2.7i

[Red88]

I want to build a 2.7i, but I don't want hella low compression. Can I use the pistons out of a regular i motor with i or eta rods? I hear everything about using SETA pistons, but they look the same as i pistons to me.

[PeaveyBassist]

Eta crank has a longer stroke. If you use i pistons, they will hit the head. IIRC...

[Red88]

Figured. But everyone and their mother is talking about SETA pistons with the i head on the eta crank with eta rods. The i head has a domed combustion chamber. I guess my question should've been "what's the difference between SETA pistons and i pistons?"

[FREE30]

I need to build my 2.7 for high boost but everyone bombs my questions....:(

[eta]

Eta crank eta rod and 325i pistons, with 885 head works. The pistons will not hit the head. They will not reach the top of the bore either and the CR will be "low" at 8.3:1 This figure takes into account the volume of the crushed head gasket, 8.8:1 CR pistons, the piston shape and the 1.5mm difference between the piston top and the top of the bore.

An eta motor with eta pistons, eta conrods and 885 head would a CR of 8.3:1. the same build with SETA pistons would give 8.5:1 CR. SETA pistons where only available in 325e and 528e during 1987. So they are not too common.

To get the 325i pistons to reach the top of the bores you would have to deck the block and fitted a vernier pulley to get the cam timing right.

[PeaveyBassist]

So wait a minute... You're saying that the eta crank, eta rods and either the i pistons OR eta pists nets a CR of 8.3:1? That makes no sense. The piston designs are completely different. Also, Seta pistons in the US were only in 1988 and very late 1987. You can use the eta bottom end, slap an 885 head on, and have low compression, perfect for boost. I've always heard 8.1:1 with that combo though.

[StereoInstaller1]

Eta crank eta rod and 325i pistons, with 885 head works. The pistons will not hit the head. They will not reach the top of the bore either and the CR will be "low" at 8.3:1 This figure takes into account the volume of the crushed head gasket, 8.8:1 CR pistons, the piston shape and the 1.5mm difference between the piston top and the top of the bore.

An eta motor with eta pistons, eta conrods and 885 head would a CR of 8.3:1. the same build with SETA pistons would give 8.5:1 CR. SETA pistons where only available in 325e and 528e during 1987. So they are not too common.

To get the 325i pistons to reach the top of the bores you would have to deck the block and fitted a vernier pulley to get the cam timing right.

So wait a minute... You're saying that the eta crank, eta rods and either the i pistons OR eta pists nets a CR of 8.3:1? That makes no sense. The piston designs are completely different. Also, Seta pistons in the US were only in 1988 and very late 1987. You can use the eta bottom end, slap an 885 head on, and have low compression, perfect for boost. I've always heard 8.1:1 with that combo though.

Gotta love this shit.

You are both right, you are both wrong.

You each live on different continents...

[PeaveyBassist]

I was thinking that might be the case...

[kenika65]

so much trash everywhere....

[PeaveyBassist]

so much trash everywhere....

You're adding to the trash by posting in this thread without anything halfway useful. Who is wrong and who is right? Or are we both wrong or both right?

[Red88]

You're both right considering where you live. I guess I'll just try different combos and see where the deck height is, then not worry about my compression ratio.

[eta]

I was basing my calculation on U.S engines, not Euro ones. I can tell the difference.

Eta crank + 130mm rod +eta (9:1 CR pistons) with an 885 head gives a CR of 8.35:1. Calculated assuming a crushed headgasket volume of 9.57 cc.

Eta crank + 130 mm rods + 8.8:1 CR 325i piston without a deacked block and 885 head gives a CR of 0f 8.29:1 This assumes a 1.5mm gap between piston crown and top of bore which again has been caluculated from the dimension of bottom end pistons, pin position......

If the gap between the top of the bore and piston crown is 2mm which it could be if I take the block deck height from another source I calculate the CR to be 7.97:1.

I have calculated this taking into account of piston shape as well. You may not believe the results based on recieved wisdom but I post them to inform. Please do not shoot me down unless you have numbers to back up claims.

[PeaveyBassist]

No one shot you down Mr. fucking smarty pants. Sorry we hurt your feelings. Thanks for the math to backup what you say.Good thing you have wisdom to fill your posts with!

[eta]

Don't worry my feeling were not hurt, it takes alot more than that. I have to say it is only by doing some sums and asking questions I have managed to figure out the good info from the not so good.

[csab327i]

No one actually answered the op!

Ok I have searched a lot of thread, since I didnt want to be a cum spitting dumpster meth slut, and havent got a solid answer to this:If you want have an naturally aspirated m20 327i with high hp high tq which is the best way to go?
For example
1991 325i
internals:
1985 eta crankshaft
1985 eta connecting rods
1988 super eta brand new pistons
1991 325i newly rebuilt head

what will I get?
how much tq/hp?cr?

and it wasnt answered in this thread what is the difference between 325i and super eta pistons?

also read in an other thread that early m20 blocks were better oiling that post 88.

also read that with this set up you get 185 hp in other threads that it would be like 30hp less.

Can someone please clarify once and for all?