2014 Volkswagen Golf SV TDI DSG 5door

[seth1]

Toque per cubic capacity in your case measured on a braked device,dynometre,water dynometre,what ever.
Doesn't really apply to this topic though,more to do with the fundamental design of an engine.Or what designers strive to achieve.Yes I agree there is a point were the pressure drops below whats required but were nowere near that point,Diesel engines now can achieve 22bmep comfortable.I think we should start a diesel forum.ha ha.

 

[RogerL]

Understanding BMEP is vital to any tuning.

 

[JonnyG]

Understanding BMEP is vital to any tuning.

I know seth knows his stuff, and no doubt you do too roger,but arent you going off track or far too teckie.. here...explained in english and as is always the case the window for such thing [BMEP] leaves a little room for playing with

Naturally aspirated spark-ignition engines : Maximum BMEP in the range 8.5 to 10.5 bar (850 to 1050 kPa; 125 to 150 lbf/in2), at the engine speed where maximum torque is obtained. At rated power, bmep values are typically 10 to 15% lower.[2]
Boosted spark ignition engines : Maximum BMEP in the 12.5 to 17 bar range (1.25 to 1.7 MPa; 180 to 250 lbf/in2).[3]
Naturally aspirated four-stroke diesels: Maximum BMEP in the 7 to 9 bar range (700 to 900 kPa; 100 to 130 lbf/in2).[4]
Boosted automotive four-stroke diesels : Maximum BMEP in the 14 to 18 bar (1.4 to 1.8 MPa; 200 to 269 lbf/in2) range.
Two-stroke diesels have comparable values, but very large low speed diesels like the Wärtsilä-Sulzer RTA96-C can run at BMEPs of up to 19 bar (1.9 MPa; 275 lbf/in2).
Ultra boosted engines such as the engine used in the Koenigsegg Agera can run at BMEPs as high as 28 bar (32 bar for the Agera R)[5]
Top Fuel dragster engines: 80–100 bar (8.0-10 MPa)
For example, a four-stroke motor producing 160 N·m from 2 litres of displacement has a bmep of (4π)(160 N·m)/(0.002 m³) = 1,005,000 N/m2 =1,005 kPa (10.05 bar). If the same engine produces 76 kW at 5400 rpm (90 Hz), its torque is 134 N·m and its bmep is 8.42 bar (842 kPa). As piston engines always have their maximum torque at a lower rotating speed than the maximum output, the BMEP is lower at full power.

 

[JonnyG]

sorry forgot to add BMEP figures don’t tell you the whole story. They don’t show BSFC (Brake Specific Fuel Consumption) and they don’t show the spread of engine torque, the engine’s flexibility or any of those other real world characteristics. which would explain why a tuned turbodiesel engine could be better on mpg...

 

[RogerL]

Agreed - too much thread drift.

 

[seth1]

I understand BMEP, admittedly its not something I deal with daily,the process is done before our department.One thing to remember about BMEP is it does not relate directly to cylinder pressure but is a tool of measurement.But getting back to emmisions.Its heard quite often "how can a two bit company improve a vehicles charistics when a maker spends millions?"Well its quite simple,once the tested engine meets the standard the development stops.A friend of mine was before he retired head of development for Rolls Royce Diesel,at the time they were developing a Euro 1 Eagle.The engine was very dirty,but had the creditials to be good.At the same time Hawker Sidney came in with a buy out of Rolls.The only way to clean the engine up was by means of removal of the fuel injection delievery valves on the pump and by better turbocharging.After testing the second turbocharger it was found to be just good enough to pass Euro 1 and that's how it was left.Massive scope left unused.
I would say electronics play a huge part in engine development,the introduction of common rail which is not new has change poor engines into good ones and with very little redesign of components.

 

[JonnyG]

and trying to stay on the mpg bit, just remember if you can tune an engines with more torque lowdown than standard,which is what tuning boxes do mostly, and remaps can do,and you can get away with it,the fact you might not need to rev the engine as highly as before and change gear less often also straying in a higher gear for longer does mean less engine heat, less friction and less wear ...so better mpg.but lets be honest its not going to be much 2 or 3mpg on a decent diesel might be possible....

 

[seth1]

Well coming clean,ive had a module fitted for years,i would think on every electronic engine ive owned.Infact at one stage we used to sell them,we still have dealings with p box now.But early on this year I done a test on my own car by switching the module off on the outward run,and then switching it on home bound.Probably a round trip of 800 miles.Nearly a quarter of a tank better on way home.

 

[JonnyG]

on a proper run seth? doesn't surprise me. I'm hoping for a decent improvement when i finally fit my tuning box to the high geared insignia .haven't done it yet properly wont till after the new year.

 

[seth1]

With caravan,our home to bottom of cornwall.Caravans 1300kg,roof box and three bikes and heaver coming home with stuff we bought over the period.Very impressive the Signia pull really well,one surprised me a couple of years ago on the A38.Could be my next car unless alfa/fiat pull their finger out.

 

[JonnyG]

Alas Alfa /Fiat . don't see it happening.the insignia? got a 11 plate 160 eco flex. the juries out, its the 40mph per 1000rpm and 250 odd ft/Ib of torque to move it seems lacking.and me of course refsing to rev the dam thing. it'll come good i believe.oh and the newer version? apparently they haven't cracked the ECU, in time no doubt they will.. oh yes i think thats where the rea mpgl benefit of a decent tuning comes,when towing.

 

[RogerL]

Without any mechanical changes, I ALWAYS used to record better consumption coming back from Devon/Cornwall than going dowm - prevailing wind and lighter load spring to mind.

 

[seth1]

Roger I was waiting for that one.Generally we are heavier coming back.Sadly JonnyG you will have to move that thing in the middle called a gear lever.Mine is exactly the same,to me completely needless,an auto,the minute it sees a hill 10 mile way its changing down.The speed doesn't drop of but the revs climb.This year with the module re flashed for more bottom end,we travelled the length of the country on the motorsways and dropped no lower than 5th around the A38 near cornwall.Im sure that was 1500rpm at 62mph.Ive come around to Rogers way of thought now,use the correct gear for the speed and don't maul it.

 

[RogerL]

In the old days, the engine spec would quote the maximum torque and the rpm where it occurred - that rpm was/still is the sweet spot for efficiency, therefore economy.

The "problem" these days is that the enormous torque of turbo-diesels is electronically clipped/limited to allow a lower torque capacity transmission to be used - that gives a flat torque curve over a range of rpm so the owner/user can't find out the rpm where torque would max out given the chance, all you know it's somewhere in the flat bit.

Being a mathematician, I've done some curve-fitting exercises on the published torque curve for my car and my best guess is that max torque would occur at about 2,000 rpm - the quoted max torque is published at 1,800 - 2,500 rpm.

On my car, 2,000 rpm is just right in top gear for 70mph solo but when towing the autobox tries to run around 1,700 rpm when towing - so I use the Sport mode which cuts out top gear and gets it right.