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MG Midget and Sprite Technical - How much torque does your 1275 produce
I am having a bit of a contentious pub discussion with a local vintage engine restorer ( he rebuilds ERA engines amongst other things), who maintains that it is impossible to improve the standard torque performance by more than 10%. So that would give for a 1275 a max possibility of about 79 ft/lb. I disagree and state that much higher figures are attainable. So who has chapter and verse on their engine as to what the measured torque is, on either a dyno or rolling road. Cheers Roly (looking forward to the next round of dicsussion at the pub) |
Roly Alcock |
Hi Roly, I have 78 bhp and just over 90 ft/lb on my rolling road print off from Aldon Automotive (see attached). The spec was: MG Metro head +30 bore LCB and RC40 HS2's with 'midget' K&N filter I have since fitted a HIF44 with K&N on a Titan manifold so the results would hopefully be better (well they feel it!!) Thanks Mark |
Mark Whitmore |
I think it all comes down to if you knief bladed the carb butter flys or not Prop |
Prop |
If I were the guy in the pub, I would say the chart is confusing. The colors of the curves don't match up to the legends vs what's stated in the thread. |
JM Morris |
I always thought torque was directly related to displacement...but horse power related to how quickly & efficiently the air moves through the engine? Could be wrong...often am! |
Dave Rhine ('78 1500) |
My effort although mine is a 1330 with 11.1 compression (worked out on the back of a fag packet) 123 dizzy, RC40. 276 Kent cam, Peter May played around with head and a played around with Hif 44 (not a great airfilter at the mo) on a titan, Maniflow system with an RC40 box.
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Gary Lazarus |
My understanding of HP vs Torque is Hp.... is the amount of work it takes to move a stationary object... aka more displacement the more work the engine can do to move the car and the easier it can move the car torque is the amount of acceleration the engine uses to make the horse power do its job an example miniture donkey, a breamer Bull, a 2 wheel cart, and a bull whip if you hook up a donkey to a cart he can pull the cart with about 60% of his strength, and if you smack him in the booty with a good swat from the whip, he will get up and move really fast for a short distance, meaning he used his power to accelreate to get away from the whip. samething with a the bull, but the bull only uses about 10% of his strendth to do the samething as the donkey... but there wasnt much torque from the bull when he got swated in the rump, cause no doulbt the bull simply turned around and plowed the cart driver completely 6 feet under...LOL Prop... Never tick off a bull with a whip. |
Prop |
http://www.howstuffworks.com/horsepower.htm |
Prop |
JM - Mark's Graph looks like it matches his figures to me. Can't see much confusing about it. Measured Power and calculated flywheel on the left bhp axis. Torque on the right lbft axis. |
Dean Smith ('73 RWA) |
here's an MED endurance race spec engine from a couple of years ago; 1380, 286SP cam, 1.5 roller rockers, 35/30 rally head, single 45DCOE, just under 11:1 CR Ignoring the spike, peak torque is 105. You'll notice I run conservative timing too :-) |
David Smith |
Ant Cutler is getting around 25% more torque than he should have (OK its a k series). Also I was lead to belive the BHP and torque are the same number at approx 5300rpm ish |
Tim Dalton |
Yes, BHP and torque should be equal at 5,252rpm (as shown in Gary's diagram ... but not in Mark's) The power curve is obtained by multiplying torque x RPM (with the appropriate conversion factor) |
Geoff Everitt |
The same because the conversion factors numerically cancel the RPM at 5252. Presumably with those dodgy metric units it happens at a different speed. (Haven't bothered checking because I prefer to deal with real numbers) While torque does indeed relate directly to displacement, it also relates to how efficiently the cylinders fill (no use having big cylinders if they are only a fraction full) and combustion efficiency. For any given engine, the usual easy way to vary the latter is via the compression ratio but ther are other factors like chamber design & heat control. In other words, all the usual culprits! In older low speed engines peak torque came at lower speeds when the chances of getting near full cylinders was much better. Our engines tend to get peak torque at higher speeds now, especially if modified. With modern induction systems, it is possible to achieve a bit over 100% volumetric efficiency (ie cylinder pressure a bit over atmospheric - think of it as being due to pulsations in the manifold branches working in harmony to ram charge in), so there are definitely some real gains to be had. |
