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Discussion Starter #1
For a while now, I´ve been thinking about increasing the throttle bodies on the M5. This past weekend, while doing a front suspension overhaul at a friend´s shop, I spoke to one of the mechanics who works in the Brazilian Trofeo Maserati Cup. He said that it would be relatively simple to send the throttle body to a specialty shop to get them milled. The 3.8L comes with a 50mm throttle body (3.6L is 45mm). After taking some measurements, we got to the conclusion that they could be grinded on the inside until they reached 53-54mm tops. An extra millimeter would make the throttle bodies "paper thin".

We also compared the throttle body on the 3.8L with the e39 M5 throttle bodies. The latter ones are worse!! They have smaller outtakes and are curved, The ones in the 3.8L are straight and have a larger outtake.

Has anyone grinded their throttle bodies in the beast. and if so, has there been a noticeable increase in power? Could there ever be a case where increasing the throttle bodies leads to a power loss?

Thanks!!

I have been informed that a local racing shop charges US$100 per throttle body, so I would like to know if this is really worth it.
 

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There is a guy in the UK who bores throttle bodies out. I havent seen any results on an M5 however boring the single throttle body on an E30 325i does have great results. Dyno's have shown about 7 bhp increases on these.

Also, the same guy has bored E30 M3 Throttle Bodies and again there are good results. The E30 M3 engine is based on our M5 engines so that leads me to the conclusion that the m5 could benefit from this also.

However, its not as simple as that. If you increase the bore size you might decrease airspeed. This may not result in lost top end power but it will change the characteristic of the engine by giving more midrange torque and taking away the Peaky nature of the S38.

Personally I think the 3.6's could do with boring to 50mm, the results would be very very good there. As for the 3.8, someones going to have to try it.

I hope this helps.
 

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Well, instead of boring from a 45mm to a 50mm, it would be much more sensible to install the 50mm factory pieces as they are already bored and matched properly for a 50mm diameter, whereas the 45mm bored to a 50mm would probably mismatch a bit. Not enough to cause drastic consequences, but for the sake of completeness and detail, it might not be a bad idea to look into it. I know several of the E30 M3 guys try to go to a 48mm Sport Evo or 50mm M5 throttle body instead of boring out the 46mm piece as they line up much better and provide better flow characteristics. Just some food for thought.
 

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Very good point.

However, are the ports in the head in a 3.6 different to that of a 3.8? If they are then surely upgrading to 50mm would be waste of time......or not?
 

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I don't know for sure but having the S38 head ported and polished is a must do when freshening up the old heap. :M5launch:
 

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Pepmeister
IMHO I would not mess with the intake or exhaust headers on an engine that is in such a relatively high state of tune. The intake manifold is a vaccum operated variable volume system. The swept volume of air within this manifold in its open /closed position is dependent on engine speed & load.
If you open the throttle intakes beyond the current size of the indiviidual swept volumes you could introduce an imbalance in the torque / power curve as another board member has mentioned this may change the air intake port speeds,
That could introduce a flatspot or additional air intake resonance noise.

An engines specific output is limited by how much air & fuel it can consume.
The variables being where you limit the rpm (usually based on engine configuration and materials used) & intake & exhaust efficiency & local market emissions contols to name but a few.

Manufacturers use CFD analysis (computational fluid dynamics) for the theory side & dyno test to validate their results.
The tuning fraterntiy may use the above but in addition may use a flow bench for individual component test validation but this in isolation does not tell the whole story.

Steve Dinan is a sensible Guy whose Engineering skills on intake & exhaust efficiency are worth discussing with for the sake of an email or phone call.

Either way, if you opened the intakes over std you would need to increase the exhaust ports to benefit from the extra flow, but if the engine has already been optimised as indeed it would have to be maintain a stable fueling calibration then gains would be minimal.

I have a view that if increasing the port tube size would bring improvements in power & torque without sacrificing other drivability aspects, BMW would have done it. They are quite a good bunch of Engineers are'nt they.....

I have some experience in this field of engineering. I hope I have added something of use to this thread without making it sound like I have swallowed the Bosch Automotive handbook.....(currently on its 5th edition BTW) hiha

Leave it as it is my friend.

Regards
Farrell
 

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Excellent info there.

What about if you got a remap done along with the bigger bore throttle bodies, surely that would get rid of any running problems.

