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Bob Stringfield
United Kingdom
854 Posts |
 Posted - 12/04/2008 : 21:28:36
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It is fairly easy to work out the Brake Horse Power / Litre figures for standard MMM cars in that a PA on SUs produces about 42 ( life, the universe and everything ) BHP/Litre. On its original blower, I have no idea.
Are there any authentic, documented figures for MMM competition engines such as the K3, C, J4, Q or R, for instance, or your engine, in either contemporary or today's tune?
Post-war engines are better served, in that I can look up with ease my '70s MZ motor cycle's 108 BHP/Litre or the '37 Topolino's frugal 26. |
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Bob Clare
United Kingdom
278 Posts |
Posted - 13/04/2008 : 12:57:21
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Bob,
I expect a few of the racing brigade will respond to this but, for what itÆs worth, hereÆs my 2 pennyworth:-
The quoted rating for the PA engine was 36 @ 5,500rpm (= 43bph/l as you say). The PB I have quoted as 43bhp at the same revs (= 45.8bhp/l).
The info I have here suggests that the ôquotedö bhp for the engines fitted to both QAs and RAs was 113 (= 150.7bhp/l). However, reference to Fig 6 on page 50 of ThornleyÆs ôMaintaining the Breedö shows that the ôMagic Midgetö engine with bronze head and 8ö Zoller blower running at 0.7 engine speed and blown at something like 35psi (good way to produce a bomb one might think!) gave an indicated power of around 145bph (= 193bhp/l).
The K3 1087cc engine is said to have given 120bhp @ 6,500 (= 110.4bhp/l). This is probably conservative and the graph on page 73 of ThornleyÆs book indicates that approx 125bph was produced when the Powerplus blower was used. But even this was peanuts compared with the indicated 200bhp @ 7,500rpm which appeared to be possible with the Centric blower running at 0.7 times engine speed as tried for EX 135 (see page 111 of ThornleyÆs book).
Hope that helps but I donÆt recommend anyone trying this at home with a P or N Type!
Cheers,
Bob Clare
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Rodney Collins
United Kingdom
424 Posts |
Posted - 13/04/2008 : 15:56:33
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Bob, my PB engined PA produces 88bhp at 5500 rpm at the wheels with a volumex blower running at 12 psi, This was on a very reliable rolling road in Cambridge which is used by meny of the serious mini racing boys. The engine is pretty standered other than the blower. For such a small engine it has masses of torque, making it a pleasure to drive.
Rodney |
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Bob Stringfield
United Kingdom
854 Posts |
Posted - 13/04/2008 : 17:57:43
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Thanks, chaps.
The reason for this query is that an owner of what the VSCC calls a 'prestigious vintage car' expressed extreme scepticism at my remark that MG had got something approaching 200 BHP/Litre from a MMM engine. Too cheap, I suppose.
It irritates some in the bike world that Walter Kaaden got 200 BHP/Litre from a 125 MZ in the early 'sixties. Again, too cheap.
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Peter Scott
United Kingdom
1240 Posts |
Posted - 13/04/2008 : 18:03:39
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quote:
Originally posted by Rodney Collins
.............. The engine is pretty standered other than the blower.
Rodney
But 'Tom Dark' standard rather than MG standard???
Peter |
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bahnisch
Australia
674 Posts |
Posted - 14/04/2008 : 00:39:50
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| I think that the nearly 200bhp/litre produced by MG in 1935 was easily the highest in the world to that time and in fact for some years to come (the GP Mercedes-Benz and Auto Unions produced not much over 100) until ultimately surpassed by the later "Formula One" Alfa Romeo 158's in the early 1950's (with two-stage supercharging!). |
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David Allison
United Kingdom
665 Posts |
Posted - 14/04/2008 : 11:39:19
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The chapters in Maintaining the Breed are very entertaining and give insight into how highly regarded MG Car Company were within the motor industry at the time.
