Carryfast:
How do you ‘estimate’ ‘peak cylinder’ pressure as a multiple of BMEP ( specific torque at the flywheel ) when more leverage, in the form of a longer stroke, means the same torque output for less force on the piston or more torque output for equivalent force, and assuming a piston area deficit v leverage advantage.As in the case of TL12 v TD120 and RR Eagle.
Which part of, you need to match 43% more specific torque, x 7% more load on your end bearings, and x 2% on your head fastenings, didn’t you understand.
There’s only one charlatan here and it ain’t me.
If you increase (for example) turbo boost, you will increase the BMEP of the engine. You will also increase peak cylinder pressures, so the two are roughly proportional. It would give you an approximate means of justifying (or otherwise) your arguments. You need to brush up on your maths, if you think a 43% increase in BMEP effects a 2% increase in head bolt load.
Edit- BMEP is exactly what it says- it is the average pressure during the combustion stroke. It ends up as a ratio of torque to cylinder volume. See if you can do the maths to prove that. IIRC, that derivation is taught in the first or second week of any vehicle engineering apprenticeship.
You really think that real cylinder pressure has any connection whatsoever to a non existent fictitious abstract derived from the specific torque figure.
BMEP is just another way of expressing peak specific torque at the flywheel nothing more nothing less.Just like power is torque x engine speed.
There is no such thing as an ‘average cylinder pressure’ it’ a non existent oxymoron.Your fatigue life for head fastenings will be based on the ‘peak’ cylinder pressure not a bs fictitious average and that peak is massive.Or you obviously wouldn’t need fastenings with a 150,000 + psi tensile strength to hold it.
You’ll only need to increase cylinder pressures if you’ve got a net piston area deficit for the equivalent pressure.
If you use more force on the piston to compensate for less leverage that’s proportionally more load applied to your end bearings.Regardless of whether it’s from more piston area or more cylinder pressure or a combination of both.
In the case of the TL12 v Eagle you’ve got a 43% specific torque at the flywheel ( BMEP ) deficit.
You’ve got a 7% leverage deficit.
You’ve got a 2% net piston area v leverage deficit.
That’s 43% x 7 % more load required on your end bearings and 43% x 2% more load required on your head fastenings to match the Eagle’s specific torque ( BMEP ) output potential.
So let’s get this right you think that you can deduce an engine’s peak cylinder pressure just from the specific torque figure at the flywheel which is all that BMEP is.BS.
When the torque figure is determined by the ‘combination’ of leverage multiplying the force on the piston.
More leverage and less force for the equivalent output means less fuel and less stress.
ramone:
You are quite correct CF i haven’t got a clue what i’m on about , i always thought leverage was a force from an angle not straight down but my point is it’s ■■■■ annoying when someone contredicts and disses everything that someone else states just for the sake of it
You have told well known and successful hauliers where they went wrong with their buying polices ( Gardner180/240 boat anchors ffs) when they would have been much better advised to use V8 Detroits
You have advised very experienced drivers i know one personally how to rope n sheet in the correct manner and put them right on where they have gone wrong . Here’s a wool hook go load and rope n sheet that lot … i don’t think
We’ve had engineers and fully qualified mechanics that have been doing their respective jobs all their lives … wrongly according to you
We have had researchers and book writers who have studied in great depth their subjects only to be told they are wrong.
We’ve had a guy who spent 30 years restoring a vehicle into a work of art but we can’t see it because he wont post on here anymore due to your ridiculous comments.
We’ve heard how you worked for a guy and didn’t (couldn’t) like driving his Marathon so you took turns in driving the Volvo he ran even though you relentlessly bang on about Fullers being superior to synchros , sounds to me you never mastered a Fuller.
So i think you should shake your hand pat yourself on the back and tell yourself you are wonderful , because i can’t see anyone else saying it .
Go and pour yourself a pint Ramone, you’re surrounded by an idiot, and you know you can’t possibly win.
[zb]
anorak:
I’ve just worked out why CF’s posts appear later than other posts, but are shown chronologically prior to those other posts: he must be on the pre-moderation naughty step. FFS- even with a proof-reader, he still manages to talk tiddlywinks, EG Brake Mean Effective Pressure is not pressure. It’s all up there^^^.
Which part of BMEP is just an abstract, non existent, AVERAGE measure, of cylinder pressure, which actually just means specific torque at the flywheel, obviously dependent on piston area and leverage, didn’t you understand.Here’s a clue there is no ‘average’ cylinder pressure figure happening in the cylinder.Just building and waning pressure each side of a massive peak pressure.
