2.7 with i pistons

[Gabi_323i]

ok so i have a 10.2:1 eta engine in my car. last night my timing belt slipped and one valve broke and made a huge hole in one piston, i bought 6 2.5 pistons, my question is will this work ok in the eta block? i also have the 2.5 head, intake, t/body etc

[dimebag_from_hell]

i wish i knew what all this stuff meant!

[Jimbob]

The block will need decking slightly (can't remember how much!) and the piston skirts will need shaving (bout 8mm I think from when I had mine done).

[Gabi_323i]

The block will need decking slightly (can't remember how much!) and the piston skirts will need shaving (bout 8mm I think from when I had mine done).

i want to go turbo so i think i can benefit the lower cr i don't like the piston shaving too ... i thought it needed only with the 2.8 conversion?

[Jimbob]

you will have a higher CR but as most people only run 4-7psi the given CR will be fine.

If you don't shave the skirts they will hit the crank!

[Simon13]

i'd use later 2.5 pistons then lower CR so more boost!

[Gabi_323i]

how can i have a higher cr if the pistons sits 2mm down the block??

[Jimbob]

The earlier pistons were a higher comp than later ones, i was assuming you had the earlier ones
and the reason for to lower the block was to have the pistons sit in the same place at their highest point

[Gabi_323i]

well i read a thread posted by mops

http://www.e30zone.co.uk/modules.php?na ... ht=stroker

and no one mentioned the piston needed shaving and the cr will be 8.3:1

[Simon13]

we need a picture of the pistons!

[Jimbob]

Look for any other info (loads in this section) and Ant will have posted somewhere the piston skirts being shaved. Like I said, I've had it done myself and had a very good engine as a result of the work I've previously stated!!

[Gabi_323i]

and i really don't know what 2.5 pistons i have, early or late, how can i found out? i take a pic tomorow
here is the 2.7, dead
http://i82.photobucket.com/albums/j266/ ... mag007.jpg

[Jimbob]

Here's my early piston:


Hope that can help.

[kam-325i]

the later 325i pistons have an inverted dome/dish where the flat section is on the early ones.

[Gabi_323i]

tomorow i will post pics with the pistons, i want to go turbo so i need a lower cr, i don't want to shave the block

[Simon13]

the later 325i pistons have an inverted dome/dish where the flat section is on the early ones.

otherway round dude!

[kam-325i]

the later 325i pistons have an inverted dome/dish where the flat section is on the early ones.

otherway round dude!

Eh ???

later = lower compression 2.5 ?

[Ant]

You can just about see in the Pic Jim has posted that the ex valve cutout is deeper in the early high CR pistons.

That section is quite a bit "meatier" on the early units when compared to the late.

using 8.8:1 with the 2.7 build will give a CR around 9.5:1 with all the usual stroker mods.

Skirts must be machined on the early pistons, it will not turn over otherwise !

[Gabi_323i]

with the 2.7 block crank and rods and 2.5 pistons the piston will be 2mm down the block? i want a lower cr for turbo

[Ant]

will give approx 7.4:1 CR then dude.

leaves a large squish band though, I'd certainly recommend uprated head bolts and welded waterways.

there is no cheap way to do what you want to achieve, reliably....

[Gabi_323i]

so i have the late pistons i very confused :-s mops said that the comp will be 8.3:1 with the eta block


edit that was with the early 9.7:1
now i get it

i will have welded water chanels and metric blues, and a holset h2d

[Gabi_323i]

http://i82.photobucket.com/albums/j266/ ... G_0029.jpg
http://i82.photobucket.com/albums/j266/ ... G_0030.jpg

these are the 2.5 piston, are they late or early model? from what pictures i've seen i think they are the late 8.8:1 ones

OK if you're using the euro i head with the euro i pistons:

VOL = Volume of 1 Cylinder
CCV = Combustion Chamber Volume
CR = Compression Ratio

First we know that the i engine has a bore of 84mm and a stroke of 75mm so:
VOL = (1/2 BORE)squared * STROKE * pi
VOL = (4.2cm*4.2cm) * 7.5cm * pi
VOL = 415.63cc

We know that the engine has a stock CR of 8.8:1 so we can figure out the CCV:
CCV = VOL / (CR - 1)
CCV = 415.63cc / (8.8 - 1)
CCV = 53.28cc

What you will be doing however is changing the stroke to 81mm so the VOL changes:
VOL = (1/2 BORE)squared * STROKE * pi
VOL = (4.2cm * 4.2cm) * 8.1cm * pi
VOL = 448.88cc

Now using this and the CCV we can figure out the new CR, but the pistons will be 2mm from the top of the deck. So we account for this empty space by calculating its volume and adding it to the CCV:
VOL = (1/2 BORE)squared * HEIGHT * pi
VOL = (4.2cm * 4.2cm) * .2cm * pi
VOL = 11.08cc
New CCV = 53.28cc + 11.08cc = 64.36cc

Ok so we did all that just so we could do this:
CR = (VOL + CCV) / CCV
CR = (448.88cc + 64.36cc) / 64.36cc
CR = 7.97

are the above calculations corect?

[Ant]

Hmm, I vote late, what do the skirts look like ??

[Gabi_323i]

damn, i'll have to take a pic
how about the cr?

[kam-325i]

those are the same pistons that are fitted in my engine, which is the lower compression 8.8:1

[scort300]

Hi everybody i'm new to this website, but very impressed. Now excuse my ignorance but the ETA block. Is that the 525e bottom end? what else used this? And what is the Euro head?