Reg Jackson and Syd Enever were invited guests during speed week to the racing depatments of Mercedes and Auto Union and are also both highly regarded by Richard Seamans' engineer Guido Ramponi (I think that is spelt right).
The works's racing department performed miracles with tiny resorces - most of it achieved with lightly modified standard components.
Steel cranks etc appearing much later on.
Indeed the Laystall crank was often regarded as too heavy and restriced accelerration within the tight knit engine building department after the war.
The engines gave very high BMEP in comparrison to other cars of the time - thanks to a very short stroke and using higher revs and boost pressures than the excepted norm at the time.
The Alfa 158-159 engine used their own experience gained pre-war plus from other companies such as MG and the German manufacturers - plus papers published by Murray Jamieson and Chris Shorrock.
Supercharging is an interesting engineering cul-de-sac.
MG did indeed manage close to 200 BHP per litre from the R type - although this was for quite short periods.
The problem they had was maintaining the boost pressure with the Zoller - the tips of the blower vanes wore out quickly.
Shorrock worked on different materials on his blowers but never really sorted the problems.
Alfa used another method - this was a larger rootes blower running at engine speed - eventually using experience gained by Mercedes and Auto Union, feeding gas into a smaller blower (two stage) for increased gas flow.
Rootes blowers rely on gas flow to gain manifold pressure - the method of increasing blower speed was found to give no real improvement - therefore the only way to increwase the flow was to speed the gas by forcing it through a smaller hole.
That said the real step forward in supercharging has only happened in the last 20 years with electronic assistance - modifying the ignition curve and even the valve timing to maximise the engines efficiency.
The most powerfull modern engines are the Top Fuel Dragsters (around 1500 BHP per litre) but F1 BMW turbo engines were producing this in qualifying in the 1980's.
Modern F1 engines produce around 350 BHP per litre a figure similar to the Moto GP bikes (250-270 BHP from 800 cc) and they are all unblown.
The fact remains that a small sports car manufacturer based in an Oxfordshire market town built a world beating reputation for safe, reliable and fast cars - not to be sniffed at except by some of the more elitest members of other car clubs!
Well done MG - all power to those who champion Reg Jackson, Syd Enever, Cecil Cousins, Fred Kindell, Henry Stone and all the other midnight oil burners within the Abingdon factory.
Someone should write a book about them.
Regards David
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MDP
United Kingdom
35 Posts |
Posted - 15/04/2008 : 16:30:28
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The R type gave a reading of 190 hp on the rolling road. Since then we've increased the Zoller boost by 10 lbs so the hp must be over 200, it certainly feels it...
Mark |
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John Reid
United Kingdom
704 Posts |
Posted - 15/04/2008 : 22:03:13
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That R type figure is impressive!
Talking of bhp/litre, I thought a top fuel dragster is nearer to 1000/litre. The engine capacity is 500cu in (about 8.2 litres) and the estimated/calculated horsepower is between 7900 and 8300 - estimated because the engines aren't designed to run for more than about 10secs so coupling to a dyno for a power run is tricky.
Digressing a little and if you go to the other end of the capacity scale ... the Halman Special 2.5cc model aeroplane engine, designed and used by Pete Halman for F2 Control Line Speed, produces 2.5bhp at 41,000rpm (!) using a tuned pipe exhaust. That's 1000bhp/litre. Pete's day job is the Technical Director of Irvine Engines and we used his expertise and Irvine model aero engine components to build the compressor for the pneumatic valve gear on the early Mercedes F1 engine.
As David says, the guys at Abingdon did a great job designing and producing the Triple-M engine. For example, the finger follower valve train is still current F1 practice and stands up well to modern scrutiny particularly where cam/rocker lubrication is concerned. The computer analysis of the MG geometry gives it a good score, whereas the R-R Merlin (similar design) has a known weakness for wear in the rocker profile.
