turbo pistons

[hass]

hi
i have an 1986 325i m20 engine which is gonna be my engine for the turbo conversion

but the engine is the high compression engine which the high comp pistons

now can i use the later type 1988> pistons in my early block?
would i need to modify anything i.e crank/conrods
what pistons rings would i need the ones for post 88 or pre 88 or are thay the same


many thanks hass

[isTURBO]

hi
i have an 1986 325i m20 engine which is gonna be my engine for the turbo conversion

but the engine is the high compression engine which the high comp pistons

now can i use the later type 1988> pistons in my early block?
would i need to modify anything i.e crank/conrods
what pistons rings would i need the ones for post 88 or pre 88 or are thay the same


many thanks hass

Have a look using the search bar or alternatively scroll through this section and you will find tons of info.

Also give Ant at A Tech a call and try Blingsta whos extremely helpfull.

[maxfield]

It depends on how much power you want.

The early engines are 9:7:1 or something along those lines.

You could stick a de-comp plate in there.

I believe the pistons are different shapes so aren't interchangeable without machining work

[blingsta]

Hass.. alot quicker, cheaper and easier to just get a late block mate

[Kos]

erel, the late blocks might be "lower compression" but that does not mean that its turbo ready

yes they are lower comp, but with a few ignition tweeks the high comp engine can take boost and be more responsive.

ultimately both block will crap them selves at boost over 7-10 psi and if used the way you really want to.

a decent set of pistions and ring IS the way to go

[Turbo-Brown]

I think the early engine is limited by the amount of ignition advance you could run under boost.

Sure you can make good power with the early engine, but the torque's not gonna be as good as it could be if you were to run more advance and also, if you keep turning the boost up and retarding the ignition, you're gonna drop an exhaust valve into the engine

[blingsta]

erel, the late blocks might be "lower compression" but that does not mean that its turbo ready

yes they are lower comp, but with a few ignition tweeks the high comp engine can take boost and be more responsive.

ultimately both block will crap them selves at boost over 7-10 psi and if used the way you really want to.

a decent set of pistions and ring IS the way to go

Reason i said complete new block Kos is because he has the early block there but he reckons the rings have gone and might also have piston slap, so rather than spending money on recon'ing that block, i reckon its cheaper and quicker to get a later 2nd hand one.

[Kos]

erel, the late blocks might be "lower compression" but that does not mean that its turbo ready

yes they are lower comp, but with a few ignition tweeks the high comp engine can take boost and be more responsive.

ultimately both block will crap them selves at boost over 7-10 psi and if used the way you really want to.

a decent set of pistions and ring IS the way to go

Reason i said complete new block Kos is because he has the early block there but he reckons the rings have gone and might also have piston slap, so rather than spending money on recon'ing that block, i reckon its cheaper and quicker to get a later 2nd hand one.

what i was getting at he may as well re built it to a proper low comp engine with a set of forged JE pistons for example, with total seal rings and not use standard parts, they dont last in the long run.

that is if he's serious rather than but a second hand "so called lower comp" engine

did you think i ment for him to re build his engine using standards parts ?? you should know me better that that, to assume that.

[surj]

well how bout if you used the later block with the the eta gasket thats normal gasket + 3mm thicker what sort of boost do recken could run on that

[Kos]

well how bout if you used the later block with the the eta gasket thats normal gasket + 3mm thicker what sort of boost do recken could run on that

using a thick head gasket is NOT the way to low comp your engine

how thick do you think the eta garket is ??

[Ant]

ETA gasket is same as any other 84mm unit for the M20 series 1.63 or 2.03mm iirc

100% agreed with KOS ( is that a 1st ? ) skrimp now, PAY later.

JE/Ross pistons are £Â£ but forged and strong as hell, you could argue the crown shape wont match the CC shape but thats open for debate, total seal rings are a good investment though, zero blow by results in lower crankcase pressure and better cylinder filling per crank revoloution.

you could achieve the same with spark eroded std items and retain the CC shape as OE but the squish will have changed...

lower CR + turbo = more lag, less midrange and possibly more top end power due to the ability to hike the ign advance a few degrees over the higher CR units.

Overall power could be the same, just the curve will have changed shape and show more peak @ the top end.

^ only my opinion/experience though, not to be taken as gospel

BIG gasket = bigger weak area, MLS/copper or otherwise, but is that a bad thing ?

you could look @ the H/G as a safety valve, beats a rod through the block

[Turbo-Brown]

On the total seal rings topic, haven't lots of people had real trouble seating these properly meaning the cylinders need honing again and a new set of rings needs fitting.

Presumably the way around these problems (as with any rings for that matter) is to follow the high load break-in routine, but the problem is that on an unmapped engine you can't really be applying lots of load.

[Ant]

Hi Load indeed M8, they break in lovely though

I only know of one set being replaced due to oil loss, @ 10K iirc.

[Turbo-Brown]

Probably one of those things that must be done otherwise you're buggered.

I've seen a couple of newly built engines smoking like fork with these rings fitted and can only assume the owners namby pambied the break-in.

[Ant]

Pussies

I run mine in before handing them over to the owners to play with, I use the fast method no sense messing around eh !

I have 3 turbo beasties to run in in the next 3 weeks, thats not as much fun