Information on 4-2-1 header design

[nick.parker]

Hi,
I am interested in finding some information on exhaust system design. In particular I have a 4-2-1 system on my car (4AGZE). In pictures of system I have seen, the 4 pipes are nearly always around 300-350mm but the 2 pipes vary from 150mm to 700mm before joining to the final single pipe! I would like to know the affect of this on torque curve etc. Any good references appreciated.
Cheers, Nick

[oldcorollas]

there is graph on Bills site somewhere that is a reasonably good rough reference..

i thought that primary and secondarys (the 4 and 2) were same length, and then the final collector was the same as pri and sec put together...

eg, for about 5-6000rpm, 1.5 foot, 1.5 foot. 3 feet, for 4-2-1....

[ed]

http://www.v-eight.com/tech_forum/viewtopic.php?t=53

[Sam_Q]

here you go:

http://forums.toymods.org.au/index.p..._view=&start=0

http://forums.toymods.org.au/index.p..._view=&start=0

http://www.v-eight.com/tech_forum/viewtopic.php?t=53


As a rough rule secondaries should be half the length of the primaries, and every single 4-2-1 system on the market is too short that I have seen.

If you have any more questions just ask me on here

[oldcorollas]

i thought secondaries should be same length as primaries, and collector the same length as the other 2 put together.,..

like..30cm, 30cm, 60cm (for example)???
and for 4-1, you would have 60cm, and then ?? for collector....
now i'm confused

why half the length for the secondary, when you want a similar frequency as the primary?

[Celica RA45]

this is all interesting my primaries are 825mm and the secondaries are 250mm go figure

[oldcorollas]

were those lengths scientifically/experimentally derived? or they are just that length because?
designed to different harmonics, or parts of waves? or for different assistance at different rpm?

[roadsailing]

use 2 inch secondaries, a mate has had good success with this on his NA 4AGE

if you think this is too big, try to prove me wrong then bite me

[Sam_Q]

This is my understanding do far: on a 4-2-1 system the secondaries should always come close to half the primary length and the pipe after doesnt mater so much because its only a minor tertiary wave. However I beleive that on a 4-1 system the spacing of the pipe after the colector is important because its possible to get a worthwhile secondary pulse. As Bill sherwood mentioned you can have a well placed muffler to "fool it into thinking" that its like another collector.

I dont know why the secondaries are meant to be half the length. When I started putting numbers into this site:

http://www.btinternet.com/~mezportin...st_length.html

It also gave figures that matched what I have been told. What I might do oldcorollas is work out the resonance princible accounting for the secondary junction and see how it works out.

... Just had a brain wave, I worked it out in my head and I think I might know what the deal is, its real hard to explain but here goes (4-2-1):

normally when the valve opens theres a presure wave that goes down, reaches the collector and then a low pressure wave goes back up the tube, if the pipes happen to be tuned for that rev range then the pulse will hit the engine as the valve opens again and effectively sucks it out, thats all good and proven;

but how about the secondaries, well we could look at each of the two collectors like a 2 cylender engine, but the difference is each collector is receiving pulses from 2 cylenders so it has twice as many pulses. Now if the same princible was involved then it would work like this: Again there would be a pulse going down and it would reach where the pipes would be going from 2-1 and then get a low pressue wave back. However because there are twice as many pulses the pipes need to be half as long to time it right, how does that sound?

If we go even further then it could happen all over again with the one collector to say a muffler, and that would have to be half the length again.

What do you think?

[Sam_Q]

shinybluesteel: apparently the secondaries should be 1.75 for a normal 4age but I am not going to argue this as I havent played with both on an engine dyno.

Heres another good one, my bud accoustic and his insanely long pipes:

http://www.my-acoustic.com/Car/intak..._extractor.htm

[roadsailing]

yeah, i had a look at my mates and thought "ge, big secondaries" but it has good torque and great power, so they don't seem to be a problem. (besides, try finding 1.75 inch pipe!)

i think i will build a venturi into my collector, as i dont like the steam that comes out of my oil catch bottle - better to have the exhaust suck it out.

[Sam_Q]

what was the specs of your mate engine?

also my exhuast supllier has 1.75 on his shelf, its a common size to him, dunno if that means much though.

[roadsailing]

the 1.75 inch thing was a guess, i haven't tried to get it, good to know you can though.

the engine with the 2 inchers is a standard bigport.

[Sam_Q]

it looks like I might be making a new set of pipes soon, heres the rough specs:

Primaries: 1.5inch, 75cm long
Secondaries: 1.75 inch, 37cm long
Gap to cat: 25 cm or less if I can do it which I doubt
Tuned for about 6500 to 7000 rpm primary resonance I beleive


I also currently also using 2 inch secondaries right now, and I also have unusually good low down torque. Maybe I am used to crap but my 20V seems to pull off quite nicely from 3000

[1jzracing]

its all quite technical but if anyone is thinking of knowing all the answers read this book

"scientific design of exhaust and intake systems"

it spells it ALL out and there are two basic types of extractors and it all really hinges on the length of the primary runners only, the secondaries only have to be at such a length as not to throw in adverse waves which upset the function of the primaries

.... well thats my understanding it all gets a bit involved and over the top in the book

one type is called "interfearance" and the primary length is around the 18" long (typically 4-2-1 set up)

the other is a true extractor and the primary length is around 32" long (typically 4-1 design)

these lengthes all vary acording to rpm of course but not as much as you might think

pipe size is dependant on engine size to keep the gas flow optumum, the other lengths are set for every capacity as sound travels at the same speed