staged heads, what's that all aboot?

[mulletmark]

Hi

I've just acquired a 1991 Mini Cooper from the old man which has had the engine replaced with a lightened balanced and bored 1275cc cooper engine, upped to 1293. been calling around insuranc companies to get a good quote and they've been asking if it has a staged head on it.

I've been saying no 'cos i'm pretty sure it hasn't. But out of interest, what work is involved in changing from a standard unit to a stage 1, 2 or 3 head. if anyone on here can spread some light I'd be most greatful. Especially if it's a cheap and reliable way of squeezing a few more Hp out of a teeny engine!!

Also, can anyone point me in the direction of a good mini specialist in the Milton Keynes or buckinghamshire region?

>> Edited by mulletmark on Thursday 29th September 23:08

[Wildfire]

Rob Walker is nearer than most for you. Stage heads generally means the degree to which it has been worked over.

Ported, flowe, bigger inlets, bigger exhaut valves, etc.

[minimax]

also highly unlikely in my view that a performance engine modification like boring to +0.20thou(?) would not also involve a better flowing cylinder head, so the answer is probably yes it does have a staged head, but the next question is which stage! and bear in mind too that stage definitions vary from manufacturer to manufaturer too

[Cooperman]

IMHO all this business about Stage 1, 2 or 3 is just b******t. Different head modifiers will do similar work, but not all heads even from the same builder will be identical. Castings vary as well, so the amount of work could be different. For example, an early 12G940 without unleaded seats has a much better inlet 'short-side radius' as standard than a leaded one. The 'Stage' is particular to specific engine builders and is not a definitive term for all modified heads. If, for example, I call a head with cleaned out ports, a modified combustion chamber shape and ground back valve guide bushes my 'Stage 1' head, then another builder may just 'clean up the chamber, skim 0.020" off, lightly clean up the inlet tract and call that his 'Stage 1'. They would be very different in practice and performance.
Bear-in-mind too that you can bore out to +0.060" (1330 cc) as a standard service re-bore and can skim the head by up to about 0.020" again as a service re-face without the car being considered modified. It's all in line with the service and repair manual(s).
In order for an insurance company to prove your vehicle was modified they would have to check your head against the standard manufacturing drawings from BMC/Rover, and where would they now get that data? Even 12G940 castings have different dimensions from one model to another, even though the root part number is the same.
For what it's worth, if you were involved in a claim in a modified Mini for which you had not declared some minor engine mods, the insurers would find some other mod first, like negative camber suspension, or a non-standard exhaust, or non-standard wheels which could invalidate the cover, so they would not need to strip the engine. In cases of engines, they look for non-declared twin carbs, or a larger carb, an other external and visible items.
I hope this helps,

Peter

[chuggaboom]

Generally a Stg 1 is most of the work....chamber clean up and volume matching, port reshaping and smoothing.

Stg 2 = stg 1 plus bigger valves.

Stg 3 = stg 2 with bigger everything.

Some might consider valve stem centre repitching as Stg 4 but it is not generally refered to as such.

Skimming is always an aspect but generally accepted as part of the Stg spec as it is open to customer req'mts...ie how much they require to be taken off to get the correct CR for their application and mix of components.

[Cooperman]

chuggaboom said:

Generally a Stg 1 is most of the work....chamber clean up and volume matching, port reshaping and smoothing. Stg 2 = stg 1 plus bigger valves. Stg 3 = stg 2 with bigger everything. Some might consider valve stem centre repitching as Stg 4 but it is not generally refered to as such. Skimming is always an aspect but generally accepted as part of the Stg spec as it is open to customer req'mts...ie how much they require to be taken off to get the correct CR for their application and mix of components.

That's about it really.
The only problem is that when you get a head for motorsport, to comply with the regs the valve sizes sometimes must meet with the vehicle homlogation which requires only standard valves. Thus you can get a really well ported head, with, maybe, a higer ratio rocker, but standard valves diameters. Then the 'stage xx' situation doesn't really apply. I've seen so-called Stage 3 heads where the chamber re-shaping was really not very good, although beautifully polished and very expensive. I guess i've got a bit cynical with old age!
I would rather discuss the application for which the head is required, then work with that in mind to create a custom modified head and not give it a 'Stage' number.
For example, the head on my '64 rally car is well ported out, the valve guide bosses taken well-back, the valves are 35.6 inlet and 30.5 ex (for reliability), the chambers are well de-shrouded and the c.r is 11.2. With all the other bits that gives good reliable power, limited, as usual, by the transmission. I know I could fit bigger inlets, but the reilability might suffer, so I haven't done this (yet).