what revs? are best?

Post by **puchmaxikid** » Thu Jun 12, 2008 6:57 pm

hi there, on my moggy 1000 i have just instaled a rev counter. i was wondering what amount of revs i should have at idle. also what would the max rpm be for a 948cc.
thanks loz

Post by **alex_holden** » Thu Jun 12, 2008 7:01 pm

Idle, as low as you can without it stalling too easily when the engine is cold. I try to aim for about 800 hot.

Maximum, I avoid taking my 1098 over 4500. I usually cruise at about 3500.

Post by **bmcecosse** » Thu Jun 12, 2008 7:51 pm

Idle as slowly as possible - to maximise engine braking and to minimise fuel consumption when idling! The valves will crash at about 5500 on a standard 948 engine. But if properly balanced/lightened/fitted good double valve springs and most essentially a crankshaft damper/ centre main strap/998 Mini or 1098 (non pinch bolt) con rods and an oil cooler the 948 is good for short bursts at up to 7000 rpm (maybe even 8000 momentarily) although continuous running should be kept down to 6000/6500 if you want the crank to last! There were special Works 'Red' cranks for this engine at one time - v hard to find one now - which were good for 8000 maybe 9000 for short bursts - but only with S rods and special forged competition pistons. The problem with 1098 engines (like Alex has) is that there is a nasty resonance period at about 6000/6500 rpm and they will break the crank if run at that speed for any great length of time. The later Spridget 1098 engine had a much stronger crankshaft with 2" mains which overcame that problem to some extent although these are not good 'revving' engines - better set up with good torque and used with lower ratio gearing to run at lower revs.

Post by **callyspoy** » Thu Jun 12, 2008 7:59 pm

out of curiosity, what can a standard 1275 rev to? i've never found out! sorry to gatecrash the question...

Post by **bmcecosse** » Thu Jun 12, 2008 8:14 pm

Standard 1275 - well - 6500 max I would say - it's very long stroke. Again - if using a Spridget 1275 with S type rods/balanced/lightened/damper (all 1275 have that anyway) lightened flywheel/forged pistons and oil cooler then 8000 momentary is certainly possible. But I wouldn't want to run it over 6000 for any great length of time.