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Just call me goose.
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Any engine fart gurus on here? I'm trying to design a system but I'm fairly new to this and don't even know where to start.

1126cc 72 degree V twin, DOHC 4 valves per cylinder, 103.0 x 67.5mm (bore x stroke), running 12.3:1 compression, redline at 11k rpm. I'm looking more beef everywhere. It's there, I'm just not sure how to get it.

At first glance, I'm thinking, individual 1 7/8" off the headers into a 45 bend, around the bottom of the collector, bump to 2" short merge X with a long split into individual 2 1/4", run it sraight under the engine then 45's turned out then 45 turned vertically into 2.5" packed short pipe.


Anyone know the formula for the calculations? What intake measurements will I need?
 

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V four honda whore
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12,487 Posts
Pipes will be unequal lenght.


And for that displacement and engine configuration i see no,other possible bike. Since this is not an agriculture tech... Ehm i mean chopper forum
 
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lɐʇuǝɯᴉɹǝdx&#4
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Unequal pipe lenght for a v twin might be ideal for scavenging, since exhaust pulses don't happen at equal intervals.

No idea what the math would be for ideal lengths though. Those look crazy short to me, but who knows?
 

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UnicycleMode
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Unequal pipe lenght for a v twin might be ideal for scavenging, since exhaust pulses don't happen at equal intervals.

No idea what the math would be for ideal lengths though. Those look crazy short to me, but who knows?
I've always had the best luck with exhaust building on twins by going unequal length on the primary pipes before the collector. Seems to smooth out the pulses quite a bit.
 

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ShamanFighter
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Man Exhaust theory is Dinosaurs. you have to take into account so damn much. where the port is where ots going to. what is the timing. so on bleh bleh bleh. the reason there's so many bends in a lot of pipes is to keep ir uncorked and still maintain back pressure to keep a solid feeling low end and to prevent suck back and detonation and the burning of the valves. . best thing to do is measure the stock set up to.get a baseline. me I just fuck with shit until I blow it up or I feel a tightening of the pants when romping on the throttle. if you ot good enough youll even leave a wet spot right on the tank where your junk rubs
 
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lɐʇuǝɯᴉɹǝdx&#4
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How do you determine which cylinders gets the longer of the unequal length pipes?
Yeah.... it wouldn't be easy to do exactly, or with predictable results. But in theory it makes sense for the pipe length before merge would be proportional to the time (in degrees) until the next cylinder goes bang, to give the gas (or pressure pulse) time to clear the merge and create scavenging.

Say its 45° V twin (yeah, one of those). The first (front) cylinder fires, the second (rear) cylinder fires 315° later, then there is a 405° gap until the first cylinder fires again. So it would seem logical to make the header lengths in a ratio of 315 to 405, because the time between a front and rear pulse is longer by that same ratio. That could be 31.5 inches and 40.5 inches before merge, for example. Its a 7-9 ratio, so you could also do 35 and 45 inches.

Oddly, unless I'm mistaken about the front cylinder firing first and direction of roatation (I got that from Wikipedia), this seems to indicate that the REAR header on a HD should be longer than the front. So ... ???
 

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Is my bike ok?
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And of course, that would only apply with merged pipes. Most every twin has individual pipes which, in that case, why even bother.

I know we used to put on a set of headers then run a straight extension ( about 18" minimum) on our drag cars and then paint a line down the extension with a brush. Make a few passes and see where the paint stopped burning...cut a couple inches longer than where the paint stopped burning, run again, etc, etc....you get the picture. Once "tuned", you could remove that extension and watch the 60' times suffer.

How we discovered this... a bud had a zoomie break so we tossed on a standard header meant for a door car to make an event. As expected, it improved bottom end, but it was a HUGE difference. Like, the rail acted like it wanted to lift. But, with the collectors pointing straight at the driver ( front engine dragster) , it was blasting him with fumes and we didn't like it pointing straight at the rear tires ( tire pressure is crucial on 1000+ hp cars with rigid suspension). So, we slipped on a pair of turnouts and , boom!, wheelie monster.

Cliff notes: collectored pipes kick ass. Too little back pressure is a real thing. That's all I got on pipe tuning. lol. Sorry for rambling
 

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V four honda whore
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i know somewhere i saw a calculator for manifold building on cars, it suggested how big and how long runners you have to run to get desired powerband.
 

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lɐʇuǝɯᴉɹǝdx&#4
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https://www.google.com/webhp?q=engine+header+calculator

They seem to vary in complexity in terms of what you enter; some just take rpm and displacement, some take info I don't even know. Reading a few, it seems header (primary) length doesn't even matter much to peak torque, diameter vs cylinder volume is what is used to determine that. Length just controls the shape of the curve (longer = faster drop off above peak, shorter = faster drop off below peak).

 

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V four honda whore
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Didnt ducati used different diameters on some models to equalize the pipe volume? or thats just i just made up in my mind!?
 

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I know we used to put on a set of headers then run a straight extension ( about 18" minimum) on our drag cars and then paint a line down the extension with a brush. Make a few passes and see where the paint stopped burning...cut a couple inches longer than where the paint stopped burning, run again, etc, etc....you get the picture. Once "tuned", you could remove that extension and watch the 60' times suffer.
Wow, you lost me there. How does heat and pipe length help you determine ideal header pipe length?
 

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ShamanFighter
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Wow, you lost me there. How does heat and pipe length help you determine ideal header pipe length?
its integral to the.Suck. Squeeze. Bang. Blow. Theory. not only does it take care of the Blow.part it helps Suck too. if its not escaping fast enough at the right pressure it will not pull in the fuel. think of the engine like a vacuum cleaner with both sucking and blowing functions on at the same.time. and the blowing enhances the sucking if done at the right ratio.
 
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