I just did this and now i get alot of sputtering, Any thoughts.
Look, I am no expert on cobras, I am just a normal auto technician. But, this mod makes no sense to me. It should not change your peak boost at all. What it will do is force the bypass closed when it is normally open. In other words, at idle it will be open like normal. At decel and no load cruise it should also be open. By open I mean venting boost. This is because vacuum should be present under all these conditions. However, as soon as the throttle is opened enough to kill intake vacuum, the car will begin making boost due to the bypass valve being forced closed.
I suppose it also could hold it closed with more force. But, I don't see how that is an issue with a spring loaded diaphragm valve. Unless, the argument is that more boost actually forces the valve open due to the spring not being strong enough, but this has never happened to me. To me figuring out how this operates is just common sense. However, my logic could be flawed.
This should not hurt your engine or blower at all. It is simply a matter of personal preference. If the mod is done correctly, there should be no adverse affects to performance or how the engine runs normally. It should simply cause the boost to come on more quickly. Which will in turn cause higher IAT2's in certain situations because boost creates heat and you will have boost in certain areas where your car did not before. But, no problems.
You could also see fuel mileage differences depending on your driving style. However, how this mod could increase max boost makes no sense to me. To understand this, you must first know how this system operates normally. This is my understanding.
Normally only vacuum connected to the control solenoid. This control solenoid was obviously controlled by the computer which turned it on and off in certain conditions. So, literally the computer supplied vacuum to the bypass valve via the bypass solenoid to open the valve (vent boost). Why would the computer vent boost at WOT when max power is being requested? My guess is it doesn't. Unless, it sees a reason such as overrev. Then it may dump boost to protect the engine. Also, I could see it doing this in other conditions such as lean A/F or something.
The only other time the computer would normally open/vent would be when boost is not required: idle, cruise, low load. When boost is being required (high load), the computer would obviously close the valve (build boost). The reason that I say this is because I am running a ported blower with pullies and I am seeing 16psi boost. My solenoid and valve are hooked up stock, and the solenoid is not turned off in the tune. So, why is my valve not dumping 8psi worth of boost? Because it doesn't. My car drives like stock. The valve closes under heavy load and the car builds boost. Just a lot more of it. Under all other circumstances the computer is dumping boost via the dump solenoid to the dump valve. No problems.
I do not see how this mod is required at all. Try it. If you like it, leave it. If not, change it back. Mine will stay as it is. Good luck.
I just did this and now i get alot of sputtering, Any thoughts.
Sounds like you need to go back and make sure that you made all of the right connections. If you have a leak, then you will hear a whistle.
Quote:
Originally Posted by mdrc347
Look, I am no expert on cobras, I am just a normal auto technician. But, this mod makes no sense to me. It should not change your peak boost at all. What it will do is force the bypass closed when it is normally open. In other words, at idle it will be open like normal. At decel and no load cruise it should also be open. By open I mean venting boost. This is because vacuum should be present under all these conditions. However, as soon as the throttle is opened enough to kill intake vacuum, the car will begin making boost due to the bypass valve being forced closed.
I suppose it also could hold it closed with more force. But, I don't see how that is an issue with a spring loaded diaphragm valve. Unless, the argument is that more boost actually forces the valve open due to the spring not being strong enough, but this has never happened to me. To me figuring out how this operates is just common sense. However, my logic could be flawed.
My understanding is that your assumption is basically correct. The spring tension inside the bypass valve is effective to hold the valve closed with 8 psi of stock boost pushing against it. This is essentially why when ever the bypass valve is installed, the rod must be preloaded to increase the spring tension that holds the valve closed under boost. However when the boost gets up to higher levels, in some cases it can crack open the valve when you don't want it to just by the pressure over powering the spring inside.
My bypass valve has never been removed from the car. With it hooked up the stock way I was loosing some boost under WOT with a 2.8 pulley. Then when I hooked it up this way I got the full 14 lbs of boost I am supposed to get. Perhaps there are variances in how strong the springs are inside the actuator. My understanding of why it was hooked up this way from the factory is because the factory tune had provisions in it to pull boost over certain IAT2 temps. For those of us who do not go out and do silly top speed runs, this is not needed.
