12 replies to this topic

[daz90]

I recently removed the head off my 1330cc to get some work done and it was the first time i have inspected the pistons. The Bores are perfect and everything fine I just couldnt find much Info on the Pistons. The only information i could find was on minispeed and there wasnt much, just wondering if anybody has any info and could help me out.

They are Marked 21250 + .060

Thanks

[surfblue63]

Bit of info here

http://www.minimania...m?DisplayID=106


21250 Pistons
High performance replacement pistons suitable for up to 7,000 RPM. Pin height is 1.498 which could result in a compression ratio of 9.4:1. They also have 4mm oil rings and 1.5mm compression rings. Available sizes are std., +.020, +.040, +.060.

[albo]

hi all,,i have just got a set of these,,nos from e bay,,they are at plus 40,,

many say these are now not available,,mini speed stock these as now,,these are rated to 7k rpm,, 

so prob be safe to push them that bit further,,these was to of been superceded by 21253 pistons,,

cant see 21253 been much better,,i plan to run these at 10,1 with a 270 cam,,

i put these on me new electronic scales and was happy to find they are perfectly ballanced regards weight,

these performance rated pistons are also much cheaper then 21253 s,,and new ring sets are easily available if needed,

any one had a bad experience with these,

 

thanks alan

[carbon]

Additional info - the set of 21250's saw have a long deep slot behind the oil ring, rather than the series of small drilled holes which you typically get on higher performance pistons for greater strength.

 

These 21250's also had the 'slipper' skirt, but not sure if I would class the 21250 as a high rpm piston.

[albo]

thanks ,i know about the bigger oil slot,they are identicle to 21251s which many regard as chocolate,

but with a lower pin hight and better/stronger grade alloy casting according to ae that is,

cant realy see ae messing with dif melting pots and alloy grades for every different piston they make,

is`nt the slipper piston an improvment over say a cup piston/lighter and less drag

[Cooperman]

Actually the 21250, 21251 & 21253 are all good pistons. The 21250 can rev OK, but maybe not quite as high or for as long as a 21253.

I've used the 21251 and happily revved it to 6500 with no issues. I did this on a block which had already been decked for that type of piston.

[albo]

thanks coops tor your reassurance,,i remenber sum time bk that you acquired a cooper then found it had been rebuilt with 21251 pistons decked flush and set to run on i think you said 10,3,1 compression with no issues,but stated that time will tell,

i often wondered if they did,

 

thanks alan.

[Cooperman]

Yes, that was an Innocenti 1300 Export. It went very well and I sold it earlier this year to make space for the 1964 850 I'm currently restoring.

Modern pistons are all of a good standard. There are no really poor ones, just some that are slightly better. I built a 1330 rally Cooper about 8 years ago with 21253 pistons and I revved it to over 7000 quite often. A friend of mine now has it and he has used it in club competition. It still has the same pistons and is going well, over 25000 miles further on.

[albo]

well that just goes to show that 21251s are not as chocolate as a lot on hear believe,

but i would feel more comfortable my self going beyond 6500 with 21253s,

i now feel more confident to use these 21250s i have just acquired, 

[Cooperman]

Very few owners really rev their cars and many on here rarely go over 5000 rpm.

[albo]

mm quite hard to belive that as most on hear seem to ask about upgrades,cams heads bigger carbs ect ect,,

im aiming for about 90 bhp with the useual 44 hiff mg head lcb,10,1 com,or and i have a 270 cam, plus 40 with pistons mentioned,

do you think that is poss with above spec,or and a yellow dissy.

 

thanks again

[Cooperman]

Best advice is not to be concentrating on bhp unless it's a race car, but concentrate on getting a really good torque figure.

By itself 90 bhp will not give you really good road performance, but a significant improvement in torque will.

As others have said, it's not the top engine performance which make a great car, it's the way the engine delivers its performance across the rev range.

A 270 cam can give excellent torque and +0.040" will give 1310 cc, so a slight gain from the additional capacity.

Your spec does sound good and I would guess at 85 bhp if well and accurately built. You will need a differently curved distributor, but talk to Aldon Automotive about that and they will curve one for you.

Be a good idea to lighten the flywheel a bit to improve acceleration.

You do have folks on here who have cams which give peak power at over 6000 rpm but who will admit to rarely revving to much over 5500 rpm. They have spent too much time reading the monthly 'Mini Comics' where all sorts of poor specifications for the use of the cars are bandied about. It tends to make people think that unless they have a full-on race cam, 37 mm inlet valves, vented brakes, etc, etc., then their cars won't go well. It's a lot of sales 'hype' IMHO. Cynical, moi? .

[albo]

torque will be my aim then,,nice to know 270 is a good cam,i think it`s power band is from 1500/6500,don`t know it`s cam timing as yet,maybe at 106 btdc is that correct,we have a good engineers shop hear in hull to which is very handy (alex cars)

 

thanks again for your time

and a piece of your wisdom.