Topic: Thoughts on "crossover" headers?

[fxef79]

I'm referring to the 4-into-2 headers that take one cylinder from the left side and join to one from the right side.  Not only do they look cool, but my understanding is they have good potential for moving torque to the lower end (which is what I'd prefer).  Anyone actually running any of these?

[seanbarney41]

Exhaust design is a black art guessing game.  I have had virtually every configuration on a cb750 at one time or another and performance differences are not detectable by butt dyno.

[Stev-o]

Anyone actually running any of these?

I had a set of Action Four exhaust on my K4 836 when I got it, bike ran and sounded great.

Action Four was a CA company that made hipo parts back in the day.  Cylinders 1&4 went to the left side and 2&3 to the other.

I have since put stock exhaust on the bike, this is the only pic I can find, but check this thread for pics I posted in the exhaust reference thread 8 years ago...

http://forums.sohc4.net/index.php?topic=97959.75



Here's an interesting article on after market exhaust from '72 that includes the Action Four...

https://piledriverz.com/2014/02/04/may-1972-cycle-magazine-honda-cb750-exhaust-system-test/

I doubt I will be reusing them and may be persuaded in selling.

[Don R]

 I had a set of action 4's shorties. They sounded awesome.

[Stev-o]

I had a set of action 4's shorties. They sounded awesome.

Hey Don...noticed your photos are gone in the exhaust reference thread...

http://forums.sohc4.net/index.php/topic,97959.75.html

[fxef79]

I watched a video of someone running pipes (can't find the video now!) that used this 1-4 and 2-3 combo.  I really liked the sound.  I know I'm being sacrilegious when I say this, on this forum, but the typical inline 4 sound has never really done much for me.

The report of moving torque to the lower end also seems sacrilegious for this group, but more in line with what I'd like to have.

[ckahleer]

An inline 4 should sound like a sewing machine. Have you considered getting a Sportster?

[seanbarney41]

The problem is that these really dont have significant amounts of torque to move around in the power band.  They make power by being capable of high rpm.  Of course, this is technically imprecise and a generalisation.  There are only a few ft lbs. To gain down low at the expense of several peak hp.

[fxef79]

An inline 4 should sound like a sewing machine. Have you considered getting a Sportster?

Had one. Have a shovelhead superglide now. This is actually my wife’s trike and her observation of the current (admittedly crappy - I think homemade) exhaust is “it sounds like a lawnmower”.

[fxef79]

The problem is that these really dont have significant amounts of torque to move around in the power band.  They make power by being capable of high rpm.  Of course, this is technically imprecise and a generalisation.  There are only a few ft lbs. To gain down low at the expense of several peak hp.

Thank you.  That’s actually a really good and useful response - sometimes I think I (we?) get carried away worrying about what probably amounts to minutia. What’s the saying?: “le mieux est l'ennemi du bien”

[fxef79]

Anyone actually running any of these?

I had a set of Action Four exhaust on my K4 836 when I got it, bike ran and sounded great.

Action Four was a CA company that made hipo parts back in the day.  Cylinders 1&4 went to the left side and 2&3 to the other.

I have since put stock exhaust on the bike, this is the only pic I can find, but check this thread for pics I posted in the exhaust reference thread 8 years ago...

http://forums.sohc4.net/index.php?topic=97959.75



Here's an interesting article on after market exhaust from '72 that includes the Action Four...

https://piledriverz.com/2014/02/04/may-1972-cycle-magazine-honda-cb750-exhaust-system-test/

I doubt I will be reusing them and may be persuaded in selling.

Not sure if the pic you linked is yours or just an example of a “reference type”. I might be persuaded to be interested. Can you get a pic of current state of the pipes?

[754]

I will tell you what I found, but have not proven on a dyno. I ran a 836 a lot of years,  have not been able to get back into another of late . But all of the time on that motor I ran the Webers, and it had lovely low end response. ,EVEN when I had run them on a stock motor , no hot cam. You have to feel it. On the 836 , I mostly ran the high pipe. But I also ran a 4 into 1 Hooker pipe.
 I at one point  got the high pipe back, and ran it till the motor packed it in.
 Now keep in mind , that pipe is smaller diameter tubing, than any header or custom exhaust, and UNEQUAL  lengths as well , yet it  performed  would  well , and I  would say had better bottom end  than the 4 into 1.

So that US something to think about..now .remember  stock pipes fit INSIDE the spigot, so they are smaller than custom pipes, double wall too.

