bypass valve wired open

No mate the one we are talking about can only found on the 355. Beautiful cars are the 308s by the way

 

Thanks, I have owned it for 24 years. It saved my life. I told my wife if I could stop smoking for 30 days I would by a sports car. I forgot to tell her which kind and how much, LOL? Do you have any idea what causes my beautiful howl coming from my engine when it hits 5000 RPM? I always thought it was the timing belts and if so I am worried belts maybe giving me problem. Belts are new this year but intermittent sound just started few days ago. Marty

 

I thought I would play devils advocate on why you shouldn't wire open your bypass valve.
The reason why the CELS are coming on with the 2.7 cars and part of the reason why they do in the 5.2 cars is because with the valve open at lower RPMs air is being sucked/drawn into the lower exhaust part of the system(outer pipe on the tail pipe arrangment) or ie; the main cat portion. The upper portion of the exhaust flows better than the lower portion, the exhaust is taking the least route of resistance. Ferrari had to add the valve to get the exhaust to flow through the main cats at low RPM so they could keep the engine emissions legal. When this happens (valve open at low rpm) fresh air is drawn into the system and over the 02 senser, in reverse, which inturn signals the ECU its reading is out of parameter(O2 is way to high) and then turns on the CELs. The light will go off at WOT or when you step into the throttle right? This means the 02 sensors signal is not being used to fine tune the fuel mixture and also that there is enough exhaust presure to push exhaust flow over the 02 sensors in the lower part of the system. When those lights are on with the valve open at low rpm you are sucking unfiltered air into the engine.
There was a theory discussed a year or so ago that 355's may be ingesting their cat material as they age and may be part of the valve guide problem and in some rarer cases of the early cylinder wear problem. Having the valve open at low rpm and the reverse air flow that it causes through the main cat side of the exhaust IMO can cause trouble, ie; where is that ingested air going and whats in it?

 

Llenroc, I've got to disagree with your theory. First of all, you are not going to ingest unfiltered air into the engine by having the valve wired open...period (have you ever ran a race car with open exhaust) Secondly, if this were actually happening, ALL challenge cars would have burnt valve guides and melted cylinder bores by now, since they do not even run a bypass valve, and therfore would be sucking unfiltered air through the motor. Just a little history on my car. At about 10k miles, I had to have the drivers side exhaust replaced, and sure enough the drivers side cat was bad. I believe this is the biggest factor in damaging the exhaust (bad cats). Shortly after that (about 5 years ago) I wired my bypass open. I now have 35k on the car and have not had a single exhaust related problem with the car. Why? I believe it has to do with lower exhaust temps of the car. BTW during the major service the car showed 2% leakdown, and the compression at 200 across the board.


Darrell.

 

Actually you are wrong on the bypass part, I have a 355CH with no valve, When I bnought the car the check engine lights were on just as the OP described. Took about 2 weeks to figure why they were. I put a piece of paper over the outside of the exhaust pipe(the outer pipe) and the paper was sucked to the pipe. What I did to correct the problem was to weld 2 header baffles into the upper Y pipe(CH cars use the Y pipe that has no cats) to cause just enough back presure to push some exhaust at idle through the lower exhaust and over the 02 sensor so they could get a proper signal to the ECU(lights went out)
So tell me where the air is going? I still say that valve is there for more than one reason
Wiring open the exhaust valve isn't going to reduce temps much you need to remove the cats, muffler, shielding and air pump if you want to really effectively reduce temps inside the exhaust system. I still have one originall exhaust header.
Not all cats go bad at the same time and maybe some of them have used inferior material. I know from first hand experiance that there is a reversionary effect going on in the engine do to the exhaust system design. With that said, cats that have broken up inside
could be engested into the engine. Your car may have been one of the ones that didn't have cats where the material had broken up enough.

 

Thank you Vern.

I spent about 3 months a couple of years ago here on Fchat trying to explain all of this.

I guess it's kind of hard for people who have never designed and built engines from scratch to understand all of what REALLY goes on in a complete engine system.

1. YES the 355 exhaust system was designed using what was then pretty decent engine modeling software....TODAY's stuff is much much better.

