47 replies to this topic

[Cooperman]

It must be understood that to get a power increase with a normally aspirated 998 engine it is necessary to improve the engine breathing by gas-flowing the head and changing the cam. When this is done the power & torque band shift up the rev range and the more power the 'hotter' the cam, higher the revs need to be.
A 998 will never perform like a 1275 and the torque of a 1275 is high even in standard form.
What you cannot have is a 998 which gives smooth and good low-end torque and then gives high power at the top end. You have to choose which you want.
So, a 998 with, say, a 276 cam, a 12G295 head, twin HS2 carbs, a lightened flywheel, higher compression ratio, etc., could give around 70 bhp, but that would be at over 6000 rpm asnd there would be little useable torque much below about 3800 rpm so, yes, you would need to rev it all the time to get it to go really well. Then a closer ratio gearbox would be better to keep it 'on the cam'.
As I have often said, the Mini is an old-design classic car and that fact is important to remember. Modern multi-valve multi-cam engines have different characteristics, but if a classic car is what is wanted the limitations of that have to be accepted.

[Vipernoir]

I wish I had a "rolling road" within 1000km of me.......I'd love to know what my 1098 puts out. Someone give me a guess:

1130cc ( 1098 +40 )
12g295 ( shaved to 24cc chambers......080" )
SW5
twin 1.125" ( sometimes I run an HIF38 with AAU )
LCB
rc40 equiv.

Now...as it's a long stroke engine I'm not going to be running at 6k + very often so may be hard to compare with a 998 running at 6600.
( I did install a better piston that doesn't have the ring below the pin )

63-65bhp at the flywheel - based on the fact that our engines are very very similar.

[Spitz]

Thanks for that!
I actually had 60hp in my mind....although the seat of my pants told me a little more maybe

Edited by Spitz, 25 April 2013 - 02:50 PM.

[minimk1]

How about a 1275 cam ? Heard there simular to the 266

[Cooperman]

There are a lot of different 1275 cams. The original cooper 'S' used a 510 and that was quite nice in a 998. The standard 1275 cam from later cars won't improve a 998 much, if at all. You need to decide what you are looking for: good mid-range torque or better top end power - you can't have both I'm sorry to say. What is the car used for? That will give the answer. if it's mainly used in traffic and in town, then mid-range torque is most important. If you drive on country roads where using high revs most of the time will not be an issue, then a more cammy engine revving to well over 6000 rpm would be fine so long as you don't mind more frequent 'strip & rebuild' sessions.

[minimk1]

Yeah it will be more country roads what sort of cam would be the best to use a 276 ?

[Cooperman]

with the sort of spec you are proposing a 276 will require use of 5500 to 6400 rpm to get the best performance. That is a bit high for a road car and a 266 might prove better for road driving. A Mini is never going to go like a modern car as it's a classic car, so it will be best to make the best driving car possible. You don't want to have to use over 6000 rpm to get best power really.

[minimk1]

Thinking about keeping the engine as it is with uprated exhaust system and trumpets on the carbs

[minimk1]

As I don't have the Money to spend 1000's on it and think that 55 hp is more than adequate for my first car

[minimk1]

Plans now are to try to find a reasonably price 12g295 head and fit a 266 cam and a lightened flywheel with a mainiflow exhaust manifold and a rc40 twin box centre exit with trumpets on the carbs hope for 60 hp but I expect the engine has lost a few hp over the years so I would be happy with the standered 55hp

[minimk1]

Does anyone know the sizes of the inlet and outlet valves on a 12g295 head standered and the inlet and outlet valves on the 12a185 as standered just want to know what the size difference is between my worked 12a185 and standered 12a185 and compare this to a 295 many thanks

[minimk1]

http://www.minimania..._casting_number

Found this website and this says there bigger than a 295 ? Little confused by the layout

[minimk1]

That is an 11 stud head the 997 and cooper s head had the same markings that's why I was confused but with the work that has been done to my head my inlet valves are huge roughly measuring about 1.65 inches and the exhaust measure the same as a 295 at 1"

Edited by minimk1, 18 May 2013 - 03:47 PM.

[minimk1]

Also is it worth me splitting the block to clean out and inspect the gearbox or should I just leave it as it is as I have little exoerience of engine building any comments would be much appreciated

[minimk1]

found a cheap 12g940 head worked to about stage 2 or 3 would this work with the exhaust valves sunken in as i also have d top pistons and would be using a 266 cam so would clearance be and issue or not, also does sinking the valves work as-well as a pocketed block as sinking the valves  would work better for me as transporting the engine would be a hassle as i am not completely stripping it of pistons and cranks etc