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5.4 4 valve intake manifold question

18K views 18 replies 5 participants last post by  EECIV351C 
#1 ·
Hey guys just a quick qustion.
After much discussion with my mechanic (and usefull info provided by these forums) we have decided to build our own intake system comprising of a boss 260 lower intake manifold and twin 80mm fly by wire throttle bodies. The question I have is with the upper plenum chamber, is it true the larger you make the internal volume of the plenum the more torque will be made across the mid rev range and in general? Also I would like to utilise twin air boxes behind the headlights would the intake tube NEED to be connected to both throttles rather than a seperate tube for each throttle body? The car will be rev limited to 7200rpm, does anyone else have any ideas as to what would suit a N/A build like this?
 
#3 ·
The general rule for the plenum is large = HP,
smaller = Torque
Plenum volume matching displacement volume (5.4 liters) as a guide.
On the heads, the Boss heads are the same as our Cobra/Mach 1 heads
and are better suited for the motor tha Navi heads, although they will work..
 
#4 ·
ok so i'm aiming for my power and torque to be suited around the 4000rpm to 7000rpm mark. The motor will only ever be n/a (maybe some nitrous at some stage), the car is used for drag racing and is a 5 speed manual (I know slower in the 1/4 but so much more fun) I will post pics soon but at the moment i have no internet at home (work only and they don't like forums about fords when you work for M.A.N trucks). I'm trying to improve my 1/8 mile times and trap speed ant recommendations? The general consensus over here is to just bolt a vortech or K/B blower on and no-one is interested in n/a builds so any info from the people in the know about these motors would be helpfull
 
#7 ·
Have looked at the yella terra however for the price it works out far cheaper to simply fabricate a new top plenum chamber to suit my individual needs as the yella terra is also designed for use with the yella terra whipple supercharger.
 
#11 ·
G'day Darkshine,
Here's the setup that my mate Tony makes. It improves distribution substantially and you pick up torque and power through the whole rev range. This would be the shot for your engine and it means easy interface with the stock PCM. This actually works better than the 315 intake that has been referred to.
As for your suggestion...I think two 80mm t-bodies would just drown the intake plenum and throw away any port velocity you may have had. It's a bit like the old 5.0 where guy's would use 75+mm t-bodies on mild engines and wonder why the thing was a slug.
Cheers,
Pete.

 
#13 ·
Manifold is complete!!!! In the end i still went with twin 80mm units, box plenum with 7L internal displacement, front mount throttles smoothed the trumpet intakes and painted with ripple black paint. So far (by seat of pants test) coming on stronger throughout rev range, but the noise it makes is amazing and worth the effort alone. Despite what I said at the beggining of this thread the car WILL be turbocharged I'm not really happy with the results from the nos with the work that was/is involved so hopefully a high comp {11.2:1} single turbo will make this all worth it :). Next dyno tune is booked for 19/06 so I'll post my results and pics then.
B.T.W EECIV351C where did that manifold come from?
 
#14 ·
The manifold came from here in Perth. Tony made it out of a stock one. I'm trying to find a 2nd hand upper(or whole intake) at the moment so I can make one the same. There was one on ebay not long ago but the guy did the dodge with the auction(how unusual!?) so I didn't get it.
 
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