2. YES the 355 exhaust was tuned using Wave Harmonics, with back-pressure optimization so as to increase low end torque.

3. Yes the 355 has the kind of cam overlap and a rather large reversion wave produce the phenomenon known as "backsliding"

4. YES the 355 ingests some of its' exhaust which = pump loss(low. VE)

5. YES I have seen particulate matter from cat disintegration in the combustion chamber and even as far up as into the intake valve port.

6. YES the by-pass valve open can and does show erroneous lean AFR's due to reversion effects in the stock exh. system....this will be most noticeable at idle, part throttle low RPM cruise, and decel. i.e. CLOSED LOOP MODE.

These are not just theories.....they are FACT's..period!!

But when all the facts are put forward,DMOORE and others, it's still your car and your money so do whatever suites your fancy.....

 

+1 .............. Hey Bruce good to see you are back !!! IMO most of the severe 'exhaust ingesting' and 'cat particles in the intake' are caused during downshifts/engine braking ....... this is when one will see the most vacuum in the intake tract and will draw in alot of 'contaminated' exhaust air during valve overlap ........

....... and what Vern said about exhaust taking the path of least resistance when the valve is wired open is true ......

 

Hi OZ

If you get the VE at 1 or 1+ you don't have to worry about a contaminated intake...yippeee NO vacuum. So whip us up a new postive pressure intake system and keep it normally aspirated..I'd also like a large order of fry's and a vanilla milkshake to go with my order please...lol

Yes VERN is spot-on...he is pretty smart when it comes to fluid dynamics. When I go over to help him paint his porch we are going to see how fast Newton's Law(or is it Bernoulli's principle??) can empty a case of Coor's Light.....in the scientific community this is called a "Case" study.

We may have to do several cases for the sake of accuracy.

 

Hmmm... I'm thinkin' its that Newton guys deal, unless we attacked a hose to the hole in the can then its gonna be that Bernoulli guys deal.
Anyway you 2, the 355 is one very interesting exercise in mech. engineering very complicated or maybe I should say interestingly complicated.
Hey Bruce you keep blabbering about my paint on my deck, well that ain't gettin it done you know! Regards, Vern

 

I agree that the 355 is interestingly complicated..especially in the 2.7 version..it's like have two distinct 4cyl. engines sharing a common crank. I definitely see both side's of the coin in developement of this engine..the all out racing heritage engineers being constantly hampered by sales/marketing/certification guys. Trying to design/build an engine system that will run on varying gasoline qualities worldwide and pass all the market areas varied environmental certifications and keep it right at race car hp/liter output is way beyond my skills.

Sorry Vern, I was trying to apply the same technique I've been using on my project car to the painting of your front porch.....I've been blabbering about my car and I can honestly say that not one bolt or nut has gotten installed no matter how much I talk about getting it put back together...lol


I am so bored right now I was even going to ask Dave if I could go to Honduras with him and Kris, but no matter how many times I droped a hint he never extended an invite...all I got was an email about some new lingerie that had a GPS locater hidden it....WHAT THA!!!!!!!!!!!!!!!!!

Guess I'll just go to PRI for my vacation....

 

Hmmm, I think I can explain it....

Yup I will go with what you are saying Vern and can only add that "An old dog at rest tends to stay at rest". Somebody famous said something like that once....
Bruce is busy putting pen to napkin designing a device now that includes a Pulse Jet, a hose and a can of Coors light. We need to put blinders on that guy. He's going for the +2 thing and will never have the car ready for RA next summer let alone get the porch painted.

I too agree with Vern's findings and as long as I am going on vacation and dont have to be here to deal with the resulting debate so I will add to what Vern stated.

The valve wired open results in extra oxygen being drawn across the O2 sensor and the ECU then has to deal with that artificially false reading.
Add to that the alcohol now being added to the fuel and with ethanol’s higher oxygen content yet more O2 is seen by the sensor.
The stoichiometric for pure gasoline is 14.7:1 yet the 10% alcohol fuels tend to run much closer to 14.05:1.
Add yet another factor where is falsely presumed that 10% Ethanol is the Max. we would ever get out of the gas pump at a station.... The Motronic maps are plotted based on characteristics of pure gasoline and an expected exhaust flow amount across the O2 sensors....

