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4.6 inlet on a 3.5?


dave88sw

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Hi,

I'm in the process of converting my dads V8 defender to megasquirt.  The engine was a 3.5 flapper from an early range rover so we sourced another inlet manifold with the later injectors.  The manifold is from a 4.6 gems V8 P38 Range Rover.  I'm at the stage now where the loom is made and i can fit the plenum but I'm not sure about the trumpets.  Is there any reason why I shouldn't use the 4.6 trumpets on a 3.5?  I understand they're different lengths depending on the engine size but what are the upsides/downsides of each?  I still have the 3.5 inlet i can take the trumpets and base plate off if necessary.

Many thanks

Dave

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I doubt it will make much/any difference, but you can pretty much mix & match it all barring minor details that should be obvious with a bit of squinting at it.

The flapper bottom section will have different drillings/tappings for sensors, the base plate with trumpets will have different ports for the brake servo etc. and the plenum has a different idle valve etc. although the basics are about the same.

Biggest pain really is just making sure you have a one-way valve takeoff screwed into the base-plate for the servo, the flapper will have this, can't remember if the P38 does.

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I have a 4.6 plenum and manifold on my 3.5 because I like the neater stepper valve arrangement. Pretty sure I kept the flapper ram housing because I was being lazy and didn't want to swap all the threaded connections over for vacuum takeoffs for map sensor, fuel rail, brake servo etc when I performed the swap from full flapper arrangement.


I *think* I read somewhere that the 4.6 trumpets are closer to the top of the plenum to cause faster airflow at lower engine speeds and increase torque, but I could be wrong about that, and have never compared myself to validate this.

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On 3/3/2019 at 10:17 PM, FridgeFreezer said:

Biggest pain really is just making sure you have a one-way valve takeoff screwed into the base-plate for the servo, the flapper will have this, can't remember if the P38 does.

The P38 uses an hydraulic booster instead of a vacuum operated brake servo. So o take-off or one-way valve present in the base plate. But should be easy enough to swap over.

I agree with above it probably wont make a noticeable difference which one you use.

Filip

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I hadn't considered the servo take off - which is stupid really, as i owned a P38 not long ago...

Thanks for all your replies, i'll mix and match the bits to end up with everything i need, but it sounds like i can't go far wrong with it.

Thanks

Dave

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