12 replies to this topic

[woollenp]

Model: Mni Clubman Saloon
Year:1979

Hi - help with my engine upgrade would be awesome!

In 2008 I built and fit a Minisport 'Stage 2' 1293 engine to replace the standard 1098 that came with the car.

This came with one of their 'Fast Road' CA2 camshafts (ST948) and a head with valves sized 35mm inlet and 25mm exhaust.

I use a HIF44 carb with K&N filter and LCB exhaust.

Bit gutted at the original rolling road when it acheived 75bhp at flywheel rather than nearer the advertised 91bhp

I just had my gearbox fail and have replaced it with a 6 piece S/C box, cross-pin diff and centre oil pickup - hopefully able to stand a lot more power through it than my last helical box! (thanks to Tony @ bournemouth mini centre)

Now looking to uprate my engine.

I like the reliabilty of the 1293 - I here larger bores lose this, seeing head gasket failure sooner and other issues.

Looking at a friends mini which has a 998 giving out around 70bhp AT THE WHEELS! which is 25bhp more than mine - how can I tune mine to this standard? He maintains it is still very drivable.


So...question.... Do I uprate the Cam? Head? Carb? All three? I have a duplex chain, timed by dot-to-dot method - when do I need to worry about vernier gears? I hear they are only really needed on full race engines.

Spoken with minisport and they say to uprate the cam would lose drivability given its already 'fast road' and the head is ported to suit the valves and might be hard to modify. They say the HIF44 is good to 1380 engines so no need for twins or weber really and both could again lose drivability in lower revs. They suggest their 1.5 roller rockers, offering a MAYBE 8bhp more.


Has anyone any other advice? I've looked at Cam specs but they confuse me massively - not that clued up on cams really. I'm not fussed about a 'quick' power fix, but low cost would be awesome - I'd be as happy whipping the engine out to change the cam as to fit roller rockers and both seem about the same price (ish).

100bhp is my aim - bit gutted my 1293 is only just more than the standard 1275GT is meant to be (75 flywheel down to 45 at the wheels - prob bit better at the wheels now s/c box fitted)!

Any helps is much appreciated anyway.

Cheers, Pete

O - and want to keep it Naturally Aspirated if possible - uprating my pistons and getting supercharger/turbo is a bit costly for me at this point - to keep cost below £500 would be awesome

[Cooperman]

100 bhp is quite a lot and you won't get anywhere near that figure with the spec you have. To build a 100 bhp unit requires very careful and accurate building and a lot of measurement and correct machining.
First of all, 75 bhp is the power the original 1275 Cooper 'S' gave with a 510 cam, twin 1.25" SU carbs, a fairly good head, a 3-into-1 exhaust manifold, etc. That is certainly as good as spec as yours.
To get 100 bhp will require a much hotter cam, probably a Kent 286 or equivalent, twin HS4 1.5" SU's on a good alloy manifold, a compression ratio of around 10.5"1, a re-curved distributor, 35.6 mm inlet valves and 30.5 mm exhaust valves in a well-flowed head, top-quality pistons, a fully balanced bottom end to allow for revving to the necessary 6500 rpm+, a lightened flywheel, possibly a cross-drilled crank for the high revs, all parts matched to ensure compatibility. Then you would get to 100 bhp at around 6400 rpm. That lot with a 276 cam would probably give in the region of 92 bhp at about 6000 rpm.
A 100 bhp engine woulkd be quite lumpy and there would not be much useable power or torque below about 3000 rpm coming in strongly at around 4500, so a lower final drive ratio might be needed to make it driveable in traffic but this would give a lower cruising speed, or the same cruising speed but at higher revs.
You say you have a friend with a 998 giving 70 bhp at the wheels. This does seem unlikely as that would be a full-race engine and almost unuseable on the road. 70 bhp at the flywheel on a 998 is reasonably attainable.
It's not too expensive to get to around 75 to 80 bhp, but the cost per extra hp goes up alarmingly after that and a 100 bhp engine is expensive and will require re-building more often.
I hope this helps.

[bmcecosse]

Your cylinder head must have more than 25mm exhaust valves - or it's not a large bore head! But as above - you need to change the cam (yes 286 will be good) and get a big valve head (ex MG Metro will be fine - then modify it as per Vizard) - your HIF 44 will be fine, and assuming an LCB exhaust you should be up for 90 bhp. My advice - don't waste money on the silly rockers!

[Cooperman]

Your cylinder head must have more than 25mm exhaust valves - or it's not a large bore head! But as above - you need to change the cam (yes 286 will be good) and get a big valve head (ex MG Metro will be fine - then modify it as per Vizard) - your HIF 44 will be fine, and assuming an LCB exhaust you should be up for 90 bhp. My advice - don't waste money on the silly rockers!

