De Catting the exhaust

[londonrob]

I've seen an ad on e bay from Sabre Engineering who are offering a De Cat service for the Stelvio.

Has anyone had it done?

If so whats your thoughts, any improvement?

 

[Penis Rotor]

Why? All it will do is upset the fuelling and make it run worse. The 8V motor is designed to run with a lot of restriction in the exhaust. Remove that and it'll run like a three legged donkey. The Cat is part of the whole equation AND it helps reduce emissions? Is there something wrong with that???

As long as people still try and apply 1950's tuning theory to a 2000 motor they will never get the results they desire or expect. Head design, combustion chamber design and very importantly valve head back-shape design also play a very important part in optimising the engines volumetric efficiency but nobody ever mentions them. Why?

pete

 

[Mi_ka]

Is there any significant weight saving? I suppose not for these heavy bikes...

Pete, are there any cams that could be fitted with a less restrictive exhaust that could provide a good punch to the 8V (of course after intake and fueling have been altered too)?
Not for a loud track use but for street bike use.
Or it does not worth it anyway? Too little gain for the cost?

 

[Penis Rotor]

No idea. I have neither the time, money or interest in developing such things. To do so would be very expensive and time consuming. My 8V makes 104 RWHP with a nice linear power and torque curve. I don't need any more. If I did I'd be riding an RSV4.

Pete

 

[Mi_ka]

I too believe that ca. 100hp are more than enough for real life.
It is just a theoretical question.
You have mentioned of the big valve overlap of current restricted exhaust engines.
Could different cams with proper not loud exhaust (vs the stock strict catalytic exhaust and stock (big overlap?) cams) be any different in the middle range where real life riding takes place?
What do you think?
I thought you might have seen or heard of any different cam installs...

 

[Penis Rotor]

I haven't graphed the A8 cams yet. When I get the chance I will. It'll be interesting to see what the results are.

Pete

 

[SUPERMOTO]

Why? All it will do is upset the fuelling and make it run worse. The 8V motor is designed to run with a lot of restriction in the exhaust. Remove that and it'll run like a three legged donkey. The Cat is part of the whole equation AND it helps reduce emissions? Is there something wrong with that???

As long as people still try and apply 1950's tuning theory to a 2000 motor they will never get the results they desire or expect. Head design, combustion chamber design and very importantly valve head back-shape design also play a very important part in optimising the engines volumetric efficiency but nobody ever mentions them. Why?

pete

Myself and crazylee both had the cat removed from the original exhaust.

Maybe some people do miss the point, we had them removed because of the heat they generate, it was not to gain power as I agree 100bhp is enough, ex - on an adventure bike! Weight on this kind of bike, its never going to be light!

As a result the bikes run much cooler, at slow speeds and in traffic there is a huge difference, in general the bike runs smoother and seems to pull better in the mid range. It may be wishfull thinking from both of us!!

As an observation the cat seems to provide very little in terms of restriction / back pressure. Will it affect the fueling or make it run worse?

The o2 sensor is pre cat so does the ECU know whats going out the exhaust? Or if the cat is even there?

Both bikes are using less fuel but emissions are higher, but then the bikes are more efficent!

Does this mean we should all avoid all aftermarket exhausts like the GTX? I do agree that its very important to have the correct amount of back pressure in an exhaust system but the cats are there for emissions only and they have many negative effects, like heat.

 

[SUPERMOTO]

I've seen an ad on e bay from Sabre Engineering who are offering a De Cat service for the Stelvio.

Has anyone had it done?

If so whats your thoughts, any improvement?

My self and crazylee have had it done, they also did my Buell pipes which worked great.

We had it done for a little more sound and to reduce the heat, not for power. It worked, they sound a little louder with a bit of a rasp. The difference in heat is huge, within 10 min you can hold the exhaust and the whole bike cools in half the time, runs much cooler ex -at slower speeds.

