Hey guys, i noticed the other day when i pulled the vacuum hose going to the BBM diaphram then took the car for a quirt, it was lacking in power down low but when it got to about 3400-3600rpm the thing just took off like a rocket.

It seams to sound deeper and pull harder with the hose off and apart from the lack of low end power would be nice to leave it off. Or could it just mean that the BBM solenoid is stuffed. I would be interested if anyone else wants to pull thier hose off and compare findings.

There is no point leaving it off unless you have a turbo etc. Leaving it off just leaves it in short runner mode which it normally switches to at high rpm anyway. The advantage of the BBM is that at low rpm it switches to long runners which give you tons more power down low, all you are doing by taking the vaccum line off is loosing this long runner mode.

you're playing with your mind. You'll find its running like s**t below 3400, and then running like it should above. The reason it feels like a rocket is you've gone from s**t power to more power, compared to normal power to a bit more power

What he said, what else would you expect to happen

Every body says that at low rpm the long runners are used, well I beg to differ.

When the engine is below 3800rpm there is no voltage to the vac switch(because the other side is to eartg solenoid does not operate) therefor no vacuum to vac on BBM Butterflys are open which allows intake to go straight into runners and engine.
Above 3800rpm 12v from ECU operates the vac solenoid, vacuum operates the butterflys and closes them forcing the intake to go the longway up over the top part of the manifold and then into the lower runners and engine.
So it would seem that the opposite to what most people beleive is in fact the truth

I have checked out the individual operations of the individual parts and examined the manifold whilst I had it apart.
I would be very interested to hear comments.

One person commented in a previous thread that he was supprised how well his mates car went on short runners (bbm not connected to switch) well now u know, that seems to be how it was ment to be.

Cheers

nope what you are saying is the opposite of the very well known fact that long runners are good for low rpm power and short runners are good for high rpm power.

ford would not use that fact agaisnt them selves when trying to get power from an engine.

i think you should go and look at the way it works again

Sorry falconea mate, but your wrong

When there is no voltage the vac switch, the vaccum pulls the little butterflies inside the manifold shut and diverts all incomeing air thru the long runners.
When the vac switch gets 12v from the ECU the butterflies open and allow air to pass both ways - presumably most of it would pass through the short runners.

How do you explain that when they are in the normal mode ie no vac (below 3800rpm) there is nothing stopping the inrushing gasses from passing the open butterflys into the engine and that only when the butterflys are clossed they are forced the long way round.
Someone mentioned that the vac unit is held operated all the time until 3800 when it releases. I find it hard to beleive that Ford would arrange it to operate that way. Not logical as failure of the vac unit or solenoid would make driving uneasy. If u have an oportunity to look at a BBM in peices u can see what I mean.

Well I have just gone into the garage and cheched the vac system and the vac unit will not move till the solenoid is operated. So I dont know what is going on.
What u are saying is that the vac unit is held operated all the time until 3800 rpm when it releases and opens the butterflys ? That sounds like very backward engineering. y would u keep the vac unit operated and the spring under tension all the time. Seems very wrong.

Because at high rpm you are more likely to be at full throttle where there is no vacuum, whereas at idle there is s**t of vacuum.
I agree it is a little dodgy, IMO it should have been full electric.

I guess it also allows for the unit to be stuck in long runner mode upon failure, meaning that for the majoroty of people the car would drive exactly the same.

Voxace I can see your point but........... when there is novacuum the butterflys are open (short runners) also the vac lines are attached to a resovoire with a non return valve so there is vac available at WOT to hold it there or operate it. It also needs supprisingly little vac to operate it.

Has anyone who has a genuine EF/EL looked at the vac unit on the BBM when the engine is running to see if it is permanantly operated, I doubt that it will be. I am going to try and look at a friends car.

By the way I am not trying to be a smart a--se about this I would just like to clear this up.

Falconea

I will explain it as to why it is setup the way it, and i can 100% say it work the way stated, also a short note on dont disconnect it.

HOW it works:
It is held on below 3,800 rpm this is long runner very good for low down torque hence ford implemented it, tie the vaccuum closed and try rev about 4000rpm enjoy the invisible rpm brick wall you hit. So after 3,800rpm it releases vaccuum it then goes to short runner (about the same as an EA manifold in length) great for top end as has been stated.

The WHY:
If it worked reverse then imagine it broke, what would happen people would have not top end, stop revving at 4,000rpm and that could be very dangerous, hence it works backwards to logic as it then has fail safe mode.

Disconnected is wrong:
The EF/EL ecu has 2 disctinct maps one below 3,800rpm and one for above, the one for long runner (below 3,800rpm) alot of air and one for short runner less air, so while the top end is good, and it may feel pretty darn nice down low, you have lost alot of torque for a start, and will be running very rich, the computer will compensate within time and this idea is just as dumb as the lets add a resisitor as sold on ebay.


Now I hope that has cleared up some things

Hey delboy, Thankyou for the explanation and warning.

Tell me Y there is no vacuum to the vac unit when engine runs as the solenoid is no operating. All units are known to be in working order. checking vac sol no vac to vac unit unless volts applied to sol. As per above 3800rpm from ecu.
Call me thick, but how does the vac unit get operated in the first place when the vac sol suggests working the other way round.

If it is working as you have stated Flaconea then its not working but as the runners are open (short) you will have full RPM avaliable, as I have said cable tie it shut and test it, then tell me I am wrong.

That's because the solenoid is to BLOCK vacuum, not to let it through.
When it sees 12V, it blocks the vacuum getting through and the switch valve opens the butterflies.

 

 

Attachments:

File comment: See how the butterflies are open when theres is no vacuum applied to the valve. bbm.jpg [ 79.6 KiB | Viewed 197 times ]