Just want to get some opinions here on the following: What would you prefer, Bypass valve wired open for loud sound 100% of time or normal 'factory' operation for loud sound after 3000rpm? The reason I ask this is that I have a 97' 355 spider with tubi and bypass valve wired open. I don't get any fault lights, I looked underneath the rear bumper and the 3rd ECU & thermocouple for the basspass leg is not there! (note: my car is non USA model). The car sounds great when accelerating and sounds 'tuff' at idle (measures 90 dB(A) at 1m from tail pipe at idle), but can be a bit noisy when cruising. I'm thinking of making the bypass valve operational to revert back to the 'factory setting' sound and lower noise below 3000 rpm. Not sure if I will require a new valve, as I suspect the previous owner wired the thing open to stop the common rattling noise. I know that most USA 5.2 cars cannot wire the bypass valve open because the CEL will come on, but if this wasn't an issue, would most 355 owners wire it open for better sound (but more noise when cruising)? I will be interested in hearing your opinion.
Wiring the by-pass open is only really beneficial to the low end tick over especially on the standard system. It gives a deeper more meaty tick over and i suppose right up to maybe 2,000rpm. However i think the sudden by-pass opening of the exhaust at 4-5,000rpm is a very distinctive F355 trait that defines the 355 engine/sound package and takes the beautiful 355 gem sound to the next level. Distinctive classic 355 sound, leave it alone IMO. If you want more meat get another aftermarket system like Capristo or Ito were you will get a better low end sound and still have the famous 355 by-pass sound change.....but better Un wire it mate, and go "o" natural
Intersting post as I have only had my 355 for one week. The supplier put a Sports Exhaust on it which sounds beautiful above 3k revs but I got questioned about it by the police at a petrol station as it is so loud at idle to 3k revs and he expressed his concerns in a nice way. In fact my wife wont go in the car as it is so loud at idle everything in the car rattles and if you are in a traffic jam I have to say it does give you a headache after a few minutes! I have not driven the car with the standard exhaust but the dealer will fit it back on for me. Am I going to be very disappointed with the sound from the standard system? Also I think I might know what the metallic rattle is from reading this post - the bypass valve !! Also anyone know if the seat belts can be adjusted - everytime I move forward to change radio stations it thinks I am in an accident and wont allow any forward movement. It means taking the belt off and letting it re-wind fully. Bit of a pain. Besides that it is just a fantastic bit of kit.
I bet you your system is probably made by the stainless steel exhaust company in Mansfield and called there challenge system. Ask and you may find i an right They are very loud and corse but they do make a quiter one. Put it this way they supply Greypauls Regarding your seat belts check that the bolts that are holding it to the rear of your seats are tight. When the bolts become loose and do not sit straight so as to slide through the guide, the belt system can jam.
I keep mine wired open all the time. The car sounds so much better during normal driving, and isn't too loud. The wife also loves it. The check engine light will normally turn on after a few times out in the car, but I'm not comcerned with that. The stock exhaust is simply too quiet during normal driving. Darrell.
Darrell, I would at least scan for codes periodically, otherwise you may not realize the CE light has tripped for an actual problem. As you know, there are literally dozens of various things that can trip the CE light.
I'm not too worried about it. It's been that way for about 5 years now. Every 2 years I have it reset to get the smog done. I just had the major completed, and she past with flying colors. 2% leakdown across the board. I just need to have the smog completed tomorrow, and I'll open the valve again. This time I may try to simply unwind the spring to lessen the pressure. And thus allowing it to open much earlier. I believe that the light is triggered while the car is at idle with the valve open , and due to low exhaust pressure, this allows cool air to pass over the O2 sensor. We'll see. It would be nice to have it open much sooner and not trigger the light. I'll post the findings. Darrell.
Are you running test pipes, stock cats or hyperflows? Removing the cats makes a huge difference to the sound level, I have recently had my stock cats removed and test pipes fitted, the mechanics and my self were astounded at how much louder the car is now. I have a quicksilver muffler set up FYI.