E30 M3's have benefitted from this everytime but a remap is essential.
 

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Discussion Starter #9
Thank you for your answers!

I guess it´s better to leave it alone then...

I am not willing to have a slightly more powerful car with screwy acceleration/driveability.

It would be interesting to talk to someone who has done this on the S38B38 though...
 

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There is nothign wrong with this sort of modification! But youll need a remap and it will yeild improvements.

The theory that, "why didnt BMW do it in the first place" is nonsense.

Why is it that on the E30 M3 they continually developed it until the final M3 Evo.

Why did BMw bother building the 3.8?

Why is it that adding a big bore throttle body to say a 325i E30, 328i E36 makes a big difference? Why didnt BMW think of this before? I dont know the asnwer but the point is that it makes a diference and once remapped the car is usually much better to drive than when standard.
 

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I think that you'd need to modify both inlet and exhaust ports as well if you opened the bodies up a bit, as farrell has pointed out. If you were to go to all that trouble you'd be better sticking a charger on it, surley any porting gains are going to be slight and with the cost involved probably not worth it on the b38 anyway. It is worth remembering that the theoretical swept volume usually only applies at lower engine speeds and volumetric efficiency is not as good at higher rpm, so getting a greater flow of fuel and air is the answer for top end power, I think charging is the only way to achieve that effectivley. I assume that directing more air, i.e. a ram pipe at an aftermarket filter doesn't make much difference ??
But it would be interesting to find out if somebody has a spare set of TB's to bore out.
Cyrus, you are saying that remapping is essential to make any chages work, I was wondering if you can remap the standard chip or do you have to fit a specialist chip to allow remapping to be done.

cheers,
Phil
 

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The theory that, "why didnt BMW do it in the first place" is nonsense.

Why is it that on the E30 M3 they continually developed it until the final M3 Evo.

Why did BMW bother building the 3.8?

Why is it that adding a big bore throttle body to say a 325i E30, 328i E36 makes a big difference? Why didnt BMW think of this before? I dont know the asnwer but the point is that it makes a diference and once remapped the car is usually much better to drive than when standard.[/QUOTE]

Nonsense eh..
Does the E30 have a variable volume air resonance air chamber bolted to its intake ?
Does the 325i have individual throttle bodies for each of its intake tracts ?
Does it still pass an emission test.

What is the specific output of the 325 per litre ?
Its not 80 plus bhp per litre is it....!
The gains become small & the cost larger when you strive to get past 80 bhp per litre from an naturally aspirated engine

The M5 is & always has been a road car , not a homologation race development programme that the M3 was.

The E30 M3 & all its subsequent evolutions was a constant race to meet ever changing homologation rules with increased power & rev limits.

Often the larger throttle bodies used did nothing for drivability. infact they often only benefitted the car in race trim with raised rpm limits. Drivability was sacrificed for outright performance

The 3 door RS500 Cosworth is a good case in point. slower to 60 than the std 3 door car. Its larger throttle body , T4 turbo, larger charge cooler & redundant extra set of 4 injectors & rail made the car laggy & unresponsive. An air to air chargecooler improved intake chage temp efficiency & gave a 220 bhp as opposed to 204 bhp but in race trim with a pectel engine management system running 8 injectors & 37psi absolute manifoild pressure , the larger throttle body worked a treat.. (540 bhp in the last Trackstar cars I believe which were bought from Dick Johnsons Aussie touring car victories)

Race cars & road cars have vastly different requirements

Did I mention emissions....!

I dont subscribe to the nonsense comment. I have earned my living as an Automotive engineer within Tickford & Aston Martin for 16 yrs.
I studied Mechanical Enginnering at University.
I work on hard facts & Data from test & development to arrive at a conclusion.

I dont slap a Magnet on the side of my car & drive through Halfords to see how many go faster bits I pick up on the way.

Its just a fact of life that unless you have made a contribution to developing a vehicle that meets all the Criteria of power emissions & durability a lot of words fall on doubting ears through & that is precisely why I only post once or twice every couple of years.


Regards
Farrell
 

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Nice long answer.

I dont in any way doubt your experience and alot of your points are very valid.

Let me make it a bit clearer why I made the "nonsense" comment.

Lets just take one example. The M52 2.8 engine from the E36 328i and 528i.

