header pipe diameter

[mvalenti]

I am not near my bike or I'd do this myself... Can someone tell me the header pipe diameter for a 1980 GS850G please?

 

[Steve]

The inner pipe or the outer one? :-k

I am not near my bike, either, or I would give you some actual numbers.

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[mvalenti]

oh yeah... outer pipe. Forgot they were double wall... Why do they do that? Ans are the after market exhausts double wall?

 

[Steve]

They do that to keep the chrome from turning color so easily on the outer pipe.

And, although large-diameter pipes will flow better at high RPM, longer, narrower pipes will enhance the low- and mid-range operation. Using double walls will let them use a smaller pipe inside the larger one that you can see (and think that you have large pipes).

I can't vouch for all the aftermarket manufacturers, but all the ones that I have seen were all single-walled.

I won't be able to measure a pipe until about the time that you can probably measure one, but will check back with this thread this evening to see if someone else has posted any numbers.


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[mvalenti]

Thanks Steve as always for your help and a wealth of knowledge. I am thinking of lengthening my exhaust to something behind me. Its not the noise, its the exhaust smelling pant legs.... And I wont lie, even with installing baffles, I've lost more low end than I care to admit.

 

[Steve]

And I wont lie, even with installing baffles, I've lost more low end than I care to admit.

850s are not exactly known for prodigious amounts of low-end torque, so you must really be hurting there.

I don't think that baffles will tune the torque range as much as length of pipe will. The "length" that the engine needs to "see" is from the exhaust valve to a sudden change in diameter, which will reflect a wave back up the pipe. That sudden change in diameter could be at a collector, where two or four pipes join or at the end of the pipe in a four-into-four setup. If you are running individual pipes, having them long enough to get behind you might help a bit. I know you are trying to do your own thing, but have you considered a system that is already engineered for that bike? MAC makes a 4-into-2 system with turnouts that might suit you.

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[mvalenti]

850s are not exactly known for prodigious amounts of low-end torque,

Yeah, i should look at some numbers first and compare to what i'm doing, at this point its more of an assumption on my part...

I know you are trying to do your own thing, but have you considered a system that is already engineered for that bike? MAC makes a 4-into-2 system with turnouts that might suit you.

LOL @ "your own thing" thank you Steve, thats one of the more polite ways of saying it. And I kind of needed it since I ran into a GS snob the other day and I let it get to me, but thats another story...

I looked at the aftermarket stuff, and due to my loss in ground clearance, It would be tough to fit.. I should have considered that more in the whack n chop phase.... Live and learn.... I still have my stock mufflers that I think I will tie back in some how... I think I can do a cross over under the non swinging swingarm, plenty of room there.... But I think this will be done during the winter months here in New England..


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[Steve]

OK, just measured the pipes, ... 1.5" diameter.

For what it's worth, it's about 28" from the head to the "Y" collector just ahead of the muffler.

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[mvalenti]

Thanks Steve, much appreciated! I didnt get home till very late and had no energy to go out to the garage.

 

[tkent02]

And I kind of needed it since I ran into a GS snob the other day and I let it get to me, but thats another story...

Let's hear it?