AEC V8

[carryfast]

newmercman:
I’m confused. My CAT C15 is set to 550hp 1850lb/ft and the 475hp version of the C15 shares the 1850lb/ft torque rating, yet with less power. Many other engines have similar hp and torque variations too. How does BMEP work in that case?

Assuming I’ve been taught it right The BMEP figure is based on the ‘peak torque’ figure,per litre,not power in either case.

The rest is probably any of numerous different possible methods of de rating the engine power output such as by tailoring the torque curve after the peak by reducing the level of boost or just governing the respective engine speeds for example.

[railstaff]

BMEP(PSI)=151 x torque/displacement.

Its a way of working out engine efficencys by adding the unknown factors as said its theretical.

[erf]

Carryfast:
…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…

…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…

…The result being that they ended up with a worse BMEP than the Gardner…

…questions along the lines of how can a BMEP of less than the 690 be considered as a ‘breakthrough’…

…the design premise showed a total ignorance of the importance of BMEP…

…output to the point of not being able to match the BMEP of the 690 or a Gardner…

…The fact remaining that the AEC was never going to meet its 300 hp + spec with a BMEP figure of less than the 690 nor without risk of grenading with such a short stroke…

…Realistically the thing should have been written off from the point when its BMEP figure of less than 50 lb/ft per litre first appeared on the dyno…

…I was actually comparing the BMEP of the NA Rolls 220 with the NA AEC V8…

…the Rolls 220 clearly has a better specific torque output than the AEC 800 and therefore the better BMEP figure…

…the 12.1 litre Rolls 220 has a better specific torque output than the 13.1 litre AEC V8.Which corresponds directly with a better BMEP figure…

Weeding through the nonsense, you made reference to the AEC V8’s supposedly very poor BMEP figure in these 11 posts. There may be more.
All I am asking is… GIVE US SOME BMEP FIGURES to compare!!
See…you’ve got me shouting now. And I don’t shout.
Put some meat on the bone of your argument!!

[zb_anorak]

Carryfast:

[zb]
anorak:
If you use SI units, you don’t need to remember the constants.

Do you agree that BMEP is just a more ( over ) complicated way of expressing specific torque ?.Because that’s how I was taught it.

If you look at the Wikipedia page I linked in the recent past, it gives the ordinary derivation of it. Using N and m:
P=2πT/V,
so you are right. 4 stroke engines only have half a bang per rev, so one must multiply the result by two for those. You should not need to do that .

It’s not over-complicated- it gives you the average pressure in the cylinder during the firing stroke, which is simple and elegant.

[gingerfold]

ramone:
Ive mentioned this before ,wouldnt it have been better to develop the AV760 as early as its launch instead of a complete new V8 , obviously hindsight being the name of the game but the money they would have saved could have gone towards a complete new engine later on . 273 bhp in the late `60s would have been an eyebrow raiser

I’ll answer that Paul, as everyone else is obviously far too busy worrying about BMEP. AEC had turbo-charged its AV690 and AV470 engines in the late 1950s for some of its South American customers that were operating in the Andes. The use of turbo-charging in this instance was to compensate for loss of power by normally aspirated engines operating in the rarefied atmosphere of high altitude. There were also turbo-charged industrial versions of the AV470 and AV690, and a horizontal turbo-charged railcar version of the AH690 as well. So AEC was quite familiar and successful with the concept of turbo-charging pre-1962 and the Leyland merger. And that is when the waters become muddied. Leyland was not at all keen on turbo-charging (just like Gardner) and remember the A760 development programme was instigated by Stanley Markland during his brief time at Southall. When he resigned and departed anything with his name against it was deliberately ignored. Leyland finally had to investigate turbo-charging in 1968, some 10 years after AEC, when it dabbled with the O.680 and made it the turbo-charged 690 for the Two-Pedal Beaver…another “what if, maybe, and perhaps” model. The group was quite skilled at making those.

[bma_finland]

in Finland we had Vanaja lorrys whit turbocharged Av690 250 hp from 1965 ,they did well in competision to S-V DS11 and Volvo Td96

[gingerfold]

Good information bma.finland, thank you

[ramone]

gingerfold:

ramone:
Ive mentioned this before ,wouldnt it have been better to develop the AV760 as early as its launch instead of a complete new V8 , obviously hindsight being the name of the game but the money they would have saved could have gone towards a complete new engine later on . 273 bhp in the late `60s would have been an eyebrow raiser

I’ll answer that Paul, as everyone else is obviously far too busy worrying about BMEP. AEC had turbo-charged its AV690 and AV470 engines in the late 1950s for some of its South American customers that were operating in the Andes. The use of turbo-charging in this instance was to compensate for loss of power by normally aspirated engines operating in the rarefied atmosphere of high altitude. There were also turbo-charged industrial versions of the AV470 and AV690, and a horizontal turbo-charged railcar version of the AH690 as well. So AEC was quite familiar and successful with the concept of turbo-charging pre-1962 and the Leyland merger. And that is when the waters become muddied. Leyland was not at all keen on turbo-charging (just like Gardner) and remember the A760 development programme was instigated by Stanley Markland during his brief time at Southall. When he resigned and departed anything with his name against it was deliberately ignored. Leyland finally had to investigate turbo-charging in 1968, some 10 years after AEC, when it dabbled with the O.680 and made it the turbo-charged 690 for the Two-Pedal Beaver…another “what if, maybe, and perhaps” model. The group was quite skilled at making those.

