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 Post subject: bbm switching and supercharging.
Posted: Wed Jun 10, 2009 9:18 pm 
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hi guys..
im about to go aftermarket ecu(ems stinger) on my ed which is centrifugal supercharged with a bbm.
previously i was using a el ecu using the bbm function..
now my question is should i use the bbm function with the stinger? or should i just disable the bbm keeping it in the high rpm position?

ive seen a few turbo set ups with the bbm not connected or completely removed.
i know in std form the bbm is used to give a low end torque.
but im thinking as the ems is totally tunable can the timing and fuel maps be tuned to not notice or not need the bbm?
and considering the centrifugal s/c makes boost with rpm im not really wanting to loose anything down low..

this is a new realm for me so any info would be appreciated..
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 Post subject: Re: bbm switching and supercharging.
Posted: Wed Jun 10, 2009 11:40 pm 
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Definitely keep the BBM functioning - you will loose low down torque without it.
You probably find that the turbo boys come onto boost earlier than us and so it's not such a big deal for them (this is an assumption as I haven't played with a turbo falcon).

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 7:14 pm 
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twr7cx wrote:
Definitely keep the BBM functioning - you will loose low down torque without it.
You probably find that the turbo boys come onto boost earlier than us and so it's not such a big deal for them (this is an assumption as I haven't played with a turbo falcon).

Yes, keep it functioning. Like you said your is centrifugal, so with out revs, it not doing much. In your case, as you know, i would have 2 1/2' from blower to the T/B. I think this will bring boost on a bit sooner. You will just have to have a play with the rpm as to when it should switch to suit your set-up, but by the time you hit 3800, i dare say it would be pumping........

Cheers mate

8-) Daz :D

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 7:24 pm 
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thanks guys..
i decided to try keep the bbm operating.
ill have it set to 3800 as per factory and see how it goes.
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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 7:50 pm 
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DA22LE wrote:
In your case, as you know, i would have 2 1/2' from blower to the T/B. I think this will bring boost on a bit sooner.


Yes, reducing the volume of air between the supercharge and throttle body will cause the boost to start earlier and the maximum boost level to increase. But there can be downsides to this too...

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 7:54 pm 
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twr7cx wrote:
DA22LE wrote:
In your case, as you know, i would have 2 1/2' from blower to the T/B. I think this will bring boost on a bit sooner.


Yes, reducing the volume of air between the supercharge and throttle body will cause the boost to start earlier and the maximum boost level to increase. But there can be downsides to this too...

Yes.... but nothing a good tune and quality fuel wont fix.........

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 9:41 pm 
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The 3800rpm switch over point is determined by the factory as the best spot in a NA application. Do you think it would be fair to assume that as soon as you're on boost, you want to be on the short runners?

The guys with centri SC's would find they're making decent boost at around 3000rpm. Mine is certainly making around 3psi at 2500rpm. So would '3000rpm' be a better switch over point for the supercharged I6's?

Joe

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 10:08 pm 
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JoeXR6 wrote:
The 3800rpm switch over point is determined by the factory as the best spot in a NA application. Do you think it would be fair to assume that as soon as you're on boost, you want to be on the short runners?

The guys with centri SC's would find they're making decent boost at around 3000rpm. Mine is certainly making around 3psi at 2500rpm. So would '3000rpm' be a better switch over point for the supercharged I6's?

Joe


hmm you make a good point there!
mine also makes aproxx the same boost.
so you think changing it over at 3000 would be better??
im curious if the torque would still be higher between 3000 to 3800rpm on long runners under boost compared to it being on short runners at 3000rpm up?
the good thing about the ems ecu is the change over point can always be changed..
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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 11:05 pm 
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maybe?? set it to long runners permanently. by the time you make boost, which is slightly before the NA switchover, the switchover to short runners is moot, as boost is forcing air into the throttlebody. However, I do recall reading something about when its on short runners, the long runners are also active? and this may have a plenum like effect?

IDK to be honest just throwing another viewpoint on the heap.

probably best to have it swap once you get meaningfull boost, say 2.5-3k rpm.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Thu Jun 11, 2009 11:26 pm 
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TROYMAN wrote:
im curious if the torque would still be higher between 3000 to 3800rpm on long runners under boost compared to it being on short runners at 3000rpm up?
the good thing about the ems ecu is the change over point can always be changed..


