Exhaust system for auto tranny

yewly1990

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yewly1990

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I had some questions here, I heard from most exhaust shop, which tell me auto car must maintain certain level back pressure(flow velocity).
But some says auto tranny need as much back pressure as possible to get the best fc and pick up:hmmmm:??

My current exhaust set up was
4-2-1 - 1.6(piping) - 2.0 inlet straight flow long type muffler - 1.75 straight flow ( hotbits ).

The reason I using straight flow, because when I was asking the open pod method with speedwork, they ask me to do both intake and exhaust to get the best result, and end up with a straight flow. They said as long as I want performance I must have straight flow because I`m using open pod????

I was swap from 1.75inlet straight flow oval short type muffler + 1.75 inlet resonator( hotbits ) to current set up. The reason I swap because I love stainless steel, and I was technically cheated by speedworks, because they told me that they was using FULL STAINLESS STEEL, and end up with full stainless steel header and piping only...:mad:

Result after swapping the mid muffler was telling by butt dyno, I notice better response at 2k~4k rpm, but same after 5k.

Currently I`m planning to swap my rear 1.75 straight flow( hotbits ) muffler into S-flow muffler. Hope to gain back some pick up, but I worried s-flow have loses in high end.

Another exhaust shop also recommended I change my current 2.0 straight flow muffler into 2 turbulence short type to get better pick up:hmmmm:, and swap to s-flow rear muffler after that.
And I`m very curious about this as well, since some says mid resonator and muffler only makes different in different sound, and only slightly different in performance.

I was wondering would changing the mid muffler into 2 turbulence type will makes better? Or should I go for S-flow rear muffler??
I was expecting a balance between pick up and top end if possible.

I`m going to have engine tuning in future, so exhaust will be doing over again that time, but it will be a long way to go. I just want to get better outcome currently if possible.

My ride was an Almera 1.5 auto.
 
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desmond0318

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Bro, your setting kinda rojak.. First you have to make a decision low rpm or high rpm you drove the most, back in the old days there's no open pod and straight flow muffler using in a N/A engine. Rojak setting somehow makes the FC worse than stock.

Most of the stock 1.5cc below spec using 4-1 no matter what tranny because it's able to reach certain power/hp for customer to view it.
For example this is Almera's original spec: (with original stock 4-1 extractor) meets the needs for customer that looking at the brochure..
Max. Power kW (ps)/rpm 75 (102) / 6,000 (highest engine power output)
Max. Torque Nm(kg-m)/rpm 139 (14.2) / 4,000 (highest engine torque)

(Just an example) Almera with aftermarket 4-2-1: lost a little power, but gain noticeable torque
Max. Power kW (ps)/rpm 74 (100.6) / 6,000
Max. Torque Nm(kg-m)/rpm 147 (15) / 4,000

(Just an example) Almera with aftermarket 4-1: lost a noticeable pick up, but gain power some called 'my car rev happier' :driver:
Max. Power kW (ps)/rpm 79 (107.4) / 6,500
Max. Torque Nm(kg-m)/rpm 145 (14.78) / 5,800

There's a post from drexchan about exhaust and powerband, yes there's no prefect have to decide the powerband you use.
That's why tunercame out with 4-2-1 tuned length came out with gaining torque without losing power, 4longer before joining to 2. And some long4-2 long2-1 some called it hybrid or tri-Y headers.
 
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Izso

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If it works now don't bother with it la.

Personally though, I'd go for 4-2-1 + 1.7" piping throughout, a large center resonator and a S-flow rear muffler. I don't know how the Almera works but I'm quite sure all torque convertor gearboxes require some back pressure (but not too much)
 

yewly1990

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yewly1990

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Bro, your setting kinda rojak.. First you have to make a decision low rpm or high rpm you drove the most, back in the old days there's no open pod and straight flow muffler using in a N/A engine. Rojak setting somehow makes the FC worse than stock.

