Different exhaust temps

alan s4 · 10-07-2020, 11:22 AM

Bike running perfectly of late, so need to find something to worry about.....

The right hand exhaust and tip is considerably hotter then the left on my bike (S4 with high level termis). Is this normal/something to do with the exhaust routing? Or is it a sign of impending doom!

Bike not using any oil and no smoke on start up or when running.

Nickj · 10-07-2020, 02:03 PM

I'm afraid I've got to agree with you, it is a sign of impending.... No imminent doom.... NO NO already happened disaster of humongous epic proportions. You have my deepest commiserations.
Turn the motor off, never ever start it again, sell as soon as possible for as much as feasible.

The right hand pipe... have a look and see where the spaghetti leads, they are different lengths albeit joined to equalise pressures which could make a difference. There could be a little difference in the mixes between the cylinders but that shouldn't make too much difference really unless one is very lean or one is rich but you'd probably have noticed that as the motor wouldn't be running so well.

I'd think that if the pipes are not so hot that you get instant severe burns even getting close then the bikes not really up to full temperature so any difference is a bit of a non event.

Darren69 · 10-07-2020, 02:23 PM

Mine are the same S4 and 748 one is always hotter. The same for the 900 and 750SS's I had before that. I think it's a Ducati thing, as they all run/ran fine.

alan s4 · 10-07-2020, 02:55 PM

Thanks guys. I'm just not used to having a bike that starts on the button, doesn't need to be on a trickle charger after standing for more than 10 minutes, or ticks over without constantly feeling like it's about to stall.

Having a perfectly behaved Ducati is an entirely new proposition for me. I suppose I'll just need to get used to it

Dukedesmo · 10-07-2020, 05:56 PM

Quote:

Originally Posted by Darren69

Mine are the same S4 and 748 one is always hotter. The same for the 900 and 750SS's I had before that. I think it's a Ducati thing, as they all run/ran fine.

Mine used to be different one side to the other (can't remember which?), not so much since I changed the exhaust crossover for a more 'Spaghetti' style with a more direct flow but my 916 runs one side hotter/bit more pressure at idle which I put down to the pipe routing - rear cylinder pipe does a 'U' bend downwards to lengthen the pipe to about the same as the front.

So unless it's running much richer/leaner on one than the other then I think it all balances out fairly well at speed...

utopia · 10-07-2020, 07:37 PM

Hang on a minute.
Surely the exhaust flow from each cylinder is split into two at the crucifix and then flows equally through both silencers.
Thus the effects of any difference in function/performance/heat output from either cylinder will also be distributed equally to both silencers.
From which it follows that any difference in temperature of the silencers cannot be due to differences in heat output from the cylinders ... and therefore it must be due to differences in heat transfer within the silencers themselves .... which might suggest that the wadding has burnt out somewhat from one silencer.
Or am I missing something here ?

The only other explanation I can think of is that the crucifix has been poorly made and has internal restrictions which limit the flow along one of the two possible exhaust paths.

Dukedesmo · 11-07-2020, 11:12 AM

My take on it is that the crossover is not great and that it 'allows' more gases to go out of one pipe than the other due to the way that both pipes tend to favour one exit.

Originally I had a standard crossover but I opened it up as much as possible, however it still gave more 'flow' from one pipe than the other, at least at idle and this made that pipe run hotter if left just idling.

I'm certain it balances out at speed and can only assume that the pipe routing (rear cylinder having to go around more corners) and variations in back pressure from the crossover design cause it?

The Spaghetti pipes I have are made in such a way that the rear cylinder has a smoother run than the OEM pipework and this certainly helps.

But it's even more pronounced on 916 type bikes and the exhaust on that has a much more extreme bend/routing for the rear cylinder, IIRC later model supebikes; 999 etc. used larger bore rear pipework of shorter, unequal length to the front to get a better balance?

utopia · 11-07-2020, 01:59 PM

Quote:

Originally Posted by Dukedesmo

My take on it is that the crossover 'allows' more gases to go out of one pipe than the other due to the way that both pipes tend to favour one exit.

But does it ??
The way I see it, the front and rear headers hit the crossover squarely and dead centrally in the fore and aft positions respectively and the exit path from both then splits equally and symmetrically to exit at the 90 deg positions.
I can't see how the system favours one exit path over the other .... unless there is some hidden internal restriction arising out of manufacturing inaccuracies.

Its true that the rear header routing is more convoluted than the front header but this should be of no consequence if the flow from each is split and distributed equally to both silencers ... which I'm suggesting that it is.

Makes no difference on my bike though as I have a two into one system with just the single silencer. ......

Mr Gazza · 11-07-2020, 03:59 PM

I don't think the two pipes do hit the cruciform at 90deg?
Besides which the bends upstream will affect which side of the pipe the pressure is on and where the fastest moving gas is, much like the water in a meandering stream I would imagine.
Then since the pulses are uneven it could lead to the leading pulse setting the pressures in the cruciform for the following pulse to follow. So if one pipe, probably the rear, tended to go one way, it would probably leave a bigger depression behind to draw the other up behind it.

