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 Exhaust Y-piece broken....again

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Pete Roper
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motor-timothy
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PostSubject: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 7:58 am

So I'm now on my third Y-piece and today I noticed it too has cracked at the weld and in addition 1 of the 2 sides where it mounts to the frame has complete sheared through as well. Right before my motorcycle weekend to France friday....wonderful.
I think I'm going to take the risk and ride it, it's still mounted to the frame by 1 side and I don't think the headers will actually fall off if the other metal side cracks as well. but it will linger in my mind while riding which sucks.

Anyway to cut to the chase, there are 2 alternative Y-pieces that I know of, the titanium one by Arrow and the Agostini. The latter doesn't have the U-turn, and the description says this enhances performance. Can this be used without changing the map? Also, does the heat-shield mount on the Agostini Y-piece?

Also, from what I've understood the Arrow system doesn't use gaskets. If I replace the Y-piece with the arrow Y-piece but keep the stock headers and muffler, do I need any gaskets?

Thanks in advance!
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beetle
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 1:34 pm


The Agostini midpipe is a joke and should be avoided. It does not "enhance" performance. Rolling Eyes
If anything, it degrades performance.

The Arrow midpipe is vastly superior, but it also does not work as well as the stock pretzel. I run one in my GRiSO, and had to advance the ignition significantly to get some of low/mid range torque back.

The Arrow system does not use gaskets. The Arrow headers slide into the midpipe around 40mm from memory, and are a snug fit. I've not tried the stock headers with the Arrow midpipe, but you won't be able to use gaskets. There simply isn't enough room.

You won't absolutely require a new map with the Arrow, but it won't run quite as well.




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motor-timothy
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 2:13 pm

beetle wrote:

The Agostini midpipe is a joke and should be avoided. It does not "enhance" performance. Rolling Eyes
If anything, it degrades performance.

Thanks! Will be skipping that one then Smile

Quote :
The Arrow midpipe is vastly superior, but it also does not work as well as the stock pretzel. I run one in my GRiSO, and had to advance the ignition significantly to get some of low/mid range torque back.

Oh no, that is a shame. I was seriously considering the arrow headers (pretzel + headers) but I don't want my GRiSO to run worse. I'm assuming there is no beetle map for the arrow headers with stock exhaust?
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beetle
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 3:10 pm



Quote :
I'm assuming there is no beetle map for the arrow headers with stock exhaust?



Not for the Arrow midpipe + factory exhaust. I don't think it will be terrible. If you want to try it, I'm happy to tweak the map from your feedback.








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Pete Roper
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 3:41 pm

Can you not get the original re-welded and reinforced? The factory *Pretzel* is no longer available and I had the devil of a time finding one! Eventually acquiring one from Germany with the assistance of a member here.

While I'm sure that it would be possible to build something as good as the original what seems to have been overlooked by most of the aftermarket suppliers is that the loop in the pretzel was put there for a purpose and that purpose was not simply to have somewhere to put the lambda sensor!

One assumes that the somewhat simplistic thinking involved with the straight, or 'Straighter' mid pipes is that by taking out the bend you'll increase the speed of the exhaust flow. You know what? That's exactly what it does do but in the case of the Guzzi 8V it is in fact the last thing you want to do if you're after flexibility in the power and torque delivery.

The fact that the motor has a very nicely designed and 'Modern' combustion chamber is actually a hindrance when it comes to both scavenge and cylinder fill. To get the power output they needed to be able to say the engine was 'Modern' and 'Competitive' in the market meant that the side draught heads had to use cams with comparatively long overlap to ensure good scavenge and fill but at the same time the narrow included valve angle means there is a tendency for the fresh charge to tumble across the combustion chamber on overlap and hurtle straight out of the exhaust valves! This is obviously affected by a variety of factors but the tuned length of the exhaust is a major one.

