19 replies to this topic

[cormacharte]

i just got a 1275 engine and want to give it some more power. would 80-90 bhp be possible to get with a few mods without boring it out? if so what could i do to achieve this? was thinking head cam and carbs. what ones should i go for? is the mini sport 1275 road sport head any good or would it be the right thing for what i want. i want it for weekends and fun but to be a fast road mini. if i was to get this head and put a kent 286 cam in it and hs2 1.25" su twin carbs what would i get any help greatly appreciated cheers
cormac

[jaydee]

you can get to 80-90 bhp by fitting a very good cylinder head (ported, gas flowed, 35x29 valves, work done properly by a good engineering shop) feed by a pair of twin HS4, a kent 266 cam accurately timed in and an 1.75" exhaust. Then have it rolling roaded at baldwins.
Forget the twin HS2 if you want that sort of power, and i'd say forget the 286 too:
With the 286 you virtually have nothing below 3k rpm and engine will really be good only above 4500 rpm, plus you'll have emission problems at the mot and very tight rebuild intervals. And to be honest, i would never fit a cam that needs to be revved over 6k rpm on an engine with no main centre cap and no accurate balance.

[Cooperman]

Rob Walker Engineering at Witney do really dood heads with 35.6 mm inlets & 30.5 mm exhausts. Go for a comp ratio of about 10.3:1.
For a cam go for a 266 or an MG Metro cam. They are almost identical.
For carbs the HS2's are a bit too small and twin HS4's are much better.
Use an LCB exhaust manifold and a Maniflow twin-box 1.75" internal diameter exhaust pipe.
Fit a lighter flywheel and a better ignition system, typically a Megajolt or the new Aldon Amethyst so that the advance curve can be matched to the head, cam & carbs.
Just re-bore to the next size up and use AE21253 pistons.
Don't fit a 286 cam or you'll be into big money as the engine will need to rev to around 6700 rpm, you'll need a lower final drive ratio which will mean more revs at cruising speed, and in traffic it would be horrible.
Good engines are about build quality as well. So either learn a lot about engine building or get someone with a good reputation to build it for you.

[cormacharte]

cheers for the quick reply and advice are the heads from mini sport good or is there anywere i should go to or avoid and if i do all this would i easily get the bhp im looking for if i wanted a little more or to get that would i be better boring it and how much does it cost
cheers again
cormac

[cormacharte]

cheers for the reply cooperman are u suggesting i do all the above and bore or do the above or bore ?

[Cooperman]

I had a head from Mini Sport which had the wrong size chambers for my rally engine, despite giving them a full spec. Then they supplied a re-built straight-cut close-ratio gearbox and failed to fit new gear linkage bushes which meant I had to take the engine out again after fitting it.
I highly recommend Rob Walker for top quality heads and other engine work. Take a look at his web site.

[Cooperman]

cheers for the reply cooperman are u suggesting i do all the above and bore or do the above or bore ?

If doing an engine up-grae it is worth re-boring to the next size up. I've seen too many part re-built engines which last only a short time before requiring more work. Do it properly once and it'll be really good. I will never part re-build an engine as I want reliable performance.

[cormacharte]

cool cheers for the help

[bmcecosse]

I would definitely go for a 544 cam (286 in modern speak ) - the 1275 can easily pull it - and a large inlet valve head with the usual basic Vizard mods. You don't need a fancy super expensive head for the power you are after. Forget the tiny twins - single HIF 44 will be fine, or twin HS4 if you really must have twins.

[adamg1380]

Swiftune SW5 cam is a really good fast road cam, it'll run fine at low revs and pull hard from 2.5k to 7k. I'm well impressed with mine and glad I didn't go for a 286, the SW5 has none of the problems people have mentioned above.

Maniflow SIIR manifold was the other bit that made a a big difference over the cheap LCB that was on the car when I got it.

Edited by adamg1380, 06 September 2012 - 03:25 PM.

[bmcecosse]

The SW5 is a very 'flat' cam.....many have tried it, and moved on........

[adamg1380]

The SW5 is a very 'flat' cam.....many have tried it, and moved on........

A 286 will give bigger numbers on a dyno, but on a standard gearbox a big flat torque curve can make for a car that's at least as fast overall. You get more choice over whether and when to change gear and good standing starts.

I will go for a 286 when I get a close ratio box though.

SW5 in action:

Edited by adamg1380, 06 September 2012 - 06:46 PM.

[Cooperman]

To risk repeating myself, a 286, which is similar to but a bit better than the old 544, is a superb cam, but you have to rev to 6400 rpm to get peak power and change up at about 6700 rpm for maximum acceleration. So you need a fully balanced engine with a centre-main bearing strap for those sort of revs and the engine will need re-building more often.
Personally I love the 286 cam - it's my favourite - but then I run a SC CR gearbox with 11.2:1 C.R. twin H4's and all the other bits. With the 286 it's very lumpy in traffic and I run a low FDR.

[bmcecosse]

Hmmm - my 544 wasn't lumpy - it ran well - slightly higher idle speed I suppose. And pulled 'like a train' from reasonable revs. Occasional use up to 6500 won't require the strap etc. But if it's going to be thrashed constantly - then yes, of course.

[Cooperman]

Not much point in fitting a 544 if it's not going to be used all the time, Roy! The 286 is certainly a better cam than a 544 and I have used both in similar rally engines. I guess it represents 25 years more A-series cam technology. I did have a great 1293 rally 'S' back in '69/'70 and that had a 544 with twin H4's. It was very competitive. I fitted a 544 to a 1330 cc historic rally 'S' and tried HS6's. It was good, but not as good as a 286 and twin H4's.
The OP wants 80 to 90 bhp and a road engine, so I do think a 266 plus a good head, higher C.R. and twin HS4's, etc, would give that and be very nice on the road. He's not looking for much more than a standard 1275 Cooper 'S' in reality.