Cam choice query

[Mr2Mike]

Not strictly mini, but A series related. My brother recently got his 1275 Midget on the road and, after the brakes and suspension upgrades have been fitted, is keen to extract a bit more power from the venerable A-series.

It currently has an A+ engine fitted (Morris Ital at a guess). Obviously the head is the main priority, but he had a mini a number of years ago which he fitted a MED 1380 engine to, and used a 286 Scatter cam along with a DCOE 45. Based on how well that went that he's considering another 286, but looking around it seems there may be better choices available now e.g. Swiftune SW5?

This will be a fun road car for fine weather use only, so a rough idle etc. is not really too big a deal, but it needs to have a decent amount of mid range power.

edited to remove half a sentence randomly thrown in

Edited by Mr2Mike on Thursday 9th May 14:44

[guru_1071]

I would say that an SW5, whilst a great cam, would be a bit of a step down from what he had and probably wouldn't work with the weber so well.

for your engine id be looking at the SW10, which has a bit more about it will be a little more rorty in a 1380

[FWDRacer]

Capacity:

CR:

Carb:

Exhaust:

Give us the spec of these and we'll spec the Midget a cam. Either that or p!ss off to the MG forum

[Mr2Mike]

FWDRacer said:

Capacity:

CR:

Carb:

Exhaust:

Give us the spec of these and we'll spec the Midget a cam. Either that or p!ss off to the MG forum

It already has an LCB and I suspect he'll want to stick to the twin SUs for now. Just to be clear, it's not the MED engine that will be fitted, that was sold with his mini. This will remain a 1275 (or whatever it is currently) unless it needs a rebore. He has an MG Metro head ready for porting and skimming, so CR is flexible.

Planning to use standard rods and pistons and crank (unless in poor shape) so pointless having a cam that requires higher RPM than this can cope with, which is why I thought the 286 might be a bit too much.

[FWDRacer]

Twin SU's? 1.25" or 1.5" twins...

Have another go

Standard pistons aren't much good past 6K - that is about your limit so Kent 276/274 or SW5 are about the top step. Have you considered sourcing a genuine MG Metro CAM (Part No. CAM 6648) - Hugely underated cam and will go really well, timed in properly in a 1275+ with a high flowing head/SU's.

If the bore is knackered get some decent pistons and the world is your oyster on cam choice - rpm limits can be rasied to 7K on standard rods/crank.

Edited by FWDRacer on Friday 10th May 08:43

[Mr2Mike]

FWDRacer said:

Twin SU's? 1.25" or 1.5" twins...

Have another go

Standard pistons aren't much good past 6K - that is about your limit so Kent 276/274 or SW5 are about the top step. Have you considered sourcing a genuine MG Metro CAM (Part No. CAM 6648) - Hugely underated cam and will go really well, timed in properly in a 1275+ with a high flowing head/SU's.

If the bore is knackered get some decent pistons and the world is your oyster on cam choice - rpm limits can be rasied to 7K on standard rods/crank.

Edited by FWDRacer on Friday 10th May 08:43

Unless a set of 1 1/2" carbs fall into his lap it will be the standard 1 1/4" SUs. I know the manifold is pretty crap in standard form, IIRC the DV book has some info on improving them. Is a single 1 3/4" on a decent manifold still the best choice for a mildly tuned 1275?

I have already suggested that a set of decent pistons would be a wise investment, but budget is a bit tight. I completely agree about the MG Metro cam and we do have a tidy, low mileage s/h cam which was the original plan, but he wanted something a little 'hotter'. Champagne tastes and lemonade pockets

[FWDRacer]

If the budget really won't stretch use the S/h cam and buy some 1.5 ratio roller rockers (tip only) - Hi lift and short duration cam will give a great "road-able" engine. Set CR around 10:1. I think MG's left the factory at 10.4:1, (35mm Inlets too) so you can work the chambers without having to skim chunks off the casting (they all differ).

Twin 1.25" are pretty much for show queens now. As an engine metaphor, when using the tiny twins, it is like the engine trying to have a decent draw on a "Ciggie" and is sucking so hard that it's pants disappear up it ar$e....

Twin 1.5's or a single 1.75 HIF44 all the way.

Edited by FWDRacer on Friday 10th May 15:20

[nick1275]

another vote for the mg cam here

[guru_1071]

FWDRacer said:

Twin 1.25" are pretty much for show queens now. As an engine metaphor, when using the tiny twins, it is like the engine trying to have a decent draw on a "Ciggie" and is sucking so hard that it's pants disappear up it ar$e....

id disagree here, twin 1.1/4" are ace on a mildly tuned engine as they give great low down torque and excellent fuel economy - ive a set on my std 1725 engine mini and for a 'everyday' road car they are perfect. I get nearly 45mpg when its cruising and it will pull up to 6000rpm quite happily (before the electronic mg dizzy starts to misfire!)

the problem with using twin 1 1/2"s on a mildly tuned car is that they only use such a small area of the needle and it can be difficult to get the mixture right for low down / part throttle stuff, they can also 'stand off' really bad, which just ruins a car.

dont get me wrong on a big engine with a lusty cam they are perfect, better than webers on the road, my 1430 with a 649 is the perfect package with its twins.

as for hifs, I hate them, hif38s are very intolerant of needle changes and ive found on mildly tuned 1275s its impossible to get the mixture rich enough for steady state crusing, ive also found that on both types of hifs that the rubber rings on the choke barrels are often worns, so they always leak fuel in, so they always run richer than they should low down - again it makes it so had to get any sort of decent economy or decent running, this is why a lot of minis running hif44's struggle to get through the emissions test.

we seem to be going away from cam choice, sorry!

[Petrolhead]

My 2 peneth woth, if sticking to max 6000rpm and twin HS2 I would be looking at Kent 266 or Piper equivalent (255?).

However, if it is your intention to rebuild the engine and get twin HS4 I would go Kent 286 or RE130T (sold by Calver) - http://www.calverst.com/

[Cooperman]

The 266/MG Metro cam would be ideal. To go more than this will require more revs and, with a 286 for example it is necessary to be able to use around 6800 rpm as peak power won't happen until about 6400 rpm and one needs to be able to go beyond peak to get maximum advantage.
With a 266 a max rev limit of about 6200 will keep it 'on-cam' and at best power range.

[Mr2Mike]

Thanks for the excellent advice, I've passed this onto my brother. He actualy had a 266 in his mini before the MED 1380 and it worked very well, in fact it even gave better idle quality than the MG Metro cam IMO.

[Cooperman]

The Mg Metro & the 266 cams are really virtually identical. The only difference seems to be that the MG cam times in at 110 degs ATDC and the 266 at 106 degs ATDC.

[MiniRally1985]

Am I right in thinking a sports cam set for high rpm can have problems at idle?

I had a mate with a car rebuilt completely, it was that stupid he had to have his idle changed higher due to the cam causing it to stall, it was sublime at high rpm, but lower rpm, you could feel the tension, anything under 1000rpm and it was rough.

[Cooperman]

MiniRally1985 said:

Am I right in thinking a sports cam set for high rpm can have problems at idle?

I had a mate with a car rebuilt completely, it was that stupid he had to have his idle changed higher due to the cam causing it to stall, it was sublime at high rpm, but lower rpm, you could feel the tension, anything under 1000rpm and it was rough.

That sounds about right. With, say, a 286 cam it won't idle smoothly and will need to be set to tickover (or 'lump-over!) at around 1100 to 1200 rpm. But then, kit will give best power from 5700 rpm to 7000 rpm, so the engine needs to capable of sustaining those revs.