Hey guys,

some of you may know, i'm attempting the 1.8L to 2.0L conversion. Ive already got the Tii crank, but i'm puzzled at one thing. (Keep in mind that the Australian 318i's have a compression ratio of 10:1)

With the extra stroke of the Tii crank, the standard 318i pistons will travel 4.5mm further with the new crank than with the original 318i crank. This means that I need pistons that are 4.5mm shorter. Will standard 320i pistons do this. I cant find any dimensions to compare against. (I have the haines manual).

I also calculated that with the Tii stroke and the 318i pistons, I would be getting a 11:1 compression ratio, my haines manual says that the compression ratio of the 320i is 9:3:1. My understanding is that compression is controlled in the M10's via the pistons.

If 320i pistons fit. Will I get a 9:3:1 compression?

Thanks alot guys

.bump

You need 2.0 pistons, the difference is in the pin height.

You have to use the flat top 320i pistons, anything else will collide with the head. 1.8s have a bigger combustion chamber than 2.0s so your compression will be less than 9.3.

Australian cars likely have Euro specs and the 320i should have pistons like these:

http://img227.imageshack.us/img227/264/bmwpistondomehx6.th.jpg (http://img227.imageshack.us/my.php?image=bmwpistondomehx6.jpg)

These won't work with the 1.8L head if it's the same combustion chamber as the U.S. models have. It will work with the e21 casting head but you will have to figure out how you can get the CIS injector nozzles into the intake. Water cooled VWs and Volvos with CIS use a composite injector bung-you could drill your intake and epoxy those in place. The PO did that on my '82 when he made a 2.0L with Euro pistons, it worked ok but they should have been angled towards the intake ports. It even passed CA smog like that.

ken

My 2.0l, 79' 2.0l block and my cars original-block & 2.0l crank, 84' 318 1.8l head w/no injector-bungs perfect for carbs/FI-setup w/a fuel-rail. Arrow 144mm M3 s14 rods, s14 M3 main&rod bearings and the pistons are "custom" CP pistons from VAC designed to match the combustion-chambers of the 84'-85' e30 318 1.8l cyl-head, the "pivot-point" on these piston's are moved way up so you can use the longer M3 s14 rods, changeing the rod-ratio my engine-guy called it. Aside from that w/a 2002-turbo head gasket these pistons give me about 10:1-10.2:1 compression so I can still use 92-93 octane pump gas, cylinder's were bored "20-over", I guess .0020 of an inch or in terms of metric aprox. .5mm for an 89.5mm bore piston's are 89.37mm's to have enough room for the piston-rings. Thats the "nuts and bolts" on my 2.0l there are many things that are possible, s14 M3 crank? I don't even know, haven't even thought about it w/my setup I think Korman and MM do a 2.2l m10 w/the M3 crank just depends on how much you want to spend$$$, just throwin' some info. your way, best of luck w/your 2.0l build I love it when people build-up the 2.0l m10, peace out vibrant.:buttrock

hmm okay that makes things harder.... by the looks of it. its gonna be forged pistons and maybe a few thousandths of an inch off the cyl head in order to get my desired compression ratio. Would you guys say that the stock conrods on these things if precision balanced, and checked for stress, would be good for 7500-8000rpm? (i know they look pretty solidly made to me)

Cheers guys

Hal

you can deck the pistons so that they won't be too high

but at the same time. you reduce the strength of the piston, and its ability to absorb weight etc. I think... that just seems like simple physics. with high compression i assume there is a whole lot more heat and pressure involved, therefore stressing the internals more than usual.

Thats what i would think, i already considered decking the pistons actually man. but thanks anyways.

I think forged is the option.

There's a member with a built M42 with S50 decked pistons that hold up well. It would take a lot to damage the piston not the regular load from high compression

Custom forged pistons is a great options too though

That would require machining off the entire dome of the 318i pistons, plus an additional 4.5mm. They aren't very much thicker than that. I certainly hope no one is willing to try it.

That would require machining off the entire dome of the 318i pistons, plus an additional 4.5mm. They aren't very much thicker than that. I certainly hope no one is willing to try it.

my point exactly.