How important is the exhaust crossover pipe?

[growler]

I think I'll just leave it alone. No rust. Why mess with it.

Should be higher in pitch as there is less volume.

Not positive as I've left mine intact.

[Killer2600]

The reason for the crossover pipe is the inner two cylinders run hotter than the outer two. For cooling and efficiency the inner cylinders are run slightly richer and the scavenging effect from the crossover helps with the breathing required for richer fuel mixtures.

[tkent02]

The reason for the crossover pipe is the inner two cylinders run hotter than the outer two. For cooling and efficiency the inner cylinders are run slightly richer and the scavenging effect from the crossover helps with the breathing required for richer fuel mixtures.

Not true, on most GSes the jetting is the same on the inner cylinders.

[850GT_Rider]

Not true, on most GSes the jetting is the same on the inner cylinders.

Yeah - never heard of the inner cylinders running richer. All jets are the same, at least on mine.

[GSX1000E]

Stock jetting on the 1150 models the inner two main jets are larger. Same reason that the factory sync. is supposed to have lower vacuum on the center cylinders on all other 4-cylinder models (to run slightly richer).

[tkent02]

Stock jetting on the 1150 models the inner two main jets are larger. Same reason that the factory sync. is supposed to have lower vacuum on the center cylinders on all other 4-cylinder models (to run slightly richer).

The 1150 has the bigger jets, the rest don't.

Only set the synch that way on the models with the crossover pipe. The ones before that should all be set the same. That's not it.

[Steve]

The 1150 has the bigger jets, the rest don't.

The '83 550E (the one with the 4-valve head and the siamesed carbs) also had richer jets on the inner cylinders.

What made that one interesting is that in each of the two-barrel carbs, the two main jets were different sizes.

.

[Old guy]

My best guess is since exhaust restriction increases cylinder temps, the inner cylinders are allowed to breath a little easier. On the motors with mixed jetting, they probably needed a little more cooling.

[Killer2600]

The 1150 has the bigger jets, the rest don't.

Only set the synch that way on the models with the crossover pipe. The ones before that should all be set the same. That's not it.

Jetting isn't the only factor in fuel mixture e.g. a vacuum leak will lean out a cylinder even if the jets are all the same size. With that in mind add in that the carb sync across all four from the factory isn't equal.

[tkent02]

Haven't ever heard of any of the eight valve engines having troubles with cylinders getting hot. They have plenty of cooling fins and airflow. You guys are on the wrong page.

[JAG]

I don't know or care if this is right but my understanding is as follows.

The cross-over equalises the exhaust pressure across all of the system. It doesn't matter if this is before 1&2 / 3&4 join or after.

There are two pressure states to consider. The first is the increased pressure of a slug of exhaust gas travelling down the pipe. The second is the pressure during the rest of the cycle. The cross-over equalises this. The effect is subtle.

2&3 pots do run hotter on all air-cooled inline fours. The reason is simply due to less surface contact with the cold ambient air. Balancing cooling as best you can, balancing a bank of four carbs as best you can, and balancing the exhaust system as best you can, combined, results in an engine which runs cleaner. That means lower emissions from a more efficient engine in a hp to hp comparison on engine designs.

The ideal exhaust system will have downtubes (header pipes) of equal length, arranged in such a manner that they all meet at the same point i.e. a 4 into 1 pipe. The cross-over in the later 4 into 2 attempts to create the benefits of a 4 into 1 whilst maintaining the aesthetics of the 4 into 2.
-----

What a load of Bullsh1t

Thought I'd save you the trouble of replying

[Agemax]

main jets and carb synching have no effect on each other, in any way whatsoever.

[Killer2600]

The ideal exhaust system will have downtubes (header pipes) of equal length, arranged in such a manner that they all meet at the same point i.e. a 4 into 1 pipe. The cross-over in the later 4 into 2 attempts to create the benefits of a 4 into 1 whilst maintaining the aesthetics of the 4 into 2.

Applying that whole concept would mean the exhaust traveling backwards (up the pipe) and a longer distance till exit would be more efficient i.e. the path to get from the #1 cylinder to the right side outlet.

main jets and carb synching have no effect on each other, in any way whatsoever.

Not sure if that's a reply for me; but that's true, they don't affect each other. They do however both affect the burn and power contribution of the cylinder.

I don't expect anyone here to accept or understand the explanation I was given and have thus passed on anymore than I expect the amish to accept electricity and wireless communications; but, the explanation I have given explains and ties together alot. Maybe if we ever get a fluid and thermal dynamics version of posplayr here we'll have more believers

At the end of the day, it boils down to the japs made it, it works, and that's all you need to know.

[Steve]

At the end of the day, it boils down to the japs made it, it works, and that's all you need to know.

And maybe you can also accept the fact that not everything they made was perfect?

.

[Killer2600]

And maybe you can also accept the fact that not everything they made was perfect?

.

Nothing made by humans is "Perfect" nor is anyones doubt. In hindsight though, I guess what they made was good enough to trust your life on, everything in your stable originates from their corner of the globe.

I am open to all logic, if anyone wants to explain a better reason for the extra steel that is the crossover pipe then by all means get down and dirty. Put it all together and lay on all the facts you have.