What Roller Tip Rockers?, for my engine Options

[D1k1m4y]

hi i have a mini 998 the spec

hif38+pipercross filter
alloy inlet
12g295
rc40 exhaust


dont wnat to take the engine out so fancied just putting a set of rockers in but not sure whether to get 1.3 or 1.5
whats your verdict and i just want a nice road engine. im thinking these

http://www.minisport.com/mini-spare-parts/..._MSLMS0483.html

[jaydee]

Standard are fine, no need of hi lift rockers with that spec.
If you want to spend some money rockers, use 1,3s on small bores, or it wont run good. Higher lift can be used on small bore race engines only.

[Cooperman]

Have you done the compression ratio calculations for the 12G295 on a later 998 engine? The engines to which the 295 was originally fitted had raised crown D-top pistons and then the comp ratio was only 9:1 which is a bit low for a decent level of power. Ideally you need about 10:1 to make it go well. You would spend your money better if you fitted slightly larger inlet valves. Standard inlet valve size for a 295 is 1.219". You can go up to 1.319" if you are happy to run leaded fuel, or 1.25" with unleaded seats fitted (those are figures from memory and you should check them by measuring the head across the valve seats).
You would benefit from a better cam, unless you already have one. The Kent 266 is great in a 998 with larger valves and a 295 head. With the head off a 998 and with the radiator and timing gear out, you can change the cam without removing the engine if you make a hole in the iner wing to withdraw the cam. Take off the cam chest covers in the back of the engine to remove the cam followers.
With that cam and modified 295 head, plus the 38 mm carb on a decent alloy manifold, you should see over 60 bhp at around 6000 rpm if it is all set up correctly.

This post has been edited by Cooperman: Mar 9 2010, 04:57 PM