Let's talk unequal length (UEL) header! Options

[Syaoran]

I've been wondering what does it exactly consist of to make unequal length headers (in our case, header) for a straight-four. I know subies come with these stock due to design.

I like how unequal length headers sound on any car, be it 4,6,8 cyl engines... it's just not tinny and tends to resonate less. It's a sweeter, cleaner sound. So I'm all UEL Header just for the sound.

I know there is a certain science behind it, but what exactly would it involve to have this done in our celicas?

[texasnick]

Assuming this is for N/A application? or F/I (more specifically turbo)?

[celica74]

Ever seen a ramhorn turbo manifold? Im assuming youd have to base it somewhat on that. Being cyl. 2 and 3 runners have either upward or outward turn in then to compisate for how far out 1 and 4 are. Then into a collector.

[Special_Edy]

I've been wondering what does it exactly consist of to make unequal length headers (in our case, header) for a straight-four. I know subies come with these stock due to design.

I like how unequal length headers sound on any car, be it 4,6,8 cyl engines... it's just not tinny and tends to resonate less. It's a sweeter, cleaner sound. So I'm all UEL Header just for the sound.

I know there is a certain science behind it, but what exactly would it involve to have this done in our celicas?

Well, sound travels at a certain speed(600 something mph) and a normal header is going to deliver the sound waves from the exhaust valves opening at equal speed. So you get a even sound of twice every revolution coming out of our 4cylinder exhaust. V8s or V6s are not as even when they are split into dual exhaust, because the firing order between the two exhausts will be uneven.( Note- firing order will vary widely between different brands and engines).
For example, my old 350 chevy( simple cause I have the order memorized) firing order is 1-8-4-3-6-5-7-2. The exhaust pulses out L-R-R-L-R-L-L-R, with L be being left header and R being right header. So the exhaust has a certain burble sound to it because both sides fire unevenly.

An unequal length header would seek to shorten and lengthen pipes to deliver the sound waves out of order.
To make it sound like the SBC V8 I gave as an example, well Im gonna need to do some math...

8 cylinders = 4 combustions every rotation of the crank or once every 90°
4 cylinders = 2 combustions every rotation of the crank or once every 180°

one bank on the v8 in 90° increments = P _ _ P _ P P _
one bank on the I4 in 90° increments = P _ P _ P _ P _
Or fire 270° fire 180° fire 90° fire 180°
whereas the 4 cylinder is fire 180° fire 180° fire 180° fire 180°

So to make it sound the same we want to make the pipes
Normal length, 50% longer , 50% longer, normal length
So the second 2 pipes in the firing order are longer, firing order is 1342 so...

Pipe 1 normal length

Pipe 2 normal length

Pipe 3 50% longer

Pipe 4 50% longer

if you made headers with the primaries this length you would have a 5sfe or 7afe with a small block chevy V8 exhaust sound. The same math applies to all engines but firing order, cylinder numbering and number of cylinders will vary



hope this helped you understand the 'science behind it'. Its definately got me thinking about making a set.

[celica74]

Alot of detail there. I noticed on most ebay headers for the 74 the cyl. One running has a curve in it assuming it is longer then the other three. Id assume just making 1 and 4 a certin way and then making 2 and 3 have a slight curve outward to compensate would do the trick. I doubt youd be able to tell an audiable difference though. Still have the cat( if you havent taken it off), resonator(if you have one), and muffer(if you arent dumb like me and cut it off) to go through.