Aftermarket mufflers & Fuel/Air mixture

[roadventure]

What, if any, effect does adding any of the popular aftermarket mufflers (MISTRAL, AGOSTINI. etc.) have on the air/fuel ratio of the California 1400?

My thinking has always been "nil". Here is my reasoning. The air/fuel ratio is created at the inlet side of the engine. The injectors supply fuel based on the volume of incoming air. A 13:1 air to fuel ratio is what I have always read as being "ideal". I know a lot of other factors enter into the picture, but I am looking at this in a simplified way.

So, IF the air/fuel ratio is created at the inlet side of the engine then the ease at which the burnt gases exit the combustion chamber have no effect on this ration.

Given this, then the amount of back pressure that any muffler may provide does not change the air /fuel ratio.

Okay, those of you with greater knowledge, please agree, or tell me where my thinking is wrong.

 

[GTM®]

Dave, very well covered in other sections. Try a search.
In short, no current Moto F.I. system is full closed loop, meaning it will *NOT* change the fueling based on any mods you may do. The 02-sensors measure parts per million in the burnt fuel stage. However, most all 02-sensors on modern motos are narrow band, meaning they are simply a switch to throw a flag if the AFRs are out of preset range.
Stoichiometric is ~14.7:1 on a water-cooled engine. Air/Fuel cooled motors like it much richer, from 12.8-13.6. Ideal is 13.2 on the dyno for power and cooling on Guzzi engines. The C1400 motor fuels in the upper 15 to near 18:1 range as delivered bone stock; Melt down territory IMO.
I offer a fully dynamic kit on the site HERE - expensive, but part of the gains shown here; https://www.guzzitech.com/forums/threads/guzzitech-gt-rx-modded-cal-14-dyno-vs-stock.13773/

 

[roadventure]

Todd,

Thanks for the reply. My experiences in "tuning" come from air cooled and liquid cooled carbureted engines. I found in two cases the word was that each bike was delivered "lean" from the manufacturer and that this was not true. Both were somewhat lean but nowhere near what the popular opinion seemed to be. I was able to confirm this using a Dynojet dynomometer that had a exhaust gas analyzer. I was fortunate enough that my neighbor's son was, at the time, running a motorcycle performance shop. He worked on my bikes (Yamaha Road Star and Yamaha Royal Star Venture) at no cost to me so he could learn what worked gave the biggest bang-for-buck on those types of bikes since he got mostly Japanese sport bikes coming in the door. Once the jetting was changed to bring each to recommended levels (aimed for 13.5:1 on the Road Star and 14:1 on the Venture) I saw that there was very little change in the in the air/fuel ratio when the aftermarket mufflers were installed. So, this is the basis of my question.

Question #1: Does the ability to push air out (exhaust back pressure) have an effect on the air/fuel mixture coming in? The answer to this question should be about the same whether we talk about a carbureted engine, an closed loop EFI engine or one similar to the California, which is EFI, but does not have a closed loop system.

I have often heard people say that installing a more open exhaust system effects the incoming air/fuel ratio. Mostly that it makes the incoming air/fuel ratio higher (more lean). How is this?

Question #2: What is the benefit of any manufacturer selling a motorcycle that is designed to fail, such as designing it to run so hot that damage will occur? Yeah, we all know about the necessity of meeting U.S. EPA standards, but auto manufacturers seem to be able to sell cars in the U.S. that are ultra-reliable, highly fuel efficient and somehow don't seem self destruct.

 

[GTM®]

Factory mapping is all over. Lean at low and mid speed throttle, rich at more aggressive throttle.
I've been working directly with Dynojet on the development of Guzzi products since 2001. They call me their Technical Advisor for Guzzi.
KISS:
1. Highly debatable, and more so when you talk about sensor placement, but CV carbs deliver fuel way differently then digital injection.
2. Modern emission requirements are forcing manufacturers to develop engines that can withstand very high operating temps. Case in point is the new Polaris Indian 111 motor, designed to run in the upper 350-400F range. I haven't spoken with anyone at Guzzi about their new engines, but (IMO) premature failures of certain components has shown to be true so far, compared to my decade older Tonti Guzzi, which all have well over 150k, and still running strong.

End.

 

[roadventure]

Thank you again for your response. I am trying to learn!

 

[GuzziMoto]

Exhaust almost always has at least some effect on intake. That is for a number of reasons.
One is that there is usually a period where both the intake and exhaust valves are open at the same time. This "overlap" allows the exhaust side to influence the intake side.
Another reason why exhaust affects mixture is that the exhaust cycle on an internal combustion engine is rarely 100% effective. How effective it is in removing all the exhaust gases will play a part in the air/fuel mixture in the combustion chamber. The better it is at getting all the spent exhaust gases out the more fuel you will need to meet your target air/fuel ratio.
And that target varies at different RPMs and throttle positions, for example at full throttle you typically want a richer mixture than you do at small throttle openings.
There is a lot more to it than that, but that should at least get you started.

 

[roadventure]

Michael,

Thanks for the additional information.