Most of the stock 1.5cc below spec using 4-1 no matter what tranny because it's able to reach certain power/hp for customer to view it.
For example this is Almera's original spec: (with original stock 4-1 extractor) meets the needs for customer that looking at the brochure..
Max. Power kW (ps)/rpm 75 (102) / 6,000 (highest engine power output)
Max. Torque Nm(kg-m)/rpm 139 (14.2) / 4,000 (highest engine torque)

(Just an example) Almera with aftermarket 4-2-1: lost a little power, but gain noticeable torque
Max. Power kW (ps)/rpm 74 (100.6) / 6,000
Max. Torque Nm(kg-m)/rpm 147 (15) / 4,000

(Just an example) Almera with aftermarket 4-1: lost a noticeable pick up, but gain power some called 'my car rev happier' :driver:
Max. Power kW (ps)/rpm 79 (107.4) / 6,500
Max. Torque Nm(kg-m)/rpm 145 (14.78) / 5,800

There's a post from drexchan about exhaust and powerband, yes there's no prefect have to decide the powerband you use.
That's why tunercame out with 4-2-1 tuned length came out with gaining torque without losing power, 4longer before joining to 2. And some long4-2 long2-1 some called it hybrid or tri-Y headers.
Hmm, I had readied the post from drexchan I was been asking to used 4-1 all the time from jian hang, but hotbits only making 4-2-1, now my current 4-2-1 is long 4-2, and long 2-1.
Telling by butt dyno, I`m slightly harder to climb hill with 2~3k each times I go home, but I`m not sure its due to the straight flow or open pod, because when the moment I take my car, both intake and exhaust had been install.
I`m going to have small mod on engine part, adjustable cam, and lighten crank, enlarge piston, manifold and some other etc, but remain on na, super charger If the person willing and possible to do so. By that time exhaust will be doing all over again

So as your Idea, I could not have both low end torque or top end?

---------- Post added at 10:29 AM ---------- 6 hour anti-bump limit - Previous post was at 10:19 AM ----------

If it works now don't bother with it la.

Personally though, I'd go for 4-2-1 + 1.7" piping throughout, a large center resonator and a S-flow rear muffler. I don't know how the Almera works but I'm quite sure all torque convertor gearboxes require some back pressure (but not too much)
Works but just not happy with the low end torque, because I feel struggle little each time I climb hills back to my house with 2k~3k rpm.
Hmm, what I learned was engine required some back pressure, by removing oem muffler was to remove those additional back pressure, and any larger pipe size giving better gas flow means gain of hp or loss on low end :hmmmm: Correct me If I`m wrong..
I was planning to get a s-flow since I never tried it =\, I`m just curious with the gain and loss of s-flow and straight flow.

Btw, I think I got the large center resonator u mention, mine is a straight flow long type, which brought from jian hang.
I`m currently using 1.6 which is stock pipe size, 1.7 could make different?
So u suggest me to try out with the s-flow ?
 

desmond0318

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As bro Izso mentioned 4-2-1 + 1 resonator/midbox + s-flow best for city drive. Try change back to stock s-flow muffler i believe low end torque will increase. If the piping for stock is comfirmed 1.6'' would be good for low end torque and FC, if want more power go for 1.75'' but FC goes bad a little.

If able try to get some tool to measure the midbox/resonator, most exhaust shop midbox/resonator was 2'' will cause power lost for our low cc's car :banghead:
 

yewly1990

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As bro Izso mentioned 4-2-1 + 1 resonator/midbox + s-flow best for city drive. Try change back to stock s-flow muffler i believe low end torque will increase. If the piping for stock is comfirmed 1.6'' would be good for low end torque and FC, if want more power go for 1.75'' but FC goes bad a little.

