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Intake Manifold Modification 

 

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 Post subject: Intake Manifold Modification
Posted: Wed Jun 04, 2008 1:28 pm 
Tyre Shredder
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Hi All,

I'm interested to find out what the consensus is in modifying the bbm intake manifold (still don't know what 'bbm' means though) for forced induction.

I understand this manifold has butterflies inside, and swaps from long to short runners at 3800rpm.

The aftermarket solutions (for turbos) have a large plenum with throttle body at the front (short intercooler piping) and short runners. I guess this works well with a turbo that boosts early, meaning good plenum filling, and minimal bottom end doughiness, with heaps of top end air/power.

My car has a powerdyne SC, which doesn't begin boosting substantially til 3000rpm, so I think these large aftermarket plenums wouldn't work well in my application. I basically (I think - feel free to correct!) need the standard intake manifold's long runners to generate substantial torque below 3000 rpm to get things going. Does this sound right?

With this in mind, are there decent improvements available through modifying the standard intake manifold? What have others done? I'd imagine gutting it wouldn't be the answer for my application?

Thanks for the input.

Joe

 

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Posted: Fri Jun 06, 2008 6:44 pm 
Getting Side Ways
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Joe i'd say there's a few KW's to be found in there.
A boosted vehicle may not need the L/S runner deal.

 

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Posted: Fri Jun 06, 2008 8:06 pm 
Tyre Shredder
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BBM = Broad Band Manifold.

In the Raptor threads on the AU kit development, Tim mentioned that when the BBM switched over to short runners it flattened power during the early stages of tune development. Not what I expected... I'd have thought that you'd need long runners to about 3000rpm for torque, then short runners when boost comes in.

Maybe you could use the Motec to play with the point where the butterflies switch?

 

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Posted: Sat Jun 07, 2008 12:48 am 
Getting Side Ways
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In most boosted applications a bigger plenum works better with shorter runners...
So removing plates and shaft and milling out the two ports as one makes plenum bigger.. We have done it and engine doesn't seem to have lost any low end torque..Keep in mind any load ? The turbo spins into life fairly quick. 9.2 compression on std engines helps here too..Esp with throttle response..
Seeing there is some boost even at 1500 rpm with load.. I don't think the BBM really needs to operate.. The XR6T's don't have BBM plates on there manifolds...

 

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Posted: Sat Jun 07, 2008 8:10 pm 
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But Graeme the OP has a Powerdyne, not a turbo. I'd expect his engine needs the longer runners down low.

 

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Posted: Sat Jun 07, 2008 11:48 pm 
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BBM is 'broad band manifold'....thanks Sly. Does this mean anything in particular?

I'm still unsure if the gutted plenum will be an improvement for a centri blown car?

Graeme you mentioned the XR6T, from memory I think these boost quite early, round 2000rpm at about 7psi or something. I've never owned a turbo so I'm not sure exactly how they work, but I understand that once gas builds and they're spooled up, they're making full boost? So in the XR6T case, a full 7psi from 2000 - redline. I can see how this would negate the need for butterflies, as there'd be plenty of air/pressure filling the plenum volume from low rpm.

What do you guys reckon about a centri blower? In my case, the car is kind of NA before 3000rpm (not quite, it certainly doesn't feel like it). Basically I start making 1psi boost at 3000, 5psi by 4200, 10psi by peak rpm, 5700. So at less than 3000ish rpm, the engine is not recieving boost.

My thought is that with butterflies removed, and intake enlarged, there wouldn't be enough air pressure to use the plenum volume at low rpm = doughy bottom end. Would this mean gutting would be a bad idea? Or would the air being blown by the centri, even if not producing boost down low, be usable in an enlarged plenum through short runners?

I've got around 9.2 compression in my AU also. Cheers.

 

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Posted: Mon Jun 09, 2008 1:08 am 
Getting Side Ways
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Yea I knew he's runing Powerdyne..
Inlet manifolds are cheap as.. I'd try both .. In some mods especially N/A you can loose some low end torque.. BUT if you gain HEAPS more in mid rpm range ??.. It can over ride the lose.. Like you can still cruise around intersections in 3 rd gear etc... Like TE50's They lost some low end torque with there inducrion.. BUT after 1800 / 2000 rpm it more than makes up for it.. Yes thats V8 tech .. Just using as an example..
Keep in mind you have 9.2 compression..
There should be some pressure at 12 / 1500 rpm...Maybe enough to have short runners only ???
It would also depend on pulley sizes and blower speed...

 

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Posted: Mon Jun 09, 2008 1:25 am 
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What gains did you find with the opened BBM on your turbo AU?

Sly, that could be an option to change rpm that runners switch over. What rpm did Tim find worked the best?

I'd be thinking that switching to short runners when boost begins around 3000rpm would make sense as well.

 

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Posted: Mon Jun 09, 2008 9:51 am 
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It's all good.
Sounds and feels to me that something can be done here.

 

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Posted: Mon Jun 09, 2008 11:27 pm 
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JoeXR6 wrote:
Sly, that could be an option to change rpm that runners switch over. What rpm did Tim find worked the best?

I don't think Tim actually said, or whether they tried different RPM. Maybe the flattening effect was from turbulence due to the change of path.

I'll be able to experiment a bit myself when my blower kit goes on. I've found that on LPG and with the BBM vacuum line disconnected and plugged (leaving the short runners open), the response is flat until about 3200-3400 rpm. With the BBM connected and running LPG there's a bit of a dead spot between 3500 and 4000 or so, suggesting that mine should switch at around 3300 for LPG.

Anyway I'll be able to disconnect the BBM vacuum line and experiment with short runners with boost. All I then need is a way to change the changeover point if I find there is still a benefit to having the long runners up to a point.

 

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Posted: Thu Jun 12, 2008 11:37 pm 
Tyre Shredder
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Sly, where is and what's involved in disconnecting the vacuum line? I'd be keen to try this.

 

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Posted: Fri Jun 13, 2008 12:51 am 
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Vac line goes to mechanism on front of BBM... it has a black 90* connector IIRC. Pull it off, insert a joiner (4mm maybe???) into the vac line connector and put a cap on the other end of the joiner (unless you have something else to plug it with).

Will try for pics if that isn't clear enough. May not be til Monday though due to dogwatch over the weekend.

 

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Posted: Fri Jun 13, 2008 9:07 am 
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Thanks Sly, a pic would be helpful if you got a chance.

 

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Posted: Fri Jun 13, 2008 10:57 am 
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What do you guys think about this mod?

http://fordmods.com/forums/viewtopic.ph ... hlight=bbm

It's a 'ported' bbm. Would it be effective at all? I'd imagine that you could only port the ends of the runners, which would still be small diameter through the middle, meaning that any initial air flow improvement would be restricted anyway? I've heard of 'extrude honing' which I'd think would be the only useful way to port runners while maintaining the basic shape...

 

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Posted: Mon Jun 16, 2008 10:32 am 
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Any thoughts on the above modded bbm ? Its selling on ebay and ends soon.

 

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