355 bypass valve removal

Two bolts. One above and one below the valve. Once you get the air boxes and the heat shield off, it's a pretty straightforward removal.

 

Use mechanics wire to permantly hold it open and call it a day. (Easily reversable).

 

I used to think that was OK until I read the post from Capristo about the backflow that it creates if you leave it wired open. I just tried to search and find it but couldn't (will keep trying). Between that and the risk of running too rich potentially wearing the cylinder liners faster than normal scared me straight. I just went and bought the Capristo bypass valve and now blissful sounds of the engine without that annoying buzzing.

It's probably best if Dave Helms or Enginefxr weigh in here sine they've forgotten more than I know.

 

look up Daytona auto in Toronto and buy one from them. They have their own challenge type bypass(straight pipe) that will take the place of that dumb valve and no your car will run perfectly without it. No liner wear or any scary stuff like that.

 

Be careful. Damage is possible.

 

Is there emperical evidence of this or just theoretical? I know this has been kicked around at some point but couldn't find the history either. Backflow, rich mixture, cylinder liner wear....does someone have data to support one way or the other?

 

On my exhaust the chambers are separate for the bypass and main flow paths. I don't see how it can 'backflow' even if they were connected. The pressures coming out of the exhaust ports are not going to let the gasses downstream go against the flow. If you think about it having the valve closed is more restrictive than having it open. I'm not sure where people are getting these ideas.

Rob

 

Brian Crall (Rifledriver) has said removing or wiring open the bypass valves on 355s can result in engine damage.

Taz
Terry Phillips

 

Rifledriver had a specific example he had to repair. Any by repair, I mean rebuild. Please do a detailed search on the subject. I remember he explained some debris can be sucked back upstream and then bouced back and forth from cylinder to cylinder. I too was sceptical, but remember reading his detailed account; then I became a believer... Rifledriver (when posting) is/was one of the true experts on this board. I'm just an onwer with some mild mechanical abilities.

 

From bozo's like me....

Please define "backsliding" as it pertains to engine dynamics...may you rest in peace.

 

Not calling anyone a bozo. I used the term 'back flow' in quotes as a layman term to get my point across. How can the exhaust from an open bypass system go back towards the exhaust ports against the direction of flow? There's no 'u-turn' (I'm doing it again) taking place in the muffler so why would the bypass valve remaining open be an issue.


I'm speaking without sarcasm or offense, I'm not a mechanical engineer but consider myself mechanically inclined and I want to understand what's going on in the bypass world.


Rob

 

I'm not trying to flame anyone but when Brian tells us something I take it to the bank. Here's a quote from one of his posts and the link so you can tell I'm not making this up. This was the email that convinced me to not mess with wiring the bypass valve open. When you wear out a cylinder liner, you're looking at a complete rebuild....$$$$

Brian's post....

It is not hypothesized. Ferrari knows of it very well and it is easily proven.

I recently had a 355 here that failed smog. After much screwing around I loosened the center pipe and slid in a piece of sheet metal. It instantly ran correctly and cleaned up. There was so much backwash that the air was cooling the cats and making the O2s think there was too much O2 and ran the mixture full rich. Blocking the center pipe made the O2s calm down and operation differences could be seen on a scanner. The cats heated back up. I could see it all real time on SD2. It made the car run clean, correctly and it finally idled good. Also it has been well established that the back wash gets clear to the cylinders. It has been causing much of the advanced cylinder and ring wear we have seen on many motors. At low exhaust flow the motor just keeps reingesting its own exhaust. The degree of the effects change with different exhaust systems.

Its no myth. Ferrari has known about is since they built the cars.

The exhaust tract of the 355 is short. It is eight feet from the tail pipe tips to the cats in a 550 or 575. Even 360 has a longer exhaust tract than 355.

http://www.ferrarichat.com/forum/showthread.php?t=236340&highlight=355+bypass+back+flow

 

This is a very common occurance in high performance radically cam'd engines.

The F355 engine is nothing short of a full race engine with some very interesting intake and exhaust harmonics...the technology used by Ferrari in developing the F355 engine were very much inline with their F1 engine dynamics program with limiting parameters being established by the fact it was for sustained useage in every day driving(longevity/reliability), and within the applicable goverment regulations(smog/emissions).

Some of the exhaust gas that is actually expelled out of the chamber during the exhaust stroke slides back through the exhaust valve and into the combustion chamber immediately before the exhaust valve closes. This phenomenon is called “backsliding”; and it is a major cause of the pumping loss.