If able try to get some tool to measure the midbox/resonator, most exhaust shop midbox/resonator was 2'' will cause power lost for our low cc's car :banghead:
Mine is 2" mid box, so If I change from straight flow to s-flow what kind of loses will be? Gain of fc and low end torque, but will it have loss on high rpm??
And about the piping, If I`m not mistaken, any size upgrade will have loss on low end torque and fc, but slightly gain high end rite??

I was thinking, maybe a 1.5l stock engine does`t need a straight flow yet rite?:hmmmm: even in high rpm? The only different my engine from stock was just a open pod with heat shield, and the so called ignition booster fire storm:bawling: ( wasted my rm450 )

Current setting, I have almost same speed from 0~120 compare with stock city. I had tried one by one with friend in kesas last time, and after 120, I climb faster than his stock city, he can`t catch me until my meter hit 190km, then I started to brake. We was like about 4~6 cars away.

4-2-1 - 1.6 piping - 2" straight flow mid box ( long type ) - 1.75 straight flow muffler
Open pod with heat shield, DIY 5 point grounding, a vs from Izo:biggrin:, so called ignition booster firestorm which cost rm450 :bawling:.

This is the mid box
 

6UE5t

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6UE5t

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A bit weird piping setup as the sizes are all different with the biggest one in middle so more. If I were you, I'd first try to get the middle section piping and mid silencer box with the same size as the rear piping 1.7' and see how it goes. I'd think by reducing the mid section size, then you'd get back some of the low-mid rpm torque and should not suffer high end power as the setup is still free flow. I'd not use S-flow as straight flow should give the best flow provided the piping size is correct. Note that there's still the cat converter which is actually the most restriction in the exhaust flow. (unless you've removed that also).
 

desmond0318

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desmond0318

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Mine is 2" mid box, so If I change from straight flow to s-flow what kind of loses will be? Gain of fc and low end torque, but will it have loss on high rpm??
And about the piping, If I`m not mistaken, any size upgrade will have loss on low end torque and fc, but slightly gain high end rite??

I was thinking, maybe a 1.5l stock engine does`t need a straight flow yet rite?:hmmmm: even in high rpm? The only different my engine from stock was just a open pod with heat shield, and the so called ignition booster fire storm:bawling: ( wasted my rm450 )

Current setting, I have almost same speed from 0~120 compare with stock city. I had tried one by one with friend in kesas last time, and after 120, I climb faster than his stock city, he can`t catch me until my meter hit 190km, then I started to brake. We was like about 4~6 cars away.

4-2-1 - 1.6 piping - 2" straight flow mid box ( long type ) - 1.75 straight flow muffler
Open pod with heat shield, DIY 5 point grounding, a vs from Izo:biggrin:, so called ignition booster firestorm which cost rm450 :bawling:.

This is the mid box
I believe high end torque loss won't be so noticeable because is auto tranny, some more with cvt :adore: Can i have a look at ur engine bay? so curious where u locate the open pod for Almera :hmmmm:

---------- Post added at 10:07 PM ---------- 6 hour anti-bump limit - Previous post was at 10:00 PM ----------

A bit weird piping setup as the sizes are all different with the biggest one in middle so more. If I were you, I'd first try to get the middle section piping and mid silencer box with the same size as the rear piping 1.7' and see how it goes. I'd think by reducing the mid section size, then you'd get back some of the low-mid rpm torque and should not suffer high end power as the setup is still free flow. I'd not use S-flow as straight flow should give the best flow provided the piping size is correct. Note that there's still the cat converter which is actually the most restriction in the exhaust flow. (unless you've removed that also).
Yup, agreed with bro 6ues5t.. for better high flow usually the size start from extractor until rear piping should be the same while muffler can be slightly bigger 0.1-0.3'' max for street setup.. While track is different story la, they all go for 2'' or more even for a 1.3cc
 

