Aermacchi Versus Ducati

[Duccout]

A bit off topic, but something that has always puzzled me: does anyone know why Aermacchi 350's were so successful in GP racing, and in classic racing (before the Honda twins) compared to Ducati 350's?

AFAIK Aermacchis have 72°valves, so a bit of an advantage there, but the inlet port does not have a very steep downdraught, and there appears to be no magic in the head design - in fact (if my memory is correct) the works bikes were making 37 BHP at the rear wheel, yet they were able to lap the IOM at 99 MPH in 1969 or 1970. Are they much lighter than Ducatis? Or is the advantage due to their low profile? I believe that Aermacchi produced racers for sale to the public, so they may have had close ration 5 speed boxes as standard, which is a big advantage.

I asked Anthony Ainslie about this years ago and he said that once tuned properly a Ducati was just as fast....

Cheers,

Colin

[blethermaskite]

Colin, I have had the luxury of owning a couple of Macchi's, a 1960s long stroke 250 road bike turned racer put back on the road, and a 1970s 350 tv road bike. the 250 was a bit lighter than a similar 250 Duke and really quite quick, kinda Mach 1 with a lower centre of gravity, in my opinion a road derived Macchi doesn't handle as well as a Duke but it can be ridden faster, they are a bit of a tail weaver but you just keep the power on and don't back off and they are fine . The tv350 road bike was not as fast as my 350mk3 and it felt heavier, the brakes were crap and it was also a tail weaver (worryingly so ) I didn't keep it very long and didn't regret selling it. I have ridden a properly competitive late 1960s 350 racer......it was lovely, handled great (still a wee touch of tail weave brilliant brakes (front one great but weighty,with a noticeable gyro effect) again very similar to a good 350 Duke racer but felt faster and left a good impression on me......if they hadn't got so expensive I certainly would have seriously liked to own one. Is one 'better' than the other in my limited experience each have their merits....in the back of ones mind the Ducati single is always going to be a super fast and reliable road bike turned racer, but an over the counter single cylinder Aermacchi race bike is a racer???????????????????? Cheers George

[themoudie]

Aye Colin,

Better aerodynamics, stiff frame, downdraught inlet from still air beneath the tank, 6 speed cluster, 93 Kg weight, and the testicular size of the rider may have a lot to do with it!

This is a link to an article on a Syd Lawton Aermacchi Ala d'Oro, giving some insight into the development of these beasties: Ex_Ronnie_Niven_Lawton_Aermacchi_350_ Ala_d'Oro

Bill Swallow liked racing his 450 Ducati, but he won the races on quick 350+cc Aermacchi's. Syd Lawton and or Dick Linton were the suppliers/sponsors, with the really quick Aermacchi bikes in the day.

Doug Snow's wee Ducati 350 Sebring, owned by his Dad, with homemade 6 speed cluster and various other tuning bits, re-aligned inlet port, etc. along with Nigel's input completed a 99.995mph lap of the Island, with an average speed over the 4 laps of 98.075mph! If you wish to read more refer to an earlier Motoscrubs posting by Nigel:- Doug_Snow_2013_Manx_GP_win_350_Ducati

I am sure Nigel and Eldert will be happy to give their pennysworth. And if I have anything incorrect, my apologies to those who know better.

Good health to you all and I hope that you continue to wear the wee beasties out, BillR

[themoudie]

Evening George,

..in the back of ones mind the Ducati single is always going to be a super fast and reliable road bike turned racer, but an over the counter single cylinder Aermacchi race bike is a racer????????????????????

Nail on the head and I don't have the first-hand experience of yourself, apart from cantering various Farrer Ducati singles in the paddock, after push starting them.

Good health, BillR

[Jordan]

Pushrods beat OHC?

[Duccout]

I once spent a day with Anthony Ainslie in his workshop; this was about 1990 and I think that he was the first tuner who took a more scientific approach to making Ducati Singles go faster, beyond the norm of big carb, but valves, lumpy cam. When I asked why Aermacchis were faster he said that most Ducati Singles were over-tuned and simply were not running efficiently. A while after this I was watching a CRMC meeting at Brands and while standing at the exit from Clearways it was easy to see this was true, because as the different makes of Singles came through and accelerated through the gears, almost all of the Ducatis went completely flat when the rider changed up and dropped out of the power band.

Of course close ratio gearboxes would help this and I don't know what was in those bikes, and I don't know if the other Singles had six speeds, but surely the idea of tuning is to make sure that your engine has a wide enough spread of power to cope with gear changes? I do remember one Ducati that did pull when changing up, and that was Eldert's 450.

Cheers,

Colin

[themoudie]

Aye Colin,

Overly big diameter carbs, combined with poor inlet gas flowing, as the standard cylinder head casting, with offset carb position is not the best. The only time when large carbs are effective is when the inlet has been modified appropriately and the throttle is being held wide open for long periods e.g. Isle of Man TT course.

I still think that a 32mm carb is plenty big enough for on the road and short circuits. But, I am happy to be told otherwise.

As for the pushrods/OHC debate. Those Aermacchi pushrods are short and stiff, whilst the inlet port is central and has a downdraft effect, in direct contrast to the Ducati's.

Good health, Bill

[Jordan]

Offset inlet ports were most common practice for 2 valve heads, with resulting swirling turbulence of the air and fuel helping to mix them - good for complete burning which helps produce more power and economy.
That was the designers' thinking at the time, and It also made the carburettor a little easier to access, over to one side.
Maybe the advantages were mostly theoretical. Turbulence of gas flow is common and difficult to avoid I'm told. It's laminar or slipstream flow that is rare - and not desirable within a petrol engine.
Small ports and valves result in more turbulence than big ones, according to Phil Irving's "Motorcycle Engineering" book, so he's in agreement with Bill on that point. PI knew his stuff, being not just a motorbike engineer but also a successful Formula One car engine designer.
Huge carbies and wild cam timing might be good for highest speeds, but a single cylinder race engine often seems to be desperately incapable of idling at low revs.

[Bevel bob]

I understand that its possible to fit a reducing sleeve/choke tube to the SSI carb, as the 29 mm body is common with the 27 mm carb. Is the part availiable or easy to make ?.

[Jordan]

I don't think a sleeve of only 1mm wall thickness would be easy to make.