When combustion occurs, it expels two things from the combustion chamber: 1) a pulse or “wave” of exhaust gas, and 2) a pulse, or “wave” of energy.

A big difference between the “gas wave” and the “energy wave” is that the energy wave travels about 5-times faster than the gas wave—at a rate of approximately 1,500 feet per second.When the energy wave travels through the exhaust system, it encounters obstacles, such as bends in the manifold, or the catalytic converter. These obstacles cause the energy wave to “bounce” or “revert” backwards in the form of a “reversion wave”.Reversion waves transmit energy back towards the engine. At supersonic speeds, it doesn’t take long for a reversion wave to reach the engine’s exhaust valve, which is still in the process of releasing the much slower-traveling wave of exhaust gas. When a wave of reverted energy encounters the gas wave, the more energy intensive reversion wave forces pressure upon it—pushing, or “backsliding” some of its gas back into the combustion chamber. And this is how reversion waves create backsliding!

In the presence of pumping loss of backsliding, instead of having only clean air and fuel in the combustion chamber, you now have: clean air and fuel, plus dirty exhaust gas.

If you do not understand exhaust reversion waves, open/closed loop operation modes of the ecms, and how/when O2 sensors adjust fuel trim, then don't monkey with the bypass valve...just make sure it is in place and operating properly.
I don't think Ferrari put it on the secondary exhaust system to make your life miserable, if that were the case they would have made it a hood ornament.

 

Chromed!
But what direction should it be mounted to the hood to look right?

 

If you chrome it everyone will think u got a rolls royce.....

Mounting has got to be on a pivot ball so you'll know which way the wind is blowing for takeoff's and landings...lol

 

So leaving the bypass open is altering the fuel mixture (02s aren't measuring the total amount of gas since some is exiting through the bypass) which can lead to cylinder wash. Ok I'll buy that but not the fact that it causes added reversion since you are decreasing restriction.

So if the primary 02s were mounted in the collector before the "Y" going to the bypass they would function properly with the bypass open or closed. I see a new aftermarket header design.........


Rob

 

"Hood ornaments....." Bruce, do you take one or two Olives? Gary has given up on the vegetables and just gets down to business. I followed your Dr's orders last night.... thanks a lot...

Change anything from the original design and you might remedy one issue but have induced a half dozen variables with each change.

New header design? Yes, a little late to the party but it took studying the effects of various designs to fully understand the issues each brought about. Easily marketable? The Feds consider this an emissions device and make getting it approved is unrealistic. There are 4 areas of expertise involved in this and it will take a cooperative effort of specialists to correctly solve it. The study of each header design's problems leads back to Ferrari's original design being the answer. Had they built the components to withstand the operating conditions it would have been the best available but they were limited by the technology and components available at the time.

Just when you think you understand all the variables along comes alcohol fuel being used with O2 sensors and programmed fuel maps designed for gasoline. This has to be viewed as a package to fully understand it, not individual components. We are not done with this yet!

 

Ship some of that sleep aid up here, I sure need it right now!!!

 

You are young enough to go for a little while longer. Us G-FART guys need the sleep aides.

I sense another good thread headin for the ditch...lol

 

I'll try to keep this one out of the ditch. This bypass issue concerns me because I have plans of install a bypass exhaust system in my 348. Here is a picture of the exhaust. The bypass is activated by a manual switch. Do you guys think i may encounter simliar problems to the 355s previously discussed? Here's a link to more photos. http://ferrarichat.com/forum/showthread.php?t=300572 This is an engineered product by Kreissieg, so I'm fairly confindent they know what they're doing. But now I'm a little unsure.
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Also, I plan on running this without cats. For track use of course.

 

why would this not be better anyway? i used O2 reading to tune my race car and i always put it in the collector way up stream. in some cases we ran one egt on each cyl for tuning all eight. im thinking getting rid of the fact ecu and going stand alone would be much easier and then you coild get rid off the the crap. mass air meters/cats/bypass/and im sure it would run just fine. anyone use any aftermarket tuners like Motec ? or Fast. maybe ill do it over the winter but i hate to be the first. BTW what a/f is good at idle 14's ande WOT 12's on these cars i would need to know this info for a base anyway. i know i wanted 11's in my boosted cars at WOT.

 

My understanding is that you're probably OK for a track or race car going with a bypass delete or wiring the bypass open since it will live most of its life above 4,000 RPM's. The issue (as I understand it) is the lower RPM's that you encounter on a street car tooling around town. That is where you'll run into the issues that will lead to an early demise of your engine if you wire the bypass open or run a bypass delete.

Brian or Dave, please weigh in here if this is correct.