Paul Walbran |
Yes Torque is basically a function of displacement so the more the displacement effectively the higher the torque. However as stated by Paul displacement is only useful if it is efficiently used, ie are the cylinders actually filling to a full 1275cc? not on early non modified cars they weren't but with modern modifications we do a lot better. Plus we also have better fuel which allows us to run higher compressions this raises torque appreciably and therefore promotes efficient use of the displacement. Over the years however the real gains have been made by being able to fill the cylinders better at high revs, this allows the engine to develop a lot more power and therefore adds to our overall enjoyment. Fundementally I think the ERA guy was right but failed to explain his position because I always say if you want torque put a big engine in :) or if you want torque from a small engine then fit a turbo... :)) I heard the other day that in years to come ALL modern engines will be turbo ed! |
Bob Turbo Midget England |
Geoff said:- The power curve is obtained by multiplying torque x RPM (with the appropriate conversion factor) What would the appropriate conversion factor be? Roly |
Roly Alcock |
Prop, I want to clarify the first part of your torque/hp analogy (can't do better on your second part): torque is the power (work) that an engine produces hp is the rate at which it produces that power A high revving engine (motorcycle, for instance) can post impressive hp figures, but the number is high because the rpms are stratospheric compared to a plodding auto engine like ours. High RPM = fast delivery rate, even though the torque may not actually be very high. Motorcycles don't need much torque to achieve F1 like performance, their mass is very low. A steam engine, which may only run at a few hundred RPM, has a surprisingly small hp figure (a classic steam engine in the 1800s was called the "12HP". But while its delivery rate is slow, the torque is very, very high, and the thing can pull a train weighing many tons. The long stroke, large displacement engines of the early motorcar era also had very low sounding hp numbers, but relatively "modern" sounding torque outputs, with their low RPM, and huge displacement. Folks mistake "hp" with "power", because the name has that word in it, but "hp" is NOT power, it is delivery rate. Not unrelated, but NOT the same thing. Norm "not sure if I am adding to the discussion, but wanted to clarify" Kerr |
Norm Kerr |
OK ... power, torque and arithmetic. Suppose you have 50 lb.ft of torque at 4,500RPM and the throw of your crankshaft is 3 inches (0.25 feet). The "force" producing this torque is 50/0.25 = 200 lb. Power is the rate of doing work or Force * distance /time and per second there will be 4,500/60 = 75 revolutions. Each revolution will have a circumference of 2 * pi * 0.25 so the amount of work done per second will be 200 * 75 * 0.5 * pi = 7,500 * pi ft.lb = 23562 ft.lb As 1HP is 550 ft.lb/sec, 23562 ft.lb/sec is 42.8 HP If there is still 50 lb.ft of torque at 6,000RPM, this would be equivalent to 57.1HP. Regarding the numerical equality of torque and power (using Imperial units), the RPM is as I stated 5252, this being 33,000/(2 * pi) ... 33,000 being the number of foot founds per *minute* which equals one horse power. |
Geoff Everitt |
And in regards to horsepower vs. torque: "horsepower sells cars, torque wins races" :) |
JM Morris |
Roly: I agree with Bob - the man in the pub is largely correct if he was to state: 'Without fundamental changes, it's hard to get an increase in torque above 20%'. A 10% increase is normally possible depending on how good is the starting point (so probably hard for already optimised engine, unless capacity increased). I note some of the quoted Aseries upgrades include capacity increases - this is a fundamental change. Sticking to carb, manifold, cam, head changes, he's ~right. My 1275 went from std 72lb-ft to around 80-83 lb-ft with small capacity, cam, head etc changes. My Kseries seems to have improved from mid 130s lb-ft to mid 160s; removal of cat and use of Emerald are the main changes. Your (ex-Midget)engine seemed to be in the mid-90 lb-ft, which is exceptional. Peak torque (as aleady stated) is mostly a function of capacity and compression. Power is the product of torque and revs (analagous to force and speed). If you can make an engine breath at higher revs (ie. pull in a cylinder full of gas at higher revs, and expel the resulting exhaust in ever shorter time-frames as revs incr: vease), then you will make more power at the higher revs. Normally, as revs increase, the