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exhaust tuning discussion

Started by crackin, May 28, 2017, 12:01:29 AM

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crackin

So im looking at tuning my exhaust and id like to hear thoughts from anyone with some knowledge on the subject.
The first thing im going to do is remove the crossover in the primary pipes. Why is it even there? I cant get my head around it. I read that twins need that crossover for all kinds of reasons but ive never seen a harley with one. So what gives? Is it just for emissions or to smooth the power band?
  The second thing is to cut out the crappy collector and replace it with a 15 degree custom made one in hopes of improving exhaust flow and help with exhaust port scavenging.
   Then there is the issue of primary pipe length. For that i will just cut the primaries in half and insert and or remove small sections of pipe to tune the length to the rpm range i like.
  It seems to me messing with primary pipe lengths would be a total waste of time if the crossover was still in place.
Thoughts?
  Johno
  P.S I know i'm going completely over board, but if there is half a HP i'm going to find it.
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

Watcher

Usually that crossover pipe is meant to direct the exhaust pulse to the other cylinder to maintain exhaust velocity, which helps with scavenging.  Even many sportbikes have them.
That being said, I haven't researched exhaust much so I don't know the ins and outs.

Harley's don't because being a V-twin makes it very difficult to do, the headers are so far apart.
Also, it's a HARLEY.  They aren't exactly performance machines.
Best example of V-twin exhaust I can think of is a Buell.
"The point of a journey is not to arrive..."

-Neil Peart

ajensen

Exhaust systems are really easy to get wrong and really hard to get right. One thing I have wondered is if anyone has tried a dual exhaust with a little bigger diameter pipe. Back in ancient times, Harley Sprint 250s made a lot of horsepower with short 13/4 inch pipes and short megaphones. Ducati 250s, on the other hand, had long 11/2 inch pipes with long, slow tapered megaphones with almost no reverse cone on the end. Kawasaki Ninja 500s have long dual exhausts. I'm curious about what GS owners have tried.

crackin

Perhaps the cross over is necessary due to the firing order of the 180* crank? Maybe its best left alone.
  I still think there maybe small gains with a decent collector and messing with primary pipe length.
Quote from: ajensen on May 28, 2017, 01:40:10 PMOne thing I have wondered is if anyone has tried a dual exhaust with a little bigger diameter pipe.
I know a guy in england put twin pipes on his gs , but im not sure if it went any harder or not. He never put it on a dyno as far as i know. From the reading ive done about exhaust tuning i would imagine it would lose power over the stock headers.
  Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

The Buddha

Larger diameter and less restriction will let the gs almost rev up 500 rpm higher vs even a less restrictive silp on.
I had a GS specific yosh slip on on my 1 of my bikes and a GSXR D&D on the other one. They were both slip on's on the stock header.
Swapping the whole pipe I made several runs on both bikes.
The D&D was a straight through baffle that was freaking huge. The Yosh had a smaller baffle and had a restrictive insert in it at the snout end.
Oddly, the D&D was loud as freaking hell and not pleasant or burbly till ~5k past which - well it annoyed the clown in the car following me, but not me. The yosh, burbly and nice at low revs was loud to my ear at anything past 4-5k.

The end result was that either bike pulled almost 500 revs higher with the D&D in higher gears.
However neither bike wanted to run 152.5 mains over 150 (had K&N lunchbox on them both), they both lost 500 or so rpm up high with the larger mains and didn't run as well in any rpm/throttle setting, even in the dead of winter in Canadia.

So, maybe there is 1/2 a hp in the pipe hiding somewhere, however there is a few 100 revs for sure.

Cool.
Buddha.
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crackin

Thanks buddha, I already have a megecycle slip on, Dyno jet kit and K&N lunch box. The baffle is an australian made baffle and a really open design. Im not really chasing more revs as i bounce valves as it is. Im chasing Mid to high mid range torque and HP. There might be some gains by advancing the timing a degree or two also. I know every one retards the timing on these bikes (or is it the other way around) for more power low down but that's not for me as i ride high in the rev range and my GS only weighs 164kg wet. Ive run the bike on the dyno a couple of times and im getting 43HP at the back wheel but i want more. I'm only doing this for fun, I love to tinker.
Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

mr72

Quote from: crackin on May 28, 2017, 07:23:25 PMIm not really chasing more revs as i bounce valves as it is. Im chasing Mid to high mid range torque and HP.

Higher revs (all else being equal) means more HP.

HP = (torque * RPM) / 5252

That said, the problem is delivering enough fuel at those higher revs this Buddha talking about a bigger jet. And as you mention you need harder valve springs to keep up with those revs and ideally a different cam profile with more duration and overlap which may cost some torque at lower revs but yield a lot more power at the top end. A 4 valve head won't hurt.

I'm a big fan of anyone experimenting with the exhaust header simply because the stock units are all getting old and rusty. Be nice to have an aftermarket or diy replacement that didn't cost an arm and a leg. The one showbizwolf has looks great but it's half what I paid for my bike.