100% agree. Roller rockers at that state of tune would give about 2 bhp increase and then only at high revs. Those who sell those rockers claim more - well, they would, wouldn't they.
HIF44 is good for up to about 90 to 92 bhp, above that you need either twin 1.5" SU's on a decent (Torquemaster) alloy manifold, not a standard BMC one, or a Weber twin-choke 40 or 45 DCOE, for which a bulkhead mod. is necessary (see thread about modifying your Mini within the law).

[twrminisport]

As above.
I would use twin 1.5" SU carbs and a kent 286 cam then a large bore head, ported polished and maybe bigger valves.
However with this all in you will need to do the head porting yourself to keep costs down i would expect.

Edited by twrminisport, 21 July 2011 - 10:04 PM.

[tvrdave]

There is quite honestly no single or cheap option to produce big power on a small budget. If you want to achieve 100 bhp and still keep a driveable car then you need to look at all aspects of the engine, which of course won't be cheap.

You can achieve power by sorting out heads, cams, compression ratios, rockers, exhausts, carbs etc etc, but it all has a knock on effect if you want it to be driveable and reliable. You then need to beef up all of the internals and ancilliaries in order that the engine does not destroy itself. Not forgetting that once it produces more power it will also get hotter, so the cooling system needs to be upgraded. Driveability can be achieved with proper cam timing and carburation, to suit the use you have for it, but again it all has a cost.

If money is an issue then in my opinion it is better to wait until such time that you can afford to do it properly.

Dave

[Tommyboy12]

75bhp is a bit low. My MG Metro 1275 is kicking out 81bhp and thats only got a bit of head work. Straight cut box will help with power loss but it wont make your car any quieter! I would say invest in some more head work before you go changing cams and rockers.

[Cooperman]

75bhp is a bit low. My MG Metro 1275 is kicking out 81bhp and thats only got a bit of head work. Straight cut box will help with power loss but it wont make your car any quieter! I would say invest in some more head work before you go changing cams and rockers.

Don't forget that you have that wonderful MG cam - the best production cam ever made by BMC/BLMC/Austin-Rover/Rover and the valve sizes are good too at 35.6/30.5. Comp ratio is also well up so with some head work to help the mixture in and out and general tidying-up about 80 bhp is to be expected. I bet you have a decent air filter too and a good exhaust.
The MG cam and the bigger valve head are improvements over the original 1275 'S' which came in with 75 bhp and had a lower comp ratio as well.

[bmcecosse]

He says it has the 'Kent 948' cam - I'm guessing this the same as a BMC 2A948 cam - which was a fair enough improvement in it's day (997 Cooper cam) - but is not as good as the MG cam - but I loved my 544 cam which these days has been 'improved ' and is know generfally as the 286 cam. It's the way I would go! An HIF 44 with suitable Vizard type work should surely be good for 100 bhp ? It's the head that will be the limiting factor.........

[Cooperman]

He says it has the 'Kent 948' cam - I'm guessing this the same as a BMC 2A948 cam - which was a fair enough improvement in it's day (997 Cooper cam) - but is not as good as the MG cam - but I loved my 544 cam which these days has been 'improved ' and is know generfally as the 286 cam. It's the way I would go! An HIF 44 with suitable Vizard type work should surely be good for 100 bhp ? It's the head that will be the limiting factor.........

Yes, I always try to think in terms of the head giving the engine the potential to produce the power and the cam being the enabler of that potential to be realised, assuming, of course, that everything else (carbs, manifolds, etc) is done correctly.

[Ethel]

I wouldn't be scared off by forced induction - it's the way to go if you really want 100bhp & driveablity. That's only 10 horses more than a bog standard Metro turbo, which is little different to more tame A Series.

[woollenp]

Thanks everyone - really useful comments. Scrapped the rocker idea then, other threads and your comments make these a bit redundant and a waste of money when upgrading cam at any future date.

So the way forward is head work and improved cam (among other engine tweaks such as cam timing, comp ratio and ignition timing). Minisport suggest the head they supplied wont lend itself to having valves enlarged due to existing porting - not sure of the validity of this but worst case means new head. That and a cam would mean ~£1k

Maybe the comment of waiting is the best (for now) - if a 1k investment is needed to see any major power increase, forced induction might be the best next step. Look out for the thread next year titled supercharger or turbo?!

Thanks again

[Cooperman]

If you bought the head from Minisport, I would advise checking the chmber volume and thus measuring the comp ratio. I say this because I once bought a head from them for a 1071 Cooper 'S' and gave them the chamber vol.req'd. The head they supplied was nowhere near the vol. specified and had I fitted it without checking the C.R. would have been about 7.8:1. Then I would have wondered why it had no power despite a 649 cam.
Measure the valves you have. If the inlets are 35.6 mm, then it's a fair bet the exhausts are 29.5 mm or 30.5 mm. Either will be reasonably OK with good gas flowing.
As 'bmc....' says, a 544/286 is a very good cam and works best at over 10.5:1 C.R. with good breathing both in & out.
To some extent you need to balance required reliability against pow2er output. The nearer you get to a race engine the more often you will need to strip & check it.