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Tue Jan 12, 2010 3:53 am

does anyone know the mathamatics to build a 4-into-1 header, specifically the diameter and/or length of tubing for a target torq/hp (in RPM's).

also bearly know how the shape and size of the collector effects the performance too, so i could use some advice there as well.

i have the tools to build one (access to a welder). also im sure i will be able to find tubing for it somewhere, like maybe in a Jegs magazine.

i own a 1962 vw bug and i am constantly trying to squeeze the most hp/torq out of the engine as possable. i dont have any special schooling on building engines or tuning them other than my father teaching me the basics, but im getting better all the time.

i'd like to fabricate one for the engine currently in my vw bug. here are the spec's...

2054cc
dual webber 40's
009 distributor
heads are 40/35 valves port & polished by myself
9:1 compression
low-mid range cam (dont have spec's though power as is takes a dive after 4500-5000rpm)
1.25:1 ratio rockers.
now running 1 3/8 4-into-1 header (with J tubes)
I am using a spark arrestor as a muffler so i can tune for backpressure.
also using equalizer pully with stock flywheel (harmonically balanced)
as well as balanced the pistons and rods.

TORQ is my friend!

any and all advice is much appreciated!

Tue Jan 12, 2010 6:36 am

Sounds like you have a standard header,what you need is a Merged Comp Bugpack#2008-11 style, they have longer collectors 8)

Tue Jan 12, 2010 8:40 am

http://www.bigcitythunder.com/pages/understanding_exhaust.pdf

Tue Jan 12, 2010 9:47 am

you'll make more power with a 1 5/8" primary and small flange collector. The large flange collectors will kill your power.

Tue Jan 12, 2010 2:15 pm

[email protected] wrote: you'll make more power with a 1 5/8" primary and small flange collector. The large flange collectors will kill your power.

increasing the size will (for the most part) move my peak torq to a higher RPM.

do all companies have a standard length for each pipe before the collector? also does the distance and diameter from the collector to the muffler make a difference and why?

if i was to build my own, i would try increasing the length of the headers to help improve the low-mid range power a bit more. being that i have a torque'y cam is that a good idea?

also, grimace007 thanks for the link. thats good information.

Tue Jan 12, 2010 6:38 pm

Nice to see someone interested in exhaust tuning round here!
I know enough about it to tell you.................It's really hard to figure out!
But I'll try to help you out anyway.
First off I need to know EXACTLY what you want it to do, like what rpm range, and where in this range is most important?

Math? shoot, even modern computers can hardly do the math.

Tue Jan 12, 2010 11:24 pm

im also using an MSD 6A ignition box.

okay, im traveling at around 65mph at 3000rpm, so thats where im lookin for improvement. and would like my bug to pull hard to 3500rpm's at least. (3000 being the most important)

Tue Jan 12, 2010 11:49 pm

3000rpm, dam that's crawlin'
Well thats kind of an odd ball deal, the primary length on the header would need to be 50-60 inches to work at rpms that low.
Sure the collector size and length can hurt or help you at this rpm, but I would not worry too much about what length the primaries are because they are going to be too short, in fact I would use an extra short race header so it works in the first harmonic! All in all four into one headers just aren't tuned this low.

How bout a tri-y, this would be a very good use for one.

Tue Jan 12, 2010 11:58 pm

i would be more than happy to try to make a try-y. where do i begin?

like i was saying above, my power really drops off after 4500rpm's with my build combo. im all about power though so maybe shooting for a peak torque at 4500rpm's would be a good idea?

i've got a lead foot, i like to drift, peel out and haul ass. any suggestions of you own with the information i provided?

Wed Jan 13, 2010 12:03 am

so with the fireing order should i consider connecting the 1st and 3rd cylinders and then the 2nd and 4th togather before it all comes togather at the collector? and what tubing sizes do you recommend?

Wed Jan 13, 2010 12:07 am

modok wrote: in fact I would use an extra short race header so it works in the first harmonic!

what do you mean by this?

Wed Jan 13, 2010 12:17 am

I'm gonna say a bit more,
What you want the header to do is pull a vacuum through the later part of the exhaust stroke, the strength of this vacuum should increase as rpm increases. Now of course this is near impossible to do throughout the entire rpm range!. But a good setup can work over a pretty wide range.
But see, 3k-3.5k rpm is pretty slow, the engine does not need a lot of assist to breath at these low speeds, so running a super long four into one header is just silly. It would work too strong at low rpm and kill power at high rpm.
The primary length of the average vw header(34-42inches) is working against you at 3500rpm, so the function of tuning the collector and the pipe from the collector to the muffler is to prevent the reversion problems that would otherwise exist.(like with four straight pipes)..
Thats right, the collector is mainly an anti-reversion thingey that fights the action of the primaries when you don't want them doing their thang.
For rough example, 34" primaries work great at say 5000rpm, at 4000 they might pull a vac early in the stroke but then pressure goes high near the end of the stroke(not good), at 3000 rpm they go vac, then pressure, then back to vac again at the end(thats what I mean by harmonic).