They do seem to run better in the mid range - mine still pops on the over run as it did before, 2010 bike, crazylees doesn't pop as before - 2009 bike.

The surprise was the mpg, my bike went from 41mpg to 46mpg on the same run at the same speeds, in the same weather on the same road - you get the idea.

If I bought another new Stelvio I would have it done before I rode it!

 

[GTM®]

Does this mean we should all avoid all aftermarket exhausts like the GTX? I do agree that its very important to have the correct amount of back pressure in an exhaust system...

Sure you could, but of the eight or so mufflers I've sold, we'll all keep enjoying the hell out of all of the benefits it offers.

If I bought another new Stelvio I would have it done before I rode it!

Which is exactly what I did (full kit) on mine, before it ever turned a wheel once in my possession.

 

[londonrob]

Think I'll leave mine alone, at least for the warranty period.

 

[SUPERMOTO]

Think I'll leave mine alone, at least for the warranty period.

The warranty could be an issue, but only for the exhaust, my Guzzi dealer sells the Zard exhaust and fits it to the new bike if you wish - no warranty issue!

 

[crazylee]

Supermoto answered most of what I was gona say, but it is worth having done and ther is still plenty of back pressure from the other gubbins! I can ride mine a little lower in the rev range now!

 

[Penis Rotor]

I think a lot of people are mistaking my use of the term 'Resistance' in the exhaust for what is commonly reffered to as 'Back Pressure'. It's a completely separate issue but one I fear people are deaf to hearing or at least thinking about.

As for removing the cat making an engine run cooler? Doing so will tend to lean out the mixture. Leaner mixture=more heat. The cat itself operates at very high temperatures and i can see that for anyone with a high pipe with a cat in it might be a problem for a passenger, or even the rider in traffic, but I've ridden most of the current range in hot weather and heat from the cat itself has never been an issue. On Brevas and Norges f'rinstance you get a lot of heat on your legs but that is due to the positioning of the oil cooler and the way the alternator fan drags air through the valley of the engine coupled with the body venting, nothing to do with the catalyser per-se.

Pete

 

[crazylee]

Was that meant to be an insult? Please enlighten us all and tell us the difference between back pressure and resistance? I'd be interested to hear what you know about back pressure and the corrolation with valve overlap?

 

[Ray R]

Was that meant to be an insult? Please enlighten us all and tell us the difference between back pressure and resistance? I'd be interested to hear what you know about back pressure and the corrolation with valve overlap?

Oh geeze. You're new here, aren't you? :shock:

 

[Penis Rotor]

Was that meant to be an insult? Please enlighten us all and tell us the difference between back pressure and resistance? I'd be interested to hear what you know about back pressure and the corrolation with valve overlap?

No, it wasn't supposed to be an insult. Simply a statement.

Exhaust tuning is a pretty complicated science, I make no claims to being an expert. 'Back Pressure' is a term commonly used, (Or it was 30 years ago when i was learning about stuff.) that encompassed a whole host of effects regarding exhaust operation but most importantly it related to the sonic effects within the pipe and timing the effects of the returning pressure wave from the atmospheric end of the pipe to the exhaust vale. The speed of sound being *essentially* a constant this is the main contributor to how effectively an older engine will scavenge and is, unfortunately, only effective at one partuicular point in the rev range. How the engine and pipe are designed to take advantage of this effect relies on another host of factors any or all of which can move the point at which peak torque is produced by maximising the VE.

The situation with a motor with a modern combustion chamber, especially one with side-draught porting rather than downdraught porting, and long overlap is going to be significantly different. The need for scavenge enhancement is decreased by the esign of the piston crown and combustion chamber shape and with an engine with quite long overlap AND a side draught porting system the inertia of the incoming charge will tend to drive it straight across the top of the dome-less piston and out of the exhaust valves during the overlap period reducing the VE and giving poor data to the ECU via the O2 sensor. By increasing the resistance to flow of the exiting gasses UP TO A POINT you will discourage this loss of the incomming charge boosting VE and giving more accurate data about the actual burn in the combustion chamber to the O2 sensor and allowing the ECU to make correct decisions about what is needed to optimise performance. Also, unlike the reliance on sonic 'Back Pressure' as the engine speed rises any 'Physical' restraint to the egress of the spent charge will increase in a linear manner so that it won't be so affected by the sonic input from the pipe's tuning.

