325i cab power increase !!

My source is Ahmed Khan (programmer for BMW)

I don't have an argument on chips - I have one in my car and there are improvements as demonstrated on a rolling road!

What is your source re. the M20 with 191bhp? For a 2v/cylinder basic engine, that's 76.4 bhp/litre which I would seriously doubt.

chippeduk wrote: You can dissagree, thats an opinion and perfect for forums but the fact is, you fit the ported throttle body and you will notice the difference right away, not only top end but throughout the rev range.

Yep, but the problem is that I have never seen fact - only peoples opinion. I'm an engineer, so I need to be otherwise convinced of opinions (by explantion) to change my point of view. There is no logic in what you say given that a throttle plate, an airflow meter flap and a valve (or two!) with its inlet tract are also in the way.

I always wonder why BMW picked specific sizes for a throttle body. Narrower pipework keeps the air flowing faster and there are other possible resonant aspects too. It could be possible that increasing the throttle bocy aperture would reduce power!

nice !!

evo motor i presume ? 

tbh if performance was really the biggest issue with the car  we wouldnt have bought it , but we do feel its a little sluggish hence the post .

i think its probably gna end up with a cam and a chip as long as it keeps its driveability we,l be happy . if it was a real performance issue i,d be looking at doing a low comp turbo conversion or the twin supercharged jag v8 but it really isnt worth it .  i think i have spoilt myself by driving  really fast cars like my saff and now it allways feels like everything else is positivly slow . 

 

 as for high power e30's , one question ,,,,  what diff , g box would you use ? surely the e30 stuff wouldnt handle it too well ?

chippeduk wrote: Mind you, i`m probably a joker who is making a wild guess at all these claims :D

Well we didn't want to say anything

Only kidding, but you're right about that level of modding, just not worth it on the M20 IMO, if i was at a stage where i needed polishing and head porting then it'd have to be on a multivalve engine to make it worth my while.

hehehehe.

I know all about race engines and builds.

The FACT is there are not worth the high costs when modding the M20 head.

If dave walker could only get 2hp from this head by porting and flowing then you tell me someone who can get much more.

Of course this does not relate to all engines, My escort cossie saw 14hp from head work (not cams) so i know how they work but this thread was about the m20 head.

 

Anyway, back to the throttle body.

You will definately see a gain throughout with the ported throttle body.

Having said that, the gains felt when driving are more spectacular.

I am yet to find someone who has done this and said they didnt notice the difference, if you know of anyone please point them here to explain. 

chippeduk wrote: Hmmm, now for the proper answer. The ported throttle body will give you far greater pulling power throughout the rev range and it is noticable. Porting the head is worth 2-4hp (if you manage to make power) I had a 3 grand head The m20 and m30 heads are very good standard.

 

With respect, that thing about the TB is a load of cobblers. The engine wants to fill it's cylinders all the time that it's running. The throttle attenuates the flow so that they only partially fill and the engine doesn't rev it's big-ends off all the time.

Now, make the TB slightly better at flowing gas and all you'll get it slightly better power for a given throttle opening, but the power at a given engine speed it likely to be exactly the same as it ever was.

Only when the TB becomes a restriction in it's own right, at wide open throttle, will you notice a gain.

Also, the TB is bolted to a sand cast aluminium inlet manifold which is rough as a bears behind and doesn't exactly aid gas flow.

 

I'll admit that different heads respond in different ways to porting. However, if you paid £3k, then you were stiched up like a kipper! For around £700 you can get a reputable company to port a 16v head to race spec (none of this stage 1,2 and 3 <rap) so a 12v shouldn't be any more expensive.

Again though, the specific power output of these engines isn't anything to write home about and that's because they were mass produced with no particular attention being paid to the finish of the relevant bits.

chippeduk wrote: Hmmm, now for the proper answer. The ported throttle body will give you far greater pulling power throughout the rev range and it is noticable.

I disagree in the absence of other breathing mods. I have never seen evidance of this and it makes no sense anyway other that WOT given a throttle butterfly being in the way...

The E30 one won't dude, it needs the AFM and it can't interpret a MAF, but it think you buy the box which interfaces between the two. 

Edited by paul325i

I'd use a Schrick cam, the increased size throttle body, have a MAF fitted instead of the AFM then you'll have to use stand alone management to run the fuelling, that last option won't be cheap but i've seen it in a car and felt it, sounds wicked to!

Best to have it mapped on a rolling road by a reputable firm if you're after then best gains, if you want to move the power band up the rev range then fit an aftermarket exhaust.