4 Cylinder Header Design

[thescreensavers]

Currently this engine uses a 4-2-1 Setup with a crossover a few inches away from the exhaust port(on the header primaries), only on cylinders 2 and 3(which is well before the first collector)

This Engines Firing Order is 1-2-4-3


The Crossover linking Cylinders 2 and 3 confuses me since they are not paired. Since Cyl 2 Fires then next to fire is Cyl 4, so there isn't any scavenging from these two (Cyl 2 and Cyl 3). I believe this is done to alter the sound of the exhaust, is my assumption correct?


I have an idea to create a dual exhaust system which

(Cyl 1 and Cyl 2)
and
(Cyl 4 and Cyl 3)

Are paired

So the exhaust is a Dual 2-1 system. But, now two cylinders will not receive scavenging (Cyl 1 and Cyl 4)

To Remedy this I propose to put crossover pipes on the header primaries between

(Cyl 4 and Cyl 2)
and
(Cyl 1 and Cyl 3)

So now all cylinders can receive scavenging.



What are your opinions on the system? Is there any literature on crossover pipes in headers?

 

[Lou Scannon]

Not enough information. Is it a 2 stroke or 4 stroke? What is the crank configuration? What problem are you trying to solve?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[thescreensavers]

Sorry, it's a 4-Stroke 4 Cylinder engine. Each cylinder is 180 degrees apart using a Flat Plane Crank.

The Problem- Instead of running a traditional 4 to 1 setup, I propose to run a dual 2 to 1 system that can produce similar performance when compared to a 4 to 1 setup. So the ultimate question is how do crossovers by the headers function, and if there is a book that talks about them I can read so I can optimize them. The two Engine books I have do not speak about them. Also I would like to hear some opinions about this.

 

[patprimmer]

Why would you not pair 1 with 4 and 2 with 3 to get even spread of the pulses. Adjust pipe length to get the pulses at the valve at overlap.

Regards
Pat
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[thescreensavers]

That would be unsequential pairing, I believe sequential paring gives the most power, am I wrong? Can you explain?

 

[patprimmer]

1 with 4 and 2 with 3 is sequential. The sequence is every alternate cylinder by firing order.

The reason is that the exhaust gas pulse then has equal separation, ie 360 deg between each cylinder. Closer is better, but then you get uneven with a bit to close then a lot to far apart ie 180 then 540 then 180.

In my experience 3 into 1 works really good, but 4 into 1 also works fine.

Pipe layout is but one aspect of this.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[thescreensavers]

Hmmm, I must of gotten confused with all what I was reading, and would appear you are correct. Also now I can picture a 4 stroke engine properly, When Cyl 1 is in power stroke, Cyl 2 will be in power stroke when Cyl 1 Opens its Exhaust valve. So there is no scavenging until 540deg with my current idea. If we do it every 360deg then each cylinder will get the same size pulse.

So could you give your opinion and Help me better understand the Stock Engine's 4-2-1?

It pairs 1 and 2, and 3 and 4 with a crossover on 2 and 3 so these two receives 360 deg Scavenging, the other two receive 540 scavenging from its primaries and then all cylinders receive a weaker scavenging effect from the final collector. . . But The same engine just greater displacement gets rid of the crossover, otherwise it's the same setup. I cannot see why they would give the greater displacement engine less scavenging?