diy tuned length extractors

[waynos]

making some stainless extractors for the ute cause i love that blue tinge they get
was gonna copy a set my old man lent me(genie perhaps)
but they are all very different lengths
they should all be the same length to be a tuned header/extractor right?
anyway i figure i'll just cut all the tubes the same and do the old sand/ heat thing
any input appeciated.............

[OldGMHolden]

Hey Waynos,
There's no need to make the pipes EXACTLY the same length.
If you have 6 exhaust ports and are looking for the ultimate gains at high revs there MAY be some advantage, but most tuners these days don't put much faith in it.
I recently read some technical reason AGAINST exact equal length, and I will try to find it to post.
The length and diameter of the pipes are critical ONLY at a very specific narrow rev range.
Normally, if the pipes look roughly the same length, and look good, then it's probably all good performance-wise.
So save yourself a lot of blood, sweat, and tears. GO FOR IT!
Cheers,
Gaz.

[2door350]

Just my 2 bobs worth, having had a couple of headers designed (not by me) to promote pulse tuning or cylinder scavenging it is certainly worth the effort.

Both the length and diameter is cruical.  It is recognised that a difference in length of less than 1" is ideal

How you terminate you primaries is also critical, pressure waves react to large changes in cross sectional area.

The workable rev range of equal length headers can be in fact one half of your effective rev range.

The science that goes into the design is why most people don't bother/cant produce effective results.

The term 'tuned headers' when used in reference to off the shelf headers is in my opinion a bit of a joke...what are they tuned for? certainly not most engines.

Go the the library and pick up a copy of 'The scientific design of intake and exhaust systems' also plenty of good stuff to read online if you have a good search...Headers by Ed has some good info.

I'd give it a go if you have the time...you will find a 45" long 1.5 diameter primary is good from around 3600-7000rpm (ideal for a 186), and 60" long primary operates well from just over 3000rpm to around 6000 (ideal 202).

cheers

2door350

[waynos]

gaz and 2door ,thanks heaps for the info ....both answers were in the direction i needed..........think i was gettin overly technical with it.

 

[waynos]

oh by the way its a red 202 and wanna run a supercharger(m90 eaton probably),     
later on
will be a driver and occasional nostalgia drag racer,
so need some low end torque but the way i drive it shouldn't matter too much

[OldGMHolden]

Hi again Waynos,
Hope it goes well for you.
Cheers,
Gaz.

[waynos]

thanks gaz,
i am gonna run a 2 1/2 exhaust would that be ideal for the charger?
would it be ok without the charger in the meantime?
as my old man has always said YOULL HAVE NO LOW END TORQUE
runnin 2 inch exhaust at the moment ...
will wait if the 2 and a half will be crappy in traffic................



think i might make 2 sets at different lengths and  see the difference
its only a bit harder to make 2  at the same time
than one

[2door350]

I would either run 60 inch long 1.5" diameter primaries straight into an open 2.5" chambered muffler (hooker aerochamber or similar) and then run rest of exhaust 2.5" with a resonator/hotdog added if its too loud for your liking...

otherwise separate the primaries (123 / 456) and collect them into two 1 7/8" secondaries (atleast 45 inches long) then collect the secondaries into a 2.5" or bigger tailpipe with a straight though 2.5 muffler.

some more good general reading (although i don't agree with all of it)

http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/viewall.html

Supercharging you engine will negate the need for most of this exhaust tuning but you might just enjoy it as is...never know.

[waynos]

yeah mate have already made a 2.5 straight through muffler ages ago..............
good to hear this will work
im on the right track
i'll check that link
thanks

[waynos]

2 door
how does it negate this tuning charged?
its a bit down the track so im not wasting my time i dont think, am i?
what should i run once it is charged?
do ya mean i dont have to worry about low end torque once its charged?
it was my goal to run a budget build at the drags and keep improving on it
first time out(stock 202) i ran a 22, then adjusted timing and got a 18.04
wanna do it all myself and have, to this point
 i like learnin
anyone can pay for stuff
sorry i lie .i got the battery leads made and dizzy rebuilt..........
learned everything else the hard way(paint/wiring etc)

[2door350]

what i mean is instead of the tuned pipes creating a negative pressure wave at your intake port to help draw in an extra intake charge your supercharger will be stuffing the air and fuel in anyway

[waynos]

thought thats what you meant............
thanks man for all the input