classic 3.9 v8 (removing centre exhaust box)

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J

jeff

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Hi all , i have a 1991 rr 3.9 v8 ,

it currently has a cheap brit part exhaust system , which is very quiet, really i would like to be a bit louder , but no too loud if it makes sense lol

would it be ok to remove centre box and replace with a straight pipe , has any one tried this ?,

also was thinking of a K&n cone filter as the standard air box looks very restrictive ,

any help much appreciated , cheers
 
Just recently replaced the centre box on my 4.6 P38, would have put a straight through on if I could have found a cheap supplier but no luck on that front.

Was lookin at a page on rangerovers.net a few days ago about custom air filter and housing, more important things on my to-do list but might give you something to think about (as you wanna make sure you're getting cold air for the intake.)

4.0/4.6/P38A Air Box Replacement
 
You can remove the centre box. Makes it louder. Not sure what effect it would have on acceleration or top end. Probably not noticable though.
Personally I woud go for a full stainless exhaust with tubular manifolds. Give a nice exhaust note. And as fot fitting a k & n go for it. I have always used cone filters on all my vehicles. Gives a nicer engine note on full throttle. Plus the added bonus of having tubular manifolds, better exhaust and cone filter, you get a little gain on power.

Just don't go for a Double S system as I found them to be a bit ****e.
 
Removing the centre box is not worth while as it is that which helps to create back pressure for the engine to run correctly either replace with a whole system or just cut the back box off
 
Ive just bought a powerflow ss exhaust system on ebay with no center box and a rear box about 2/3 smaller than the origanal, im hoping to have it fitted this weekend and ill let you know how it sounds.
It might be worth trying powerflow to see if they will sell the pipe to replace the center box.
 
thanks for reply's ,
think i'm going to give it a try and see , i can make the pipe myself as all ready have a bit of 2.5" exhasut pipe, i will post up whats its like ,
cheers
 
:D:DI cut out the centre box and welded in a straight pipe so my 4.6 p38 so she could pass her MOT:D:D earlier on in the year, so far I have had no drop off in performance at all the only difference is the exhaust note which sounds allot better. Whether or not it would be different on a 3.9 I wouldn't know.
Hope this helps
 
Just finished fitting my powerflow ss exhaust, nightmare of a job !
nothing lined up correctly so i had to reposition all the exhaust
hangers.
Well worth it though, it sounds awesome, nice deep v8 burble.
 
well have replaced centre box with a straight 2.5" pipe now , sounds good , not too loud , not sure if it made any difference to power , but was worth it for the sound,
IMAG0350.jpg
 
I did a centre box removal on my old 3.9, made a big difference to performance and economy, sounded lovely outside but there was this awful bloody booming resonance at around 2000 - 2500 revs.
Needless to say it got revved up much more than before :D:D
 
Just got my first RR. 4.6 HSE.
It had a straight pipe with SS power flow back boxes.
Sounded far too loud for me so I fitted a standard setup in its place.
Old parts now surplus to requirements.
If anyone wants them, they are going free to a good home.
Only catch is that you have to pick them up from Wrexham.
Anyone interested?
Colin.
 

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Search through my posts, find one from feb this year called look what i made today. Got a good pic of the pipe i made for my P38 4.6.
 
Got a large cherrybomb centre and a motorbike style twin exit backbox....

I had to experiement put the right size/length decibel insert in the cherrybomb to add a little back pressure to get the engine to run smooth and stop nextdoor neighbours dog barking back.
Unfortunately that decibel insert now has a habit of rattling slightly on idle!
Homemade/custom systems can be a bit of a 'mare to be honest
 
BOOMER said:
I did a centre box removal on my old 3.9, made a big difference to performance and economy, sounded lovely outside but there was this awful bloody booming resonance at around 2000 - 2500 revs.
Needless to say it got revved up much more than before :D:D
Click to expand...

Big difference to economy in what way? More MPG or less?

Thinking of modifying my classic exhaust but i dont know the best way. These stainless exhausts look abit expensive for a cheapskate like me but she's just too quiet for me!

I have 2 separate pipes leading to the first silencer then they join to one, into the next silencer then back to 2 pipes. I was thinking of separating the pipes just before the first silencer and having one come out each side. Possibly with matching cans on depending on noise. I am unsure about the back pressure though.

I am abit wary of just chopping things about as i am unsure about the side effects on less backpressure and also side effects on MPG. I didnt buy the thing for its economy but i dont fancy making any changes if it will drastically change it
 
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