I know I've blown the baffles out of my RH silencer more times than the left and when it does it's always much louder than when the left blows.

utopia · 11-07-2020, 04:55 PM

Yep, points taken .. I concede.
It does look like the rear header favours the right hand silencer to a fairly noticeable extent, and even the front one does to a small extent too.
A picture speaks a thousand words, eh ?
I should have gone into the shed and studied my old headers instead of working from memory.
I must admit that I was already considering that the initial bends towards the right hand side might mean that the gases would tend to hug that side of the pipes, even though they straightened out further along (memory says this might be called the Coanda effect).

Anyway, yep ... it does look like the flow favours the right hand silencer.
Which tallies with Alan's experience of that can feeling hotter than the left hand one.

Mr Gazza · 11-07-2020, 07:49 PM

Quote:

Originally Posted by utopia

Yep, points taken .. I concede.

Now I feel like I have bullied you into submission! Which was not my intention... Sorry.

I've often pondered making a new cruciform out of mandrel bends and then transplanting it, by making a jig to hold all the pipes in position before cutting the old cruciform out. I can't help thinking it could be a recipe for disaster. I have found a more practical looking DIY idea whilst searching Google images. I daresay a few will have seen it before, but the idea appeals to me.. How hard can it be?

350TSS · 11-07-2020, 08:11 PM

I do not think that will work effectively as the front pipe would be blowing towards the exiting gas of the rear pipe. A big fight in the middle (or rather halfway up the pipe next to fire) and the only retreat is out either side, reluctantly.
The original cruciform at leat allows the escaping gas a choice of paths and the pulse will have the effect of drawing the next pulse into whichever path is favoured (RH side)

utopia · 11-07-2020, 08:52 PM

Quote:

Originally Posted by Mr Gazza

Now I feel like I have bullied you into submission! Which was not my intention... Sorry.

Not at all .. you have merely presented a more clarified rationale, which has deservedly won me over.

However, I'm inclined to agree with "350" that the modified crucifix you refer to will only result in the exhaust flow from each cylinder fighting each other.
Mind you, I have cut up a std crucifix and the bifurcated exhaust tracts ( oo'er) within it do look extremely narrow and constricting ... and very tightly curved too.
It certainly looks like it would benefit from modification of some sort.
For an off the shelf solution the MADASL headers are probably the way to go .. if you want to retain both cans.

Mr Gazza · 11-07-2020, 09:20 PM

Would both of you please pay more attention!.. now I am bullying you..

I didn't think the pictures required any explanation but I've found another which shows a piece of box in the middle. The first pictures clearly have a "star" shaped piece here made of 4 bits of pipe section. So it's still working as a cruciform but with less restriction.

As it happens the images come from another forum and were posted by our own Nasher.
Gilps from here too, commented that the mod did not work on his and other's 600 and 620 DD racers and did not recommend the mod.
However on yet another thread someone tried this on an SS1000 and claimed better low down and mid range power at the expense of top end. (Hence why they didn't like it on the racers I imagine?)
I am mildly tempted to try this on a spare exhaust, and maybe even try and position the "star" to bias the rear exhaust to the left a bit.
Many other comments claimed that the original cruciform is not restrictive at all and is carefully designed for the best performance.
I would kind of go with that to some extent as, if you are going to bifurcate a pipe, then each bifurcation needs to be half the area of the main pipe to retain the same flow. this is what appears to be happening in the standard cruciform, so a big part of me is saying if it ain't broke...

utopia · 11-07-2020, 09:44 PM

Oooops !
Guilty again.

Although, particularly in the case of the second example, it does look like some flow back up the other header is feasible.

10-07-2020, 11:22 AM	#1
alan s4 Registered User Join Date: Sep 2013 Location: Glasgow Bike: S4 challenge Posts: 447	Different exhaust temps Bike running perfectly of late, so need to find something to worry about..... The right hand exhaust and tip is considerably hotter then the left on my bike (S4 with high level termis). Is this normal/something to do with the exhaust routing? Or is it a sign of impending doom! Bike not using any oil and no smoke on start up or when running.

10-07-2020, 02:03 PM	#2
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,207	I'm afraid I've got to agree with you, it is a sign of impending.... No imminent doom.... NO NO already happened disaster of humongous epic proportions. You have my deepest commiserations. Turn the motor off, never ever start it again, sell as soon as possible for as much as feasible. The right hand pipe... have a look and see where the spaghetti leads, they are different lengths albeit joined to equalise pressures which could make a difference. There could be a little difference in the mixes between the cylinders but that shouldn't make too much difference really unless one is very lean or one is rich but you'd probably have noticed that as the motor wouldn't be running so well. I'd think that if the pipes are not so hot that you get instant severe burns even getting close then the bikes not really up to full temperature so any difference is a bit of a non event. __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

10-07-2020, 02:23 PM	#3
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,091	Mine are the same S4 and 748 one is always hotter. The same for the 900 and 750SS's I had before that. I think it's a Ducati thing, as they all run/ran fine. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