How do you determine peak cylinder pressure, which is what determines your fatigue level, from the non existent abstract of BMEP which is itself based on just the specific torque figure.
When the torque figure is a function of cylinder pressure/piston area ( force ) x leverage ( stroke ).
More leverage = less force required for the equivalent torque output and more torque output for the equivalent force.
So give us your idea of the tensile load on the TL12’s head fastenings at around 100 lbft per litre v 69 lbft per litre.
You’ve said you’ll be able to do it from just the BMEP figure which is obviously exactly the same thing as specific torque.
Carryfast:
…
So give us your idea of the tensile load on the TL12’s head fastenings at around 100 lbft per litre v 69 lbft per litre.
You’ve said you’ll be able to do it from just the BMEP figure which is obviously exactly the same thing as specific torque.
For those of you who are not completely turned-off by the relentless dogma of the brushman:
The mean pressure may be gleaned from the graph (for the maths-oriented, it is the area under the curve, divided by the difference in angle on the bottom axis). The mean pressure, corrected for four revolutions for a four stroke engine, is the BMEP as calculated from the torque and the capacity.
Carryfast:
…
So give us your idea of the tensile load on the TL12’s head fastenings at around 100 lbft per litre v 69 lbft per litre.
You’ve said you’ll be able to do it from just the BMEP figure which is obviously exactly the same thing as specific torque.
I didn’t say that.
You said you ‘‘may estimate the peak cylinder pressure as a multiple of BMEP’’.
How when BMEP ( specific torque ) is a function of the force x distance ( stroke ) equation and more leverage means less force required for the equivalent torque output or more torque for the equivalent force.
More piston area will also mean more torque from the equivalent cylinder pressure or less cylinder pressure required for the equivalent torque output.
So go on then.You’ve got your BMEP for the TL12 ( you do know how to get BMEP from specific torque ) now give us the figure.
When you’ve done that give us the figure for the Eagle at the equivalent torque output.
[zb]
anorak:
For those of you who are not completely turned-off by the relentless dogma of the brushman:
0
The mean pressure may be gleaned from the graph (for the maths-oriented, it is the area under the curve, divided by the difference in angle on the bottom axis). The mean pressure, corrected for four revolutions for a four stroke engine, is the BMEP as calculated from the torque and the capacity.
Here’s a clue it’s not any mean pressure which is trying to blow your head off and wreck your ends and there is no such actual pressure acting on your head bolts and piston as ‘average’ ‘mean’ pressure at all.
Which part of an abstract meant as a comparator of engines not head bolt and end bearing fatigue don’t you understand.
Remind us what pressure 1 Mpa equals in bar/psi.How many Mpa at peak cylinder pressure.
So we want 43% more specific torque x 2% more cylinder pressure to compensate for your piston area v leverage deficit.
Also 7% more force applied to your ends.
So how much force applied to your ends and head bolts at the end of the day to match the Eagle’s specific torque output ( BMEP ).
I think the 11 litre Scania and Daf engines were much better than the 12 litre Rolls , no particular reason but the 13 litre versions left the Rolls standing they would have been better producing a bigger Eagle than starting with the unreliable 220/280s . What were they thinking. Well the rest is history , 3rd choice for ERF , Foden and Sedd Atki its probably no surprise. Which was your favourite brush CF was it the long handled version or the shorter one , did Bex Bissell make one , when you weren’t gritting at the council in your V8 Detroit whatever it was were you on a roadsweeper or a brush … oh so many questions and so much bs
Off the theme a little but could I ask “The Great Leatherhead Sage” his knowledgeable opinion on the Foden FD6 Two stroke engine and what was the reason for its runaway success in the day ? Cheers Bewick.
Bewick:
Off the theme a little but could I ask “The Great Leatherhead Sage” his knowledgeable opinion on the Foden FD6 Two stroke engine and what was the reason for its runaway success in the day ? Cheers Bewick.
ramone:
I think the 11 litre Scania and Daf engines were much better than the 12 litre Rolls , no particular reason but the 13 litre versions left the Rolls standing they would have been better producing a bigger Eagle than starting with the unreliable 220/280s . What were they thinking. Well the rest is history , 3rd choice for ERF , Foden and Sedd Atki its probably no surprise.
Why would anyone have bought an F12 rather than the DAF or Scania.
But you still ain’t going to find a 142 mm stroke even in those two exceptions.The DAF’s at least being closer to the Eagle’s than the TL12’s.
400 hp Rolls more torque than the TD120 and it takes a 13 litre motor to beat it.
