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 velocity stack length Q's
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morgan
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6446 posts [93%]
just be glad your not here, nj

 velocity stack length Q's Reply  Edit


so i managed to mis-place the pages i had saved regarding some of this, mainly one thing regarding staggered length stacks.

all the info i gathered talks about shorter stacks giving more low end, and the longer you go, the more top end.

there was this japanese page i read about staggered length stacks. iirc, cyl#1 & 4 utilizing 80mm stacks, and #2 & 3 utilizing 100mm stacks(or something of that nature) and having the different lenths "optimized" the power band or equaling out something or another.

anyone have any info on that staggered theory? i googled my brains out last night for a few hours with no results. any recommendations for my ae86? heres the specs...
-completly rebuilt ST longblock
-BT electronics(open stacks)
-ported and polished ST head
-obx header/cat back

heres a flow chart comparing a stock ST head, stock BT head, and my p&p ST head.




haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.


gaijin_rokurunner




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UPPER MARLBORO MD

 Re: velocity stack length Q's (morgan) » Reply  Edit


Some FA engines use staggered stacks and a lot of motorcycles do as well...I think you got it backwards though the longer the stack the better the low end torque on low revs is and shorter give u more power on high revs.....but!!!!!! you can get really good gains on both low and top by adding short stacks inside a custom plenum where the induction wave is not lost it bounces back into the engine. The different size stacks basically tries to obtain both top and low end power....on a 4 cylinder probably wont work as good as it will on 8. 10 or 12 cylinders. To tune right you have to try all sizes on the dyno and see which one gives u the highest peak torque and HP gain or there are calculators on line where u put in your cam duration, intake length and it can calculate a length that will suit. Using a plenum is like supercharging without a supercharger....the wave bounces back and forth from the valve to the plenum at high speed so when the valves open that bounce back shoots a ton of air into the chamber where when you run open stacks you loose that bounce or wave
morgan
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6446 posts [93%]
just be glad your not here, nj

 Re: velocity stack length Q's (gaijin_rokurunner) » Reply  Edit


that is a typo, i did mean longer for low end, shorter for high end. interesting on the plenum, i didnt know that. i plan on making a set of adapters for some short 48mm weber stacks i bought some time back. what i think im going to do is make 2 sets of adapter plates. one short so the O.A.L. is 80mm, and one longer set so the O.A.L. is 100mm. i also have a ST plenum i started to convert to rwd, but never finished. ill probably do some " seat-of-the-pants" dyno testing when my car gets back up and operational(in process of body work...), and when i get a stand-alone later ill do the official real dyno.

thanks for your input.



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
n0tis 82


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City of Wind IL

 Re: velocity stack length Q's (morgan) » Reply  Edit


Nice, would be nice too see what happens with the long short stack combo. Dont forget to keep us posted.
gaijin_rokurunner




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UPPER MARLBORO MD

 Re: velocity stack length Q's (morgan) » Reply  Edit


heres an example of a plenum setup...I have this exact setup although mines is cut for a blacktop

Heres are some adapters Im trying to get SamQ to make so you can adjust lengths of velocity stacks without buying 20 different pairs.


morgan
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just be glad your not here, nj

  » Reply  Edit


the spacers, thats essentially what im planning on making, slightly different design, but same concept.

as for the plenum, are you suggesting the stock ST and/or BT plenums arent good to use, so an aftermarket one should be sourced?



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
gaijin_rokurunner




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1990 posts [100%]
UPPER MARLBORO MD

 Re: (morgan) » Reply  Edit


Not really you can use the silver or blacktop plenum modified for rwd but in regards to looks its not that appealing. The blacktop one has more volume then the silvertop so if you go that route source a blacktop plenum.
morgan
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just be glad your not here, nj

 Re: (gaijin_rokurunner) » Reply  Edit


Yeah, the after market ones are much nicer looking. Im still debating buying one, it will be down the road a bit if at all.



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
yoshimitsuspeed
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Carbondale Co

 Re: (morgan) » Reply  Edit


I would not run mixed stacks without aftermarket engine management and multiple 02 sensors.

