Isn't the pump in the back for just for secondary air? On my 5.2, vacuum comes from the intake section on both sides, through two check valves, and directly to the accumulator. The dashpot control to open the secondary air path gets its vacuum from the accumulator.
Yes. I meant tank not pump. My bad. That's what I get for doing this without my notes handy. Solenoid valve (8) closest to the center of the car manages the bypass valve. The other solenoid valve operates the air injection valve which lets the air from the air pump through to the header rail. Hose 35 hooks to a small metal tube that is tack welded to the air injection tube and pops back up by the bypass valve. You can where it pops up as it is right under the #37. Image Unavailable, Please Login
So much wrong here. Vacuum comes from manifold, not emissions pump. The thermocoupler is only there to sense heat, it does not look for cold. I believe the workshop manual states this as well. Have you tried this? I have and have spoke to others that have. My cell light is working and I do not get a 1448. Many 355s, specifically the challenge cars never had a bypass from the factory. The notions that reducing the exhaust pressure by allowing a 2nd stream of exhaust somehow damages the headers is absurd. Remember, the bypass is open most of the time when the engine is really working. It's only closed at low RPM when there's really not a lot of heat anyway. Remember, the purpose of the bypass valve is to make the car quiet sometimes and loud other times.
Lack of heat...better? I have tried exactly this and chased the hell out if it three years ago. In fact I had the damn vacuum line teed and a gauge plumbed into the cabin so I could check the initiation of the vacuum for the valve at different RPM / Gear / Throttle position. If you leave the vacuum off the valve and the ECU tells it to open and does not, it throws a CEL. Been there done that. Lack of heat... If you leave the valve open and drive around that way it throws a CEL because it is sensing heat when the ECU says it should not..... Mine does anyway. Challenge cars are a different matter.
I believe the vacuum/header theory was about the stock muffler which has a shared exhaust path and was supposed to occur even with a functioning bypass valve. When the valve closes from lifting off the accelerator it creates a vacuum which sucks hot gas back into the headers. Can’t speak time the validity of it but have heard a few times. Aftermarket exhausts supposedly solve this with separate channels.
I assume that leaving the vacuum line off the capsule won't degrade the vacuum for the Secondary Air Solenoid Valve for long enough to cause the secondary air system to throw a CEL. Maybe someone can come up with a theory on how all the experts can be right
Thanks, understood. The text does say "though only at full power", so I assumed that the throttle was involved.
based on this description, this would be an advantageous case to remove the bypass completely in order to protect the headers. There can be some scavenging in good header designs. However there is a y pipe at the end of the headers, nothing should go backwards at this point regardless on any theory of a bypass valve. If anything, with a working bypass valve, the quick closing would cause pressure, (and thus heat). The only place there be a vacuum is on the muffler side of the valve,
This. Mine has always been a bit sluggish to open. I replaced the solenoid valve last night, and that baby opens up WICKED FAST now.
Just an FYI to an old post of mine from several years ago (not sure where to find it, but here is the general info from memory): My 1997 F355 spider I owned at the time, had QV London rebuilt oem exhaust manifolds, factory catalysts, Capristo bypass valve and Capristo exhaust system. My local dealer experimented with wiring a bypass switch in my car to see how that might work. They were able to figure out the wiring, and even spoof the Motronic not to throw the P1448 code. The concerning thing they saw after driving under various conditions, was the fuel trims were getting out of wack, as so much exhaust was going through the bypass, and not enough over the pre catalyst O2 sensors. They figured the solution would be to move the pre catalyst O2 sensors to the merge collectors on the exhaust manifolds. I wasn't interested in modifying the car like that, so we ended the experiment. Interesting though. Anyone running with the valve open all the time, should probably check their short and long term fuel trims.
From the Capristo website “Under certain driving conditions with the original bypass valve in the open position, a reverse flow through the silencer causes overheating and damage to the headers on Ferrari 355 vehicles. Under these conditions, once the exhaust gas valve is open, the exhaust gases do not all flow through the main catalytic converter but mainly through the bypass. The exhaust gases flow off the exit which leads to the main catalytic converter and generate a vacuum. Thus the hot exhaust gases in the muffler are aspirated backwards through the main catalyst which additionally heats up the gases. Then the gases are guided though the bypass and recirculated by the exhaust gas valve into the muffler again. When the exhaust gas valve is open, this gas flow is circulating ceaselessly generating more and more heat. We are of the opinion that this problem is known to Ferrari. For this reason the F355 was changed since 1996 from engine 2.7 to 5.2 and the headers were modified exactly in the place where the vacuum is generated. But the problem was not eliminated by this measure. Now you can imagine that extreme back pressure is created in a case where all of the exhaust gases coming from the engine and those which are aspirated backwards have to flow through 1 exhaust gas valve. That’s the reason why the F355 does not provide the power as indicated.After some testing it was obvious for us that our theory was right and that the bypass causes this problem. One exhaust gas valve is not sufficient and thus leading to extensive heat due to the back pressure.Our exhaust systems, irrespective of the racing or the usual model, are so designed that the exhaust tubes from the main catalytic converter lead to the outer end pipes and those from the bypass to the inner end pipes. These tubes do not lead to each other. Consequently it is not possible, when the vacuum in the main cat is generated, that hot exhaust gases are recirculated. Instead cold air through the outer end pipe is drawn backwards through the catalytic converter and the bypass and the valve. Once cold air is mixed up with hot exhaust gases, the temperature of the exhaust gases decreases and also the temperature of the complete system.The original single bypass valve also did not flow enough gasses at full throttle. After recognizing this problem, CAPRISTO exhausts set out to eliminate both problems with a new design.” Anyone have a sense if this is real? Sounds like some pretty heavy marketing.
Antonio Capristo seems to have well engineered products, so it may very well be true, but using their exhaust will not prevent failure of the oem manifolds. (While I had QV London remanufactured manifolds, they still failed using the Capristo. I discovered my manifolds were repaired replacing the pipes with thicker 304 SS, but only up to the first bend. So they subsequently failed just past. I sent them back and they properly repaired/replaced the pipes all the way to the collector). Whatever cooling improvements, it is not having a significant enough impact on that. More power? Never did before and after dynos, but I doubt it makes much more than any other muffler. Capristo DOES make a muffler system that makes significant power (I forget the specs, 22hp?) and it eliminates the bypass Y pipe and installs the bypass valves (one on each side) similar to the 360/430. Only problem, is the sound is not the high pitch scream of the other Capristo 355 exhausts that utilize the Y pipe bypass.
That muffler is called the twin sound and the associated claims on the Capristo website relate only to that exhaust. Not the F1 scream sounding one that is what most get. Not sure why they include that description on the muffler when it doesn’t even apply.