No I'm not saying that if you completely bung-up and stifle the engine it will perform better than if you open it up completely. Simply that the new motors are DESIGNED on the drawing board to run, if not to their optimum, at least to a very high standard, quietly and with restrictions. The engineers who are asked to design the bikes aren't asked to build the absolutely most ball-tearingly powerfull motor they can. They are asked to design one that will work the best they can make it without it being impossible to use because it contravenes to many international laws and caveats!

Obviously a LOT of thought and effort goes into it. Things like the fact that in the 8V there is 1/2 a degree less angle on one of the sets of valves than the other. I mean? Why would you do that? I have no idea, but there has to be a reason. That's just one example.

I'm sure that you can get the motor to produce considerably more power and torque than it currently does. even with the motor in stock trim I'm damn certain that a system like the PCV will enable one to 'Build' a far better map than the one the factory sticks in the bikes. I am, as I've said before, ambivalent about relying on the auto-tune and gas analysis to get results ON THEIR OWN and I think that to start improving things greatly in terms of performance a whole host of factors like cams and port-flowing will have to be undertaken.

As I've said before and will re-state again.

1.) I think that the PCV is currently the BEST option available in the english speaking world for people wanting to start monkeying around with their FI for better prformance.

2.) Todd and I don't agree on everything. What's the problem with this? It would be a dull old world if everybody agreed with everybody else. But I DO genuinely like Todd and he stands behind his product 100%. You won't get nearly as much help from anyone else I know of to try and sort out problems on individual machines!

3.) The reason I decided against fitting the PCV/AT package that I had purchased for my bike is not because I thought it was a dodgy deal or that it wouldn't work, it was simply the fact that I, (Thats ME, Pete Roper.) am very happy with my machine exactly as it is and see no NEED to add a further level of complexity to it to achieve different when I'm already blissed out with how my bike runs. It does everything I want it to do. What YOU may want your bike to do may be completely different.

Pete

 

[RayInLA]

Regardless of what exhaust you decide to run, whether it be the stock unit (cat or no cat) or an aftermarket pipe, you owe it to yourself and your bike to address the stock fuel mapping issues. Most of us, Pete included, have not the time, money, nor inclination to begin to figure out a system to correct these issues, which is fine because Todd has already done it for us!
Todd's re-mapping and PCV setups work miracles. I should know, as I've had him do the set-up on both my 1200 Sport and my Stelvio. Those of us running the GTX pipe are also believers.

It's easy for those here to underestimate the time and money that Todd has invested in sorting out these issues. Trust me, it behooves all of us to take advantage of his knowledge and commitment.

Ray

 

[Mi_ka]

Many Kudos to Pete for his patience to originally rewrite and rewrite and rewrite his knowledge every time someone lifts his eyebrow.
I have learned useful mecha stuff through his patience.

 

[kwn306]

I removed my stock "boat anchor" yesterday to install Todd's exhaust and my cat is loose, in three peices flopping around inside the muffler. The wife has been bitchin that her left foot was on fire the last couple of times we commuted to work, now I know why. Looks like another trip to my dealer to get the muffler replaced under warranty, just got the damn thing back from a three week visit this past Friday.

 

[crazylee]

I agree on the mapping issues, I have had experience with car mapping and it's all down to the emissions legislation! You should see what a standard, modern engine with variable valve timing looks like on a dyno!
Pete, I am impressed by your knowledge, I hope you didn't copy and paste most of that as I have created an impression in my head as to how your mind works (a good thing)! And for those of you who don't know what 'VE' stands for, it's volumetric efficiency!