Intake Manifold, Throttle Body and Intake tubing design.

[Ruger099]

Hi all first post here stumbled across this gold mine of a forum through google. Awesome stuff.
Now to business.
I own a Ford Falcon BA and am looking at setting up a good intake manifold, throttle body and pipe work combo.
These falcons have a 4.0 I6 and come factory with a dual runner style manifold. it has a short long runner system, long runner for low down torque and short runner for up top in the rev range (its activated by a vacuum actuator which gets its signal from the ecu. the changeover is 3800rpm and rev limit at 5750rpm)
I dont look to modify the dual runner system at all i think its a great thing, its mainly the plenum area and throttle body size.
In the past i had a twin 70mm throttle body manifold made up but that didnt quite work. the car drove like a pig (the dual runner system was gutted for extra plenum area and there was a stack of electrical gremlins also)

My main questions are: If i extend out the manifold i will be able to enlarge the plenum by about half a litre or 1 litre maximum. Will it be worth it? The stock plenum - i cant see being any more than 3L.
The standard throttle body is 70mm. Aftermarket options go to 75mm for this particular engine. No great gains have been reported using that throttle body on the standard motor though. If i modify the manifold to make the plenum chamber area larger i will be cutting out the section where the throttle body mounts giving me an opurtunity to fit any size or style throttle body i wish. what should i do in that regard? i was thinking along the lines of 80mm or so. Thats just a number in my head though no facts put into that thought.
Is there any way of determining ideal throttle body size and flow?

The car is a street car but the motor will be as wild as i can get it (hoping upwards of 350hp, its about 310hp at the moment). with this particular motor there are no real aftermarket options for cams whilst headwork is another grey section. So that can limit me also. Im hoping this is the last time i get a manifold built because its not a cheap excercise.
For referance the motor is also fitted with race style extractors, a free flowing exhaust system and underdriven balancer.

Thanks for any help in advance.
Advice and criticism welcome
Regards,
George

 

[Ruger099]

Also (can you edit posts here?)with the induction pipe its fairly long and has a tight 180degree bend just before the throttle body followed by 10cm of straight pipe then a 45 degree bend followed by 35cm of straight pipe to the filter.
Am i right to assume this setup is not ideal?
If i relocate the battery i can have the intake pipe about 10cm shorter and with only 1 45 degree bend in it. Would the gain be worth the effort and cost involved of relocating the battery. A problem with that setup though is it will go right over the extractors making insulation mandatory. any ideas on this?
Myth has it these motors are designed for low down torque thats why they placed the throttle body where they did and made the induction pipe so long. Does that make sense? will the longer induction pipe improve the low down torque?

 

[patprimmer]

I am not sure of your terminology, but as I understand it:-

These engines have quite a long stroke, so the factory will tune them to perform best at durable piston speeds. I think this is about 6000 rpm max.

The Aussie 6 is also required in the minds of a large sector of the market to have towing capacity.

This means a nice wide power band is required and the power must start to fall of noticeably as 6000 rpm is approached.

75 mm is a 15% increase in cross sectional area, not exactly a wild modification.

80 mm is about 30% increase.

A quick calculation suggests 70 mm is not all that small, so increases wont help all that much.

Keeping the airduct from the air filter to the throttle body reasonably straight and bigger than the throttle body helps, but keeping the air cold is much more important.

I think this engine has a 4 valve twin cam head. You could get more top end power by closing down the lobe centres a bit and generally retarding valve timing.

Increasing plenum from 3/4 of engine capacity to about engine capacity still won't help much.



Regards

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[GregLocock]

To increase the power output you either increase the red line, increase the VE, or reduce the back pressure, at the max power rpm.

That's it, is it not, if you are not delving around in the combustion process itself?

I'm inclined to think that messing about with TBs is likely to be a waste of time, but I suppose at the max power point they would have some effect.

The intake setup is likely to be arranged to develop sufficient torque at low rpm, and headline-grabbing power at or near the red line.

So, the chances are that the low speed manifold setting is probably over optimised (for your purposes) towards low speed torque, and you would be better off junking the BBM and developing a more highly tuned log and runner style of intake, if your sole concern is max power. If you increase the size of the log then your end reflection effects will be a bit bigger, so your peak VE will improve, at the expense of a narrower powerband.









Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Ruger099]

Yep, this six is a long stroke motor, 99mm stroke and 93mm bore, 4V DOHC head with VCT. So its pretty high tech as far as the aussie Ford I6 goes.

You say the low speed setting would be over optimised for my purpose? i can adjust where i want the cross over to be without a problem.

Basically the only way to go is for a log style manifold? There are 2 or 3 companies that are doing this for the NA 6. Basically they are using the same manifold they use on the turbo and just bolt it to the NA donk. The result is usually about 10-15kw max and the car is gutless under 4000rpm. That would be fine if you could rev it past 6 but the cams run out of puff at about 5500-5700. So a 2000rpm power band in a 1800kg(near 4000lb)isnt all that desirable.

I was hoping to pick up maybe about 10kw by extending the plenum, fitting a larger throttle body and straightening up the intake pipe. I really dont want to get rid of the BBM setup because it is a big heavy car that needs the broad power band that manifold provides. is my 10kw or 12hp achievable by modifying this manifold?

How can i work out the flow demand for this engine? i figure that will help to determine ideal throttle body size.