10 replies to this topic

[Sammy D]

Just bought a Slark modified 12G295 head with 29mm x 35mm valves, brass valve guides, double valve springs and it's all smooth inside. Anyway, thats bigger than stage 5, thats like stage 6.. Warp speed cap'n.

Also bought a 998 block, pocketed to fit the head.

I have a spare standard 998 lump here which I will be using for basic parts, although, I'll be needing some other stuff with that crazy head.

So I plan to get;

Straight cut drop gears, don't know what ratio yet?

Some sort of high lift cam to go with that head, maybe a 266?

Re grind the crank (maybe)

New pistons (maybe) not actually sure on the bore size, it might even be 1048

Different rockers, what ratio?

Probably just a single HS4 SU, I do have a spare though so could run twin HS4s, might be too much fueling tho?

Problems;

I THINK a piston has exploded in the first cylinder. It is slightly scored down the bore, the head has small imperfections (like someone has dropped it on gravel) where I presume the piston shrapnel has hit it, and the head between the bores has been re-welded by Slarks and skimmed.

Therefore, I think I will need a rebore, or at least an Hone. What do you think?

Basically, is anyone good at working out the ratios I need?!

Sam

Edited by Sammy D, 09 February 2007 - 12:12 AM.

[Big_Adam]

Rockers,

1.3 is what you want, any more on a little engine and theirs too much overlap.

On the carb, many will suggest the equivalently HIF car (think its 34) but can I also suggest sorting the car out. Halfing the spindle and screws. I'll do it if you want.

[JetBLICK]

Sounds brilliant an' all - but do you know you don't need a pocketed block for you're head??

[Dog]

You need to pocket if using a 940 head, and to be honest, if the engine is a "stage 6" then this would be the head of choice... as stg4> uses the 1275 head, due to being able to have 37/38mm inlet valves....

For example... imgine a 998 with a 286 cam, with a 38mm inlet and a 32mm exharst!
MASSSIIIVVVVEEEE POWER - eh Jet blick

[Sammy D]

Sounds brilliant an' all - but do you know you don't need a pocketed block for you're head??

I do, the valves are actually HUGE!

[Dog]

29mm inlet.... thats the same size as the exhrast valve on a 940 head

honestly mate, get a 12g940 head!!

[Sammy D]

My Inlets are 35mm! Exhausts are 29 on this head too.

Read the first thread again carefully

Anyway, back to the thread..

Highlift cam and 1.3 rockers?

Edited by Sammy D, 09 February 2007 - 01:03 AM.

[Dog]

Even so, the 940 head is less resrited over the cooper head...

but still I have NEVER heard of a stage 6 engine... thought 5 was the highest, as that full out race engine...

[Sammy D]

Even so, the 940 head is less resrited over the cooper head...

but still I have NEVER heard of a stage 6 engine... thought 5 was the highest, as that full out race engine...

So did I, this is just different. Kind of stage 5+ :S

This heas has pretty much been modified to 940 with a few extra bits.

[JetBLICK]

Sounds brilliant an' all - but do you know you don't need a pocketed block for you're head??

I do, the valves are actually HUGE!

Fair nuff then

[Dan]

Even so, the 940 head is less resrited over the cooper head...

Hmmm.


Anyway..

Get some of the new +100 pistons from Mini Spares and give them a try. Might be able to loose the pockets then too depending how much of these valves actually are a problem. I like forged Cooper S rockers on a thick walled shaft. You might be able to make use of a bigger carb than usual for the small block with this engine, especially if you do go +100. Maybe a single 1.75. I'd still stick with a Freeflow exhaust manifold over an LCB though.

Ignore the 'Stages of tune' by the way. It's a load of rubbish. Oh and two normal HS4s doesn't make a pair. You need a left and a right, like with shoes.

Edited by Dan, 09 February 2007 - 02:23 AM.