yewly1990

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A bit weird piping setup as the sizes are all different with the biggest one in middle so more. If I were you, I'd first try to get the middle section piping and mid silencer box with the same size as the rear piping 1.7' and see how it goes. I'd think by reducing the mid section size, then you'd get back some of the low-mid rpm torque and should not suffer high end power as the setup is still free flow. I'd not use S-flow as straight flow should give the best flow provided the piping size is correct. Note that there's still the cat converter which is actually the most restriction in the exhaust flow. (unless you've removed that also).
Ya, I had removed cat, because the place I go, does`t have 1.7 mid box, and they did not mention about can place order for inlet size I wanted, so I end up with 2.0 inlet mid box.
My rear is 1.6 piping, but 1.7inlet muffler, I not sure why, but hotbits did it.

Ya, I know straight flow provided the best exhaust flow. So your idea is change mix box inlet into same size as piping? and maintain a straight flow?
 

desmond0318

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Ya, I had removed cat, because the place I go, does`t have 1.7 mid box, and they did not mention about can place order for inlet size I wanted, so I end up with 2.0 inlet mid box.
My rear is 1.6 piping, but 1.7inlet muffler, I not sure why, but hotbits did it.

Ya, I know straight flow provided the best exhaust flow. So your idea is change mix box inlet into same size as piping? and maintain a straight flow?
Don't waste so much money and time, if you still keeping the stock i believe is S-flow muffler, ask those exhaust shop weld it back.

Cause you're concern low end torque/lack of power at 2-3k rpm?
 

yewly1990

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I believe high end torque loss won't be so noticeable because is auto tranny, some more with cvt :adore: Can i have a look at ur engine bay? so curious where u locate the open pod for Almera :hmmmm:

---------- Post added at 10:07 PM ---------- 6 hour anti-bump limit - Previous post was at 10:00 PM ----------



Yup, agreed with bro 6ues5t.. for better high flow usually the size start from extractor until rear piping should be the same while muffler can be slightly bigger 0.1-0.3'' max for street setup.. While track is different story la, they all go for 2'' or more even for a 1.3cc
Sure I can give u the picture of open pod, give me few minute I go and snap the picture later.
Almera is cvtc, its something like timing valve control, not the cvt gear box like proton.

I think larh, maybe 1.5l stock engine won`t produce that much of gases which made restriction in s-flow that make loses of high end torque.
I agreed what you told me, a low cc stock engine maybe did not meet the use straight flow.

So what u mean is I should maintain same pipe size following header, and same inlet size of mid box, until the rear muffler?
0.1~0.3" bigger is the size of muffler inlet or the pipe after the muffler??

---------- Post added at 10:35 PM ---------- 6 hour anti-bump limit - Previous post was at 10:29 PM ----------

Don't waste so much money and time, if you still keeping the stock i believe is S-flow muffler, ask those exhaust shop weld it back.

Cause you're concern low end torque/lack of power at 2-3k rpm?
Oh, actually I did not cut it, I still have the stock muffler with piping with me which can plug and play,
I did not tried it, but jian hang told me the stock muffler got too much block in it, will be a very big restriction.
And some of my friend tried to use back to stock muffler and the car feel like heavier and immediately loss of high end top.
 

desmond0318

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Sure I can give u the picture of open pod, give me few minute I go and snap the picture later.
Almera is cvtc, its something like timing valve control, not the cvt gear box like proton.

I think larh, maybe 1.5l stock engine won`t produce that much of gases which made restriction in s-flow that make loses of high end torque.
I agreed what you told me, a low cc stock engine maybe did not meet the use straight flow.

So what u mean is I should maintain same pipe size following header, and same inlet size of mid box, until the rear muffler?
0.1~0.3" bigger is the size of muffler inlet or the pipe after the muffler??