While a straight mid pipe may slightly increase top end it will deplete the volumetric efficiency of the motor at low and midrange engine speeds which effectively guts the bottom end and midrange torque. Stick a tiny, short exhaust can on as well and even if mapped correctly you'll have a machine that is comparatively feeble at the bottom end and then somewhere north of 6,000 rpm it will start filling the cylinder better and it'll take off like a cut cat! Now that's all very well if your main use for the bike is drag racing at the traffic light Grand Prix but if you actually want to use the 8V's motor to the best you play to its strengths of wonderful fluid power and torque delivery from just about nowhere to 7,500 rpm and at all throttle openings, not just when you're trying to twist the nipples off the ends of the throttle cables! Even if you are chasing absolute 'Top End' you still won't be able to drag more than a few HP out of the motor, (Despite what some may claim!) because the motor, quite simply, isn't that efficient. It isn't no matter what you do, very volumetrically efficient. That's why it's fuel economy, even if tuned and mapped correctly, is so woeful compared to many other more modern designs that use down draught induction.

Anyway, whichever way you go I'd advise on getting a mid pipe with the greatest *Length* that you can. I'd guess the map will need tweaking accordingly.
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evansnows
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Sun Oct 17, 2021 5:06 pm

TIG welding a stainless steel strap should not be difficult and would solve the problem permanently.
Since it's not something I've specifically done I can't be certain but I have reinforced similar parts on other bikes.
The trick is to completely wrap the pipe and tack weld the strap to the original part.
TIG welding is necessary to control the weld and not burn through the component.
Possibly silver soldering or brazing would work.
Since I have a TIG welder that's what I've always used.
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Evilgarfield
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Mon Oct 18, 2021 12:41 am

Do you know why the pretzel is brekaing in the first place? Is it common for the GRiSO to tear through these parts? Or are you riding during winter on salty roads?
If not, is it possible that there are tensions on the pretzel when you mount the exhaust system on your bike? Sorting any potential issue before fitting a new or repaired midpipe might save you time and money in the future.

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motor-timothy
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Mon Oct 18, 2021 6:32 am

Thanks all. I have 2 cracked pretzels now and will bring both of them to a welder so I'll have a spare for the future. Don't want to loose performance through after market solutions, and the titanium arrow pipes just don't fit the tenni look imho (the blueing).
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motor-timothy
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Mon Oct 18, 2021 6:36 am

Evilgarfield wrote:
Do you know why the pretzel is brekaing in the first place? Is it common for the GRiSO to tear through these parts? Or are you riding during winter on salty roads?
If not, is it possible that there are tensions on the pretzel when you mount the exhaust system on your bike? Sorting any potential issue before fitting a new or repaired midpipe might save you time and money in the future.

It's quite common with the pretzels. My first one just has a small hole in the welding line. This one has literally cracked (zig-zag crack) from the weld into the pipe itself. I think it had been repaired once already by the precious owner (got the pretzel second hand)
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Pete Roper
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Mon Oct 18, 2021 7:39 pm

Or you could eliminate your pretzel and pipe entirely ensuring that your bike runs like an utter sack of shit and can't be made to run because of the ludicrous length of the 'Muffler'!

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Alternatively you could just put a big wodge of cash into a kettle barbecue and set fire to it and save yourself a lot of heartache!

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motor-timothy
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Mon Oct 18, 2021 11:50 pm

Pete Roper wrote:
Or you could eliminate your pretzel and pipe entirely ensuring that your bike runs like an utter sack of shit and can't be made to run because of the ludicrous length of the 'Muffler'!

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Alternatively you could just put a big wodge of cash into a kettle barbecue and set fire to it and save yourself a lot of heartache!

Hell no Wink
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Tue Oct 19, 2021 1:10 am

Having encountered cracked exhaust pipes on several vehicles.....

In theory two rigid mounts at the front (the massive headers) then two bonded rubber mounts should carry an exhaust like ours without any side thrusts or metal to metal vibration points Sad

You have probably done this but... I would recommend being very detailed (anal) in aligning every part headers, pretzel & silencer when loose.
If any part does not slip in easily then bend the header, silencer mount or pretzel mount till they do slip in loose.

Then tightening each mounting in rotation a bit at a time - like tightening a head down.

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paulbrice
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PostSubject: Re: Exhaust Y-piece broken....again   Exhaust Y-piece broken....again Icon_minitime1Tue Oct 19, 2021 3:08 am

It's quite common with Ti road bicycle frames (I'm on my 3rd in 3 years) Wink

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