7 replies to this topic

[Huw lloyd]

Hi there all! the mighty mini is back on the road ant i have been looking at the roller rockers that you can get. the engine that i have is a 1098cc and i was just thinking how much of a difference will a roller rocker give me? and which one will be the best one to go for 1.5:1 or the 1.7:1? There is also a bit of a problem with the mini engine. it seems to have developed a "flat spot" in the rev range about half way through revs. what could this be? Timing? or carb needing re adjustments?

[Ethel]

If it's rev related, rather than load or throttle, I'd be inclined to look at the timing first. If you have a strobe and a rev counter you could plot it at various various rpm. Pulling the choke out bit when you hit the flat spot might help spot a fuelling issue. High lift rockers would depend on the cam, amongst other things, 1.5's might be pushing it and I think 1.7's would be too much.


mini-mayfair.net/9981275/camshafts.xls

[Bungle]

you will loose power on both the 1.5 rockers and the 1.7, you will loose the most using the 1.7 rockers

a small bore engine doesn't need much valve lift

you could fit 1.3 rockers and might gain a very small amount of power at the very top of the rev range

[Wright&Wright]

An increase in rocker ratio is only beneficial when used in conjunction will valve and port modifications.
As Bungle has said, a small bore engine doesn't need much valve lift. The 1098's have problems with snapping cranks and destroying big ends due to high revs on a stroked crank, so any benefits at top end are so insignificant, it wont justify spending the money.
Without trying to sound patronising and sorry if I am but the 1098 still has the same bore as a 998, so it'd be better if you looked into getting a better flowing head such as the 12G295 or maybe taking your head off, getting it ported and polished, then having the valves back cut. Low lift flow is the best way to improve power/torque on a road car unless you're running a 9,000rpm race engine.

[twrminisport]

Copied from my small bore tuning guide...

Testing by the likes of Vizard and Calver show that a small bore engine requires little more than standard. This testing however has shown the flaws in standard units with an acclaimed 1.25.1. They have been shown to produce little more than 1.22.1 on a good day. Therefore a 1:3:1 roller rocker is a good upgrade. 1.5.1 is too much for the 998, 1098 really as it develops too much lift which can result in either the valve springs crushing, or worse, valves hitting pistons. 1:3:1 is optimum until about 85/90bhp for a small bore so unless you are running a 100bhp small bore Miglia specification Mini then 1:3:1 is for you.

Cheers.

[liirge]

what guide is this then?
yup agree with above for Roller Rockers..

Edited by liirge, 12 March 2011 - 04:41 PM.

[twrminisport]

Small bore tuning guide I wrote recently haha
Not quite finished yet mate but you can have a copy as long as you promise to get your finger out with yours

[bmcecosse]

Forget the rockers - big waste of money. Best mod on a 1098 is to fit a 12G940 head - the standard valve size is fine. It WORKS - very well indeed, and doesn't cost a fortune either. As alrea dy suggested - DO NOT rev it above 6000 rpm - so no need for fancy valve springs...........