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I have been contemplating the M50b25TU vs the M52b25. The m50 has 141 Kw at 5900 and 245 Nm at 4200. The M52b25 has 125 kw at 5500 and 245 Nm at 3950. Obvious difference is the lower Kw number but the torque peak comes in at 350 rpm lower. What I cant see is the torque area under the curve which I suspect is greater for the M52.

Looking at the Cam specs they are similar:

 

M50B25tu 

228º

9.0

44º

228º

9.0

35º

13º

 

M52B25 

228º

9.0

44º

228º

9.0

39º

 

The compression ratio of the engines is 10.5 to 1 and both have 84mm  bore and 75mm stroke engines. The M50 has a cast iron block and the M52 alloy. The exhaut manifolds on M52's appear to flow better on an M50 but I am unsure what the restrictions past this are, CAT's? I am also unsure of head flow and valve sizes but I read somewhere that again they are similar. Lastly is the intake and this is a hoary old chestnut; M50 with big runners and M52 with small runners for better torque. The M50BTU has 140mm rods so less side thrust. 

So where is the extra 16kw hiding? is it purely the inlet manifold, rods or is it in the DME, do I just have to let it rev higher, after all 5500 for a Modern DOHC engine is pretty low, pushrod territory. I am asking as I am considering an m52b25 E36 for 2k Cup and if there is some cheap free HP hiding somewhere I would like it. 

Edited by Herbmiester
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M52 b25 runs the 2.0 manifold I believe and some very boring tuning. 

The difference in real world torque is negligible, the m50 is the nicer to drive of the two. 

The rod to stroke ratio is certainly better with the m50 but with such piss poor cam specs and low rev range your advantages of tdc/bdc dwell time and cylinder filling is really not a lot at all. 

As far as I know the valves are the same between both variations of 25 and the b28 also

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they use the same head etc .

only real difference is in the manifolds and tunning of the ecu

if you fit a m52b25 in place of a m50b25tu and hook up all the m50 stuff , it will make the some power and torque as the m50 did

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Its very easy to get more power out of the M52 , the primary  issue is it is choked on the exhaust side , despite the headers being marginally better than the cast iron M50 headers , do that and allow a bit more air in ( but don't use the M50 manifold) and  you can easily get the power of the 50B25 but with  a much fatter torque curve and  a re-map  will be beneficial. 

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Yes I thought their would be exhaust side issues but as the car is destined for 2k cup I am rather limited as to what I can do on the exhaust. As to the inlet I am not thinking about an m50 at this stage as any potetial increase in HP will need an accompanying remap to make it worthwhile. As it will be predominantly a track car the loss of torque vs gain in hp and revs needs further consideration, an extra 5 to 600 rpm could be beneficial. 2k cup rules are interesting as they have just moved from cc based classes to power to weight classes, might give the heavier BMWs a chance agaist the lightweight Jap cars that dominate.

 

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Steal someones M3 3 litre headers - my M52B28 pulls 7 grand with 'stock' intake manifold and M3B32 exhaust  system - the smaller section 3 litre pipes are a good match for the B25

I'll see if I can find the dyno 

Edited by 3pedals
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Here is the dyno  with  just the exhaust done this  shifted max power to 5,700 Rpm from 5,300  a few more upstream mods since this have seen max power shift to about 6,300 RPM . What is also eliminated is the dip at about 6 grand on the stock exhaust. 

 Note the red dyno line already had some intake work done upstream of the intake manifold which shifted peak power from 5,300 to 5,500 

Used to be slow getting to the red line before this now hits the rev limiter frequently in second and easily gets there in third.  

328 Dyno.pdf

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Looks good but from what I understand there is no way I can get an m3 exhaust in on 2k cup rules. 

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The M52 has the advantage of being alloy block, so you lose  a fair bit of weight over the front axle as well.

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The way the rules are written you can't do anything that  will  enhance the performance so the best option would be to put an M52 alloy block under an M50 head and see of you can then get away with the m52 exhaust manifold  16 kW is 16kW - you will just end up thrashing it more to get the power & torque. 

logic:

  • M52 alloy block is lighter so you will have less weight in the car and less over the front axle - better power to weight and balance. 
  • M52 block cools better so able to get rid of excess heat from around bores - better under race conditions,
  • The M50 ( head) simply makes more power because it is set up to operate at higher RPM,
  • The M52 exhaust does flow better than the M50 cast iron ones you might pick up  a kilowatt or two. 

The question then is what bodyshell ?

Edited by 3pedals

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Yes agree I was thinking of a hybrid engine, the alloy block is a must from a weight cooling perspective. Body shell is a toss up there is very little difference weight wise between the Coupe and Sedan and again nothing rigidity. The coupe looks infinitely better but there are some cheap 323is available. The other option is to get the 318is coupe body as they come stock with the bigger brakes and an LSD, albeit only a small case. 323i are hard to find with an LSD. 

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The shell weights are similar, but the sedan is stiffer and it carries the weight a  bit further back 49% front 51% rear  - This gives slightly better traction  (makes the LSD possibly a moot point?)

The rear weight bias allows you to carry more speed into a corner, generates less scrub and also allows you to carry the speed through the corner, it also lets you brake a bit later due to less weight transfer forward - Subtle but if you know how to capitalise on the  attributes it can be highly advantageous in lower power to weight ratio vehicles.