A tri-y header is your best bet for some boost at 3-3.5k rpm without killing power at higher rpms.
I'll pm ya.

Wed Jan 13, 2010 1:52 am

Good read so far....lets hear more theory.

Wed Jan 13, 2010 11:10 am

So this is a try Y

just got to work out how to package design that around a flat 4 now :?

Wed Jan 13, 2010 5:38 pm

yea, thats a tri-y, that one's odd fire. Odd fire works better for the ricers for some reason. Here is one on a WBX: http://i105.photobucket.com/albums/m218/tencentlife/WBXaust/DSC01763.jpg
Made by samba member Tencentlife.

Also notice the Tangerine header Jake Raby so often mentions is a tri-y.
I am running my own version as well on my 2007cc type 1.

I think it would be good to talk about how headers work, but it is almost as complex as alchemy. Even thinking about it is exhausting(ha ha).
I will try to think up some example that makes sense.
Got any specific questions?

Wed Jan 13, 2010 11:06 pm

Hello-

I'm looking for someone who fabricate a muffler that's configured to meet the performance goals of my engine, and looks stock. Any suggestions? The hard part is the later requirement.

Thanks,

Paul

Thu Jan 14, 2010 2:24 am

modok wrote: yea, thats a tri-y, that one's odd fire. Odd fire works better for the ricers for some reason. Here is one on a WBX: http://i105.photobucket.com/albums/m218/tencentlife/WBXaust/DSC01763.jpg
Made by samba member Tencentlife.

Also notice the Tangerine header Jake Raby so often mentions is a tri-y.
I am running my own version as well on my 2007cc type 1.

I think it would be good to talk about how headers work, but it is almost as complex as alchemy. Even thinking about it is exhausting(ha ha).
I will try to think up some example that makes sense.
Got any specific questions?

Ah very cool had never seen any before, seeing 1 and 3, and 2 and 4 go together that makes packaging easier.

So now we have primaries and secondaries, how does that work out in tube sizes , does the secondaries need to be bigger, 1 1/2" running into 1 5/8" s for example?

I really like this design, I though it would be a packaging nightmare, but not I see a whole world of possibility's :D

http://www.tangerineracing.com/

Thu Jan 14, 2010 7:44 am

you should try the tri Y as Modok mentioned

the pairing , if done right (primary length) and secondary too

should provide good scavenging, thus good low (3k ish) power

actual math on it.. modok myt know the answers

, about that 4cylinder inline 4 tri Y

its by smsp , dave stadoulis

its sequencially paired (on firing)

the honda motors fire 1 3 4 2 , so from left to right (or in the pick nearest to farthest) its 1234

with 1-2 paird and 3-4 paird.. sequencially? sounds like its not..

but count it a few more times

1 3 4 2 1 3 4 (3 and 4 fires in sequence , and 1 2 fires in sequence)

hytech has a different sequencial pairing..
pairing it to actual ignition firing sequence..

on honda's when this is done right and sized correct
it can mimic a 4-1 with merged collector's output..

Thu Jan 14, 2010 8:15 am

You forgot "and sells for less than $60" :D

and for the record I'm just cracking a joke aimed at the typical VW Guy, I'm NOT mocking the OP

gimmesomeshelter wrote: Hello-

I'm looking for someone who fabricate a muffler that's configured to meet the performance goals of my engine, and looks stock. Any suggestions? The hard part is the later requirement.

Thanks,

Paul

Thu Jan 14, 2010 6:48 pm

"sequentially paired" is a strange term, dude likely made it up. I call it "odd fire" pairing It is the equivalent of pairing the cyls on one side of a VW engine, like kadrons! I don't know for sure, but I believe odd-fire is best used on engines with short valve timing(think 4 valves per cyl).

Generally in a tri-y the secondaries are one or two tube sizes larger than the primaries. The secondaries are also best kept to at least half the primary length, and no longer than the primary length.

A four into one header setup(in general) has a point in the rev range when you really feel it get "on the pipe", it's like it just turns on! Performance right below the rpms where it "turns on" is kinda weak and funky.
The main advantage of the tri-y is it comes on smoother as you go through the rev range.. It is said a tri-y has a wider powerband, I don't know if this is really true all things considered, but it IS a smoother powerband, more like an arch rather than the two plateaus of a four into one system.
I hope that made sense.