Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) What choices

Heinz ... if you drove your car onto the rollers, ran it, and got the graph then that will be wheel horsepower and will already include the losses in the transmission ... so no more to subtract in your case.

To get crank horsepower a different type of engine dyno would be used .... or if you asked (for bar-room bragging rights or some such) then your dyno place might add some figure arrived at by a formula to give you a contrived 'crank horsepower' figure derived from your real-world wheel horsepower.

To me the only figure I've ever been interested in is wheel horsepower .... because that tells you what you have where it counts ... where the rubber meets the tarmac!! 🙂

K

Image, I don't know exactly, but I would assume that in my case something was added to indicate the crankshaft horsepower., otherwise my engine would generate 180PS at the crank shaft… If the manufacturer gives the power, e.g. 110 hp or similar for the Sigma 4/4 without tuning, is that crankshaft hp? which I would suspect.

Heinz ... I'm afraid I have little German to know whether this company may add some sort of function to take the wheel power reading from the rollers and add a calculated 'drag' figure to it when generating the graph. The motorsport guys don't do this as racers are really only interested in what's actually reaching the road 🙂

K

Image & Heinz. Thank you. Seeing John’s post re the drag. I guess in reality when my car was standard it was not producing a lot to the wheels.
The car also has a 4.1:1 diff so pulls well anyway. I was very pleased with the re-map at the time & still am.

Just goes to show what choice is a big question.

IcePack, you must be so lucky to have a 4.4:1 diff. I have another question about this, perhaps for Image. Is drag reduced if all values remain constant for a given car but the diff ratio becomes shorter?

Heinz ... by 'shorter' I assume you mean an overall lower gearing giving better acceleration? ..... my guess would be that any differential effect of Pd would be so minor as to be of only theoretical interest .... for a given speed the revs would be a bit higher but the Pd trace on the graph is pretty much linear and quite shallow so the increase in losses would be minor .....and for one significant part (the rolling resistance of the tyres on the road and the frictional losses of the rear axle bearings and brakes ) unchanged .... wouldn't lose sleep over it ... but if you wanted to compensate then give the carpets a good vacuuming and leave the loose change out of your pockets!! 🙂

K


Ps .. just eyeballing your graph on my little phone screen I reckon if the diff increased the revs by 10% for a given road speed then the Pd losses would increase by less than 5 bhp and, with the fact that the tyre and rear axle losses are speed, not revs, dependent then in real life it would be somewhat less than that in real 'rubher to road' terms

I would like this thread to return to its original topic so that the OP's questions can be discussed again, sorry for my enthusiasm regarding power measurement on the dynamometer. I'm opening a new thread because I still have a few questions about this, even though most of it may have already been said.

Yep! ... we are a bit good at thread drift on here! 🙂

K

Wot no fish

Being serious test drive a few cars. The dealers have a lot of stock and your car will find you.

Manufacturers always quote power at the crank, this is because they use engine dynos; at the time of recording the numbers there are no wheels

Engine dynos are where it's at because they give a true number the engine genuinely produces, the only reason we use a rolling road or a hub dyno is because it's inconvenient to remove the engine from a car just to record the engine's output, but of course people then try to work the numbers back to the crank because that's where manufacturer base numbers come from.

It should be quite straightforward to get a little ballerina 1.6 Sigma to make 100hp per litre, and in theory it should also make good power everywhere as it benefits from variable valve timing on both the inlet and exhaust camshaft, at 90kg that would be an excellent 1.78 horsepower per kilogram of engine mass.

But the elephant in the room for the plucky little Sigma is always going to be the 2.0 Duratec, in the same relatively modest state of tune as that tweaked 160hp Sigma, the Duratec romps away to deliver an easy 200hp, and without making a light car like a Trad Morgan nose heavy. The Duratec achieves this because you're only adding 10% more weight (10kg) to achieve a whopping 25% increase in power over the Sigma, that's the sort of deal you call a 'No-Brainer'!

Add more than 10% weight and I suspect that's where you'll start to feel the balance of the car change, don't get me wrong the Cyclone 3.7 V6 is an excellent engine but at 170kg it's 70% heavier than a 2.0 Duratec. I've been a V8 man all my life, but more recently I've found a new respect for the humble four banger, modern twin cam four cylinder engines are incredible things and as long as you don't go too far above 2.0 litres they are also super smooth allowing for very high engine speeds without vibration.

Most people will tell you 'King of the Hill' in the world of four bangers is the Honda K20, it's certainly an amazing engine that was right from day one but Honda just kept on developing it to make it even better, but what they don't tell you is, these Honda four banger 'K' series engines are quite heavy at 125kg

We think Monty's Duratec should be making 205hp, and at just 100kg that's an outstanding figure of 2.05 horsepower per kilogram of engine mass.



We also believe the Type-R K20 in my mate Dave's Z-Cars Mini 'Molly' pushes out 220hp from the 125kg lump, which is 1.76 horsepower per kilogram of engine mass, that's more or less the same as the Sigma.

You can just imagine the friendly 'Monty vs Molly' banter when the two Dave's get into down the pub

Only last week I said..... "Ditch the washing machine Dave"

Merry Christmas to you all

Dave.