Dished pistons.
Even with them, my 1310 still had too much compression because both the head and block had been skimmed.

Then put in a 3mm copper gasket, dropped CR to an acceptable level.

As for stroking, you must select the right pistons/rods or they'll stick right out the top of the block



PS Don't make your own copper gaskets. There is an art to the grade used and annealing process to make them last. It's not just a matter of laser cutting to the right size.

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Too many cars, and too little time.

ok,,,to clear this comp ratio thing up a bit,,,it`s easy

make sure when you`re setting up the stroker donk, that you talk with people who have done them for years & years & years

there are some people around saying all sorts of crapo that just confuses the average Joe Blow,,,we have purpose built pistons for exactly this application.

when we build 1415cc stroker """ROAD""" motors, we slice off the top of the piston to make the comp ratio correct for pump road fuel,,,,Now don`t go saying anything about how weak that makes the piston because my dad DESIGNED these pistons to be able to do exactly that!!!!!!!!!!!!!!!!!!!!!!!!!!!!

for race donks we simply leave them the way they are with the big thick strong head on em.

the first ring land is way down the piston so it`s well away from the flame even when the piston top has been lopped off for a roady stroker donk

the very same pistons we use in "NON stroked" 1360cc road & race donks & also leave them as they are

this piston design is now basically , finally being appreciated by others all around the world & some major UK & European piston makers are doing a very similar piston these days,,,FINALLY!!!!!!!

ours are still very good value for money & exceptionally strong,,,you just can`t bust em!!!!!!!!!

It`s all very simple ....-----> In all the cases below, please realize that when """""WE""" build these donks """""WE"""" set the comp ratios to suit the application, but they wil end up pretty close to what`s needed straight out of the box , simply from good design work

so, here`s the list--->

1363cc roady,,,leave the piston how it is,,,just fit it with a std stroke crank & std(ish) cyl head volume

1363cc race donk,,,fit it as it is & use a small chamber head (they`re everywhere these days, just about every race cyl head you see has been decked to the sh!t house so, no problem there)

1415cc road stroker,,,Lop the top off the pistons & select a decent (std-ish) volume road cyl head to suit

1415cc race donk,,,leave piston the way it is (however i do lighten them a fair bit ) & select the very best. big motha cyl head you can get your hands on & set it up at about 13.5:1 or even 14:1 Comp ratio, (Av-Gas only) & then hang on

they are plenty of other types & sizes of stroker able to be built, many many many, different bore sizes, different strokes, different makes /brands of pistons etc etc etc & there are plenty of people around doing all different things in that regard, us included (ala 1510cc & 1600cc & 1430cc & 1450cc & 1470cc etc etc etc), However ,we are very happy to stick with what we KNOW works very well,,,tried & prooven for yonks & yonks, i expect that my dad was "probably" one of the very first in the country to actually stroke a large journal 1275 crank, back in 1969 when the very first Large journal crank came out here,,,my dad (being the Largest Leyland distributor in Qld at the time) had heard about it being produced & imediately thought "HHHhhmmm,,,instant strong stroker mini donk" & grabbed one straight away , they originally used the good old datsun 1200 piston but they were simply not up to the job so he then designed his own piston to suit & hey presto, WICKED STRONG!!!,,, the rest my friends is history, & we`ve done em over & over & over ever since,,,, man i can build em blind folded!!!!!!


anyways,,,keep the thread going, it`s very interesting reading & i also get to understand who actually "Knows" what they`re talking about

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Hmmm.. Matt... it seems Graham Russell designed the exact same 73.0mm pistons your dad did, and they come in a Hypatec box too...
You are correct that they are thick enough in the crown to slice some off for strokers, the dish can be enlarged too if required.

I'm about to get another set for my stroker block.... haven't decided whether 73.0 or 73.5mm yet.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

With the 73mm hyper tech piston i get 11.6.25:1 compresion ratio if the pistons are flush with the block.. isn't this a bit high for 98 octane petrol. I thought 10.5:1 was a safer option

1360/4 = 340

head cc 21.2
head gasket 2.8
piston cc 8.0
total 32cc

340+32=372

372/32= 11.625:1

So if i am correct would have to either increase the piston dish size or increase the head cc or drop the piston down the bore to reduce CC to the 10.5:1..