The Buddha

Midrange HP. Yea good luck with that. You're floating the valves ? what rpm does it run ?
Yikes, low and mid range is high compression and is you can longer stroke, and you have a cam with a lot of lift ??? OK that explains the valve float.
I dunno, you're different than any other racer I've heard of using this bike for anything HP related.
Cool.
Buddha.
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I run a business based on other people's junk.
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gregjet

OK here are the figures I got for the GS500 using a readily available calculator.
Length of header FROM the valve face: 508mm/35mmID
Collector box:139mm
Tailpipe: 455mm/45mmID.
Overall pipe length before muffler FROM VALVE FACE: 1102mm
The big problem with the Gs is the 180deg cranks ANd the massive valve overlap that will occur because of it. This will screw op the waves arriving back at the ports ( and they will be severly assymmetric).
Here is an alternative I found for 180deg offset crank.
Header: 508mm/35mmID into 127mm/45mmID
The collector and tail the same as above.
Overall pipe length before muffler FROM VALVE FACE: 1229mm

For 2 single pipes:
From valve face header and tailpipe single pipe: 963mm/35mmID.
2 singles should give better peak HP and be shorter. If you choose very ligfht cans it will be Lighter.

Not sure which will give you more torque at mid/lower but suspect the 2 into 1 180deg crank design should.
These are theroybase figures. Proper dyno tuning is needed for optimium.

INTERESTINGLY there is a new maths set designed for non 360deg crank offsets that MotoGP( yamaha)  and Formula 1 motors are using with steps in the headers. But nobody is letting the formulae for these into public gaze. They would be perfect for this engine to get around the pulse interference and have nice short pipes with 2 into 1.

crackin

#9
Thanks for all the input guys, lots of good information here and lots to consider.
Quote from: The Buddha on May 29, 2017, 04:59:28 AM
Midrange HP. Yea good luck with that. You're floating the valves ? what rpm does it run ?
I couldn't say exactly, as i dont have a tacho on the bike. Im bouncing valves in low gears simply from over revving the engine. The head has been fully rebuilt and im running 1mm oversize piston and rings. I'll stick the tacho on and see what revs they bounce at.
Quote from: gregjet on May 29, 2017, 01:58:31 PM
OK here are the figures I got for the GS500 using a readily available calculator.
Length of header FROM the valve face: 508mm/35mmID
Collector box:139mm
Tailpipe: 455mm/45mmID.
Overall pipe length before muffler FROM VALVE FACE: 1102mm
The big problem with the Gs is the 180deg cranks ANd the massive valve overlap that will occur because of it. This will screw op the waves arriving back at the ports ( and they will be severly assymmetric).
Here is an alternative I found for 180deg offset crank.
Header: 508mm/35mmID into 127mm/45mmID
The collector and tail the same as above.
Overall pipe length before muffler FROM VALVE FACE: 1229mm

For 2 single pipes:
From valve face header and tailpipe single pipe: 963mm/35mmID.
2 singles should give better peak HP and be shorter. If you choose very ligfht cans it will be Lighter.

Not sure which will give you more torque at mid/lower but suspect the 2 into 1 180deg crank design should.
These are theroybase figures. Proper dyno tuning is needed for optimium.

INTERESTINGLY there is a new maths set designed for non 360deg crank offsets that MotoGP( yamaha)  and Formula 1 motors are using with steps in the headers. But nobody is letting the formulae for these into public gaze. They would be perfect for this engine to get around the pulse interference and have nice short pipes with 2 into 1.

Thank for chimming in here gregjet, I know you have lots of race experience.
Adding in the extra 127mm/45mmID is very interesting. I dont have a center stand so it should be doable on my machine. Still, I may need to go a little shorter on the primarys as the collector i'm going to make will be 200/250mm long and I may put a short cone on it too. Any idea what size the collect outlet should be?
  Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

The Buddha

BTW for midrange your exhaust may need to be more restrictive and that bridge connector would probably play a positive role.
If you're running high revs the crossover scavenging action could suck the mix out of the other chamber but at lower revs its likely to keep the back pressure up especially with a exhaust that wasn't WFO.

Anyway midrange is compression and pistons etc etc and not as much head and exhaust. Heavier rotating parts help, not hurt too.

Cool.
Buddha.
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I run a business based on other people's junk.
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crackin

Thanks Buddha, i'm learning alot here.
I was looking at my dyno run sheet, and from 5200rpm the torque output is 35nm and it rises gradually to 36.8nm at 7900rpm then drops away to 35nm at 8200rpm and just keeps dropping. Max hp is 43 at 8700rpm to 9000rpm then it drops off. So i think the area to try and make some power for me, is between 6000rpm to 9000rpm but i will get my tacho on and see how hard i actually rev it.
From the reading ive done, longer primary pipes make more power in the low and mid range area. Shorter primarys make more top end power. This validates gregjet's suggestions so i think that maybe a good starting point for me. I need to read up on the stepped primarys grejet mentioned.
I also noticed on the dyno run sheet that the air fuel mixture drops below 13/1 at around 4800rpm to 12/1 and stays there till  8000rpm where it returns to 13/1. So i think my needle needs lowering one clip. Thats might give me half a horse lol.
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

