View Full Version : Briggs Engine RPM

Don83000 - n/a
8-Jul-06, 12:23 AM
What is the max rpm the 30bhp modified Briggs supposed to run at.

Jeremy - n/a
8-Jul-06, 12:57 PM
It varies with the state of tune and internal mods, as far as I know. The chap that built mine reckons they give max power at 5,200 rpm, but it does have a few goodies inside to get it to that, like billet con rods, stiffer valve springs to stop valve bounce, a modified cam and roller rockers to improve cylinder filling etc.

I know of a couple of people regularly running standard B&S bottom ends to just over 4,000 rpm with no ill-effects, but from what I can gather it's the con rods that seem to be the weakest bit if you rev them much more than that.

Russ may be able to add more as he's got more experience with them.

I do know that once you've got the bugs ironed out they seem to be pretty reliable, even when revved beyond their original 3600 rpm design limit for long periods.


Don83000 - n/a
9-Jul-06, 01:09 AM
Thanks Jeremy, What size fan are you using and what pulley ratio.

Jeremy - n/a
10-Jul-06, 05:09 PM
I'm driving a propeller, rather than a fan, although the engine and prop is only fitted to a test stand at the moment, just to check it's reliability.

The prop is a two blade, 62" Powerfin carbon fibre one and the reduction ratio is 2.38:1, using a polyvee belt to try and damp some of the torsional pulses from the V twin.

The reduction drive works well and the combination seems both quiet and reasonably powerful. I've not done a proper thrust test yet as I haven't got enough hours on the engine to run it flat out for a few minutes.