Once one steps back and looks at the big picture and inserts all of the variables (At least the ones I have identified here so far ) this gets a bit complicated. I have been testing fuel at various stations in the area for a few months now and can say without reservation that the alcohol levels change drastically week to week and that was before we started to get the dreaded "Winter Blend" here which is a whole story in itself. When oil was at $140/barrel do you think maybe someone might have been tempted to stretch supplies a little? There are far too many variables in play for anyone to make a statement that "this works" because it works on my car. Some of my design spread sheets got so foolishly complicated due to the lists of identified variables I threw them in the bottom desk drawer and started over again. The best we can do is make generalizations, add a safety factor and try to predict which way the fuel trends will go in the future and then use those base parameters to design from. Want to chip an ECU now? For what fuel grade, what header design, what exhaust back pressure for which muffler, the general use of the car will be what, predicted time at WOT and what are the long term effects to longevity?

Backyard designs went out when the computers came in. There are a heck of a lot of questions to ask before I would suggest one changes anything on computer controlled cars that are already stretched and tuned to High C right from the factory. Take just the few variables I threw in here and now look at what Vern did. Pure genius in my book and he "put a potato in the tail pipe" if you compare it to some of the exhaust designs currently being marketed. When Vern writes something, its worth reading, everything except the part where he thinks his deck will get painted...be real!

When I get back from vacation some of my experiments regarding the fuel today will be completed and I am sure there will be more to add then.

Dave

 

Here is a pic/diagram of the ch exhaust. You are right the ch does not use a valve according to this diagram.

My experience is with the 5.2 motronic 355 and because of the extra o2 sensors after the cat matrix ....... I have gotten CEL when I wired the valve open...... more reference data: when the bypass diaphram broke the valve stayed closed and I never got a CEL with this 'closed valve' scenario.

But from what I have heard and understand the 2.7 motronic can wire the valve open without a CEL maybe because it has only the two pre-cat o2 sensors.

I do not have any experience with a 355ch but since it uses the 2.7 motronic, it may explain why the challenge does not need a bypass as you said.

True, I think this is a much better place when there discussion and regard for all participating members. IMO since not one person knows everything there is to know ....... there is always something to learn with a civil exchange of ideas and information .
Image Unavailable, Please Login

 

I am trying to get more feedback/research on this as well. I guess maybe the best way we can research this would be some dyno time and look at the AFRs? I know what a lot of people will argue regarding the challenge cars not having the valve, and that is because most of the challenge cars are at higher rpms all the time anyways when the valve should be open, and the valve not there is just to prevent it failing at high rpms.


I am stuck on whether or not to leave mine wired open or shut it because I get all these conflicting reports. All I do know is that I noticed the engine/engine bay area is quite a bit cooler and the air coming out of the exhaust tips is much hotter, wouldnt this actually increase engine life?

 

Why can't we just put the bypass valve vacuum line on permanent vacuum rather than a solenoid switched vacuum if a bad solenoid is suspected (provided you have a complete, aftermarket exhaust)? I suppose this would cause a CEL on 96+ F355's, but hell, I'm getting that already. Connecting to permanent vacuum (provided the bypass actuator is in good working order) eliminates the need of wiring the valve open, right? the valve should go open on a non-switched vacuum source as soon as the car starts.

Just unplug the tee that connects to the bottom nipple of the controlling solenoid, connect the hose from the top nipple of the same solenoid (line to bypass actuator) to the side of the tee removed from the lower nipple, then cap both nipples of the controlling solenoid.

Shouldn't that work? I think I'll try it. Should quit me down at idle (rattles and buzzes). manually opening the valve while idling gets rid of the annoying sounds. So, connecting to non-switched vacuum should do the same for me.

We'll see.

 

Never-mind. Bad idea.

In process of doing this, I thought about the fact that the valve actuator probably isn't designed to hold the valve open permanently. This would probably be too much stress on the internal diaphragm.

 

I can't find the Capristo valve. Who sells this? I've visited the Forza website but don't see it listed.

--Nick

 

I am sure if you call him he has it.

I got mine from Competizione. Helpful with installation questions too.