There was no TL12 choice at all in Leyland Roadtrain after 1983 going by your own logic.
ramone:
I think the 11 litre Scania and Daf engines were much better than the 12 litre Rolls , no particular reason but the 13 litre versions left the Rolls standing they would have been better producing a bigger Eagle than starting with the unreliable 220/280s . What were they thinking. Well the rest is history , 3rd choice for ERF , Foden and Sedd Atki its probably no surprise.
Why would anyone have bought an F12 rather than the DAF or Scania.
But you still ain’t going to find a 142 mm stroke even in those two exceptions.The DAF’s at least being closer to the Eagle’s than the TL12’s.
400 hp Rolls more torque than the TD120 and it takes a 13 litre motor to beat it.
There was no TL12 choice at all in Leyland Roadtrain after 1983 going by your own logic.
The Eagle 400Tx gets a glowing report in the above road test- its torque output is almost as much as a ■■■■■■■ N14-465, according to the text. Both engines have a 152mm stroke, but the ■■■■■■■ has a 140mm bore, versus the Rolls’ 130mm. The ■■■■■■■ engineers were obviously frightened to death by that extra 8%. LOL.
Now for your next test: do the derivation showing why BMEP is proportional to the ratio of torque to cylinder capacity, to establish your credentials as a top design man, for benefit of all reading this thread.
ramone:
I think the 11 litre Scania and Daf engines were much better than the 12 litre Rolls , no particular reason but the 13 litre versions left the Rolls standing they would have been better producing a bigger Eagle than starting with the unreliable 220/280s . What were they thinking. Well the rest is history , 3rd choice for ERF , Foden and Sedd Atki its probably no surprise.
Why would anyone have bought an F12 rather than the DAF or Scania.
But you still ain’t going to find a 142 mm stroke even in those two exceptions.The DAF’s at least being closer to the Eagle’s than the TL12’s.
400 hp Rolls more torque than the TD120 and it takes a 13 litre motor to beat it.
There was no TL12 choice at all in Leyland Roadtrain after 1983 going by your own logic.
Probably for more power at launch from the 12 litre Volvo compared with the 11 litres from the other two. Then again it might have been personal choice or a good experience or bad as it were. Horses for courses.
ramone:
I think the 11 litre Scania and Daf engines were much better than the 12 litre Rolls , no particular reason but the 13 litre versions left the Rolls standing they would have been better producing a bigger Eagle than starting with the unreliable 220/280s . What were they thinking. Well the rest is history , 3rd choice for ERF , Foden and Sedd Atki its probably no surprise.
Why would anyone have bought an F12 rather than the DAF or Scania.
But you still ain’t going to find a 142 mm stroke even in those two exceptions.The DAF’s at least being closer to the Eagle’s than the TL12’s.
400 hp Rolls more torque than the TD120 and it takes a 13 litre motor to beat it.
There was no TL12 choice at all in Leyland Roadtrain after 1983 going by your own logic.
The Eagle 400Tx gets a glowing report in the above road test- its torque output is almost as much as a ■■■■■■■ N14-465, according to the text. Both engines have a 152mm stroke, but the ■■■■■■■ has a 140mm bore, versus the Rolls’ 130mm. The ■■■■■■■ engineers were obviously frightened to death by that extra 8%. LOL.
Now for your next test: do the derivation showing why BMEP is proportional to the ratio of torque to cylinder capacity, to establish your credentials as a top design man, for benefit of all reading this thread.
CF’s Wikipedia finger has clearly not been working too well because the Rolls/ Perkins Eagle didn’t stop at the figures he is SO SO fond of quoting.
It’s very strange that there’s no mention of its output being achieved by its stroke yet there is mention of a significant increase in compression ratio, induction tuning, and higher injection pressures along with its torque increase and spread being attributable to the Bosch K type Governor. There appears to have been a TX430 with an even higher compression ratio but mention of that seems to have disappeared behind a paywall.
The Eagle 400Tx gets a glowing report in the above road test- its torque output is almost as much as a ■■■■■■■ N14-465, according to the text. Both engines have a 152mm stroke, but the ■■■■■■■ has a 140mm bore, versus the Rolls’ 130mm. The ■■■■■■■ engineers were obviously frightened to death by that extra 8%. LOL.
Now for your next test: do the derivation showing why BMEP is proportional to the ratio of torque to cylinder capacity, to establish your credentials as a top design man, for benefit of all reading this thread.
The Eagle TX 400 gets a glowing report it made more specific torque than the TD120.
The TL12 has rightly long ago been put out of its misery.Which makes the case for the TL12 how.
You said that you can deduce peak cylinder pressure from just an arbitrary multiple of the BMEP figure.Go on then do it for both the TL12 and Eagle.I’m still waiting.
Oh wait you can’t because torque is also dependent on the two other variables of piston area and leverage.
