I am going to try asking this question again as noone has been able to clearly answer my question:

Quotes from several different sites/people:

The boost dump is there to protect people who don't know how to drive.

Be careful if you have a boost bypass, you can damage your motor.

Boost dump is there to protect the motor when you do burnouts.

Make sure you understand the ramifications of a boost bypass.

The boost dump is there so that if you overboost, the engine will dump boost to protect itself.

Don't worry about installing a boost bypass as the rev limiter will keep you from damaging anything.

Sound familiar?

SO:
What, exactly, does a boost bypass do.
Why, exactly does it do it.
What, exactly, will happen to a motor if you are not "careful" after installing a boost bypass?
What, exactly, does knowing how to drive have to do with a boost bypass keeping your motor safe.

Thanks

Ken

 

Ken,
I guess that's the million dollar question....I have no idea as to what, why or whatever...All I know is I did it and have had absolutely not one problem.......
Guess I'm completely no help(worthless?).......JR

 

What, exactly, does a boost bypass do?
Boost is activated by the lack of vacuum when the throttle is opened. The bypass is an electrical solenoid valve in the vacuum line, giving the PCM computer the ability to shut off the boost.

Why, exactly does it do it?
The main reason for the boost bypass is to protect the transmission. Full boost and eight cylinders are hard on the tranny during the 1 - 2 shift. When stock, the engine cuts to four cylinders and the boost bypass activates for the 1 - 2 shift at WOT. The duration of both the bypass and four cyl mode is about 1/2 second. The engine recovers nicely from the four cyl mode, but the S/C takes longer to recover from the loss of boost.

What, exactly, will happen to a motor if you are not "careful" after installing a boost bypass?
Again, it's the tranny that comes up a little short, not the engine (the engine is protected by the rev limiter - stock anyways). Defeating the boost bypass and/or the four cylinder mode may shorten the life of the tranny.

What, exactly, does knowing how to drive have to do with a boost bypass keeping your motor safe?
Again, transmission. How long the tranny will last with the boost bypass and the four cyl mode defeated depends on several variables. How often do you WOT the 1 - 2 shift, and how much have you increased the overall boost are the two most important questions. Also, never back off from WOT at the shift. The tranny "slam shifts" into 2nd, and doesn't like it.


Recommendations for best tranny life without sacrificing performance:
1. Defeat the boost bypass by bypassing the solenoid valve with vacuum line.
2. If you run a chip - a) have the duration of the four cyl mode shortened to around 0.2 sec, but do not defeat entirely; b) do not raise the shift RPM by much, if any; c) do not raise the rev limit by much, if any.
3. Install valve body in tranny (for less slippage and heat buildup during shifts).

Notes:
* If you put better rods in the engine, you can raise the rev limit and shift RPM.
* If you have the tranny built (better clutch packs), you can think about defeating the four cylinder mode entirely.

The "recommendations" are good for 'daily driver'. For 'daily driver', "notes" are probably going a bit overboard.

Do some searches for "Transmission" / "Tranny" here and on NLOC and you will get an idea of what it takes to tear one up.

PT

 

There is a waist gate on these trucks that will vent excess boost while under no-load (vacume). When you give it gas, and put the motor under load, the vacume will decrease or go away (WOT). The lack of vacume will allow boost.

Now, when the PCM sees something it doesn't like (Rev Limiter Hit, Excessive Trans Heat, Ect...), it will trigger a electric solenoid to open the vacume line and allow vacume to the waist gate dumpping your boost.

You can go with the $25 kit from JDM, or go with the free route and live with a soft code sitting in the PCM. Either way, it will have the exact same effect.

Ford (SVE/SVT) did put the 4cyc knock out and boost vent on the 1-2 for a reason; to pro-long the life of the transmission. But it has been out experiance (now on the 4th transmission), that those concerns are not warrented on a fairly stock truck (Chip, Filter, and small pulley). But when you do run large amounts of boost and/or nitrous, blowing clutch packs will be a problem.