When changing the stack length you are changing the VE curve of the motor.
Lets say (making these numbers completely up) A 3" stack consumes 80 CFM and a 4" 100 CFM at 3000 RPM. Now let's say a 3" consumes 220 and the 4" 180 CFM at 8000 RPM.
On a stock ECU you are sending the same amount of fuel to each cyl but each cyl is consuming a considerably different amount of air. This will throw off your AFRs. It could be enough to just have less than optimal performance or it could be enough to damage the motor. Any way you cut it there is no way to optimize multi length TBs without independent cyl fuel control and AFR monitoring.
beyond that I would say it's just not worth it for most cars. If you want to split the low end of a 4" and the top end of a 3" then buy a 3.5".



http://matrixgarage.com/
AW11
E51
Blacktop, all stock internals
4AGZE ECU, 3SGTE AFM, 4runner coil, DSM T25, 1JZ 380CC injectors, W2A IC
morgan
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just be glad your not here, nj

 Re: (yoshimitsuspeed) » Reply  Edit


maybe this is a dumb Q, but how can a larger stack "consume" more air? the butterfly is still the same diameter, and the vacuum is still the same from the piston pulling in the air. how is a shorter stack more restrictive to the volume used per intake cycle?



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
gaijin_rokurunner




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UPPER MARLBORO MD

 Re: (morgan) » Reply  Edit


Velocity stacks change the velocity of the air entering the engine...different lengths different speeds..hence the name velocity stack...like i said bikes come with different length from factory, BMWs also...Try it on the dyno and see what you come up with..
morgan
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just be glad your not here, nj

  » Reply  Edit


please dont think im trying to argue with you guys, or prove you wrong. im just having this discussion so i can wrap my head around the concept, and its getting interesting. thanks a bunch for your input, i appreciate it!

i understand the velocity part and the speed, but im curious on the "more volume" part. speed is one thing, but theres still the same amount of space in the cylinder, regardless of how fast the air enters. so what your saying is that the fact of it going faster is "compressing" it so more air, volume wise, gets crammed in? that just sounds off to me. a longer stack has a larger volume, but its not going to put more air into the cylinder.

Quote, originally posted by yoshimitsuspeed »
Lets say (making these numbers completely up) A 3" stack consumes 80 CFM and a 4" 100 CFM at 3000 RPM. Now let's say a 3" consumes 220 and the 4" 180 CFM at 8000 RPM.

^with the different lengths, i understand the concept of the low to high end benefiting pending the length, since the air will flow more "smoothly"(for lack of a better term at the moment) at different rpm's, and produce a different power band pending the length because there is less restriction at that sweet spot for the length of stack. less restrictive=more hp

Quote, originally posted by yoshimitsuspeed »
On a stock ECU you are sending the same amount of fuel to each cyl but each cyl is consuming a considerably different amount of air. Any way you cut it there is no way to optimize multi length TBs without independent cyl fuel control and AFR monitoring.

^i just dont believe that different lengths will let more air in. if thats the case, then the compression ratio of the motor is capable of being altered by velocity stacks. velocity is a speed, volume is an amount. smoother bores/removing flashings/porting/velocity stacks will aid in the velocity of the air going through the ITB's. a supercharger or turbo can alter the volume.

the article(d@mn i wish i could locate it) mentioned the sweet spots(rpm range for that length) that the different length stacks have. so by slightly making the 2 mentioned, a little longer, you have 4 equal cylinders(volume, compression, fuel...) with 2 pairs of "sweet spots" to help aid the other 2 cylinders that arent at their sweet spot yet or already passed theirs...making the motor perform slightly better.

this makes sense in my head...i need to do some more research.



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
yoshimitsuspeed
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Carbondale Co

 Re: (morgan) » Reply  Edit


One of the hardest parts about trying to understand induction and exhaust theory is wrapping your mind around and factoring for the extremely chaotic environment under which this all takes place. People want to think of the air going into the engine as a steady flow. This is not the case.

Velocity stacks and tuned intake runners work off the principle of resonant induction. http://www.howstuffworks.com/question517.htm

Getting air into the cylinders is all that's important. I would say volume but it's actually mass or air density that is important. Velocity is important because it plays a role in how much air mass you will get into a cylinder.

