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Octane Rating of Canadian WWII vehicles
In researching why, during the Normandy campaign, the British Army received 1,400 trucks (Austin K5's) that were not operable and had to be scrapped, I found myself enmeshed in the minutiae of octane ratings, compression ratios and the difference between American and British made engines. Which leads me to my question about Canadian manufactured trucks.
As Canada was supplying trucks and cars to the British Army as well as to the Canadians in Britain from the beginning of the war, and the British Army was using low octane fuel up till 1943 exclusively, were the aforementioned vehicles that arrived in Britain early in the war operating on British Army low octane fuel or North American high octane? And, if low octane, when did Canadian manufacturers change over to high octane engines? Thanks for any help, Dan. |
#2
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As a start point I believe a Jeep built in April 1942 has 68 minimum octane on its data plate.
When you ask about manufacturers changing over to high octane engines. I would suggest that all that would have happened was that they altered the ignition timing specs?
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... Last edited by Lynn Eades; 21-04-20 at 21:55. |
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Quote:
Cheers, Dan. |
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Hi Dan, While looking for the answerI found this:
"That process would make a crucial difference in mid-1940 when the Royal Air Force started filling its Spitfires and Hurricanes with the 100-octane gasoline imported from the United States instead of the 87-octane gasoline it had formerly used." And this: Quote:
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
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And then I found this from Doug Greville's site: In the text, it explains how the octane rating is arrived at.
Quote:
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
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Another point to consider is the physical design of Automotive engines.
Britain was lumbered from the introduction of internal combustion vehicles with the peculiar notion of "Taxable Horsepower" or RAC Hp. This meant that a certain car or truck was taxed annually for the road based on it's "taxable" Hp. But this figure bore no resemblance to the actual horsepower of the engine! Taxable Horsepower was a notional value derived solely from the total area of the piston crowns. It was not concerned with the stroke or the total capacity of the engine, and certainly not the output of the engine. So two comparable 4 cyl engines, one of a bore of 3" and a stroke of 3" (cap of 85ci or 1.4l), and another with a bore of 3" and a stroke of 3 1/2" (cap of 99ci or 1.62l) would both have an identical "Taxable Hp" of 14.4Hp. But plainly the 3.5" stroke would be a larger capacity and make more actual power and torque. So the tendency for British motor manufacturers was to design engines of an "Undersquare" design where the Stroke was proportionately longer than the Bore. This was an inherently inefficient restriction to best design practise (a point that was not evident to the UK Govt, who continued to encourage inefficient products for far too long!). The US auto industry was not hampered by this inefficiency, and refined engine designs to produce better Hp/ci ratios from "Square" (ie equal Bore/Stroke) and "Oversquare" (Bore larger than Stroke) engines that were able to achieve higher RPMs, and therefore more power. However, the stroke of an engine directly relates to the speed of the piston as it moves up and down the bore as the crank rotates. As the piston in a short stroke motor does not move far in 1 revolution, it's speed is lower. A long stroke piston, in that same 1 revolution the piston moves a further distance, the piston speed is higher. Material properties of the pistons, (initially steel or iron, later aluminum), lubricants and ring material all contributed to what the actual maximum speed of those pistons could be, but for any material, the short stroke engine was ALWAYS capable of higher Rpms than the long stroke engine. The one benefit of of the slower speeds imposed on long stroke engines is that the compressed fuel mixture had longer time to burn as the piston travelled down the bore. Low Octane fuel is a slower burning fuel and works best in a long stroke engine. In fact, the US move to find Higher Octane fuels was a direct result of their development of oversquare engine designs. A higher rpm engine has less time to burn the fuel mixture, and a higher CR was needed to increase burn time within a much shorter duration "Power Stroke", and this in turn required a higher Octane rating of fuel. Conversely, using quick burning High Octane fuel in a long stroke motor results in lower power output as the fuel has completed burning well before the piston has completed the Power Stroke.
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You can help Keep Mapleleafup Up! See Here how you can help, and why you should! |
#7
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In saying all that, for Dan's benefit, The relatively low compression ratios of most war time engines was in the area of 5 or 6 to 1. This in most cases would have been pretty forgiving except that (as per Tony's post) most British vehicles had a very low power to weight ratio.(iets say a conservative approach to horse power)
Nowadays Dan, most European and Asian built cars are running about a 10 to1 compression ratio (often, on top of which goes a turbo) It's all about volumetric efficiency which means stuffing as much as you possibly can, down the hole (the air fuel mix, that is) I hope this all makes sense and I am sorry I've not yet found any info on the standard octane ratings of British fuel, during WWII.