The TL12 if launched 5 years earlier would have been a safer bet then , and then designing a larger V8 with more potential for higher outputs would have been a better bet with no rush for a launch . Everything was there in front of them , the Marathon cab the turbo TL12 in `68 would have definitely made the grade giving AEC a platform to work from and valuable time. But as usual decisions from Lancashire scuppered things

[ramone]

bma.finland:
in Finland we had Vanaja lorrys whit turbocharged Av690 250 hp from 1965 ,they did well in competision to S-V DS11 and Volvo Td96

Did the AV690 turbo compare well with Volvo and Scania “bma” ?

[bma_finland]

as i heard about it they did good , even some 760 were over here under the ergo cab ,and a few V8 was teted before Sisu take over Vanaja 68 ,lastVanaja was of line 70 theturbo 690 was in bonneted lorrys

[carryfast]

ERF:
Weeding through the nonsense, you made reference to the AEC V8’s supposedly very poor BMEP figure
All I am asking is… GIVE US SOME BMEP FIGURES to compare!!
See…you’ve got me shouting now. And I don’t shout.
Put some meat on the bone of your argument!!

Rolls 220 12.1 litres 610 lb/ft = 50.4 lb/ft per litre x 2.464 = 124 psi.

AEC 800 13.1 litres 580 - 638 lb/ft = 44.2 - 48.7 lb/ft per litre x 2.464 = 109 - 120 psi.Which leaves the question can the latter torque figure be believed bearing in mind Scammell’s obvious choice of transmission spec for it ?.

So there we have it 13.1 litres and 8 cylinders with at best worse specific torque of less than 50 lb/ft per litre than 12.1 litres and 6 cylinders.As I said might as well have condemned it at that point sooner rather than later. .

While the Rolls 305 at 70 lb/ft per litre showed a similar advantage over the TL12’s less than 65 lb/ft per litre.Which again suggests that more leverage beats more piston area.With the ■■■■■■■ 855 in NA 250 form just being an under stressed exception which proved the rule.With its level of built in redundancy being clear from the point when they turbocharged it.

With both the Mack 856 and Scania DS14 being the relevant architectural break point where a V8 starts to work and make sense,resulting in the definitive Scania V8 design of today.

[carryfast]

Edit Mack 864 ?.All this maths and these numbers are doing my head in.

[bma_finland]

like this Vanaja 690

[erf]

AEC V8 engines were tested by Vanaja over the 1967/68 winter.
Although described by AEC as prototype development engines, these engines were all identical to production units.

It is believed that four engines were sent to Vanaja, and that all were returned to Southall for examination after the testing was completed.
It is also believed that these V8 engines were the four engines sent for sectioning, and then displayed inside perspex domes with their crankshafts turned by geared electric motors at various trade shows, including the Mandator V8 launch event. If that is the case, then two were AV740’s and two AV800’s.

[carryfast]

ramone:
The TL12 if launched 5 years earlier would have been a safer bet then , and then designing a larger V8 with more potential for higher outputs would have been a better bet with no rush for a launch . Everything was there in front of them , the Marathon cab the turbo TL12 in `68 would have definitely made the grade giving AEC a platform to work from and valuable time. But as usual decisions from Lancashire scuppered things

Can’t see how struggling on with yet another compromised Ergo derivative beats using the 3 VTG cab.

While as shown in the figures the TL12 was always going to struggle v the ■■■■■■■ and Rolls for similar reasons to the V8 ( lack of torque potential ).While people seem to under estimate just what a formidable package the Rolls actually was and that’s the ideal which AEC needed to be following.Possibly in slightly bigger 13 litre form thereby fitting perfectly between the Rolls and the ■■■■■■■ in terms of capacity and keep the 690 type architecture for a proper V8.‘If’ they really needed a big V8 in their armoury ( doubtful ).

While it seems obvious that the basic design premise of the V8 had everything to do with AEC betting the farm on an already obsolete idea going back to the 1950’s of a pointlessly small V8 to fit in under an equally pointless silly small low set cab.Nothing to do with Lancashire.

