a 4-1 because it gains more in that range. Whatever gain in zone A (from a 4-2-1) is near to useless to you, and the gain in zone B from a typical 4-2-1 is lower than that from a typical 4-1. So a 4-1 is better for sprint.

Situation B:
You drive the car in town with traffic and you shift at 4k rpm max. You will need a 4-2-1 because you will be using the low to mid range most. The loss in zone A from a typical 4-1 will make your car more lethargic to drive at low speed with high gear ratios.

Situation C:
You are cruising on highway in 5th gear at 110km/h or slightly higher, and occasionally speed up to 140km/h to overtake some slow cars. You will be using zone B most of the time. So a typical 4-1 will be more suitable for you.

Situation D:
TOP SPEED? From the graphs, it has to be a 4-1 but since aerodynamic property of the entire car is more important at that speed, you won't experience much differences between the two. One may find the need to use 4th gear instead of 5th when a 4-2-1 is used, and it's easier in 5th with a 4-1.

So, it's all about the power band! Nothing to do with 4-2-1 or 4-1. It's also about how you use the power band, nothing to do with 4-2-1 or 4-1. CLEAR?

:biggrin:


i really like the situations and those recommendations as well..:biggrin::itsme:
 

zec22

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zec22

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Does the type of gearbox affect the differences in extractors too ?

I see that the second graph is applicable for auto transmissions too but I've asked around before. All I got back was that the auto box needs more back pressure and was advised to go with the 4-2-1 instead of the 4-1.

Sorry if I posted anything silly. Newbie here.
 

skazareth

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skazareth

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whoa... the back pressure... thats fluid mechanic.. thats not silly question... go on, i'd like to know this too.
 

Izso

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Izso

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Does the type of gearbox affect the differences in extractors too ?

I see that the second graph is applicable for auto transmissions too but I've asked around before. All I got back was that the auto box needs more back pressure and was advised to go with the 4-2-1 instead of the 4-1.

Sorry if I posted anything silly. Newbie here.
whoa... the back pressure... thats fluid mechanic.. thats not silly question... go on, i'd like to know this too.
Auto gearboxes rely to a certain extent on the backpressure to change gears. Last time I plonked in a straight flow setup for my car for experiment and even when driving slow, the gear would only change at 3.5k rpm. It was ridiculously hard to drive!

4-2-1 or 4-1 will not affect the back pressure, it's the end muffler (and to some extent the center muffler / resonator). S-Flow, straight flow, twin-loop, etc all will either provide or remove back pressure.

Im lost !! Hahahah too much info :nurse:
Hehe.. well if you understand physics in general and how it applies to your car, this'll all make sense

---------- Post added at 07:20 AM ---------- 6 hour anti-bump limit - Previous post was at 07:18 AM ----------

make one review on TB? hehe
nice reading all yr post :)
Erm.. what sort of review you want?


but there's the hybrid 4-2-2-1 headers that combines the best of both. i'd take that anyday!

great write up, gives a good insight on understanding one of the most asked question.
4-2-2-1? Wah.. you'd need a pretty big amount of space to fit that if it's truly tuned length. Some cars like the Myvi can't really fit a 4-2-1 (even though there are some who claim theirs is) because it's just too small a space. And if there are 4-2-1 extractors for the Myvi, they aren't true 4-2-1 because they aren't tuned length and is probably working like a 4-1 anyway

---------- Post added at 07:21 AM ---------- 6 hour anti-bump limit - Previous post was at 07:20 AM ----------

Oh I'd like to point out : This writeup is done by Drexchan. Not me. I'm just quoting it here and sharing with you guys
 

Izso

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any reviews on fuel consumption between those 2 extractor? Normal condition and aggressive condition :adore:
I personally don't think extractors affect fuel consumption. The more aggressive you drive the more fuel you use.
 

Zeroed

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Hi guys. I would like to take the opportunity to discuss a little about "backpressure".

"Backpressure" is a huge misconception that has spread to a lot of Malaysians. Im not an expert, but have studied many technical articles that has made this apparent.

"Backpressure", aka reverse pressure / congestion in the exhaust system, is *always* bad. When most people say "backpressure" they are actually referring to a more restrictive exhaust system, i.e. smaller diameter pipe. What this creates is *exhaust velocity*.

There are two aspects to exhaust flow, velocity and volume. A big pipe will flow more volume, but at a slower speed (less velocity). A small pipe will flow less volume but at a higher exit speed / velocity. Remember our physics lesson where if you squeeze the water hose, the water shoots out further? Thats because velocity has increased at the small opening.

The common misconception comes, I guess, from the exhaust in the smaller pipe having a higher air pressure. Technically however higher pressure is not "backpressure".

A higher velocity in the exhaust flow will allow the exhaust system to make full use of the scavenging effect, i.e. the exhaust pulse from one cylinder actually creates a vacuum which "pulls" out the exhaust gasses from the other cylinders, reducing engine pumping losses (parasitic loss). This then improves torque.

However, there is a limit as to how fast the exhaust can flow, and when the engine hits this limit, the smaller pipe will be restricting the exhaust flow, causing "backpressure". This is bad because the engine is then pushing out the exhaust gasses, whereas a good exhaust system will actually help the engine pull out the gasses.

It is very important then, that someone who tunes his exhaust chooses the correct piping sizes. Like extractors, there is no 100% good or bad size, there is only compromise. On a 4G93 for example, a 2" will create more torque at lower rpms, but lose horsepower at higher rpms, while a 2.3" will lose torque at low rpms but gain horsepower at higher rpms. A smaller diameter pipe will also always benefit cruising, since your engine will not be pushing large amounts of exhaust gasses at this time and would greatly benefit from exhaust scavenging (reducing pumping losses).

Keep in mind however that you have to weigh the benefits against the sacrifices. On a stock 4G93 for example, a 2.3" system will give you very little benefits, while sacrificing a lot, when compared to a 2" (meaning you gain very little high end power across a small range, but lose a lot of low end power across a wide range).

The above is however only applicable on N/A engines, turbocharged engines have a whole different physics lesson to their exhaust systems.


My 2 cents from my understanding of exhaust systems, do correct me if Im wrong. :)
 
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Izso

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Scavenging effect and 'back pressure' in a nutshell! Very good sharing!
 

zmays

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zmays

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Very good info bro Iszo, Zeroed

Reading your writings remind me about what I have learnt few years ago. If not mistaken the science formula that consist fluid pressure, velocity, temperature is as follow (maybe incorrect but this is what I recall);

PV=RT

P = fluid pressure
V = fluid velocity
R = fluid constant (I guess)
T = fluid temperature

As mentioned by bro Zeroed, the small exhaust pipe will have higher velocity and low pressure. The equation is below:

P = RT/V

From the equation, if the exhaust temperature is same for whole rpm range, then the faster the exhaust speed will create lower pressure in the exhaust system. Therefore I was wondering is it possible to cool down the exhaust temperature? Because due to the formula, high velocity, low temperature exhaust system can create less pressure thus can pull out more exhaust gasses from engine cylinder. Is my assumption correct?
 

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