Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.
cav551:
Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.
Might be good to post on Marathon thread also,lot of educational development on the short stroke theme.
cav551:
Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.
Robert Fryars, AEC Chief Engineer, and later Leyland Chief Engineer, is on the record as saying that the V8 was regarded as nothing more than a concept project when they started development. There was no defined application for the engine and he was horrified when Leyland instructed it to be fitted into the V8 Mandator.
railstaff:
cav551:
Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.Might be good to post on Marathon thread also,lot of educational development on the short stroke theme.
It seems obvious that they were designing engines based on the totally false premise that it was all about piston area v piston speeds. 
When even the most lowly apprentice vehicle builder let alone engine designer was taught that BMEP ( specific torque ),which is a function of force applied to a ‘given’ piston area x leverage at the crank,is king.IE it’s all about how much air you can get into the cylinders on the induction stroke multiplied by how much leverage you can apply at the crank.The more leverage the better meaning more torque for a given force at the piston.The logical result being a net gain in torque and with it power ( because power is just a function of torque at any given engine speed ) for a net ‘reduction’ in ‘piston’ speed.
The logical conclusion of that being the specific torque and power output of the MX v the TL12 obviously with less piston area.DAF didn’t even need the help of the bankers to take out AEC when AEC was more than capable of doing that for itself especially when turbocharging arrived on the scene and blew ( pun intended ) their ridiculous design mantra apart. 
gingerfold:
cav551:
Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.Robert Fryars, AEC Chief Engineer, and later Leyland Chief Engineer, is on the record as saying that the V8 was regarded as nothing more than a concept project when they started development. There was no defined application for the engine and he was horrified when Leyland instructed it to be fitted into the V8 Mandator.
I’m wondering if AEC’s designers actually believed what was written in that article themselves ?.Or was it more a case of we can’t tell em that the bankers won’t give us the money to make a proper long stroke truck engine so we’ll have to baffle the readers with bs,to make what we’ve got to work with look good.
railstaff:
cav551:
Having trawled through this thread, strangely there is no reference to the thinking behind the V8 by its design team way back in 1962.Might be good to post on Marathon thread also,lot of educational development on the short stroke theme.
Some figures to ponder.
AEC 800.Piston area = 5.1 inches divided x 2 =2.55 inches x 3.141 = 8.03 x squared = 64.6 square inches x 8 = 516 square inches. 154 hp at 1,400 rpm piston speed = 1,047 FPM.250 hp at 2,600 rpm piston speed = 1944 FPM.
Rolls Eagle piston area = 64.6 square inches x 6 = 387 square inches.194 hp at 1,200 rpm piston speed = 1196 FPM.280 hp at 1,800 rpm piston speed = 1795 FPM.
Yes I’ve deliberately compared the turbocharged Rolls with the NA AEC.Remind us which turbocharged V8 ever made it into production and why not and what was the piston speed of the TL12 at 280 hp bearing in mind its also larger piston area than the Rolls’ ?.
Carryfast:
AEC 800.Piston area = 5.1 inches divided x 2 =2.55 inches x 3.141 = 8.03 x squared = 64.6 square inches x 8 = 516 square inches. 154 hp at 1,400 rpm piston speed = 1,047 FPM.250 hp at 2,600 rpm piston speed = 1944 FPM.Rolls Eagle piston area = 64.6 square inches x 6 = 387 square inches.194 hp at 1,200 rpm piston speed = 1196 FPM.280 hp at 1,800 rpm piston speed = 1795 FPM.
Please can you please explain to me how you calculated the piston area?
Carryfast:
It seems obvious that they were designing engines based on the totally false premise that it was all about piston area v piston speeds.
This is the very argument which has fuelled your daft ramblings all along.
Please do as I suggested about this time last year- go and sniff around a few pubs in areas where there are engineering consultancies working for IC engine design firms. You will soon be put right, by people who actually do the job for a living.
So this time we are not just comparing apples with oranges then, are we comparing an apple with a grapefruit, a banana or a pineapple?
Which Rolls engine?
A Rolls Royce Eagle 280? a Rolls E 290? a Rolls Eagle300? a Rolls300x? a Rolls Eagle 305?
So why are we comparing the AEC engine at its rated speed (2600) when these Rolls engines are rated at either 1900 or 2100 rpm? would that be because the vital six inches you seem obsessed with always results in the mean piston speed figure being the same number as the revolutions? so you choose a lower rpm to make things look better
I haven’t got a Rolls Royce Eagle E265 spec sheet to hand, but I’m guessing that a nominal 265 bhp engine is going to be more like a Worcester Pearmain to Golden Delicious comparison with the 250 bhp AEC V8 in its smaller guise.
cav551:
So this time we are not just comparing apples with oranges then, are we comparing an apple with a grapefruit, a banana or a pineapple?Which Rolls engine?