John R |
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William Opie
United Kingdom
28 Posts |
Posted - 16/04/2008 : 13:42:41
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My PB with an original Centric 125 set up produces 58 BHP at 5200 revs. Engine is fully rebuilt with cosworth pistons etc but I suppose returning to reality on this topic represents what could be expected in the 30's. Boost is only about 3lbs but she is a pleasure to drive. That is about 30% up on standard. Next project is to fit a 160 centric!
regards
William Opie |
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Rodney Collins
United Kingdom
424 Posts |
Posted - 17/04/2008 : 09:24:09
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Intresting subject, however are the figures quoted at the flywheel or the rear wheels? Marks R type must be at the wheels as it was done on a rolling road as was mine. I have no idea how much bhp would be lost in the transmission of power from flywheel to rear wheels!
Rodney. |
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Gordon
United Kingdom
692 Posts |
Posted - 17/04/2008 : 10:47:12
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Rodney,
You say that your PB is pretty standard apart from the s/c. Are you certain that the rolling road people have not converted their figres to flywheel bhp? Obviously the figure at the wheels will be dependant on which gear was selected at the time the max power figure was taken and so the losses associated with the transmission will depend on gear selection to some degree. If the reading was taken in an intermediate gear then would anyone like to comment on the losses. My GUESS is it could be 35%! My own car, a PB, was measured on a rolling road and gave 56bhp at the wheels and I was told that this equated to 85BHP at the flywheel. The car has standard compression ratio, standard valve timing and cam profile and is running at about 12psi with a very cool inlet manifold. It does have the benefit of forged pistons, steel billet crank and Phoenix rods but is otherwise standard. The blower is a Wade of 1 liter capacity running at crank speed.
Gordon.
Gordon |
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ags
United Kingdom
275 Posts |
Posted - 17/04/2008 : 15:10:23
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Hi All,
I am with Gordon on this one. Losses in the transmission, even in a direct drive (in the gearbox) top gear can indeed be 25% to 35%. The first time I put my PB on a rolling road, Oselli's in Oxford about 1973, I was extremely disappointed to find that the rear wheel output was only 29 hp in top. Adjustment of carburettor needles and ignition timing got this to 32.5 hp at the end of the session. The biggest gain being from departing from the "book" ignition timing, see my earlier posts. The youngish man who was operating the road confirmed that my losses were not unusually high and that his personal mental adjustment was to take a third off flywheel figures for typical transmissions.
My engine at that time was nearly standard, the compression ratio being the biggest difference at about 7.3. The ratio was that because that was the only head that I had at that time and it had been thinned down before it got to me. It was unblown of course, the carburettors being standard OMs on a standard manifold and though I had matched the ports on both inlet and exhaust sides there was little other tuning. The camshaft was standard and though the timing was reasonable I had not paid as much attention to it as I was to do later. My guess as to a flywheel figure would be the book 43 hp and the rolling road did confirm that this was achieved at the standard 5500 rpm when everything was optimum.
So my car gave approximately 24% lost from flywheel to road, based on the flywheel guess, or 32% of the measured figure at the wheels. I therefore still use one third for my own pinch of salt to add to claimed figures at the wheels.
More technical ramblings from
Andrew Smith MMM571 |
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David Allison
United Kingdom
665 Posts |
Posted - 17/04/2008 : 17:03:52
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I was always told that 33% was correct for transmission losses - supercharged engines cause an additional loss of around + 5-10% - but make up for this in power achieved by fitting the blower.
This is why it was often considered that less than 10 psi boost was hardly worth bothering with.
A blower giving only 5 psi gives a power increase of around 10-15% - subtract the power losses and suddenly all you have achieved is better torque.
My Dad is "anti" rolling road - but that is just him.
The rolling road is of most use for high revving engines (motor cycles, racing cars) where you are trying to gain power improvements at very high throttle openings (not possible during road driving - well not legally).
I am not convinced of the use of rolling roads with pre-war cars - the strain on the car is too high and the operators normally only achieve a minor improvement.