[carryfast]

ERF:
AEC V8 engines were tested by Vanaja over the 1967/68 winter.
Although described by AEC as prototype development engines, these engines were all identical to production units.

It is believed that four engines were sent to Vanaja, and that all were returned to Southall for examination after the testing was completed.
It is also believed that these V8 engines were the four engines sent for sectioning, and then displayed inside perspex domes with their crankshafts turned by geared electric motors at various trade shows, including the Mandator V8 launch event. If that is the case, then two were AV740’s and two AV800’s.

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Great idea.Let’s test it in the 6 wheeler rigid sector,that it should have been used for instead of the 500,then tell everyone that it will work in a 32-40t gross artic.

[zb_anorak]

Carryfast:
Great idea.Let’s test it in the 6 wheeler rigid sector,that it should have been used for instead of the 500,then tell everyone that it will work in a 32-40t gross artic.

Those Vanaja rigids would have had 3 axle drawbar trailers, and been run at 50-odd tons gross. Benkku will know the actual figures.

[carryfast]

[zb]
anorak:

Carryfast:
Great idea.Let’s test it in the 6 wheeler rigid sector,that it should have been used for instead of the 500,then tell everyone that it will work in a 32-40t gross artic.

Those Vanaja rigids would have had 3 axle drawbar trailers, and been run at 50-odd tons gross. Benkku will know the actual figures.

Blimey around 600 lb/ft to haul up to around 50t. I’d guess that the turbo 690 would have produced a fair bit more ? but can’t seem to find any torque output for it.

While the photographic evidence seems to suggest that the T6 was often used as just a rigid.If not only pulling a light one or two axle trailer.The former might explain false over optimistic results being fed back as to the V8’s durability.

[erf]

Carryfast:

ERF:
All I am asking is… GIVE US SOME BMEP FIGURES to compare!!

Rolls 220 12.1 litres 610 lb/ft = 50.4 lb/ft per litre x 2.464 = 124 psi.

AEC 800 13.1 litres 580 - 638 lb/ft = 44.2 - 48.7 lb/ft per litre x 2.464 = 109 - 120 psi.

So there we have it 13.1 litres and 8 cylinders with at best worse specific torque of less than 50 lb/ft per litre than 12.1 litres and 6 cylinders.As I said might as well have condemned it at that point sooner rather than later. .

While the Rolls 305 at 70 lb/ft per litre showed a similar advantage over the TL12’s less than 65 lb/ft per litre.Which again suggests that more leverage beats more piston area…

Thank you CF!.
At last!.
Although quite why have you chosen to compare the AV800 with the Rolls 220 I don’t know.
The AV740 engine makes a better comparison because both engines have the same bore size, both have the same 12.1 litre cubic capacity, and both produce their maximum torque at the same RPM - 1400, thus making the only difference their basic architecture (as you like to call it) - the ‘all important stroke’!.

The first thing we need to do is to make sure we’re all singing rom the same sheet, ie all figures quoted are produced to the same standard. In the case of AEC, playing by the rules as ever, all figures were quoted to BSAU 141:1967 (Atmospheric pressure 760mm, Inlet air temperature 20 dec C…etc). Just at this exact moment I can’t find the figures for the Rolls 220 where they have been expressly quoted to this standard, but I will try when I have more time later so that we can complete our comparison.

The whole point of using BMEP figures is that they remove cubic capacity from the comparison.
This makes it possible to realistically compare the ‘work’ ability of engines produced with different overall capacities, which is why I can’t quite understand why you are re-introducing capacities, and different ones at that, into your thinking above.
With BMEP we can accurately asses the ability of an engine design to inhale air, compress it, inject fuel, burn it and get usable power from it.

Without wishing to get into an argument on the why’s, the formula used in the engine development profession to calculate BMEP runs along these lines (sorry it is a scan of a sheet issued to Perkins students, but I’m not clever enough to get the characters on my keyboard)…

You will note that no torque figure is introduced into the actual equation, the torque being used to calculate the Brake Power.
Using this formula, the AEC AV740 engine produces a BMEP of 115.1 psi - so actually not wildly different from your figures.
For a direct BSAU 141:1967 comparison, the Perkins V8 in both 510 and 540 form produce 112psi.
The 130mm bore AEC AV691 produces a BMEP of between 115 and 116 psi.
When we have confirmed the Rolls 220 figures to the standard, we will compare that too.

[erf]

Carryfast:
AEC 800 13.1 litres 580 - 638 lb/ft = 44.2 - 48.7 lb/ft per litre x 2.464 = 109 - 120 psi.Which leaves the question can the latter torque figure be believed bearing in mind Scammell’s obvious choice of transmission spec for it ?.

Sorry, missed this in my reply above.
You will note from my post showing the same vehicle entering service with Bass in 1970, that the gearbox had by then been changed to the TET D251 ten-speed splitter.