---------- Post added at 10:35 PM ---------- 6 hour anti-bump limit - Previous post was at 10:29 PM ----------



Oh, actually I did not cut it, I still have the stock muffler with piping with me which can plug and play,
I did not tried it, but jian hang told me the stock muffler got too much block in it, will be a very big restriction.
And some of my friend tried to use back to stock muffler and the car feel like heavier and immediately loss of high end top.
0.1~0.3'' bigger is inlet of muffler. hmm actually all s-flow is restrict that's make back pressure.
Yup it till loss some high end torque, but the partial throttle 2k-4.5k rpm our back stick with the seat 1 eh :biggrin:
Your friend that change back to stock muffler also using 4-2-1?
 

yewly1990

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0.1~0.3'' bigger is inlet of muffler. hmm actually all s-flow is restrict that's make back pressure.
Yup it till loss some high end torque, but the partial throttle 2k-4.5k rpm our back stick with the seat 1 eh :biggrin:
Your friend that change back to stock muffler also using 4-2-1?
:proud:Haha, I know what u mean, that is best feelings, but I`m not seeking that feelings hehe.
ya, he using 4-2-1, its a nissan march which using impul muffler which same as the tc selling to almera, I`m not using the impul one, so it should be better than mine.

0.1~0.3'' bigger inlet, but piping remain same rite??
Did u know about those turbulence mid box?? Got one exhaust shop recommended me to use those mid box to maintain back pressure x_x... Although I`m not so believe in.

So the mid section I should change to 1.6 inlet mid box??? will be having better flow? and gain back some low end torque?
My rear is using a 1.7 inlet hotbits straight flow, I planning to change to s-flow, since u and most ppl recommended me to use s-flow with stock engine.

Maybe I should start with change the mid box into 1.6" to fix the unbalance air flow first?? and last changing a s-flow to try out?



The engine bay photo that u requested
 
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desmond0318

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:proud:Haha, I know what u mean, that is best feelings, but I`m not seeking that feelings hehe.
ya, he using 4-2-1, its a nissan march which using impul muffler which same as the tc selling to almera, I`m not using the impul one, so it should be better than mine.

0.1~0.3'' bigger inlet, but piping remain same rite??
Did u know about those turbulence mid box?? Got one exhaust shop recommended me to use those mid box to maintain back pressure x_x... Although I`m not so believe in.

So the mid section I should change to 1.6 inlet mid box??? will be having better flow? and gain back some low end torque?
My rear is using a 1.7 inlet hotbits straight flow, I planning to change to s-flow, since u and most ppl recommended me to use s-flow with stock engine.

Maybe I should start with change the mid box into 1.6" to fix the unbalance air flow first?? and last changing a s-flow to try out?



The engine bay photo that u requested
Yeah agreed with you, im not a fan of turbulence center bullet or even surbo for the intake -.-' those things is there for nothing. Exhaust shop usually push this to customer cause it earn quite much, supply price rm15 for bulk order, and retail selling how much? :biggrin:
Your mid section so big already -.-' don't add more la.. 1.6'' midbox have to custom most exhaust shop stock with 2'' from factory.. Muffler with 1.7/1.8 inlet also hard to find, usually get at halfcut, some said 1.6''pipe with 2'' s-flow muffler inlet is ok, but i dunno how it feels haven't try :p
 

yewly1990

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Yeah agreed with you, im not a fan of turbulence center bullet or even surbo for the intake -.-' those things is there for nothing. Exhaust shop usually push this to customer cause it earn quite much, supply price rm15 for bulk order, and retail selling how much? :biggrin:
Your mid section so big already -.-' don't add more la.. 1.6'' midbox have to custom most exhaust shop stock with 2'' from factory.. Muffler with 1.7/1.8 inlet also hard to find, usually get at halfcut, some said 1.6''pipe with 2'' s-flow muffler inlet is ok, but i dunno how it feels haven't try :p
I mean I change the mid 2" mid box into a 1.6" box to fix the air flow, since my whole piping is 1.6, only the muffler and mid box inlet are different.
Following theory.. I believe so, a same size piping include inlet should be the best hi flow, I`m just worry about the different after change to s-flow.