I suppose if someone wanted to ensure full boost and keep the stock set up, they could try going with a little more preload on the actuator spring so long as you did not go to far and restrict how much the valve can open. I personally love the enhanced throttle response of hooking it up the way I did in this mod. Makes the car feel more powerful at part throttle. I checked my IATs and they where the same as normal out of boost. It takes less pedal to achieve the same power as before, therefore to equalize the mileage you just adjust to the new throttle response. On the highway for example the mileage is identical.
here is what my boost looks like before this mod. i have a 2.76 pulley with a steeda idler. i will be doing this mod this weekend and let you guys know how it works out.
here is what my boost looks like before this mod. i have a 2.76 pulley with a steeda idler. i will be doing this mod this weekend and let you guys know how it works out.
Some of what you are seeing there could be belt slip. Are you running a non-slip pulley?
Some of what you are seeing there could be belt slip. Are you running a non-slip pulley?
steeda steel pulley, steeda idler, gates belt, and no residue that is typical with belt slip. the idler was added weeks after the dyno pull.
did the mod this weekend, super easy, noticed i picked up 1.5psi in 3 and 4th but still losing a little bit up top, not as much as before tho. throttle response is much quicker.
Good deal, the stock unported blower will all ways drop off boost a little in the upper rpms if pullied. If you put a non-slip pulley on there you will pick up some more boost.
Good deal, the stock unported blower will all ways drop off boost a little in the upper rpms if pullied. If you put a non-slip pulley on there you will pick up some more boost.
cog-pulley is the only true non-slip pulley. But, I don't think you have any belt slip issue. Your graph looks typical to me. Eatons always drop off on high end until ported.
I would like to see this tested on a dyno. Not, that I don't think it would add some hp. Just curious as to how much. Mostly, how level the curve would be.
A non slip pulley is almost identical to a normal pulley. The only difference is that there are some small missing sections of the ribs on it so that it will bite into the belt better.
Just did this today and can most definitely tell a difference. Rather than the T-fitting and zip-ties though I used actual vacuum fittings that lock the hose into them. Boost goes right to where it should be and holds, runs and pulls MUCH better. Excellent mod IMO and great write up. Thanks!!
I am all for this mod I drag my cobra all day long...first my car eaton got super hot...now it doesnt i know for a fact...second my ported eaton dropped @5800 bcuz its all torque but not after this mod my boost stays @ 18psi all through 6200 instead of spiking to 14 @ 5800 like before...car pulls up top instead of falling on its face...so this mod works awesome IMO!!!
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2004 Ford Mustang Cobra (VNMOUS1)
2003 Ford Mustang Cobra (2VNOMUS)
So I am reading this right that this mod is needed even if the solenoid is disabled in the tune?
Thanks.
The only thing holding the bypass valve shut under boost with the stock set up is the spring inside of the boost bypass actuator (black canister / metal rod). In many cases when higher than stock boost is happening the boost can over come the strength of the spring and force the valve open.
So you are essentially allowing the boost itself to assist in holding the valve shut under boost only when you do this mod. Some people have reported that it did not do anything much. Some people have reported that it did a lot for their car. It seems as though the higher the boost the more that this mod is needed.
That was the long answer, the short answer is more than likely yes if you are above stock levels of boost. There is the chance that the spring is stronger inside of the actuator of your particular is stronger than others and it would not make much difference.
The only way to know if it will make a difference is to try it. If you want to test it out with out hacking into the hard vacuum lines, then you can just put a Y vacuum fitting coming out of the fuel rail pressure sensor and run a line over to the top port on the actuator.
That is the way that I did it originally when I was testing out the concept that I learned by reading about it in a mod fords thread post by the tuner RWTD. It worked just as well but looked lame, therefore I redid it the way I posted in this thread.
If you want to see the original way that is quick and easy and can be reversed quickly if you change your mind, then you should follow the link that I put in the original post in this thread in giant red block letters.
Linear Mode
