2.7 with early pistons

[oze30]

How much do i need to shave off..

10mm is what i heard, but do i do a straight across shaving? or a scallop shape like the late model pistons?

also whats the best way to clean pistons?? i did the dishwasher, but i think i should have got at them with some thinners!

[Ant]

bucket of red derv dude

as for the machining, 10mm off the skirts on a mill is spot on, the scallops will prevent excessive piston slap from the rocking motion though,

If you have an ETA piton, just dupliate the lower skirt same as, dont forget to measure from the gudgeon pin downwards, the crowns are taller on the ETA.

[oze30]

bucket of red derv dude

as for the machining, 10mm off the skirts on a mill is spot on, the scallops will prevent excessive piston slap from the rocking motion though,

If you have an ETA piton, just dupliate the lower skirt same as, dont forget to measure from the gudgeon pin downwards, the crowns are taller on the ETA.

erm.. in english??

Basically I get the machine shop to make my early pistons look like the eta ones. Like for like? L:eave the top and machine the bottoms off???

What do you mean by from the pin down? I thought i measure up 10mm from the bottom and go from there? Could I just shave 10mm off the whole lot ala m3 ish pistons (I think are flattish all the way round the skirts)?

What cam will i need? do I still need the venier pulley if i get a different cam?
Do you have any pics?

[Simon13]

what Ant means is match the bottom of the early 2.5 pistons to eta ones, the same shape and depth, scallop, and to do it correctly u will need to measure from the gudgeon pin down.

so roughly this will mean u need 10mm or so of the 2.5 ones

get me?! i've tried! it's hard with no pictures!

[oze30]

so if I take both eta and early pistons to machine shop and get them to replicate it.. that would work? or do I need to take more off?

[Mops]

i would just reuse stock i pistons... then deck the block to achieve desired compression ratio...

[oze30]

bucket of red derv dude

as for the machining, 10mm off the skirts on a mill is spot on, the scallops will prevent excessive piston slap from the rocking motion though,

If you have an ETA piton, just dupliate the lower skirt same as, dont forget to measure from the gudgeon pin downwards, the crowns are taller on the ETA.

erm.. in english??

Basically I get the machine shop to make my early pistons look like the eta ones. Like for like? L:eave the top and machine the bottoms off???

What do you mean by from the pin down? I thought i measure up 10mm from the bottom and go from there? Could I just shave 10mm off the whole lot ala m3 ish pistons (I think are flattish all the way round the skirts)?

What cam will i need? do I still need the venier pulley if i get a different cam?
Do you have any pics?

anybody??

[oze30]

can anybiody tell me what cam i need? I don't want a rev monster, just a torquey one

[Mops]

stock cam will be ok then. ideally 323i cam (longest duration oem cam for m20)

[ed325i]

stock cam will be ok then. ideally 323i cam (longest duration oem cam for m20)

So is the 323 cam better then a 325 cam ?

[Simon13]

Colin someone needs to build your bottom end up regardless of block pistons used and measure properly what needs maching. Then it's all apart and off to get that done.

Then u can build the engine up fully

if u start mixing pistons with different blocks from other engines then it's rebores and more money, so my advice is use the best pistons block from the 2 u have.

eta pistons are supposed to not work with a 2.5 head

so early ones are most ideal if they are ok along with the block condition wise, without spending more money on custom pistons

hth

[Mops]

stock cam will be ok then. ideally 323i cam (longest duration oem cam for m20)

So is the 323 cam better then a 325 cam ?

what is what i 've hear on the internet... severl time in fact. i cant confirm it myself, , but best to check with OEM...

[oze30]

Colin someone needs to build your bottom end up regardless of block pistons used and measure properly what needs maching. Then it's all apart and off to get that done.