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
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as an asside
After the war was over, my Father mounted an expedition to visit Ain Dalla. This uninhabited oasis is NE of Farafra oasis to the East of the Great Sand Sea. It was a jumping off base for the LRDG and there were reputed to be stores dumps still there. And so it proved. There were boxes of flimseys and some jerry cans. Some of the flimseys still had petrol in them and my Father drove back to Cairo on it in his Jeep, some 370 miles. When he got the chance he sent a sample to the Shell offices and they analysed it for him. They pronounced it to be 53 octane and "should not be used in a motor vehicle"!
Having said that he also fitted a second fuel tank to his Jeep and would run on paraffin when the Police were not in evidence. We still have his desert equipment including his bubble sextant and Cole sun compass. In a burst of enthusiasm I have just finished making a small batch of replica Bagnold sun compasses. Alastair F60S Lynx I MkIII* |
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I love the (9.00?) x 16 sand tyre on the jeep. Does that equal low range starts?
53 octane. That is pretty low. Had all the petrol evaporated leaving the bunker oil?
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
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100 octane aviation gasoline
Read the Imperial Oil Review, Summer 1944 for an article on "100 octane aviation gasoline - The story behind the develpment of the fuel that helped to give the United Nations air superiority over Germany"
http://wartimecanada.ca/document/wor...ew-summer-1944
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Regards, Hanno -------------------------- |
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Agreed. Like Lynn, the only references I can find on this subject seem to point to only wartime US aviation fuel being a higher Octane than British production.
It seems that US motor fuel was just as low as Britain's until the Post-War years
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You can help Keep Mapleleafup Up! See Here how you can help, and why you should! |
#12
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I originally read about this on the "Axis History Forum" under the thread "Unserviceable Lorries - Jul - Sep 44." It runs to 26 pages in total.
On post #12 it reads: Quote:
Cheers, Dan. |
#13
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Dan, as the octane rating goes up, the flame front travels faster and so, the ignition timing requires retarding. (not advancing)This allows the piston to reach t.d.c. before the pressure on the piston builds too much.
I'm surprised that Richard F. hasn't chimed in because I faintly recall a discussion about Bedfords and Morris's that had piston problems and I don't recall the reason.
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Bluebell Carrier Armoured O.P. No1 Mk3 W. T84991 Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6. Dodge WC55. 37mm Gun Motor Carriage M6 Jeep Mb #135668 So many questions.... |
#14
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Found this info from my copy of Supplies and Transport Voll 2, i can put more info from the REME Vol 2 Technical if you want more.
Keith
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Keith |
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Quote:
This subject came up before, I think on HMVF forum, which I participated in. Also on an Axis form, I have lost the links now. The lorries of concern were a batch of Austin K5 4x4 in NW Europe campaign which were having engine problems, apparently with excess bore wear.. The discussions on Axis forum were with non-technical people as I recall (I could only read that forum), but from my research I found that there were a batch of Austin K5's which were supplied for wading, at a guess for unloading from sea transport. These had a special waterproof brake servo. What I did find out from Austin manuals was that the bores were given a greater piston clearance, my guess is that when the engine was warmed up on the landing craft, then plunged into cold water the rapid chill could seize the engine, but of course later on the extra clearance would then mean oil consumption and low compression. If REME were not aware of this they would automatically think that the engines were faulty. To quote the K5 manual; "piston skirt clearance has been increased from .0025"-.0028" to .004"-.0045" to make engines with new pistons immediately suitable for wading through water without fear of seizure. Pistons with the original smaller clearance can be used for engines of vehicles which it is known will not be called upon for wading". Regarding the change to leaded petrol, it was the deposits on valve stems that caused problems and many British manuals gave information on combating the problem, with mods to valve guides, increased valve clearances and alterations to ignition timing. I have quite a bit of tech info on this but am short of time at present. regards, Richard
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Richard 1943 Bedford QLD lorry - 1941 BSA WM20 m/cycle - 1943 Daimler Scout Car Mk2 Member of MVT, IMPS, MVG of NSW, KVE and AMVCS KVE President & KVE News Editor |
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