A Rolls Royce Eagle 280? a Rolls E 290? a Rolls Eagle300? a Rolls300x? a Rolls Eagle 305?
So why are we comparing the AEC engine at its rated speed (2600) when these Rolls engines are rated at either 1900 or 2100 rpm? would that be because the vital six inches you seem obsessed with always results in the mean piston speed figure being the same number as the revolutions? so you choose a lower rpm to make things look better
I haven’t got a Rolls Royce Eagle E265 spec sheet to hand, but I’m guessing that a nominal 265 bhp engine is going to be more like a Worcester Pearmain to Golden Delicious comparison with the 250 bhp AEC V8 in its smaller guise.
The article clearly infers a general rule that hp is related to piston area and piston speed which is bs.
When what matters is specific torque.Which is why the turbocharged Rolls also beats a turbocharged TL12 in terms of producing an equivalent power output from less piston area and at a lower piston speed from a smaller overall capacity.Which seems to be an apples v apples comparison.On that note I didn’t ‘choose’ the lower rpm figure I chose an ‘equivalent’ if not more ‘hp’ figure.In this case just the Rolls 305 will do fine.Bearing in mind the mythical formula of more piston area means more power seemed to be being applied on a general basis,while if not who were they trying to fool except themselves.
Why are we comparing the Paccar MX engine which is less than 10yrs old with an engine that hasn’t been built for over 30yrs (TL12) ■■?
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newmercman:
Why are we comparing the Paccar MX engine which is less than 10yrs old with an engine that hasn’t been built for over 30yrs (TL12) ■■?
Because it proves that hp isn’t dependent on piston area just like the Rolls Eagle did v the TL12 40 years ago.In all cases BMEP ( specific torque ) being the usually accepted figure.Which is why DAF obviously chose to stay with the bore size of the old DK engine when going from 11.6 to around 13 litre.That obviously being less than the TL12’s.Probably also why ■■■■■■■ reduced the bore diameter of the ISX from that of the N14 in the move up to 15 litre. 
Surely the way the engine performed in service would swing it , how reliable , how economical ,how it performed ,so no matter how big the bore was how short the stroke was how high it was revving the most important thing was those 3 factors ,something it passed with flying colours ,Im not too sure the Rolls of the day did back in the early 70s
ramone:
Surely the way the engine performed in service would swing it , how reliable , how economical ,how it performed ,so no matter how big the bore was how short the stroke was how high it was revving the most important thing was those 3 factors ,something it passed with flying colours ,Im not too sure the Rolls of the day did back in the early70s
As opposed to a lemon that even its own designers said don’t use and can’t handle being turbocharged at all and another which can’t be boosted to more than 62 lb/ft per litre without grenading,that’ll work.But look on the bright side who needs a turbocharger when it’s all about how big you can make the bores/pistons and how short you can make the stroke to keep piston speeds down at let’s say 280 hp +.Oh wait.
Carryfast:
newmercman:
Why are we comparing the Paccar MX engine which is less than 10yrs old with an engine that hasn’t been built for over 30yrs (TL12) ■■?Because it proves that hp isn’t dependent on piston area just like the Rolls Eagle did v the TL12 40 years ago.In all cases BMEP ( specific torque ) being the usually accepted figure.Which is why DAF obviously chose to stay with the bore size of the old DK engine when going from 11.6 to around 13 litre.That obviously being less than the TL12’s.Probably also why ■■■■■■■ reduced the bore diameter of the ISX from that of the N14 in the move up to 15 litre.
We are here again.The ISX bore was reduced to keep it in sub 16 litre territory but still keep the ultra long stroke(6.65).At the time of signature release the 12/13 litre ISX/ISZ was not produced.
Oversquare engines are generally more reliable, wear less, and can be run at a higher speed. In oversquare engines power does not suffer, but low end torque does, with it being relative to crank throw.
Breathing is an important advantage for oversquare engines, as the edges of the valves are less obstructed by the cylinder wall, the big bore can fit larger or more valves into the head.
With shorter crankshaft stroke and therefore piston travel, crankshaft strength is increased and parasitic losses are reduced. Ring drag is a major source of internal friction and the crankshaft also rotates in a smaller arc, so the windage is reduced. Oil-pressure problems caused by windage and oil aeration are reduced. Engines used at sustained high rpm are usually better suited to running with less stroke and more bore.