Gives 193 bhp and about 204 lb.ft. Not alot considering the 325i gave roughly the same BHP. iTs now common knowledge that due to german tax laws BMw wanted to keep the 2.8 under a certian bracket and hence detuned the engine in more than on way.
Bmw could have got alot more power out of this engine and kept within emmission regulations and had much better driveability. Alot of people are fitting modified 325i inlet manifolds, getting remaps and fitting slighlty uprated cams and getting inbetween 220 bhp and 230 bhp. The driveability is hugely increased, fuel economy is still the same and emmissions are if anything better.

This is not the only engine BMW has made which is "detuned" and could have been much better. Same engine, M52 323i, 523i. Its a 2.5 and gives less power than the outgoing M50 2.5 engine! A whole 22 bhp less!

The E30 325i's have dyno proven peak power gains of 7 bhp with the bigger throttle bodies (17% more cross sectional area). Again, emmission unaffected, better fuel economy and noticeably better driveability. With a sensible remap (not done for the track and not one that takes the car to its limits) it gives a much enhanced 325i.

The M5's, surely if you take some of the good bits from the 3.8 and usethem on the 3.6 and then get a "sensible remap" done its going to give enhanced driveability and a hike in power throughout the rev range.

I dont think im entirely wrong in my statement.

Conclusion: IM not entirely wrong and nor are you.
 

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Cyrus
What you say makes good sense in the context you have written. Bad day yesterday.
Sorry I bit at you.
I apologise.

I had heard of the 325 's response to this mod & the market forces behind why it could be successful. Your point of fact is much clearer.
Messing about with the fuel lookup tables can improve matters to.

Please consider that that in the 325's case the engines specific output is over 20 bhp per litre less than a 3.8 M5. Even when you modify an 325 as you describe using the upper end of the output figures you describe you are 10 bhp per litre short of our 3.8

The intake system on our cars caters for varying engines speed & load by
vacuum actuated internal geometry change thereby maintaining intake velocity in much the same way the race cars would use different length velocity ramstacks to improve air flow into the combustion chamber.

I believe that BMW tuned this system to give the best of both worlds.
To improve upon may be possible but you would need to dump the whole intake system & a new ECU calibration as you state would be required.
To gain how much....?

There is also the consideration that climates & altitude have a major effect on performance as does bad / indifferent servicing so that a fuel map from the OE will take account of these aspects so its not unusual for the more mainstream vehicle engines to have some reserve there. The currrent crop of engines are being stifled by Global tier 3 emissions which are strangling performance even further. BMW as others are increasing capacity but maintaining performance is the main goal.

The 3.8 is knocking on the door of 90 bhp per litre.
The changes over the 3.5 to get what amounts to an 8% improvement in performance were far reaching. Ignition system, compression & valve size changed. different engine management system. Im doing this from memory but that is not the half of it.

I would like to say that the 3.8 is a vastly superior performer than the 3.5 just beacuse I own the later :haha: but if im honest, when driven hard, I cant tell much of a difference between them performance wise.
Sorry fellas, maybe you can but I cant...

So which parts would you swap from 3.5 to 3.8 to get what amounts to an 8% gain even if you included every internal mod. (Even the cats on both are metal matrix with a very thin wash coat on the substrates to allow less restrictive gas flow)

I guess it boils down to the fact that I dont want you guys on the Forum from whom I have had a lot of laughs & learned a lot (Ivan D, Raymond W & Gustav in particular) doing a load of stuff to your cars that could end costing considerable sums to put right that did not need fixing in the first place.

Happy Christmas & again sorry Cyrus.

Regards
Farrell
 

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No offense taken Farrell.

Again youve raised some very good points and its clear that just messing around with only one of the beter things the 3.8 has is not really going to do much because the 3.8 has so much mroe other improvment and only yeilds a small percentage increase in power.

Ive been in a 3.8 recently and to be honest I didnt feel that much difference when flat out. Yes there was a defintaley more Torque through the rev range on part throttling but flat out.......the 3.8 might pull 2 car lenghts to 120 mph.

I did feel that the 3.6 was much more of a screamer and had to be driven properly to get the best out of it.

IM at a slight advantage because I have no Cats on my car because the previous owner removed them.

I think a remap however is a great idea. These are mostly old engines now with wear and tear. Therefore its not a bad idea to adjust the fuelling to cater for this. A good mapping techinican can bring alot more out of a car and retain the driveability. I find that too many people map cars to get best performacne out of them, they push the engines a bit too far and hence reduce longilivity.