If you do take a car to a rolling road - make sure to tell the guy want you want.
I always tune for maximium spread of torque - this makes the car more tractible - rather than asking for maximum power.
I am sure that if you find a dependable operator then a rolling road will achieve good results (I always used Aldon who are very good) and it is always interesting to do it once!
Regards David |
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Rodney Collins
United Kingdom
424 Posts |
Posted - 18/04/2008 : 09:19:35
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| My 88 bhp at the wheels was at the wheels, the car was running in top gear and the operator was controlling the RPM with the rolling road. He (Peter the operator) has been doing his job as a racing machanic for 35 years and operating a rolling road for as long as they have been avalaible, so I have every faith in him. I was recommended to him by a friend that has just about the fastest Frog Eye currently racing and he is a stickler for keeping within the rules so hia frog eye has no hidden extras, like some of the Goodwood revival E types & Cobra's were found to have! So I have every faith in the rolling road figures. I find with a rolling road you can make timing adjustment while the car is running, this is where a good operater can find the extra BHP,Peter also recons there is a furthe 5BHP to be found if I could take a selection of SU needles which fit my 1"5/8th carb all the ones he had did not fit. when I drove away from the garage the car was a different car altogether, the torque was increased 10 fold. My Volumex blower reaches 13 pst with my foot flat on the floor I have a phenix crank and rods and cosworth pistons, I think Tom Dark used a standard cam. The car really is a plesure to drive. Rodney |
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Mike Allison
United Kingdom
196 Posts |
Posted - 18/04/2008 : 17:02:07
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Hello: I think this is my first contribution, but since I see my name taken in vain, I thought I would have two-penn'orth.
The Triple-M Engine did produce the highest specific ourput of any engine pre-war: indeed the 100bhp/litre was regarded as the datum to which to work for racing engines until around 1956. It is fairly easily achievable with forced induction, although MG really were the first to do so. The J4 officially produced 72 bhp, which is 96/litre, and this was on methanol based fuel. The contemporary K3 engine was therefore the first, with 120bhp, or 109/litre, running on alcohol fuel. On Petrol/Benzole mixtures, power was nearer 100bhp.
The Q and R type engines produced 113 as standard, but this was improved by using higher boost, different fuels, and ultimately on the Harvey-Noble and EX127 cars, using a bronze head, and something around 164 was the best achieved, and this by the Factory. This represents 218bhp/litre.
The Alfa 158 was the next leap forward, these were 1500cc units, and prewar were producing just short of 300bhp, but the engines were quite a lot more sophisticated than MG's single cam layout.
After the was they were claiming 440bhp.
Then came the BRM, which eventually was giving just short of 600 bhp, using sixteen cylinders, but still only 1500cc. If only things had gone to plan with that engine, Raymond Mays' dreams might have come true!
The MG was real though, and the little factory in Abingdon (it used to be in Berkshire up till about 1970) acheived so much with such small resources. I told the story as it was told to me in "The Works MG", which is still in print, availble from Haynes of Sparkford, and other good bookshops. (end of commercial)
About fifteen years ago I set out to emulate some of this with the engine in the family NO. Using 1100cc and a boost of 25/27psi, running on methanol-toluene fuel we achieved 204bhp at 6800rpm on the dyno. The engine has a lightweight flywheel (6lbs weight) a Fardon Crank and Phoenix rods. We used a very high overlap camshaft. Sadly I was getting on in years, and although we won a few events, the decibel level was too high for modern ears, and we have now curtailed its power.
It now has 10/12 psi boost, and runs on what passes for petrol these days. Thanks to the efforts of Oliver Richardson, the car is now in road trim, and has just passed the MOT test, and will be seen at future events driven by my daughter Jane and her husband Tim Metcalfe. Who knows, I might still get a look in every now and then.
Enough of my ramblings: keep up the good work.
Mike
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