Discussion
hey fellas really need some help sorting out our head ,reason being we have been advised from a number of people all with differing opinions and with us being complete novices on mini's we need to find a solution somewhere between them.
starting from when we first planned to build the engine everyone advised us to fit a 206 or a 295 head to help with the cam (286). so this is what we planned up until this week when we started to ring round for prices etc.
i wont mention the people we spoke to but they are established professionals in the field and im in no way questioning their knowledge its just we dont know which route to take.
so firstly we were told to fit a standard 295 with the bigger valves and that would be fine, now some are saying just fit a stage 3 998 head , then it would be better to stage the original 295 casting we have into a stage 3 cooper head,.......
whats confusing is : is a stage 3 998 head ported the same as a 295 as we have twin su's to fit and the ports on our standard head are smaller than the su manifold, and do they fit the maximum size valve as in the 295 (30.96mm i think)
if so i can understand that it will do the job.
another person said not to develop the 295 as it would not be as good as a 998 stage three head if so why??? everyone told us to get hold of one of these in the first place..
so i guess we have three options: 1 have unleaded seats fitted to the 295 and refit as standard 2. have the 295 ported / flowed etc or 3. stage three 998 head.
your help and knowledge would be gratefully recieved.
just to put you in the picture the spec so far is as follows;; flat top pistons,286 cam(and i know its a bit over the top but its in now sorry),
minispares clubman straight cut gear kit, min-its straight cut drops, changed diff from 3.1 to 3.44, torquemaster inlet with 38 hif carb,latest stage 2 new hiflow maniflow lcb and single box rc40.
thanks everybody.
David Vizard wrote several outstanding books on this. Clive Tricky was an earlier A series expert. I would get hold of copies and read them.
The post you made is somewhat haphazard and not easy to follow.
If you could list your needs in a simple logical format I will answer each one as far as I can.
Been racing Minis since 1963 still own five (four and a Mininmarcos) so I do have some experience.
My suggestion for reading Vizard is it gives you background.
A lot of the questions you are asking are interelated you need a knowledge framework to make more sense of this process.
The post you made is somewhat haphazard and not easy to follow.
If you could list your needs in a simple logical format I will answer each one as far as I can.
Been racing Minis since 1963 still own five (four and a Mininmarcos) so I do have some experience.
My suggestion for reading Vizard is it gives you background.
A lot of the questions you are asking are interelated you need a knowledge framework to make more sense of this process.
The 295 is the best head for a 998 and is way better than a gas-flowed standard 998 head.
A 295 canand should be gas-flowed in accordance with normal practice as shown in Vizard's book and slightly larger inlet valves can be fitted. The 295 is not suitable for unleaded fuel unless you have harder valve seats fitted (or it has already been done.
The original 998 had D-top raised pistons, so a 295 with standard 998 pistons will have too low a comp ratio. You need to measure and skim the head after gas-flowing and assembling with new valves. Calculate & measure what capacity you need in the chamber and see how much needs to be skimmed off (how to do this is also in 'the book').
If you want a recommendation as to someone to do the head work, Rob Walker Engineering in Witney, Oxon, is really good and I can highly recommend him
A 295 canand should be gas-flowed in accordance with normal practice as shown in Vizard's book and slightly larger inlet valves can be fitted. The 295 is not suitable for unleaded fuel unless you have harder valve seats fitted (or it has already been done.
The original 998 had D-top raised pistons, so a 295 with standard 998 pistons will have too low a comp ratio. You need to measure and skim the head after gas-flowing and assembling with new valves. Calculate & measure what capacity you need in the chamber and see how much needs to be skimmed off (how to do this is also in 'the book').
If you want a recommendation as to someone to do the head work, Rob Walker Engineering in Witney, Oxon, is really good and I can highly recommend him
the 295 head is a great thing, but the problem with it is that to work with dished or flat top pistons you need to skim a lot from it (80 thou i think?)
the other two problems are that valves are not readily avalible for it (unless you go for expensive 'race' ones). they are also not unleaded.
so, by the time you have found a decent 295, skimmed it, converted it to unleaded and re-valved it you will have spent a large chunk of money. there is also the possibilty that the casting wont take the work needed either (a mate of mine recently scrapped two 295 castings, before a third came good for him!
this is probably why a head seller would rather just sell you a ported 'normal' head casting - its a cheaper product for them to produce with far less hassle and risk.
your other option would be to pocket the block and use a 1275 12g940 head casting.
the other two problems are that valves are not readily avalible for it (unless you go for expensive 'race' ones). they are also not unleaded.
so, by the time you have found a decent 295, skimmed it, converted it to unleaded and re-valved it you will have spent a large chunk of money. there is also the possibilty that the casting wont take the work needed either (a mate of mine recently scrapped two 295 castings, before a third came good for him!
this is probably why a head seller would rather just sell you a ported 'normal' head casting - its a cheaper product for them to produce with far less hassle and risk.
your other option would be to pocket the block and use a 1275 12g940 head casting.
Edited by guru_1071 on Friday 7th October 09:18
From memory, the available depth on a standard 295 from face to the bottom of the oil way hole is 0.125", so 0.080" is the max you would really want to remove. This isn't a problem if the 998 has flat-top pistons with the piston top coming within a few thou of the deck level at TDC. With, say, dished pistons and the piston tops a way down the bores it can be impossible to get the combustion chamber in the 295 small enough for a decent C.R. If the 998 is over-bored to 0.080" (1061 cc) and Hastings flat-tops used it is not an issue.
A 12G940 is a good idea and, if the cam has standard lift, pocketing the block is not always necessary. If you put a straight edge across the block face, you need a minimum of 0.320" to the face of the valves in order to be safe. The valve head to block deck clearance at max. opening will then be the gasket thickness. You use a gasket for a 1275. It is possible to recess the valves into the head by around 0.030" for a slightly higher lift cam or to get more clearance if the head has been previously skimmed. To be safe, though, pocketing the block is the safest way to go with the 12G940 head casting.
A 12G940 is a good idea and, if the cam has standard lift, pocketing the block is not always necessary. If you put a straight edge across the block face, you need a minimum of 0.320" to the face of the valves in order to be safe. The valve head to block deck clearance at max. opening will then be the gasket thickness. You use a gasket for a 1275. It is possible to recess the valves into the head by around 0.030" for a slightly higher lift cam or to get more clearance if the head has been previously skimmed. To be safe, though, pocketing the block is the safest way to go with the 12G940 head casting.
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