A.M.I. May 2003
latest ASP .91 's' (compact like a .61 - with .91 power!!)
note safety prop locking nut supplied as standard (front needle shown - rear needle available at no extra cost)
Take a long hard look at the engine featured in this review and pay close attention to its finish and general appearance before focussing your gaze upon the images of the internal components. Have another look at the quality of finish on the castings and then turn your attention to the sheen on the machine work and then compare the general look of your favourite make of engine with this one and it will be quite obvious that the differences are getting smaller between one manufacturer and another.
The latest ASP 91 's' is an impressive engine and from the moment one opens the lid of the box to inspect the unit at close quarters it becomes apparent that this one is unlikely to disappoint even the most cynical and partisan engine buyer.
The ASP 91 is a Schneurle ported engine that retains its nominal 15cc's cubic capacity, within the overall dimensions of the average 10cc device (just like O.S. did with the .91fx) and this has naturally resulted in an ultra compact and very powerful unit for its physical size. It is important to recognise that the actual cylinder capacity of a chosen engine is a total irrelevance, competition rules apart, because power output per unit of weight allied to overall physical size of an engine determines its usefulness as a model aviation unit, so a 91 sitting in a 60 shoes, so to speak, is a great idea.
Looking at the construction of the ASP 91 a little more closely we can see that a ground and hardened crankshaft, carried on twin ball bearings, allied to its aluminium piston carrying a single ring runs inside a steel cylinder liner, all suggestive of a durable and unfussy workhorse of an engine. The twin needle carburettor, of time honoured design is thoroughly representative of today's glow ignition two stroke engine and leads one to assume that the 91 will enjoy effective and reliable throttling characteristics . The crankcase and cylinder fins and head are finely finished investment castings produced to exacting standards and as such they are very far removed from those of the earlier generations of ASP's. The exhaust system, comprising of twin castings and a machined baffle clamped between the latter, with a long threaded rod, is huge and in direct response to similar products and strictly in keeping with the latest generation of quieter model engines. Thank goodness that
the engine producers now appreciate the need for quiet performance which is more important to the UK buyer than the absolute power output generally speaking. To help you get the most from your investment, a very readable and sensibly worded
instruction sheet is included in the package, produced and written in clear English by the suppliers - Just Engines - and it contains relevant and good advice, the contents of which should be thoroughly absorbed by the purchaser before laying a hand on the
engine. The plug supplied for the test engine was ASP's own which proved a perfect match.
Until quite recently, despite the availability of reliable alternative lubricants, the majority of the worlds model engine manufacturers continued to recommended castor oil based fuels only and some entrenched suppliers still do, putting customers between a rock and a hard place from the outset! I was therefore relieved and pleased to see a more enlightened response from ASP as the instructions for this latest 91 state that both castor and synthetic lubricants are fine, providing that the percentages are correct and I heartily concur with that. I have been using fully synthetic fuels on a vast range of two and four stroke engines for years now, but I readily concede that if you are going to try to run an engine to destruction by howling around for ten minutes on full throttle on an obviously lean and distressed setting, then total meltdown is more difficult to achieve with a castor based fuel because of that oils unique behaviour at extremely high temperatures, where simplistically, it thickens before (unfortunately.....) eventually turning to a toffee like gum. If you are an intelligent engine user with some degree of mechanical sympathy and share an empathy with your engines then you won't experience problems with modern synthetic based fuels and that brown sticky appearance that your old engines assumed (inside and out of course.......) with prolonged use will thankfully be a thing of the past. As they say - you pays your money and you takes your choice. Just Engines are with you either way.
Once firmly affixed to my test rig, I looked up to my propeller rack for a suitable foil and triumphantly held aloft a Bolly 12.5 x 6, which turned out to be laughably inadequate for taming this monstrously powerful engine, although the handling was sweet enough, even on this relatively light load. Replacing the propeller with a Bolly 13.5 x 8 produced a much less frenetic and useful sounding response and I immediately knew that we were in the ball park with this increased workload. A quick check with my Tachometer produced a reading approaching 10000 RPM and for a big 91, just about where I would run the engine in a sports aerobatic ship. Actually, as the propeller test figures show, this engine was equally happy revving hard on small propellers or swinging huge 16 inch diameter blades, making the 91 equally useful for sport or scale work and as such quite a jack of all trades. Put this one on the nose of your 61 size seven or eight pound aerobatic machine and fit something like a 12 x 8 and you will be punching holes in the sky with the turbines, or load it up with a large prop and let the torque quietly and effectively pull your large scale model aloft! Use something approaching a 13x8 or 10 for aerobatics with a tuned pipe system, which will harness that lovely torque effectively.
I haven't mentioned starting the engine as yet because it turned out to be rather a non event. Big engines like this one can be intimidating but providing you take the sensible precaution of wearing a glove, priming the engine with a few choked turns of the propeller followed by a healthy flick at a fast idle setting will produce an immediate hand start. You can use an electric starter if you prefer, but this one is a cinch to hand start with no nasty tendencies or finger biting snappiness, even on relatively small
With the engine firmly affixed to the test rig, I ran the 91on a rich setting for around five minutes on half throttle, before opening the taps and letting her rip. My goodness, that's a lot of air being moved there and what a response with superb instantaneous throttling and that with a new unit yet to realise its full potential. With half an hour or so on the clock, the ASP 91 sounded strong and constant and I would have been perfectly happy to bolt the engine to an aeroplane and go flying with it. "Flying in" is much better than "Running in" if you catch my drift, ie that is to say that putting the engine into a model is a good way of breaking in a new unit, because it gives the engine a variable load to work against whilst plenty of cooling air is forced through the fins - in a word, ideal! Use the throttle and limit hard working climbs for the first three or four flights and from then on all will be well for sure.
To summarise then, the new ASP 91 's' is a compact, powerful, beautifully made good throttling engine that idles very consistently and starts immediately. The exhaust stub dimensions are those used by OS and others, thereby facilitating many after market silencer options and the engine comes with a healthy two year warranty, which should give you confidence in its longevity. Really this one is pretty much state of the art and promises the purchaser a long and useful working life. At the money the ASP 91 retails for, you get an awful lot of power for around half the outlay that you might reasonably expect to pay for an engine of this stature and treated well, it should provide you with years dependable use. Take a look at the specifications and propeller figures which make interesting reading and compare them with other engines of this size and weight! In a word - Impressive!
- 12.5 x 6 BOLLY = 13800 RPM
- 13.5 x 8 BOLLY = 10000 RPM
- 13 x 6 APC = 12400 RPM
- 16 x 6 APC = 8200 RPM
An easy idle speed of 1800 RPM was achieved on the smallest of these propellers!
Fuel used was Model Technics - 5% Nitromethane
Plug ASP No: 4
Cubic Capacity 14.95cc
Claimed BHP = 2.750 @ 15000 RPM
Extrapolated BHP = 2.748 @ 13800 RPM
= 1.560@ 8200 RPM
You can find more ASP engine reviews here.