Happy Xmas:M5thumbs:
 

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Discussion Starter #16
Hi Guys,

You both have valid points, I am still leaning towards the more skeptical side though. On the other hand, check out this 3.5L M1 engine (480bhp). You can fit your hand inside those throttle bodies!!
 

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Hi there guys

I am of the belief that the original set up of the engine can be improved, but at what cost ? and how much would be gained ?

Regarding what BMW did to the S38 engine when they brought out the 3.8 litre version in theory you would have expected larger gains, but as farrell pointed out BMW had to do this maintaining reliability and meet emission standards ( you have to bear in mind that the emision test procedures through which a manufacturer has to pass are far tougher than the subsequent tests on a MOT )

You have to look at the whole picture, and take into consideration what resources where available at the time of the design that could be implemented at reasonable cost.

Take for example the M5 3.8 engine introduced in 1992 aprox, developed 340 bhp versus the E46 M3 3.4 engine develops 343 bhp.

The major diffrences between these engines of the top of my head that allow the later M3 engine to develop more power are :

* higher compression ratio ( but in order to allow this to be done reliably it requires knock sensors, and 98 octane fuel )

* Variable cam timing on inlet and exhaust cams ( BMW fitted double vanos )

* higher revs ( rev limit is almost 8000 rpm, bmw here got its sums wrong in the first place , how many early M3 engines went bang, quite a few, I believe )

Obviously the whole engine was optimised, and still managed to pass all its emissions test, etc, but if you study both engines designs you would see that BMW went to a lot of trouble before they got there.

Now back to reality, what can be done to improve the performance from the 3.8 m5 engine, you would have to strip the engine and see in which way the volumetric efficiency could be improved.

Things that can be done:
* Raise compression ratio slightly this will allow the engine to produce more power and torque, but you cant go very far here since there is no knock sensor, you will have to use 98 octone fuel all the time

*Gas flow the cylinder head, valves, inlet and exhaust ports, match all ports, remove ridges etc, this will allow the engine to produce more and torque, but the gains will be at high rpm mainly

*Install different cams, like the schrick 280º units, expect some slight loss power and torque at low rpm and some gains from midrange to rev limit cut out.

* Remove original induction system and fit carbon fibre airbox without MAF, this will require new engine management system and complete remaping. (this set up may well provide significant gains with the previous modifications)

What can you expect from these mods, well your engine will develop somewhere in the region of 400 bhp depending on how well the modifications have been done and how well the engine map was programed.

The biggest problem is the fact that all these mods would probably exceed the value of the car and make them a no go.

I would love to mod my engine, but has anyone consired the amount of induction noise the carbon fibre airbox in conjunction with a free flow air filter set up, it could be very noisey indeed and make the car quite tiresome to drive over long distances, High compression pistons, no one makes them of the shelf, so you would have to have them custom made, that wont be cheap either, I wont bore every one with the details, but in my opinion due to the lack of tuning components available of the shelf, perhaps the most sensible set up would be to have the head gas flowed and install schrick cams and have engine remaped to make the most of it.

Regards

Joe Rubido
 

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Yes... Flow the heads, cams, remapping.
That's what I intend to do come rebuild time.
It's good for significant power improvements, and not all that expensive.
 

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jrturbo said:
Hi there guys
.......
......biggest problem is the fact that all these mods would probably exceed the value of the car and make them a no go.

I would love to mod my engine, but has anyone consired the amount of induction noise the carbon fibre airbox in conjunction with a free flow air filter set up, it could be very noisey indeed and make the car quite tiresome to drive over long distances, High compression pistons, no one makes them of the shelf, so you would have to have them custom made, that wont be cheap either, I wont bore every one with the details, but in my opinion due to the lack of tuning components available of the shelf, perhaps the most sensible set up would be to have the head gas flowed and install schrick cams and have engine remaped to make the most of it.

Regards

Joe Rubido
----------------
Hi Joe

After having done the cams (a quality job by BMW), Race kats again by a quality company that only do kats for a living and then a UNICHIP on a rolling dyno, I can quite honestly say I am extremely happy with the cars performance and reliability.

I would consider porting the cylinder head but am still recovering from the cost of the above work, I think you are right - get the cams, kats and remapp - this should be enough to make what was once a broad smile into a ear to ear learing grin!!

rgd

J
 
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