crackin

#12
If you goggle "coneeng" you will find some interesting info in their "tech assistance & assembly articles" tab. Some of it is motorcycle specific and very interesting in deed.
I had a good look at the GS exhaust and saw that the collector angle is close to 45 degrees on the left pipe and almost straight on the right. And that collector is huge, the exhaust gases must loose velocity in it.
Ive made my collector but still need to weld it up. It's a 15 degree merge with 35mm OD primarys to 45mm OD which gives around 50% growth area of the primary tube, give or take. Thats in the ball park according to the charts found at cone engineering.
Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

gregjet

If you are interested I have a theory that I developed for a bike that needed  insanely short header pipes ( 11" on a 4), that were so short you couldn't actually fit them together. Build a 2 into one that is actually a tuned 2 into 2.
Ok the GS's low rev range actually may make this not totally practical because of the long tuned length needed but:
Make 2 pipes single pipe tuned length.
Run them into a common box with a volume greater than the expanded volune of the expelled gas. Because the gas cools hugely as it expands that ends up being smaller than you think. The idea is to fool the gas into thinking it has hit the atmosphere ( ie no restriction).  For the 250 it was greater 750cc chamber ( free volume), so normally for a single or a 360 degree twin the required volume would be greater than 1500cc. That's pretty small. BUT with the 180deg crank the two pipes will be feeding is at the same time for a while so double the volume. Still only 3000cc which isn't big. The outlet again normally would be the same size as the inlet except for the overlap so I think a safe margin would be 25% greater crossection. Added advantage of needing a smaller muffler as the chamber would disapate a fair bit of the pressure fronts ( noise). And it will make officials think you have a Cat fitted.
Remember the chamber has to have a volume EXCLUDING the volume of the pipes inside the chamber.
The problem is the length of the pipes would mean curving them back or similar inside or outside the chamber. But you get proper tuning without interference.

I had a design that I was going to use for a V twin that would work for this bike as well that ran the pipes into a flat cyldrical chamber at a tangent and exhausted from the centre. That acted as a extractor via the gas momentum. Almost didn't need a muffler ( for the track) at all.

'

crackin

#14
 Today i fitted the new collector and there is a clear difference in power delivery. She pulls hard off the line and all the way through the rev range in all gears. It seems there is now more available torque throughout the rev range. I will need to dyno it for exact numbers but I am extremely happy with the results.
I used 120mm of 35mm ID tube which slips over the original primarys. The outlet is 100m of 45mmOD tube which is the same diameter as the original outlet, then straight into the slip on tail pipe. My tail goes from 45mm to 50mm as i have an after market baffle that suits an F model. My bike is an E and the original tail pipe was 45mm OD.
The original collector is a piece of junk. There is perforated metal welded to the internal walls (top and bottom) and a metal rod running vertically though the center of it, WTF Suzuki? So between the hugely oversized collector ,45 degree merge angle, the metal rod and the perforated metal welded inside it, I believe it severely slows the velocity of exhaust gas.
This mod cost me the princely sum of $13 AU and is the best mod by far in terms of cost vs performance that i have done. Well worth the effort if you want more performance out of this little scooter.
Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

crackin

Quote from: gregjet on June 05, 2017, 02:16:08 PM
If you are interested I have a theory that I developed for a bike that needed  insanely short header pipes ( 11" on a 4), that were so short you couldn't actually fit them together. Build a 2 into one that is actually a tuned 2 into 2.
Ok the GS's low rev range actually may make this not totally practical because of the long tuned length needed but:
Make 2 pipes single pipe tuned length.
Run them into a common box with a volume greater than the expanded volune of the expelled gas. Because the gas cools hugely as it expands that ends up being smaller than you think. The idea is to fool the gas into thinking it has hit the atmosphere ( ie no restriction).  For the 250 it was greater 750cc chamber ( free volume), so normally for a single or a 360 degree twin the required volume would be greater than 1500cc. That's pretty small. BUT with the 180deg crank the two pipes will be feeding is at the same time for a while so double the volume. Still only 3000cc which isn't big. The outlet again normally would be the same size as the inlet except for the overlap so I think a safe margin would be 25% greater crossection. Added advantage of needing a smaller muffler as the chamber would disapate a fair bit of the pressure fronts ( noise). And it will make officials think you have a Cat fitted.
Remember the chamber has to have a volume EXCLUDING the volume of the pipes inside the chamber.
The problem is the length of the pipes would mean curving them back or similar inside or outside the chamber. But you get proper tuning without interference.

I had a design that I was going to use for a V twin that would work for this bike as well that ran the pipes into a flat cyldrical chamber at a tangent and exhausted from the centre. That acted as a extractor via the gas momentum. Almost didn't need a muffler ( for the track) at all.

Thanks gregjet, Interesting stuff and gives me alot to think about. Looks like i may be chopping up my pipes again in the future. LOL
Johno
No matter what i do to it, it's still a GS
It's not how fast your bike is, it's how long you are prepared to hold the throttle on.

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