Troyman, sounds like you'll need to do some experimenting with the stinger once its installed and finally running nicely! I'd definately be interested to see what effect different change over points would make.

Grimketel, you have an interesting point. If boost is being made at 3000rpm, there may be no benefit in swapping to the short runners? I guess in this case the standard switch point is best, as this allows good NA style driving characteristics when driving off-boost.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Fri Jun 12, 2009 8:43 am 
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DA22LE wrote:
twr7cx wrote:
DA22LE wrote:
In your case, as you know, i would have 2 1/2' from blower to the T/B. I think this will bring boost on a bit sooner.


Yes, reducing the volume of air between the supercharge and throttle body will cause the boost to start earlier and the maximum boost level to increase. But there can be downsides to this too...

Yes.... but nothing a good tune and quality fuel wont fix.........


A tune cannot increase the maximum boost level or how early the boost comes on in a supercharged car. That stuff is physically controlled and limited by the pulley system and volume of air between the compressor and engine.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Fri Jun 12, 2009 8:50 am 
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TROYMAN wrote:
JoeXR6 wrote:
The 3800rpm switch over point is determined by the factory as the best spot in a NA application. Do you think it would be fair to assume that as soon as you're on boost, you want to be on the short runners?

The guys with centri SC's would find they're making decent boost at around 3000rpm. Mine is certainly making around 3psi at 2500rpm. So would '3000rpm' be a better switch over point for the supercharged I6's?

Joe


hmm you make a good point there!
mine also makes aproxx the same boost.
so you think changing it over at 3000 would be better??
im curious if the torque would still be higher between 3000 to 3800rpm on long runners under boost compared to it being on short runners at 3000rpm up?
the good thing about the ems ecu is the change over point can always be changed..


As soon as you are on boost you want the short runners as this will reduce the volume of air, meaning more boost (probably not significantly more, but more all the same) - the longer runners will provide no advantage at all when on boost (but they will provide a disadvantage of more air to compress, therefore lowering your boost level slightly).
Find out what rpm boost comes on and set the BBM switch over point there.
The only advantage I can think of for retaining the higher RPM switch over point though is for when your cruising around not on boost and not booting it, but then who cruises at 3,800 rpm?
But as you say, you can always change over the RPM point so have a play with it.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Fri Jun 12, 2009 8:55 am 
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Grimketel wrote:
However, I do recall reading something about when its on short runners, the long runners are also active? and this may have a plenum like effect?


You raise a good point, one which I didn't previously consider, that when the short runners are open the long runners are still open too, giving a greater volume.
Problem with having a plenum effect is it means that there is more air to compress, more air means boost will come on later (as more air takes longer to compress to the same level, so more rpm is required) and your maximum boost level is reduced. However, with that said the volume of the runners isn't that great, so not going to effect it greatly, but theoretically, it's best off going to short runners only - but that's not possible as the long runners still stay open.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Fri Jun 12, 2009 1:10 pm 
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twr7cx wrote:
You raise a good point, one which I didn't previously consider, that when the short runners are open the long runners are still open too, giving a greater volume.
Problem with having a plenum effect is it means that there is more air to compress, more air means boost will come on later (as more air takes longer to compress to the same level, so more rpm is required) and your maximum boost level is reduced. However, with that said the volume of the runners isn't that great, so not going to effect it greatly, but theoretically, it's best off going to short runners only - but that's not possible as the long runners still stay open.


only way to find out is hire a dyno for an hour, do some runs with the bbm left on long runners, and then short runners, then stock. see which one performs best.

i dont think it will take much to boost the BBM on short runners. the volume isnt that much, and you already have some boost pressure in there as it rises in a linear fashion. By the time your at 3k rpm, making good boost, the BBM will already be under abot 2.5-3k psi, which means its got good pressure, and you shouldnt loose any psi filling the BBM.

 

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 Post subject: Re: bbm switching and supercharging.
Posted: Fri Jun 12, 2009 10:02 pm 
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I think you'll have to mod the BBM actuator to work on boost..
As there wouldn't be any vacuum to activate it !!
When on boost..

 

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