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My 4.8is

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Hi there. You guys on here allseem to know your stuff about BMWs so I'm after some advice. I own a 2005 4.8is with 90k on the clock. The engine is factory standard. What would be the best engine mods to do to gain a good bhp boost without it running rough on idle and sluggish through the gears. I have about 5 k to spend at present. Ideas please. Many thanks. Ricky lazenby. riklazsgn@gmail.com

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Hi rik. 
a good dyno remap should see ok gains. 
for 5k i would guess a low pressure turbo kit wouldn’t be too far out of reach?

how handy are you with the spanners? 

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Good afternoon. 

Thanks for your reply.. I'm not mechanic atall I can change a wheel and that's about it. A Dyno remap stage one is looking at a 20 bhp gain and that's about 300 quid. What do I do with the other 4.7k lol.. 

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Morning Ricky

A normally aspirated engine (your 4.8is) will see an increase by an ECU tune alone but will never see the type of gains a Forced induction engine will 

So you need a target and a plan, Carol Shelby famously said "Speed costs money, how fast can you afford to go"

A good ECU tuner will need to know what other upgrades have been done in order for him to optimise them.  Look for a rolling road tuner so you will see printed proof of increases before and after. A cheap chip tune will rarely see the gains claimed.

Standard engine should be in the region of 350/360 bhp a rolling road session will let you know how many are there for sure and is your start point. I would look at intake and Exhaust to start. Bigger throttle body and free flow headers and Cats then back on the Rolling Road and and tune the ECU. If that doesn't give enough then more aggressive Cams but now your into engine work when I rebuilt my 4.6is 10 years ago now the engine parts bill alone was almost £3k if you are going to add garage labour then more than double that. I also added a Dinan Super Charger kit from the USA 

Also remember the Transmission when you reach 400+hp there is a lot more torque going through the Gearbox Transfer case and Diffs they need to be tip top or upgraded to handle the extra grunt, and last but not least Brakes and Suspension.

Good Luck with whatever you do



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Good morning.


That is brilliant information thank you very much. I am currently doing my homework to find out where I can get these bits done but take in to consideration the bhp and effects elsewhere on the vehicle so I will carefully consider my options. So I won't see any change out of 5k and it looks like I will have to find another 5k 😀

Many thanks.


Ricky lazenby 

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