Thanks for your responce brother. My bypass valve is as per factory specs, I like it, the switch is part of the character of the sound for me. I would look into having the bypass restored to operating specs, depending on cost it might be worth while.
Graham, I recommend getting your headers checked ASAP, a "metallic rattle" is one of the first signs of headers going bad, this is how I discovered mine needed doing. We don't want to take the risk of running the car for a long time with leaking headers.
Thanks. I agree with you. The owners manual says the valve opens at 2800rpm except third gear which is at 4000rpm. Does this actually happen? Is it really different for third gear? My bypass valve looks like its been wired open for a long time. I'm not sure of it condition. My mechanic says he can repair it, but I'm wondering whether its better to buy a new one and just fit it. Have you had any problems with your bypass valve?
No, my valve has been trouble free, most are I think? Only heard of one having a problem over here in NZ(first hand info). I am not sure about the valve opening, it is rev and throttle position dependent, over 3500(ish)rpm and 3/4 throttle is what I thought it was but I could be way off the mark. Maybe one of the experts here will post and answer that question for sure. If you are thinking of replacement look into aftermarket suppliers, I am fairly certain "fabspeed" do a valve or was it "Capristo", can't quite remember but a search of this forum should answer that and also put you in touch with a supplier. $$ to be saved and a more robust product from what I have heard. Works in reverse to the factory valve so some vacuum hoses need to be swapped over but simple stuff really.
If you reduce the pre-load tension on the valve, it will probably rattle at idle. The tension has very little to do with how quickly it opens. It gets the vacuum signal from the electrovalve to open, and the electrovalve is triggered by the Motronic. It may open 100 or 200 rpm sooner, but very likely to rattle. Adding preload or tension is how you can get rid of the common rattle problem. But only add a couple turns at a time, as it has been found that too much can, on occaision, cause it to not open at all. The "check engine" light is triggered by the exhaust valve when the Motronic senses from the thermal probe (by temperature) that the valve is either open or closed, when it shouldn't be. Since the Motronic triggers when it should open, if it tells by temperature it is not open, or open when it shouldn't, then the CE light comes on. The reason you can wire open the 2.7 (1995) cars, is they do not have the third themo probe on the exhaust valve bypass. So the Motronic does not know it is constantly open.
I wired mine open and found something interesting.... Before it was wired open, the engine bay area after fully warm would be extremely hot. If you put your hand in front of the exhaust pipes it wasnt too hot. Now with it wired open, the engine bay area stays 50 times cooler and when you put your hand in front of the exhaust now it is extremely hot. Would this have any positive/negative effects on anything?
Can't see how the engine bay is cooler with the bypass wired open. Wiring the bypass open lets more exhaust gas through the Y pipe. I've notice on mine that there's a lot of heat coming through the exhaust heat shield where the bypass valve opening is. This places more heat on the rubber intake tubes (5.2 setup) sitting directly above the bypass valve. I suspect in time, this excess heat may cause the rubber tube to fail. This may not be a problem on your car because it is a 2.7 setup.
Thanks for that - the car is going back to the supplier as the reversing lights dont work. Sounds like a vibrating heatshield but only noticable at idle up to 2k revs. I'll let you know the outcome. Thanks again
I didnt think it would be like that either but it is, I guess its because all that hot exhaust gas is allowed to escape out of the exhaust at idle rather than being pushed back in if the valve was closed?
Yeah you maybe right. Is yours a 2.7 set up? why did you wire your bypass open? do you run a stock muffler and cats?
96' spider, stock muffler, high flow cats. I wired it open because I could constantly hear it rattling when opening/closing. When I tested it, the valve itself was very stiff so I decided to wire it open. The heat difference is not just a small one that could be in my head, its a matter of night and day.
Is there a bypass valve on my '82 308. The engine changes sound at 5000 RPM but it has become a little intermittent recently. The engine make this beautifull howl over 5000 RPM most times but not always now. Is this bypass valve you are speaking of doing this? Marty