So before the era of low revving high hp per litre engines, the oversquare design wasn’t a compromise at all, it allowed a shorter and correspondingly lighter engine block and could sustain higher rpms to enable a simple 6spd gearbox to be used and still reach an adequate cruising speed. Low end torque was the trade off, to a degree at least, a driving style suited to the engine characteristics would allow an oversquare engined lorry to cover the ground in the same time as a low revving long stroke competitor driving in a style that suited it’s characteristics.
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During the course of development testing one of the AEC’s current production engines was used for comparison - the ‘datum engine’ The results were interesting.
“In the development stage, the stroke of a modified 180 bhp datum six-cylinder engine with the same bore as the proposed V8 was reduced to 4.5in. to match the V8’s stroke, and the unit produced more power and a higher torque than the standard engine. It also operated at a lower fuel consumption, corresponding to the consumption of the 800 series V8 of 0.369 lb/bhp /hr.”
Read more at archive.commercialmotor.com/arti … dAizr8w.99
As mentioned elsewhere in the article, the V8 was intended to be used initially ahead of a six speed gearbox. At the time (late 1960s) there was by coincidence an American engine that had made an appearance in the UK which perchance had an almost identical displacement: 743 cu in against the 741 cu in of the AEC V8 and almost identical bore size. (5.1" 130mm) This engine was at that time very frequently mated with a six speed transmission. This engine was less powerful than the AEC, but its rated output was at 2100 rpm and its peak torque occurred at 1550 rpm where it produced 600 lbft … very similar to the AEC V8’s (580lbft) which was however at a slightly lower speed (1400rpm)
Now all this may be pedantic technical mumbo jumbo, but from a driver’s aspect if stuck with only five or six available gears, then an engine which has a 1200rpm spread of useful torque and power is less tiring to drive and more appealing than one which only has 550 rpm available.
However one engine had two more cylinders so maybe we shouldn’t compare the two.
railstaff:
Carryfast:
Because it proves that hp isn’t dependent on piston area just like the Rolls Eagle did v the TL12 40 years ago.In all cases BMEP ( specific torque ) being the usually accepted figure.Which is why DAF obviously chose to stay with the bore size of the old DK engine when going from 11.6 to around 13 litre.That obviously being less than the TL12’s.Probably also why ■■■■■■■ reduced the bore diameter of the ISX from that of the N14 in the move up to 15 litre.We are here again.The ISX bore was reduced to keep it in sub 16 litre territory but still keep the ultra long stroke(6.65).
The N14 didn’t have an ‘ultra long’ 6.65 stroke it retained the usual 855 6 inch one.
While if piston area is supposedly the relevant calculation as inferred in the article,rather than leverage at the crank,in making power why would ■■■■■■■ have wanted to reduce the bore and increase the stroke compared to the that of the N14 in the move from 14 litre to 15 ?.When BMEP ( specific torque ) is obviously all about the amount of force applied to a ‘given’ piston area x leverage at the crank.
Carryfast:
ramone:
Surely the way the engine performed in service would swing it , how reliable , how economical ,how it performed ,so no matter how big the bore was how short the stroke was how high it was revving the most important thing was those 3 factors ,something it passed with flying colours ,Im not too sure the Rolls of the day did back in the early70sAs opposed to a lemon that even its own designers said don’t use and can’t handle being turbocharged at all and another which can’t be boosted to more than 62 lb/ft per litre without grenading,that’ll work.But look on the bright side who needs a turbocharger when it’s all about how big you can make the bores/pistons and how short you can make the stroke to keep piston speeds down at let’s say 280 hp +.Oh wait.
So answer the question , what problems did the TL12 pose for operators while in service , was it poor on fuel ,did it prove troublesome in service and was its performance on the road not up to scratch.■■?
ramone:
So answer the question , what problems did the TL12 pose for operators while in service , was it poor on fuel ,did it prove troublesome in service and was its performance on the road not up to scratch.■■?
There are references out there to it having a penchant for piston breakages ? ( maybe as expected of a design based on the premise of trading leverage at the crank for more force at the piston ? ).That at around less than just 65 lb/ft per litre.Which leaves the question of what stopped the supposed after cooled 325 hp version in its tracks and what made Leyland drop the thing shortly after going to all the trouble of transferring production of it from AEC to Leyland ?.In favour of just using ■■■■■■■ and Rolls ?.Bearing in mind I don’t buy after cooling being too much to get their heads around in the day or cost.
So yes maybe just about good enough in service by the standards of the day but a disaster for Leyland’s in house engine manufacturing business model.In not having the necessary redundancy for development built in of the Rolls and ■■■■■■■■■■ the form of the required leverage at the crank.
Which leaves the question of the AEC V8.Which its own designers seem to have rightly disowned as being a lemon in them wanting it shelved ?.