Now volumetric efficiency is really what you are trying to wrap your mind around.
start with a 1.6 liter engine, divide by 4 and we have a 400cc cylinder. If we pull the piston down to BDC that cyl will contain 400ccs of air at atmospheric pressure. The problem is that when the cylinder is going up and down 100 times per second it doesn't have very much time to fill the cyl with air. The valve opens as the piston is going down and the piston creates a great low pressure wave as it does. This low pressure tries to suck in as much air as it can but in the ms it takes to travel down the air doesn't have time to equalize pressure. When the piston hits BDC there is still 400cc of space but it isn't at atmospheric pressure so there are less air molecules per volume. Everything is actually going so fast that as the piston is travelling up air is still flowing in trying to fill that low pressure zone. This means in a dynamic situation there is generally less air mass per volume in the cylinder than there is under atmospheric conditions.
This is what we call VE. Most engines operate in the 80-90% VE range in their strong areas. So if a car is in a range of it's powerband where it has a ve of 80% then there is the equivalent of 320 atmospheric ccs of air filling that 400CC cylinder. If you put in a different cam that gives you a VE of 90% there then there is the equivalent of 360 atmospheric CCs of air entering the cylinder.

Now things like cams and intake runners need to be timed for the characteristics you want in the motor. Small cams don't stay open long enough to take in much air at high RPM but work well down low. Big cams need to stay open longer to give the air more time to enter the cyl but that means at low RPM they can stay open too long and blow air and fuel back into the intake as the piston goes up.
I won't go too much into cams since it's off topic.
Now that you have read how the pulses effect induction you should see how it can actually effect the density of air inside the cylinder. If an intake is tuned right for the RPM then the air coming in will hit the closed valve, bounce back to the inlet, bounce back to the valve and usually on the second or third reflection the pulse will arrive right as the valve opens. This high pressure wave rushes into the cylinder pulling the whole intake charge with it causing more air to fill the cylinder. This increases air density and VE but only around that RPM. If you have a long intake you can be lucky and catch the second, third and fourth reflections at different areas in the powerband. By the fourth it doesn't count for a whole lot. The problem is inbetween these strong points are weak points. Let's say the engine perfectly catches the second harmonic at 6k and the third at 3k RPM. Well around 4500 the valve is going to open right after the pressure wave has hit the valve and is travelling back up the intake. This means the valve is opening to a low pressure zone and the piston is trying to suck air against that pressure wave trying to suck in the opposite direction. This equates to a much lower density of air going into the cyl and less power coming from the engine.
If you have different length velocity stacks you are changing the VE of two cylinders separately from the other two. This equates to different volumes of air entering the two separate sets. The stock ECU adjusts fuel off the assumption that everything is the same and feeds the same amount of fuel to each cyl. If it's using the 02 sensor then it uses the combined exhaust from all four cyls to calculate AFR. With a VE change like this you could have two cyls running really rich and two running really lean and the 02 sensor would think it was fine because they balanced each other out in the pipe. Once you go WOT you have the same issue but the ECU ignores the 02 and just delivers a fixed amount of fuel to each cyl.




http://matrixgarage.com/
AW11
E51
Blacktop, all stock internals
4AGZE ECU, 3SGTE AFM, 4runner coil, DSM T25, 1JZ 380CC injectors, W2A IC
yoshimitsuspeed
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Carbondale Co

 Re: (gaijin_rokurunner) » Reply  Edit


Quote, originally posted by gaijin_rokurunner »
like i said bikes come with different length from factory, BMWs also...Try it on the dyno and see what you come up with..
Most bikes come with carbs. This meters the fuel individually based of the amount of air going to that cylinder. This will compensate for the changes in VE.
If it's a fuel injected bike then it's likely mapped for fuel and spark for each set of stacks.



http://matrixgarage.com/
AW11
E51
Blacktop, all stock internals
4AGZE ECU, 3SGTE AFM, 4runner coil, DSM T25, 1JZ 380CC injectors, W2A IC
Sam_Q
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Australia vic

 Re: (morgan) » Reply  Edit


Morgan your right, it's not differing volumes going into each chanber but rather differing air densitys. The volume is a constant but the air density in the chamber is a function of the volumetric efficiency which is altered by the velocity stacks.



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morgan
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 Re: (Sam_Q) » Reply  Edit


That makes sense. I did a lil more reading on this, and I'm starting to understand it better. Thanks guys!



haha cali...i got one of you 86's, and your not getting it back.
my 20v in an 86 swap guide
my mess of an 86...
*east coast toyotas forum*
A fool takes no pleasure in understanding, but only in expressing his opinion.
gaijin_rokurunner




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1990 posts [100%]
UPPER MARLBORO MD

 Re: (morgan) » Reply  Edit


Sam make us some curved ones like this in 200mm http://forums.rennlist.com/upl...1.jpg
 



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