Then u can build the engine up fully

if u start mixing pistons with different blocks from other engines then it's rebores and more money, so my advice is use the best pistons block from the 2 u have.

eta pistons are supposed to not work with a 2.5 head

so early ones are most ideal if they are ok along with the block condition wise, without spending more money on custom pistons

hth

thats what I intend to do. But need to know what pistons to use first. If i can find a cam with a decent lift ie323, Will i still need a venier pulley? I have early pistons, and new rings. Will i need to get the block bored or honed at all?

[Ant]

bottom line, if you deck the block the dimention between the two rotating parts will change, thus the cam timing will become incorrect

Vernier is a must have item on the hybrid 2.7 build dudes

[oze30]

but what cam do i get for a torque monster?

[Andyboy]

For ease, just use Eta pistons. They are more than good enough. If you're using the later Eta engine (mid 85 onwards) the CR (compression ratio) with a stock 325i head is 9.4:1 which is more than enough. No pissing about with machining pistons or blocks plus you don't get piston slap when cold. Ignore all the bollocks about how stupidly low CR will be and how 325i heads don't work with Eta pistons - they do, I've done it! The 325i head is only 3 cc more volume than the old Eta head.

Where most of the experts fall over is by thinking the 325i has domed pistons - it doesn't. 325i pistons have a huge dish which becomes a weird raised swept up bit at the front whereas Eta pistons are flat. The 325i head has a slightly raised roof at the front of each chamber, but the larger valves and the rasied areas around the valves make up for most of that. There really is very little difference. The way to measure a chamber volume is to use a flat piece of perspex over a chamber with a small hole in the centre. Using grease stick the perspex over a chamber and fill it with paraffin through the small hole with an accurate measuring srynge (I use a proper NHS one). When the chamber is full, suck it all out again, measuring as you go and comparing it with what upu put in (it's 99% the same). I spent 2 hours doing this with 325i and Eta/320i heads. The Eta head has the same chamber volume as any other non 325i M20 head. The 325i head chambers were 3cc bigger.

If you want to use 325i pistons:

Early 325i's had a 9.75:1 CR. You'd think that using these pistons in a 2.7 with a 325i head would also give 9.75 which is what many think - but it's not. A 2.7 is compressing 200cc's more air so the ratio goes up to 10.4:1 which is getting a bit high for ordinary fuels although it would be really perky on Super Unleaded. To use these, just machine 10 mm from the bottom skirt. The top of the piston does not need machining but the block will need 60 thou shaving off so that the psitons reach the tops of the bores. Yes you will need a vernier pulley to set the cam timing as the cam will now be retarded

Later 325i's have a CR of 8.8:1. In a 2.7 the CR with these pistons would be 9.4:1 (ideal) and they need no machining at all.

As for the cam, only the E21 323i cam is worth having and it's not that great - it's the same as the carburettor 320/520 cam. You won't find a good used one now and if you go to ECP all you'll get is a standard 'one size fits all' M20 cam. So you're off to BMW with £200 plus quid by which time you might as well get a Piper fast road cam. Something around 270 degrees is spot on for torque.

[oze30]

For ease, just use Eta pistons. They are more than good enough. If you're using the later Eta engine (mid 85 onwards) the CR (compression ratio) with a stock 325i head is 9.4:1 which is more than enough. No pissing about with machining pistons or blocks plus you don't get piston slap when cold. Ignore all the bollocks about how stupidly low CR will be and how 325i heads don't work with Eta pistons - they do, I've done it! The 325i head is only 3 cc more volume than the old Eta head.

Where most of the experts fall over is by thinking the 325i has domed pistons - it doesn't. 325i pistons have a huge dish which becomes a weird raised swept up bit at the front whereas Eta pistons are flat. The 325i head has a slightly raised roof at the front of each chamber, but the larger valves and the rasied areas around the valves make up for most of that. There really is very little difference. The way to measure a chamber volume is to use a flat piece of perspex over a chamber with a small hole in the centre. Using grease stick the perspex over a chamber and fill it with paraffin through the small hole with an accurate measuring srynge (I use a proper NHS one). When the chamber is full, suck it all out again, measuring as you go and comparing it with what upu put in (it's 99% the same). I spent 2 hours doing this with 325i and Eta/320i heads. The Eta head has the same chamber volume as any other non 325i M20 head. The 325i head chambers were 3cc bigger.

