19 replies to this topic

[IainNeon91]

Hi all,

I have recently started to think of things i could do to get that little extra and whether it would be worth it.

To fit some 1.5 high lift rockers is it necessary that i change the cam and/or head?

Would i gain anything if i just changed the rockers first? (if possible)

If i do have to change anything else, what cam's, heads and other parts would you recommend to make a fast road 998 :)

Cheers,

Iain.

[bmcecosse]

Forget high lift rockers!!!! Has anything (ie Stage 1 kit) been done to the engine so far?

[IainNeon91]

I have got a stage 1 kit yes, 1 3/4" exhaust system, HIF38(cone filter with stub stack), converted to electronic ignition and lucus gold coil... Just the basic's done so far.

The rockers... Would they have gains only on 1275's? Or would they be good for a 998 with say... 12g295 or 12g940 head, double valve springs etc...?

Iain.

Edited by IainNeon91, 24 February 2013 - 10:51 PM.

[BritishRacingGreen]

If you don't want to (can't) remove the engine, I would go for a stage 1 kit, and a reconditioned 12G295 head, possibly ported depending on budget (but factor in cost of unleaded valve seats and probably new guides). You'll also need to get the head skimmed to get a sensible compression ratio (9.8-10/1). This will mean calculating your existing compression ratio and working out by how much the head needs to be skimmed.

And higher ratio rockers (most advise the 1.3s on small bores) can't hurt, but I would favour a cam change over them.

Edited by BritishRacingGreen, 24 February 2013 - 10:52 PM.

[IainNeon91]

How can the compression ratio be worked out?

Could be interesting to know.

Could i get my head skimmed (until funds are raised) ?? Will this provide some gains?

[BritishRacingGreen]

Try a google search, that will explain the basics, but in essence it is the ratio between the volume the fuel/air mix has to occupy at tdc to the volume it has at bdc.

Skimming the standard head will give some gains (though i doubt particularly noticeable). And the cost of getting the standard head ported to the standard of the 295 would be more than a 295. Just keep an eye out on ebay, but do check before you buy. 295's are old, so it's likely they will have cracks, or will have been previously skimmed. make sure if you buy one it will suit your needs.

[IainNeon91]

Ok thanks for the good advise BRG!

But sorry, a couple more questions

Will the block need to be pocketed to fit a 12g295

What about a 12g202 1098 head? Would this fit straight on with no problems?

[BritishRacingGreen]

thats the beauty, the 295 is the small bore cooper head, so will fit straight on to your block.

The 202 as fitted to the 1098s is very similar, but does not perform as well. It is an improvement over the standard head mind you.

[IainNeon91]

Ok so the 12g295 is the one i shall be looking out for!

Working out the compression ratio:

Is my Rover Mini Neon 1991, 998cc a low or high compression engine?

Low: 9.6:1
High: 8.5:1

Edited by IainNeon91, 24 February 2013 - 11:19 PM.

[BritishRacingGreen]

Not a clue. Use guess-works.com engine number to help, if not, the only way to tell is to take the head off and have a look. I believe the difference is the low compression one has dished pistons.

Although for some reason I think the newer cars were the high compression version (don't take that for certain though)

[bmcecosse]

The BEST head by far is the 12G940 - best power increase for low cost. You may need to sink the exhaust valves into the head slightly until you get 320 thou clearance. No skimming required! 295 heads are almost as good - but - will need skimming if not already done, and are EXPENSIVE. 202 head - small power increase -and it too will require skimming. It's not worthwhile skimming the standard head to increase the CR. You would do well to get a copy of Vizard and read it!

[IainNeon91]

I've already got the yellow bible I have been memorising the carburation and ignition system sections at the moment though

I will have a look at guess works

[daenesh]

yeah a better cam maybe 246 or Sw5 would be better.. but if you could get ur hands on a cooper s head with those big valves it would be amazing.. or you could port and polish your current head.. hmmm dont forget to use an uprated carb needle at this point.. 1.3 lift rockers are perfect for small bores and if you're going to go through with all the changes wouldnt hurt to have some double valve springs(if ur a high revver)

[IainNeon91]

Whaht code is a Cooper s head?

So it's 12g295 head skimmed to correct specification, kent 286 cam, double valve springs and keep the standard 1.3 rockers?

Edited by IainNeon91, 25 February 2013 - 02:14 PM.

[BritishRacingGreen]

the 286 seems a bit wild? what do you use the car for?