A 'poverty pack' body shell is the way to go if you are not doing a cage  as it minimises the trim weight. 

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I'd personally go with the earliest body you can find. My very early 316 has no abs, ac, or electric windows, has the lightest heater matrix with no selectable recirculate. 

The only issue would be getting it past scrutineering with an alloy block 6 cyl, 328 brakes and vented rear rotors 

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also early 316i had thinner door glass :)

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10 hours ago, dirtydoogle said:

I'd personally go with the earliest body you can find. My very early 316 has no abs, ac, or electric windows, has the lightest heater matrix with no selectable recirculate. 

The only issue would be getting it past scrutineering with an alloy block 6 cyl, 328 brakes and vented rear rotors 

I need to assess what level of detail 2k cup looks at. Maybe a badge change might do it?

 

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12 hours ago, Herbmiester said:

I need to assess what level of detail 2k cup looks at. Maybe a badge change might do it?

 

They'll be none the wiser ;)

13 hours ago, BM WORLD said:

also early 316i had thinner door glass :)

Is this true? Imy not going to admit anything after I measure mine and fund you're pulling my leg 

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13 minutes ago, dirtydoogle said:

They'll be none the wiser ;)

 

Will be now that it's all over the internet...😉

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On 7/2/2018 at 10:59 AM, 3pedals said:

Here is the dyno  with  just the exhaust done this  shifted max power to 5,700 Rpm from 5,300  a few more upstream mods since this have seen max power shift to about 6,300 RPM . What is also eliminated is the dip at about 6 grand on the stock exhaust. 

 Note the red dyno line already had some intake work done upstream of the intake manifold which shifted peak power from 5,300 to 5,500 

Used to be slow getting to the red line before this now hits the rev limiter frequently in second and easily gets there in third.  

328 Dyno.pdf

Nice dyno.

 

Do you have a more recent dyno with the upstream mods you mentioned?

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No because I haven't dyno'd it since and the main reason for that is all the changes are a bit subtle , the next set of changes will bring them fully into play. 

 I did model an M50 manifold with the same internal mods  an d the attached graph gives the comparo,  the key features are:

  • Retaining Vanos and higher port velocity plus  increasing compression gives stronger low end performance,
  • Better cylinder filling and control gives good mid and top end power,
  • Ultimately the 60% greater flow of the M50 manifold ( over the stock M52 manifold) comes into play at about 7,000 RPM - but other dynamics  mean power is already dropping off.

I could design a manifold that betters the M50 above 7 grand but thats not what I am after  - as  modelled the M52 carbon custom starts with more power stays strong right through the range and drops off at a sensible point for a road car that is to be a bit of fun but also good  for the long haul ( drive and reliability)  

M50-52 carbon comparo.PNG

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Nice to see someone else who sees sense with the m50 manifold craze. 

Bigger is not always better, so many examples of far too much port volume around, B6/BP Mazda engines are one great example 

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Did some numbers on the M50 manifold about 10 years ago;  from memory if I took the inlet valves out by 2mm and exhaust by 1.5, bored it to 90mm and used the 3 litre crank then the manifold started to match up okay - got to about 230kW at 6,800 from memory .

But it still had the nasty harmonics from the straight tracts and the dips got deeper and bottom end plummeted  below 3,000RPM 

 

 

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Cars competing in 2kcup are put on the dyno so there’s no point trying to do anything cheeky.

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For anyone interested - here is the straight comparo with an un-modified M50 intake manifold - the graph above is in fact of a modified version I modelled to deal with the dip at about 5,200 RPM seen below.

The dips are caused by harmonic standing waves in the constant cross section runners  causing pressure fluctuations which reduce cylinder filling efficency when out of phase but boost it slightly when in phase. 

M50-52 - untreated harmonics.PNG

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6 hours ago, 3pedals said:

No because I haven't dyno'd it since and the main reason for that is all the changes are a bit subtle , the next set of changes will bring them fully into play. 

 I did model an M50 manifold with the same internal mods  an d the attached graph gives the comparo,  the key features are:

  • Retaining Vanos and higher port velocity plus  increasing compression gives stronger low end performance,
  • Better cylinder filling and control gives good mid and top end power,
  • Ultimately the 60% greater flow of the M50 manifold ( over the stock M52 manifold) comes into play at about 7,000 RPM - but other dynamics  mean power is already dropping off.

I could design a manifold that betters the M50 above 7 grand but thats not what I am after  - as  modelled the M52 carbon custom starts with more power stays strong right through the range and drops off at a sensible point for a road car that is to be a bit of fun but also good  for the long haul ( drive and reliability)  

M50-52 carbon comparo.PNG

So you made a custom manifold?

 

Thats pretty amazing - do you have any pics?

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Yep , aramid/ carbon hybrid - I'm still working on the front part ( it splits like the Schrick intake)   to get flow into each runner a gnats closer,  1 & 6 are usually short on air at high RPM, will put  pix up when it is on the engine with the rest of the bits.  

 It's a complete system from the inlet beside the radiator/ headlight  to the side of the head with an M3 air box in the middle 

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