7 replies to this topic

[carts60]

I'v got a 91 Cooper with a totally standard engine with an HIF44 carb (i think), and i want it to give a bit more of a kick without having to take the engine out and really get into the hardcore engine tuning.

Therefore, I want to put a stage 3 head on, 1.5 roller rockers and a performance air filter - but who makes the best cylinder heads for the most decent money.

Should i go for a first hand or second hand cylinder head?
Which company should i use for the roller rockers?
Which company makes the best air filters - obviously K&N are very good, but i'v also heard good things about pipercross and a couple of other companies ilke simota etc.

Any views and opinions would be really helpful.

As a side point, how much extra power would this add. Im gussing about 30 odd?

[turbominicooper]

all the main companys like avonbar minisport etc are renound for top quality heads so go with them, mini sport do decent rockers so mayaswel get the head and rockers form them. when it comes to airfilters youve got the likes of pipercross and k&n, each are made from different materials that give different sounds/performance so its really trial and error with what you prefer. hope this helps with your answer.

have you considered getting a different carb needle, fuel pump, ignition stuff - all helps in the end

[Cooperman]

The Mini Spares heads are very good, but check the compression ratio before fitting as if your pistons are some way down the bore at TDC you'll maybe need to skim a bit more off the head to get the desired comp. ratio.
The roller rockers won't really give you any more power, maybe 2 or 3 bhp at the very top end.
K & N do make the best filters.
With the better head and better inlet filter you'll gain, maybe, 10 to 12 bhp.
You engine has, in good standard condition around 65 bhp. To get an additional 30 you'll need a much better cam (at least a 276), a big-valve very flowed head with at least 10.5:1 comp ratio and running premium fuel, a really good exhaust system with a 1.75" int. dia exhaust pipe and a single or twein-box RC40 modified distributor with better advance curve and an improved inlet manifold.
After the head, the cam is the key to A-series performance and you can fit any other parts you want, but without the right cam it'll not really go much better.
I built a 1990 Cooper engine with an MG Metro cam timed accurately in with offset woodruff keys, 35.5 mm inlet valves, bored it to 1330 cc, set 10.5:1 CR, fitted a 2-box RC40 centre exit at 1.75" ID all the way to the outlet, an Aldon 'Red' dizzy, Mk 1 flywheel slightly lightened, and gas-flowed the HIF44 and fitted a K & N filter with stub stack. It gave a measured 84 bhp at 6000 rpm. Of that increase, 4 to 5 bhp was the result of going from 1275 to 1330, so all the other work gave around just 15 bhp additional.

[huw_jenks]

The first mod for a standard engine should be a decent Stage One kit (Reusable air fliter, water heated inlet manifold, LCB exhauust manifold, 1.75" exhaust, carb needle). This will sort out the breathing on the engine which will make a big difference on a Mini (most manufacturers claim a 20% power increase and around 12% torque increase). MiniSpares do (or did?) a good kit, using K&N filter, Maniflow manifold and RC40 exhaust. K&N air filters are known to be excellent, but the modern foam filters (RamAir, ITG) flow more air (I think!). Whatever you choose, make sure you get a stubstack/rampipe, otherwise the new filter will be next to useless.

The next stage should be a decent cylinder head to further improve the breathing of the engine. Do be aware that most companies use 'Stage 2, 3, 4, whatever' to refer to different head specifications, but this is not standardised and can depend who you buy a head off. With a new cylinder head you will see the benefit of an uprated camshaft too, but I can't comment on the worthiness of using roller rockers with a standard camshaft.

The best thing you can do before buying anything is read David Vizards book, 'Tuning The A Series Engine...'. Very, very useful.

[carts60]

Will changing the camshaft involve removal of the engine?

Thanks Huw, your reply was very helpful. From what i can tell, iv already got a stage one manifold and i also have a 1.75" maniflow exhaust (though its not on the car because i took it off in favour of a twin exit one which saps the power but sounds lovely).

Il check that tomorrow though.

Ok, so if all the companies refer to their heads as the same but in reality they're different, what size inlet and exhaust valves are best suited to tuning a 1275?

[huw_jenks]

Will changing the camshaft involve removal of the engine?

Thanks Huw, your reply was very helpful. From what i can tell, iv already got a stage one manifold and i also have a 1.75" maniflow exhaust (though its not on the car because i took it off in favour of a twin exit one which saps the power but sounds lovely).

Il check that tomorrow though.

Ok, so if all the companies refer to their heads as the same but in reality they're different, what size inlet and exhaust valves are best suited to tuning a 1275?

On a 1275 motor, the engine needs to be out of the car to remove the camshaft. Some engines were fitted with tappet covers, so if you removed the radiator and drilled a hole in the inner wing, you could remove the camshaft with the engine in-situ. If you have non standard manifolds and exhaust it sound like you have most of a Stage One kit. You will have to decide if you want pancake/cone/sock airfilter or a K&N element in the original airbox. If you keep the standard airbox you will have to drill some big holes in the front to get enough air in, but does have the advantage of keeping things a bit quieter.

As for which cylinder head to go for, my knowledge does not extend that far I'm afraid! But you're on TMF, so shouldn't be too hard to find out.

[Cooperman]

In terms of valve sizes you are probably best to go for 35.5 mm inlets and, ideally, 30.5 mm exhausts, all with unleaded seats. 37 mm inlets are possible, but it can be difficult to get with good unleaded seats this size and the exhausts may then need to be smaller. The 35.5/30.5 is a good compromise.
On all 1275 engines with the exception of the original Cooper 'S' blocks, the engine must come out to remove the cam. The cam on the 998 an be changed in-situ. However, if you are looking for a serious increase in power of 20% or more, then you would be advised to inspect the bottom end bearings, including the crankshaft end float and changing the bottom end bearings and the oil pump. So many people have changed for a better head, etc, and then found that the increase in power has brought the existing wear to the surface resulting in an early re-build.
Don't expect to gain much extra unless you change the cam together with the other parts mentioned. Yes, the suppliers of 'Stage this, that and the other' kits claim all sorts of increases, but after all they want you to buy their kits. So be a bit sceptical. You need to treat the increase in power as a complete engineering exercise and you can't 'pick' at it and hope for real noticeable improvements. In fact a well-built standard engine will be noticeably better than an old standard one if the cam is timed-in acurately, the rings are all good, the ignition system is correct, the compressions are as original, etc.

[bmcecosse]

Your proposed modifications are likely to get you ~ 10 extra BHP at best! Is the engine in tip top condition to start with ?