If you want to use 325i pistons:

Early 325i's had a 9.75:1 CR. You'd think that using these pistons in a 2.7 with a 325i head would also give 9.75 which is what many think - but it's not. A 2.7 is compressing 200cc's more air so the ratio goes up to 10.4:1 which is getting a bit high for ordinary fuels although it would be really perky on Super Unleaded. To use these, just machine 10 mm from the bottom skirt. The top of the piston does not need machining but the block will need 60 thou shaving off so that the psitons reach the tops of the bores. Yes you will need a vernier pulley to set the cam timing as the cam will now be retarded

Later 325i's have a CR of 8.8:1. In a 2.7 the CR with these pistons would be 9.4:1 (ideal) and they need no machining at all.

As for the cam, only the E21 323i cam is worth having and it's not that great - it's the same as the carburettor 320/520 cam. You won't find a good used one now and if you go to ECP all you'll get is a standard 'one size fits all' M20 cam. So you're off to BMW with £200 plus quid by which time you might as well get a Piper fast road cam. Something around 270 degrees is spot on for torque.

So I f i want to build a torquey motor, what do I need. I already have a late 2.5 which will be the donor, and early 2.5 pistons. So I have 2 options. Not worried about the easiest method, but want the most fun.

So a 272 cam then?

How much is 60 thou?

[Andyboy]

Use your block and psitons. use the Eta crank and rod. Skim 60 thou from the block, fit a 272 cam in your head with a vernier pulley and bold it together with all the usual bits - rings, crank shells, rod bolts etc. You'll need another chip as well ebcause the ignition timing will be out but your existing injectors will be okay.

[oze30]

Use your block and psitons. use the Eta crank and rod. Skim 60 thou from the block, fit a 272 cam in your head with a vernier pulley and bold it together with all the usual bits - rings, crank shells, rod bolts etc. You'll need another chip as well ebcause the ignition timing will be out but your existing injectors will be okay.

So can I use the eta block? which pistons?? early or late?

[SPADGE]

Use your block and psitons. use the Eta crank and rod. Skim 60 thou from the block, fit a 272 cam in your head with a vernier pulley and bold it together with all the usual bits - rings, crank shells, rod bolts etc. You'll need another chip as well ebcause the ignition timing will be out but your existing injectors will be okay.

So can I use the eta block? which pistons?? early or late?

Andy has just told you mate!
Use the 325 block and pistons and the Eta Crank and Rods. 60 thou off the block etc etc...

[Andyboy]

You can use either an Eta or a 325i block. There is supposedly 0.5mm difference in block height but with the Eta crank fitted along with an Eta rod and 325i piston you'll see how much the block needs to be shaved by - the top edge of the piston needs to be at the very top of the bore. It won't clout the head because the head gasket gives it some breathing space!

[oze30]

Use your block and psitons. use the Eta crank and rod. Skim 60 thou from the block, fit a 272 cam in your head with a vernier pulley and bold it together with all the usual bits - rings, crank shells, rod bolts etc. You'll need another chip as well ebcause the ignition timing will be out but your existing injectors will be okay.

So can I use the eta block? which pistons?? early or late?

Andy has just told you mate!
Use the 325 block and pistons and the Eta Crank and Rods. 60 thou off the block etc etc...

Dude, theyre both from a 2.5 so i dunno which!!! Have you paypald yet?

[SPADGE]

So can I use the eta block? which pistons?? early or late?

Andy has just told you mate!
Use the 325 block and pistons and the Eta Crank and Rods. 60 thou off the block etc etc...

Dude, theyre both from a 2.5 so i dunno which!!! Have you paypald yet?

Only one is from a 325 though mate!
Will do the Paypal thing in a minute

[oze30]

Does anyone have a pic of the pistons? Im tempted to throw it in and 3.5 it.. if I can fit the A/C in aswell