Do you know the power of 3 1/2

[pasi42]

Does anyone know why the 3 1/2 ´s motor power decrease in late seventies. My bike was registered 1979 in Italy. The model maybe 78-79.
The motorpover is 21 kw (27-28 hp) in paper. The older models have more power, why? Is there some rational reason to limit the power?

How the power decrease has been done? Camsaft or...?

:?

[EVguru]

The original power figures for the Sport, 42bhp (SAE) or 39bhp (DIN) were most certainly not obtained at the back wheel. I suspect that they're not even taken at the gearbox sprocket. They are instead the power at the crankshaft.

Different Countries had different rules about what power motorcycle you could ride on different levels of licence. Often this was 'manufacturers stated power' and no specification was given as to where this power was to be measured. Changing which power output you quote can make the bike compliant without ever actually changing the state of tube.

In the UK there is a 33bhp limit for newly qualified riders unless they have taken a 'Direct Access' test on a larger machine. The law does not specify where the power is to be measured and I believe that NLM will sell you a 350 (or possibly even 500) Morini with a certificate stating the power complies with the 33bhp rule. If you were ever challenged the bike would have to be tested. Since this would be done on a rolling road dynamometer, there's little chance that you'd exceed 33bhp at the rear wheel.

[morinipete]

Perhaps also Morini were truthful in later years ? If you read any technical articles on the v-twins they tend to come from the first years of production and talk about pistons which were machined to give the correct compression ratio (different for sport and strada). I do have one set of pistons like this, which are not only machined in the combusion chamber but on the upper surface also.

Other than that I've only ever seen cast pistons with imprecise top crowns, which is what you'll get if you buy new now (unless anyone knows otherwise ?). I think from the late 70s Stradas and Sports had identical pistons also, so perhaps the lower figure comes from this 'standard format' engine, which probably had to have a lower compression ratio to be on the safe side ?

Anyway, on output figures I think the rule is always 'not enough..........'

Cheers

Pete

[EVguru]

I think from the late 70s Stradas and Sports had identical pistons also, so perhaps the lower figure comes from this 'standard format' engine, which probably had to have a lower compression ratio to be on the safe side ?

Morini apparently had trouble making sure Sport and Strada engines had the correct internals, so they standardised the later engines.

I've got quite an early Sport engine, which has cast finish pistons. I would speculate that the pistons originally had solid crowns with the Combustion chamber machined in. Once happy with the design, the production was changed to die cast, which should give more than adequate accuracy.

The difference between Sport and Strada pistons is in the height, the top of Sport pistons come to the top of the bore, Strada pistons don't. Later engines all use the taller pistons and Morini certainly quotes 11:1 compression for all later 350's. Other than greater stress on the engine, which it seems well capable of taking, there's little downside to the higher compression and it should give better torque.

Stradas, Kanguaros, Darts, and Excaliburs all quote approx 35bhp and similar torque, but at slighty different rpm points.

[stuart]

I've just had my morini set up on a rolling road with (K&N filters). It was reading 21 BHP when it arrived (measured at back wheel of course) and now is 27 bhp. Is this a sensible figure to expect from a 1978 350 Sport? (standard except for K&Ns, using std Lafranconi exhausts). The exhausts did raise another question... The pulse seemed stronger from one exhaust than the other, leading to suspicion of poor power from one cylinder, however the dyno chap says one exhaust is straight through whether the other is blocked/baffled - and I'm certainly baffled! Any thoughts? (ps left side baffled)

[moriniuk]

I've had mine dyno'd twice. Unfortunately on both occasions I was later to find that the engine was not in its best condition.

The first time it peaked at 19 BHP but I later discovered that two of the rocker retaining studs were broken. That was a standard sport engine, carbs and exhaust. I did a few races with it running like that!

The second time it peaked at 26 BHP. At the time starting had become unusually very difficult and I later discovered that the valve clearances were virtually zero. The engine was a 370cc with an L5 cam, lightened primary gears, free flow airfilters, standard carbs, standard exhaust downpipes and open megas.

If the valve clearances had been ok, I would expect a maximum of around 30 BHP.

H.

[EVguru]

Dynamometers measure two basic things; torque and rpm. From these you can get a power figure.

There may be losses in the Dynamometer that give an error in the torque figure. If it's a rolling road type dyno, then errors are inevitable and all you can really hope for is that the errors are repeatable.

You should always test with the same tyre at the same pressure at the same temperature and with the same tension in the tie down straps. The engine should always have the same oil temperature and the chain should always be at the same tension and properly lubricated. The test procedure should always be the same. There are a LOT of things that can affect the results.

Ideally the air pressure, temperature and humidity should also be the same, but in reality 'standard' correction factors are used. There are several standards to chose from, so raw figures are useful, you can always plug them into your 'favorite' formulae.

Differences in power of more than 10% are not uncommon between two different 'well run' dynos. Other dynos, particularly those who specialise in 'power runs' rather than development are much less accurate and nearly always over-read.

A rear wheel power of about 28bhp for a Sport is perhaps a little low, but probably not bad really. The Factory figure of 39bhp is almost certainly a 'corrected' figure for a carefully built (but stock) engine in perfect tune.

The original UK Dart demonstrator was dynoed at 27bhp and by all accounts wasn't running particularly well (maybe more of a rideability issue than power loss).