22 replies to this topic

[Guess-Works.com]

back to topic....

The amount of spacer required will be determined by the thickness of the clutch plate and the height of the posts on the back plate... As bmc' has mentioned earlier, the drive strap should lie flat across post when fixed to the flywheel, therefore attach one end to the backplate ( with clutch plate installed ) and the distance between the strap and the flywheel will be the height of the required spacer.

[Mini Mad Drakeley]

sorry to hi-jack the thread but i was thinking, is it possible to make an alloy flywheel and fit the steel ring with the teeth on it after so it is still looking standard but lighter? and as for using your self-lightened flywheel, if you have any doubts dont use it

[minihewson]

Thanks for the reply lads, it has helped me out no end. at least now i can start building the motor back up. there is still a ridge at the ring gear. although the few spot welds on the ring gear does sound good. i am building a 1380 fast road motor that i have bored myself at work and i am just experimenting with the engine. i have polished the crank, lightened the flywheel, ported and polished the cylinder head, bigger valves, skimmed 0.020" off the head & 0.030" off the block with a compression ratio 11.1. and a piper 270 cam. but as i am in the process of building it im not sure what it will rev round to as yet but i would of thought between 7 & 8000rpm. but back to the flywheel it looks pretty strong as i have kept the strength where it matters and have not made it super thin. Thanks again lads will let you know how the engine building goes. thanks again

[bmcecosse]

I suggest you don't need to go for such high revs with a 1380 engine -and certainly not unless you fully balance the engine and re-inforce the centre main cap.

[minihewson]

Thanks for the info. what revs would you recommend for a 1380? I have had the crank, flywheel, and rods balanced and have machined the centre cap flat and reinforced it with a main centre strap. is there anything else you would recommend re inforcing? Or is anything prone to going wrong when you upgrade the engine?

[bmcecosse]

The full power airflow will be limited by the cylinder head breathing ability - so probably better to concentrate on making the cam choice to give you a good 'slogger' rather than a screamer!

[Cooperman]

The full power airflow will be limited by the cylinder head breathing ability - so probably better to concentrate on making the cam choice to give you a good 'slogger' rather than a screamer!

For much over 7000 rpm it might be wise to look for a Cooper 'S' EN40B crank and use 'S' rods with everything fully balanced.
However, a 270 cam will not give power much over about 6250 rpm anyway, so aim for that as a nominal maximuml A look at the cam graphs will give you the information you need and if you can't find a Piper data set, the Kent ones would do if you look at mid way between a 266 and a 276 as an approximation.
The comment about the head's ability to flow sufficient mixture to power a 1380 is just so true.

[MRA]

A well built 1380 will rev to 7500 without the need of any centre main strap, they simply are not necessary. you can rev a 1380 simply because they create a higher air velocity than a 1275, look at some of the 1380 race engines out there....

The issue with the 5 port cylinder head effects them all not just big bore engines.

1380cc BHP curves will exceed similar 1275, 1310 & 1330's

The difference between a 1275 & a 1380 with the same cam is not the CC's it's due to the fact that the cam "feels milder the larger the cubic capacity, if for instance you fitted a 1275 with a 286 cam and a 1380 with a 296 cam the driveability of these engine's would be similar, and the power curves would be similar, but the power figures would show that you get more power with a larger capacity engine.

And yes a 1380 on a standard bottom end with a 296 cam will easily rev to 7500 rpm... and higher if well set up

Edited by mra-minis.co.uk, 23 March 2011 - 07:04 PM.