added by Emma
April 5, 2012
Few subjects attract more outrageous claims by unscrupulous sellers than…engine tuning and hovercraft! As a company that supplies hovercraft and also modifies stock engines, we felt it was about time we put up or shut up! So, Wednesday saw three of our engines bolted onto the dynamometer at Double O Racing www.ooracing.com to test once and for all the power being produced by both the standard and modified Briggs & Stratton engines we use in the Flying Fish range of personal hovercraft.
Adrian at Double O Racing is a top guy, fantastically helpful and knowledgeable. His dyno is fully calibrated, so it was a fantastic opportunity for us to ascertain, once and for all, the true figures that our engines produce.
The three engine specifications we tested were as follows.
Standard, completely unmodified Vanguard 35bhp engine, brand new – The ‘Boggo!’
‘Savage’ specification 35bhp Vanguard. Brand new with light modifications to increase torque and drivability.
‘Rampage’ specification 35bhp Vanguard (twin carbs, CDi system and internal modifications)
After some modifications to the dynamometer drive to allow our engines to be safely installed, we fitted the Boggo engine. Commercial engines (Kohler, Briggs & Stratton, Honda etc) have a ‘governor’ fitted to prevent over-revving, something we can remove for hovercraft usage. This is because the hovercraft fan load is fixed and prevents the engine from exceeding its maximum revs….and unlike one or two of our competitors, we do not run past the design limit of 3800 to gain more power. In the case of the Boggo, other than the marinisation required to make it run in a marine environment, removing the governor is the only modification made.
So, first power run and the 35bhp Briggs & Stratton produced 35.4bhp! Remember this is a brand new engine – and we always get more power once they’ve got 15-20 hours on them. This was excellent news and a great base to work from.
So, to the Savage Engine. This engine is modified slightly with the aim of improving throttle response, torque and power. It still runs at a maximum of 3800rpm, just like the standard engine. Test results…37.1bhp, so up a little of 1.5bhp. Now, that doesn’t sound a lot, but the torque figure was incredible, increasing from 55lb/ft to 65lb/ft! A 10lb increase is a great result, and the reason why, when coupled to a different fan specification, the Savage craft is faster, more responsive and cruises at tiny throttle settings for 25mpg economy! We were genuinely delighted with this test.
Well, so far so good and it was time to bolt on the Rampage. This engine has been developed over the last twelve months and features twin carburetors, a bespoke CDi system and some internal work (sorry to be vague but we don’t want to give it all away!) But then we hit a snag – following some recent development work on it, we’d overlooked setting up the timing accurately and it was only ‘guesstimated’ – Doh! Adrian advised against running it too hard/too long without correct setting and we were running out of time for the day. So, we decided to do one quick run and see what we’d got, then knock it on the head until after Easter, when we’d have the time to set it up correctly.
I’m not going to tell you what we got from our test…but were very happy…..and still are but we also know that there’s lots more to come. Check out previous video of Adrians reaction as he sees the screen display after the run we’ll give full results and power graphs next week! VIDEO
The attached photo shows the screen display of the Savage and Boggo runs – the Rampage ones have been veiled for now!
Because we use new engines we can be sure that the engine you get in your Flying Fish recreational/personal hovercraft matches the results that you see here. Many hovercraft manufacturers use two stroke engines that rarely produce what they claim – and some even use ‘reconditioned’ (ie second hand!) car engines from Subaru or BMW. In those cases, you could be getting as little as 75% of the claimed figures! So we’re chuffed with the results so far…and can’t wait til Easters over and we can get back into the workshop!