breathing efficiency drops and so the torque curve dips after its speak. In BHP and lb-ft the equation is: power = (rpm * torque)/5252 Quite often, tuning an engine (as opposed to increasing capacity) moves the torque curve 'slightly up and to the right' in the dyno chart; sometimes decreasing the torque at low revs (engine becomes 'cammy' through poor trapping of gas); increasing peak slightly at higher revs, with a slower dip in the curve at higher revs (4K+) which increases power. I always transfer my dyno curves to a spread-sheet so I can see exactly where I've gained and lossed; helps me make the best use of the engine. As stated, torque provides the force for acceleration; but at any speed, the engine needs to make power to overcome drag, friction etc. So the acceleration a vehicle can achieve is determined by the amount of torque 'left' after subtracting the torque needed (at current revs) to generate power required to maintain current speed. Hence accel drops off with speed. A |
Anthony Cutler |
Although it is true that torque produces the acceleration, the cars total acceleration depends on the torque at the wheels ... ie a combination of torque at the engine and the multiplier effect of the gearing in the transmission. Because of theis, ultimately it is HP which determines acceleration by the time you take the transmission into account. 200BHP produced at 8000RPM from an 1800 4 cyl will (in the same car) produce similar acceleration and top speed as a V8 with twice the capacity and peaking with 200BHP at 5000 RPM if the gear ratios are optimised in each case. Lower gearing for the 4 cyl allows it to rev and gives a greater multiplier by the time it gets to the rear wheels which makes up for the lack of torque at the flywheel. (As the torque curves will likely be different shapes, there will be relative gains and losses in acceleration between the two at different engine speeds, but overall they will be similar) People with a default setting of 4WD or big V8 as a tow car scratch their heads I have used my 1800 K Rover for towing the Midget on a trailer, expressing amazement at how well it does it. If drive it like a big V8 and lug it in top gear of course it won't hack it, but using the gears to keep engine speed around 4000 RPM (effortless in a K) to produce the necessary torque at the wheels makes it a piece of cake even though it is very hilly here. |
Paul Walbran |
Hi, just one question: "BHP and torque should be equal at 5,252rpm (as shown in Gary's diagram ... but not in Mark's)" How much of an issue is this and what can cause this, should i be worried? Thanks Mark |
Mark Whitmore |
Sorry Mark, I'm afraid I didn't look at the graphs closely enough. I am used to seeing the power and torque curves using the same vertical scale (as with Gary's) ... in your case the scales are different. Looking more closely, I see that both power and torque are both about 78 in your case at 5250RPM so things are "normal". I must go for a litle drive to clear my head. |
Geoff Everitt |
Some pub torque here and old wives tales ""And in regards to horsepower vs. torque: "horsepower sells cars, torque wins races" :) "" Sadly very wrong consider present day F1 engines they have limited the RPM of these engines to 18000 RPM to save money, because teams were getting an advantage over other teams by finding ways to make their engines Rev high, produce more power and win more races. As has been stated a steam engine produces FAR more torque than a F1 engine but I know where my money would be. I think the problem in understanding is that BHP can not exist without torque and it is as simple as this How much torque is produced in 1 rev is a function of fuel used! How much power is produced is a function of how many times that amount of fuel can be consumed in 1 minute! Thus word done (power) is directly proportional to fuel used. As Paul states a high reving correctly geared small capacity engine is capable of doing the same amount of work as a slow reving huge engine the laws of physics apply and both will be using the same amount of fuel, (all things being equal) :) Mark, certainly nothing to worry about, however not sure why Aldon have done that? |
Bob Turbo Midget England |
Well, I'm 0 for 2 on old wives tales :). So here's another try: "There's no substitute for cubic inches". Ooops! I think that one has also been disproven! Strike three. Many thanks to all for helping me, at least, to get a better grasp of the relationships. |
JM Morris |
...all very interesting I'm sure and to each their own.. but I just want to sit in mine and drive it down the lane... |
David Cox |
This thread was discussed between 14/05/2010 and 18/05/2010
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