BMEP is just specific torque in just the same way that power is torque x engine speed.
Specific torque x 2.464 = BMEP.
Specific torque is deduced by dividing peak torque at the flywheel by engine capacity.
In which case why bother with BMEP anyway specific torque is exactly the same thing.
BMEP or Specific Torque is just a way of comparing different engine outputs at the flywheel not cylinder pressures or end bearing loads.
Less leverage then you’ll need more force on the piston in the form of more piston area and/or more cylinder pressure for the equivalent torque.Which means more end bearing loads and more head fastening loads respectively.
Carryfast:
Why would anyone have bought an F12 rather than the DAF or Scania.
But you still ain’t going to find a 142 mm stroke even in those two exceptions.The DAF’s at least being closer to the Eagle’s than the TL12’s.
400 hp Rolls more torque than the TD120 and it takes a 13 litre motor to beat it.
There was no TL12 choice at all in Leyland Roadtrain after 1983 going by your own logic.
Probably for more power at launch from the 12 litre Volvo compared with the 11 litres from the other two. Then again it might have been personal choice or a good experience or bad as it were. Horses for courses.
Let’s stay with specific torque outputs.Power output is of no interest that it will look after itself if we get the torque output.That’s why BMEP was invented to compare engines not specific power output.
The Scania even with after cooling is behind the TD120 at this point. archive.commercialmotor.com/page … er-1982/15
So both aftercooled turbo how do you explain the difference in specific torque.Why not just boost the Scania motor to match the Volvo’s specific torque output of 95 lbft per litre.
While we know that the Eagle is going to trump the TD120.
Also where is the TL12 here at this point.Oh wait still the same 69lbft per litre.The decision already made to knock it on the head.The only thing that Edwardes ever got right but ironically for nefarious reasons.Like lumbering the Roadtrain with it at launch.
The Eagle 400Tx gets a glowing report in the above road test- its torque output is almost as much as a ■■■■■■■ N14-465, according to the text. Both engines have a 152mm stroke, but the ■■■■■■■ has a 140mm bore, versus the Rolls’ 130mm. The ■■■■■■■ engineers were obviously frightened to death by that extra 8%. LOL.
Now for your next test: do the derivation showing why BMEP is proportional to the ratio of torque to cylinder capacity, to establish your credentials as a top design man, for benefit of all reading this thread.
The Eagle TX 400 gets a glowing report it made more specific torque than the TD120.
The TL12 has rightly long ago been put out of its misery.Which makes the case for the TL12 how.
You said that you can deduce peak cylinder pressure from just an arbitrary multiple of the BMEP figure.Go on then do it for both the TL12 and Eagle.I’m still waiting.
Oh wait you can’t because torque is also dependent on the two other variables of piston area and leverage.
BMEP is just specific torque in just the same way that power is torque x engine speed.
Specific torque x 2.464 = BMEP.
Specific torque is deduced by dividing peak torque at the flywheel by engine capacity.
In which case why bother with BMEP anyway specific torque is exactly the same thing.
BMEP or Specific Torque is just a way of comparing different engine outputs at the flywheel not cylinder pressures or end bearing loads.
Less leverage then you’ll need more force on the piston in the form of more piston area and/or more cylinder pressure for the equivalent torque.Which means more end bearing loads and more head fastening loads respectively.
cav551:
CF’s Wikipedia finger has clearly not been working too well because the Rolls/ Perkins Eagle didn’t stop at the figures he is SO SO fond of quoting.
It’s very strange that there’s no mention of its output being achieved by its stroke yet there is mention of a significant increase in compression ratio, induction tuning, and higher injection pressures along with its torque increase and spread being attributable to the Bosch K type Governor. There appears to have been a TX430 with an even higher compression ratio but mention of that seems to have disappeared behind a paywall.
Assuming that the increase was the result of more torque.The constant force multiplier of the extra leverage over TD120 let alone TL12 couldn’t possibly not have been a factor in the increase as it was in all the previous increases.
The fact is it trumped the TD120’s specific torque output albeit by a close margin.Seemingly too close not to closely reflect the respective stroke/leverage differences.
No one is saying that containing the extra forces involved, in obtaining similar specific outputs with less leverage, was impossible in the case of the exceptions which proved the rule.Although even in those cases 142 mm seems to be a bridge too far.
But why would anyone want to.
So here we are with much lower bore stroke ratios than the TL12 and even the TD120 and Eagle being the rule rather than the exception.In everything from Scania, Volvo to MX.
Leverage matters.
on your maths, if you think a 43% increase in BMEP effects a 2% increase in head bolt load.