My advice for a fun daily driver that can still rip up the strip pretty hard with out risking damage would be: a Chip (Tuner of Choice), Filter (Tuner of Choice), Pulley (2Lb from Tuner of Choice), and a Shift Kit (Methoid of Choice).

 

Thanks to Lightning Boy and PT's02L for two of the most concise and informative posts I have ever seen!

 

Boost Bypass Kit



This kit is designed to allow your engine's PCM to continue to control your engine smoothly, with not interruption of boost output from your supercharger

The bypass valve is a release which vents off pressure in a rapid de-acceleration situation. When the Supercharger is producing boost and you abruptly let off the gas, closing the throttle plates, the boost has nowhere to go (also known as compressor surge) kind of hard on everything. The Bypass helps relieve this and also helps smooth out your idle. It is also helpful in building up boost faster, and as a bonus it helps to prevent parasitic power loss. Under idle or normal driving (vacuum) the valve is open. When it sees a boost signal it closes.

 

as if there wasn't enough posts on this.

The PCM does uses this when it sees 'faults' anyone that has ever run a supercharged car will tell you when you hit the rev limiter and the computer cuts FUEL while under boost you got VERY lean and BAM. During a burnout you don't have a load on the motor and can hit the limiter quicker than the tranny can shift out. Thus cutitng fuel and possible engine damage. If you are a good driver this will not come into play during a burnout(ie watch the rpms and be concious of it during normal play)

I believe it will also dump boost if it senses knock. Not 100% sure on that one though. Just any 'fault' be it limiter, knock, ect ect. I have not had mine dump boost with my chip, soo i left it intact. without the chip it always does it. Its mainly because the limiter is at 6000 now vs 5500. and the shift duration is shorter.

Hope this helps
Brandon

Sal care to chime in?

 

For what it's worth, here is an excerpt from the Ford Service Shop CD.


"Supercharger Bypass Vacuum Solenoid and Actuator:

The Supercharger Bypass Vacuum Solenoid will bleed off boost during sudden throttle closing. This prevents damage that can occur if the throttle is quickly closed while the engine is still under heavy boost. The solenoid is located on the upper LH side of the engine. The solenoid uses engine vacuum to operate a actuator and linkage that connects to the pressure bleed off valve. The actuator is located near the solenoid and is connected to it by a vacuum line."

"At partial-throttle opening or when vacuum is present in the intake system, a vacuum-controlled bypass valve reroutes some discharged air from the supercharger back through the intake plenum. This prevents the supercharger from cavitating, causing reduced performance, increased temperatures, and poor economy."


David

 

Thanks, gentlemen. I finally got what I was looking for...

One note from the responses confirmed what I was concerned about and that is when the engine intentially bleeds off boost without throttle applied. With the boost bypass installed, the engine cannot do this and you are most certainly going lean in that scenario, even if just for a half second or so. So, if I get on it hard in 1st and then jump right back off again, I am up at 7-8lbs and I have let off the throttle, thereby starving the engine... I think I will try to have the chip set so i don't bump into the rev limiter at WOT, and shorten the shift duration to 200ms to keep from revving past the shift point. It seems everyone's chip burns are set to shift 1-2 at 5400rpms instead of 5200 at the factory. Where is the factory rev limiter set at? 5500?

Thanks

Ken

 

Well most of the chips run the limiter at 6000. snapping the throttle closed with all that excessive boost is tough on the throttle blade, which is why the bypass valve is installed on most vehicles that are supercharged, be it a stock mustang with a vortech or whatever. There is obviously a point for it to be there. If its not there then all that air having to be compressed over and over will heat the inlet charge temps dramatically and you can lose up for 75-100hp (think about the kenne bells that started out with no bypass valve, at cruise the inlet temps were in excess of 300 degrees, install a bypass valve and they dropped for 145ish.

Remember that if you lose traction your tranny cannot shift out as quick enough, so there is still a posibility for it to over rev.
As I mentioned above, i leave mine intact, and have only hit it once since adding the chip. and it was on the 1/2 shift when it FRIED the tires.

You can also adjust teh actuator arm on it which can help...

Brandon

 

Will disconnecting the connector prevent the boost from being dumped under decel or at idle?

