So it was back into the workshops at OO Racing today to finalise the setup of our tuned Briggs & Stratton ‘Rampage’ engine.
You’ll have seen the results from the standard and ‘Savage’ engines from last week but of course, we were excited to test the most powerful engine in our range. With timing set and carburetors balanced…it was time to run it on the calibrated dynamometer.
Our goal is clearly to tune our engines for the maximum torque, rather than the ‘headline grabbing’ bhp figure. Torque is the true measure of the ‘turning force’ of an engine which is absolutely crucial in a hovercraft engine. This is because hovercraft do not use a gearbox – instead they have a simple transmission and a fan which provides a fixed load. With a ‘peaky’ or high revving engine such as a two-stroke, response can be poor as you cannot select a lower gear to multiply the available torque like you can with a motorbike or car engine. So, the goal of a hovercraft engine is low revs (economy/noise) and a flat torque curve for good response and easy cruising at speed.
Below is the power graph showing both the horsepower and torque output of the Rampage engine – compared with the standard Briggs & Stratton 35bhp Vanguard engine.
- Maximum Torque 70lb/ft at 3000rpm
- Maximum BHP 55bhp at 4700rpm.
Now, because we run these engines to a maximum of 4000rpm, the engine can more accurately rated at 50bhp, which is what it produces at that figure. It’s quite possible to run the engine up to 4700rpm for maximum power, but this means further modifications to ensure no loss of the incredible reliability of these Briggs & Stratton engines.
However, looking at the torque curve more carefully tells the real figure. The Rampage has a peak torque figure 15lb/ft higher than the standard engine… but offers over 80% of this figure from 2100rpm right through to 4000rpm.
You can see the huge difference from the other curves which compare the two engines.
So, 70lb/ft throughout a substantial part of the rev range is figure of interest to the hovercraft builder! Having tested this engine in one of our hovercraft at some length, the throttle response, performance and ability to cruise easily when well loaded is exceptional.
Just remember – no other personal / small hovercraft manufacturer that we know of has actually produced their own, ‘real-world’ power and torque figures for their engines by putting them on a dynamometer.
It should also be stressed that we’ve extensively tested the Rampage engine, installing it into real hovercraft and using it in a real environment. We don’t exceed the safe usable rev limit that we’ve used for six years, and everything that needed to be done to ensure reliability… has been done!
So what now?
We’re currently working on making the engine available as a kit of parts for hovercraft builders to install themselves. If you’re looking to buy a personal hovercraft, then this engine is going to be of big interest! We’ve developed this engine (in association with OO Racing) for our new Coastal Pro Hovercraft but are making it an ‘off the shelf’ bespoke hovercraft engine for folks who wish to build a hovercraft, or re-engine their older two-stroke hovercraft. The aim is to have it available by the end of May 2012 – so please drop us a line to register your interest and we’ll keep you posted with pricing and delivery times.
- Layout – V-Twin
- Cubic Capacity – 993cc
- Bore -86mm
- Stroke – 87mm
- Max BHP – 50bhp @ 4000rpm
- Max Torque – 70lb/ft @ 2800rpm
- Carburettion -Twin Mikuni
- Ignition – Bespoke CDi system
- Engine weight – 56kgs
- Cooling – Forced air cooling, no radiator/water system necessary.
- Rotation – Clockwise when viewed from PTO side.
- Starting – Electric, pre-engaged starter motor.
- Cylinder Block – Aluminum Alloy with Dura-Bore Cast Iron Sleeve
- Crankshaft – Ductile Iron
The team at Flying Fish Hovercraft would like to thanks to Adrian at OO Racing – a genuinely lovely feller with an astonishing knowledge of small four-stroke engines. www.ooracing.com
BRIGGS & STRATTON ‘STOCK’ ENGINE VERSUS ‘RAMPAGE’ TORQUE CURVE
RAMPAGE POWER & TORQUE CURVES
BRIGGS & STRATTON ‘STOCK’ VANGUARD ENGINE VERSUS RAMPAGE – BHP