m42 pistons in m20 block with pics

[bigbhpwannabe]

im sure that some one in the past has posted some thing like this but when i serched for info on this i couldnt find much
m20 2.5 post 90 standard pistons


and m20 2.5 with m42 318 is pistons



i would say that the m42 piston sits a little under 2mm under block hight
will be going to engine builders in about 3 weeks for a compression calculation and will be pulled apart the block slightly skimed ,honed bores
and new rings , i will post up the comression ratio when i get the block back , gary

[DanThe]

They are probably lighter, but even if you deck the block 2mm the compression ratio will still be lower due to the shape

Unless you are planning on a blown lump

[murran]

should imagine the block will need a good skim taking off it to get the compression ratio back up to normal?
why fit m42 pistons in an m20 anyway?

[bigbhpwannabe]

sorry guys i did mean to put a bit more to the thred than above
it is a turbo conversion so i am tryingto lower the compression the only reason for skiming the block to fit a mls head gasket
ihave another thred in discusion is you wanna take a peek

[DanThe]

it is a turbo conversion

I knew it!

[murran]

that makes more sence then!

what ratio you aiming for? what kind of boost levels?

[bigbhpwannabe]

it is a turbo conversion

I knew it!

yup 10/10

i am hopeing that the compession will be lowered to around 8-1 hopefully less , and boost levels will be around 14psi then i will rise as high as i can ,probly to distruction , and not because i am a nob because i wish to find the amount of power that a standard grind crank and standard rods can take

[Colonel Sanders]

the comp with m42 pistons is 7.2.1 way to low unless your gonna run over 2 BAR.
get your standard pistons and shave the squish off to give you 8.0.1 comp and its good for around 1.7bar and will happily hold 500hp all day long..
but for your goals i wouldnt advise to go that low on cr..

[bigbhpwannabe]

the comp with m42 pistons is 7.2.1 way to low unless your gonna run over 2 BAR.
get your standard pistons and shave the squish off to give you 8.0.1 comp and its good for around 1.7bar and will happily hold 500hp all day long..
but for your goals i wouldnt advise to go that low on cr..

thanks for the info rossle , i didnt rlly want to go that low , but i am going to use a stud and nut kit and metal head gasket ,so if i have to run a bit more boost thats ok ,is 7.2.1 with a .070 thickness headgasket and unskimed head then rossle?

[Colonel Sanders]

7.2.1 with standard headgasket and undecked block. heres a vid of robbz e30 when he had the m20 in, it had m42 pistons and was runnig 2.2BAR producing 602HP........

[bigbhpwannabe]

7.2.1 with standard headgasket and undecked block. heres a vid of robbz e30 when he had the m20 in, it had m42 pistons and was runnig 2.2BAR producing 602HP........

i have seen this vid before and it is an mental car , if results like this are possible with that compression ratio,then i will have a minimal skim from the block and run over two bar boot pressure ,
do you know if robbz was useing a ported head ?
thanks again for the info rossle very helpfull

[Colonel Sanders]

he had extencive work done on the motor, there are lots of tricks and tips.
like using an m21 diesel oil pump in the block for higher pressure.
he had a ppf cam, bigger valves, stiffer valve springs, welded coolent channels, fully ported..
it was a well sorted motor and you just couldnt run those pressures every day.
he also told me he snapped alot of rockers in the head.

[bigbhpwannabe]

he had extencive work done on the motor, there are lots of tricks and tips.
like using an m21 diesel oil pump in the block for higher pressure.
he had a ppf cam, bigger valves, stiffer valve springs, welded coolent channels, fully ported..
it was a well sorted motor and you just couldnt run those pressures every day.
he also told me he snapped alot of rockers in the head.

lovely i will look into that m21 diesel oil pump the water chanels in the head should be getting welded next week ,im not sure wether i should port the head ,and doubt i will do a big valve conversion , as for every day use ,this is just and engine build at the moment as i had to scrap the shell ,and its my third car ( dont get the wrong idear there all shit lol) so it will only rlly be used for a laugh at the weekends and maybe a few drag events .
was he useing the 324td crank in this engine or just original ? thanks

[Colonel Sanders]

no, standard crank, you cant use the 324td with m42 pistons.
if you get a 324td or eta crank, 320 conrods, standard post 87 pistons, you get a low comp 2.7

[bigbhpwannabe]

lovely great info many thanks rossle . top man