11-07-2020, 11:12 AM	#7
Dukedesmo Registered User Join Date: Sep 2010 Location: Leics Bike: M900 Posts: 2,894	My take on it is that the crossover is not great and that it 'allows' more gases to go out of one pipe than the other due to the way that both pipes tend to favour one exit. Originally I had a standard crossover but I opened it up as much as possible, however it still gave more 'flow' from one pipe than the other, at least at idle and this made that pipe run hotter if left just idling. I'm certain it balances out at speed and can only assume that the pipe routing (rear cylinder having to go around more corners) and variations in back pressure from the crossover design cause it? The Spaghetti pipes I have are made in such a way that the rear cylinder has a smoother run than the OEM pipework and this certainly helps. But it's even more pronounced on 916 type bikes and the exhaust on that has a much more extreme bend/routing for the rear cylinder, IIRC later model supebikes; 999 etc. used larger bore rear pipework of shorter, unequal length to the front to get a better balance? __________________ M900, 916, LeMans II.

11-07-2020, 03:59 PM	#9
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,972	I don't think the two pipes do hit the cruciform at 90deg? Besides which the bends upstream will affect which side of the pipe the pressure is on and where the fastest moving gas is, much like the water in a meandering stream I would imagine. Then since the pulses are uneven it could lead to the leading pulse setting the pressures in the cruciform for the following pulse to follow. So if one pipe, probably the rear, tended to go one way, it would probably leave a bigger depression behind to draw the other up behind it. I know I've blown the baffles out of my RH silencer more times than the left and when it does it's always much louder than when the left blows. __________________

10-07-2020, 02:55 PM	#4
alan s4 Registered User Join Date: Sep 2013 Location: Glasgow Bike: S4 challenge Posts: 447	Thanks guys. I'm just not used to having a bike that starts on the button, doesn't need to be on a trickle charger after standing for more than 10 minutes, or ticks over without constantly feeling like it's about to stall. Having a perfectly behaved Ducati is an entirely new proposition for me. I suppose I'll just need to get used to it

10-07-2020, 07:37 PM	#6
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,561	Hang on a minute. Surely the exhaust flow from each cylinder is split into two at the crucifix and then flows equally through both silencers. Thus the effects of any difference in function/performance/heat output from either cylinder will also be distributed equally to both silencers. From which it follows that any difference in temperature of the silencers cannot be due to differences in heat output from the cylinders ... and therefore it must be due to differences in heat transfer within the silencers themselves .... which might suggest that the wadding has burnt out somewhat from one silencer. Or am I missing something here ? The only other explanation I can think of is that the crucifix has been poorly made and has internal restrictions which limit the flow along one of the two possible exhaust paths.

11-07-2020, 04:55 PM	#10
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,561	Yep, points taken .. I concede. It does look like the rear header favours the right hand silencer to a fairly noticeable extent, and even the front one does to a small extent too. A picture speaks a thousand words, eh ? I should have gone into the shed and studied my old headers instead of working from memory. I must admit that I was already considering that the initial bends towards the right hand side might mean that the gases would tend to hug that side of the pipes, even though they straightened out further along (memory says this might be called the Coanda effect). Anyway, yep ... it does look like the flow favours the right hand silencer. Which tallies with Alan's experience of that can feeling hotter than the left hand one.

11-07-2020, 08:11 PM	#12
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,422	I do not think that will work effectively as the front pipe would be blowing towards the exiting gas of the rear pipe. A big fight in the middle (or rather halfway up the pipe next to fire) and the only retreat is out either side, reluctantly. The original cruciform at leat allows the escaping gas a choice of paths and the pulse will have the effect of drawing the next pulse into whichever path is favoured (RH side)

11-07-2020, 09:20 PM	#14
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,972	Would both of you please pay more attention!.. now I am bullying you.. I didn't think the pictures required any explanation but I've found another which shows a piece of box in the middle. The first pictures clearly have a "star" shaped piece here made of 4 bits of pipe section. So it's still working as a cruciform but with less restriction. As it happens the images come from another forum and were posted by our own Nasher. Gilps from here too, commented that the mod did not work on his and other's 600 and 620 DD racers and did not recommend the mod. However on yet another thread someone tried this on an SS1000 and claimed better low down and mid range power at the expense of top end. (Hence why they didn't like it on the racers I imagine?) I am mildly tempted to try this on a spare exhaust, and maybe even try and position the "star" to bias the rear exhaust to the left a bit. Many other comments claimed that the original cruciform is not restrictive at all and is carefully designed for the best performance. I would kind of go with that to some extent as, if you are going to bifurcate a pipe, then each bifurcation needs to be half the area of the main pipe to retain the same flow. this is what appears to be happening in the standard cruciform, so a big part of me is saying if it ain't broke... __________________ Last edited by Mr Gazza; 11-07-2020 at 10:14 PM..

11-07-2020, 09:44 PM	#15
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,561	Oooops ! Guilty again. Although, particularly in the case of the second example, it does look like some flow back up the other header is feasible. Last edited by utopia; 11-07-2020 at 09:47 PM..