Cannot see how you can use the Hypertec psiton in its standard form.. unless the Pistons Matts is talking about are different to the Hypertec ones..

what am i missing

Kiwiinwgtn

Piston cc is 8.7, allow 1cc for the ring land, mine are .010" down from flush, I finished up at 10.7:1.
My chambers are a little bigger though, but not much. Dunno where my scrapbook with the figures is right now..

BTW it's running fine on 98 octane- BP Ultimate or Mobil 8000.
Cam is an RE 13 with 1.5 forged rockers.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc
The Hypatech pistons from Ken at Mini Automotive are only about $270 a set with rings.
Bargain

How much clearance is needed to avoid piston to valve contact?

Or is the a-series a non interference kinda engine?

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Metal to burn, sparks to fly...

kiwiinwgtn,,,your engine woulkd actually end up at around 11.1:1 as the head gasket will be more like 3.5cc & if Kev s right & the heps are 8.7cc

so it`s still a fair bit high, but i would suggest a little piston lopping or better still, chamber enlarging to be more worthwhile ,,,as with chamber shaping, you can de-shroud the valve area & re-shape it nicely & then pollish them all up all yummy, so easy & good to do a heap there & keeping the piston pretty high in the bore is a far better way to go than just lopping the piston, i`ve got 35cc out of one head before & have done many many many 32cc & 33cc cyl heads too,,,so ripping out 4cc in each chamber is easy peasy & well worth it.

::-)

the formula is---> Swept volume, plus combusted volume, divided by combusted volume.

so an easy way to do it is --->swept volume, divided by combusted volume,,, plus 1

as the combusted volume divided by combusted volume allready = 1

got it???



lots of people divide the swept volume by the combusted volume & forget that they need to add 1,,,,you however have done it right, just make sure all your volume measurments are correct,,,as Kev said,,,you can even add 1cc for the top ring land area, but i don`t bother as the engine really doesn`t notice it that much & it also leaves room for error on the good side, that it you sort of have a cc in hand, if you know what i mean

easy-peasy

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

it would want to be puttin out a lot for that moneys

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Nigel Morton/ Team Brickworx
never late in a 998

As Matt says it's quite easy to make the chambers bigger, and the relieving will help it flow better too. Mine were out to 28cc (as I had flat top pistons in it..) with no heart shape left- I actually needed to deck it another .050" to get the C/R back up when I bored it to 73mm.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Matt, Kev, are the 1100 (0.020" - 0.040" over) Pistons also this magical design ?

I'm thinking about pulling the 998 down, adding the 1100 Crank and now you've put the idea in my head, Lopping a few mm off the top of the piston AND enlarging the chamber of a 12G202 head ......

I've got the materials to make Manifold Mk5 for the new turbo, and with the GR Cam.... hhhmmmm maybe one day.... maybe .....



J

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Hey james,,,we one made the big ones mate,,,the Heps & the Hypertechs have recently changed to a design similar to my dads, but the small bore ones,,,well,,,mate,,,they`re just a small bore Hypertechs are probly the go for what you want to do , but please do some checking on their thickness before you rip the tops off em,,,

i must admit that i do more work on the bigger bore engines these days so i havn`t kept up with much of the small bore stuff, so i can`t really help you much there.

& for the funny stuff,,,here`s a pic from my site of a friends 1415cc stroker we fitted to his car about 8 years ago,,, the engine has just been sold to Roundy on this message board , cause the old owner was scared of it



good sticker hey?

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

I heard there were no 1100 Hypatec pistons around, recently. Might be now.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

yeah, i got told they were out of stock a few months ago & were making a new batch & should be avaliable in may(ish) so,,,i spose that makes em avaliable seeing as it`s may(ish) right now eh?

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Hey James how about getting some nice bike pistons..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.