[fxef79]

On the 836 , I mostly ran the high pipe.

Not sure I'm understanding the meaning of "high pipe" ?

[Stev-o]

Anyone actually running any of these?

I had a set of Action Four exhaust on my K4 836 when I got it, bike ran and sounded great.

Action Four was a CA company that made hipo parts back in the day.  Cylinders 1&4 went to the left side and 2&3 to the other.

I have since put stock exhaust on the bike, this is the only pic I can find, but check this thread for pics I posted in the exhaust reference thread 8 years ago...

http://forums.sohc4.net/index.php?topic=97959.75



Here's an interesting article on after market exhaust from '72 that includes the Action Four...

https://piledriverz.com/2014/02/04/may-1972-cycle-magazine-honda-cb750-exhaust-system-test/

I doubt I will be reusing them and may be persuaded in selling.

Not sure if the pic you linked is yours or just an example of a “reference type”. I might be persuaded to be interested. Can you get a pic of current state of the pipes?

Look at this thread, reply #87, that is my bike in original paint [before the blue]

http://forums.sohc4.net/index.php/topic,97959.75.html

The pipes are in great shape, but in storage.  I'll grab 'em next time I am near there [it's an hour away.]

Send me a PM...thx

[754]

 The rest of my theory..
 By high pipe I mean the one on my red bike I posted in your carb question thread.
 It is in fact a turbo header, that I bought because I liked the look and I wanted ground clearance.

 So look at what that it is. A 4 into 1 with small primary pipes. On a turbo this is done to Increase exhaust velocity to spin up the turbo quicker. ...as far as I know, feel free to correct me if it's wrong.
 
 So let's look at stock exhaust. Small primary pipes as well. Stock pipes with stock air box pulled very well at low rpms. In fact they would advertise smooth acceleration in 5th gear from 2o mph !  And ut worked well . NOW  you may surmise it's not by accident they chose small diameter pipes, they knew what they were doing.

 So what I get from all this is if you want  better bottom end, try small diameter pipes. They will be hard to find . What might work for you is the 2 into 1 pipes that came on some years of Automatic 750,s...excellent ground clearance and probably small diameter..  I am thinking it will get you what you are looking for..
 

[fxef79]

The rest of my theory..
 By high pipe I mean the one on my red bike I posted in your carb question thread.
 It is in fact a turbo header, that I bought because I liked the look and I wanted ground clearance.

 So look at what that it is. A 4 into 1 with small primary pipes. On a turbo this is done to Increase exhaust velocity to spin up the turbo quicker. ...as far as I know, feel free to correct me if it's wrong.
 
 So let's look at stock exhaust. Small primary pipes as well. Stock pipes with stock air box pulled very well at low rpms. In fact they would advertise smooth acceleration in 5th gear from 2o mph !  And ut worked well . NOW  you may surmise it's not by accident they chose small diameter pipes, they knew what they were doing.

 So what I get from all this is if you want  better bottom end, try small diameter pipes. They will be hard to find . What might work for you is the 2 into 1 pipes that came on some years of Automatic 750,s...excellent ground clearance and probably small diameter..  I am thinking it will get you what you are looking for..
 

I certainly can’t argue with your logic!

[HondaMan]

When the pipes were connected 1-3 and 2-4 they have a small RPM range (about 3500-4500) where the timing of the pulse is just right to suck a little bit on the other's pipe, like headers are supposed to do. But as the opening between the 2 pipes is small, the effect is, too. The only pipes I ever saw that increased power worth their $$ were the Dunstall, and to look at them you would never believe it: but they WORKED. Part of it was, without doubt, the fact that the 2 reverse-cone mufflers were longer than the bike: this lent enough length to actually cause an exhaust suction moment within the RPM range of the engine, and they worked from 3500-6000 RPM.

[MauiK3]

Well, this thread needs another unscientific observation :-))
I think that unless a person is targeting a very narrow RPM range, it's pretty hard to beat the stock exhaust.
Yes, they weigh more. The Daytona bike got 4 into but a light version, that should tell you something.
Plus, they have the advantage of being the best looking by far, just my $0.02.

I found the same is true of my 49cc Ruckus. I did some checking and all the claims about the aftermarket pipes are pretty much rubbish. Not much you can do with 49cc unless you are targeting a VERY narrow RPM range.
My Ruckus hits the rev limiter at 45mph and it sings along happily at that speed, my tach says it's at just about 10,000 RPM. You'd never guess it. Gotta love a Honda.
Happy Social Distancing.