Is there a way to only prevent boost from being dumped during the 1-2 shift without a chip?

All questions and no answers.... sorry!

 

I think there is a little confusion. Doing the boost bypass by either disconnecting the plug or by the JDM way will get the same thing accomplished. The computer will not have the ability to force a bypass if the motor over-revs or over-heats or any other abnormality is seen. The down side of the "remove the plug" method is a "soft code" is set in the computer memory, but this does not seem to be an issue. Either way will still bypass air any time the motor is running with a vacuum under the blower (most of the time).

Hope this helps

 

Ok, there is some good info and some not so good info in this post. I will try to address all the questions here in one post, sorry if I am repeating what someone has already said on certain parts.

What, exactly, does a boost bypass do.

The boost bypass is a vacuum activated valve that has a butterfly plate inside the blower case. When vacuum is applied, the bypass opens and allows air to bypass the blower rotors.

Why, exactly does it do it.

There are several reasons. One as previously described, is to vent boost off on sudden decel. This is more damaging on a centrifugal blower like a vortech, but on a roots blower, it's not too healthy either and can cause premature rotor gear wear. Another reason is to reduce heat. With no bypass, the blower would be constantly heating the intake charge. Anyone here who's ever owned a Gen 1 Lightning or Mustang with a 1500 Kenne Bell blower (no by pass) will tell you that you can cook your breakfast on it. And some have even had thier IAT sensors max out (256 degrees) using those blowers with no bypass. With the bypass open, you don't superheat your intake charge when you see vacuum, which is 90% of the time you are driving.

What, exactly, will happen to a motor if you are not "careful" after installing a boost bypass?
What, exactly, does knowing how to drive have to do with a boost bypass keeping your motor safe.

I don't think these two questions are valid questions, because it appears there is some serious confusion going on here...

There seem to be three different things being discussed in this thread, that some people think are all the same thing.

Boost Bypass - this is what I described above. It's the vacuum activated valve that allows air to bypass the blower rotors.

Boost Dump Solenoid - this is an electrical solenoid that can vent boost off if the PCM commands it.

The $25 bypass kit - this "bypasses" the dump solenoid, giving normal control to the boost bypass, and not allowing the PCM to shut it off.

As for WHY we have a device that would kill boost on the truck, here goes.. The PCM monitors everything that is going on with the drivetrain. There are several "failsafes" (7 I beleive) that if the PCM sees, it will kill boost to the motor, in order to decrease power output. The main reason people started disconnecting the boost solenoid, is a failsafe called Brake Torque. This failsafe occurs when the PCM sees the brake pedal applied, and the throttle at WOT, also known as a burnout. When you are at the track, and you do a burnout, then make your pass, and the truck hits second gear and kills boost, then you run a 16 second ET, thats because of the Brake Torque failsafe . There are several other ones, such as excessive misfire, high ECT temp, malfunctioning sensor default, high trans temp, rev limit, and a few others. Contrary to what some believe, there is NO overboost failsafe. The PCM does not sense boost, and there is no sensor on the truck that reads boost. The boost solenoid is not there to kill power to the trans on shifts, that is done through the PCM via Torque Reduction (kills injectors). However we've noticed on the 01s that there does seem to be a boost dump occuring on the 1-2 shift if you don't disconnect it.

As for damage that could occur from disabling the solenoid... Well, I've stated most of the important failsafes above. If you are going to disable yours, whether it's with a vacuum bypass kit or just unplugging the solenoid, you should just be aware that if those issues arise, the PCM won't be able to kill boost. But also keep in mind that the PCM does take other action during failsafes other than killing boost.

Hope this helps.

 

very well stated SAl, and very inlightning,wow its easy to see how someone reading the boards could get confused or do ,or not do the correct mod,based on misleading info,thanks for correcting this thread,b4 it gets to be too misleading.

 

LightningTuner,

Thanks for straightning me out! Seems I was only partially correct, and had my terminology all screwed up.
If the 1 - 2 shift boost dump is not present on the 02's, I may just hook my dump valve back up. Looks like it serves more of a purpose than I thought.

Sorry to all that I might have mislead!