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From digest.v7.n1345 Thu Mar 19 13:00:34 1998
From: "T VanAusdal" <>
Date: Thu, 19 Mar 1998 07:29:59 PST
Subject: Re: E30 2.7l vs. 2.5l

>From: Joe Cook <>
>Date: Wed, 18 Mar 1998 11:57:59 -0600
>Subject: E30 2.7l vs 2.5l
>> > Helttula Jouni (NCP/SA) asked:
>> >
>> > What differences 2.5l and 2.7l engines have?
>> > Are they complete different motors or is there any congruences?
>> And Nimrod <> responded:
>> The main block is the same both are M20 engines. I belive they have
same bore

>> but the stroke is longer in the 2.7l engine. The 2.7 is an eta engine

  • -

    >> lower revs and more torque. It called 325e as the 2.5l is 325i.
    >> The eta is a carburator engine as the 2.5l is clearly injection
    >If this is true, my 325e has some funny looking carbs on it! *grin*
    >No, really, it may have been true at one point, but it doesn't seem
    that it was true for ALL 2.7 liter eta engines.

    >Anyone have some clarity for this point? All the other points I agree
    with. (as if what this babboon had to say was worth anything). ;)

    >Joe Cook
    >85 325e

Eta (2.7L) motors are NOT carb'd. The 'e' concept motor was a larger-displacement motor, optimized for high-torque, lower-rev, lower-loss motor. Carbs do not fit into the efficiency scheme.

Think about gas mileage/emissions/power in street cars, and realize that the FI car is generally more capable in ALL those measurements than the carb'd. Fuel metering is more precise with fuel injection than with carbs. Duh.

The 'e' motor v. The 'i' motor: fewer cam brgs for less friction v. all 7 brgs for cam integrity at high revs
5200 rpm redline v. 6500 rpm redline small intake ports for lower rpm torque peak v. larger ports for better high rpm breathing
30 mpg (due to taller gear ratio, really) v. 25 mpg (with a heavvvy foot!!!)
longer stroke for torque at low(er) revs v. shorter stroke for high-rpm capability
9.0:1 CR dished pistons v. 9.8:1? CR, domed, flycut pistons

The 'i' head has larger ports and valves, larger intake runners, more agressive cam (longer duration --> high rpm torque peak). You wanna rev? Take the 2.5. You want torquey, easy city driving? Take the 2.7. Better yet, build a 2.7l 'i' motor: the cast crank in the 'e' is suspect at higher rpms. (I would NOT build a 8000rpm 'e' crank-based motor, unless I was like Mark N. and had cash to spare to make hand grenade motors ... :0 )

For budget builders, I believe the crank and rods from an 'e' motor, put into an 'i' motor, will give you a nice setup. More torque than either motor, nice 6000 motor, like an 'i' with more low end guts.

These days, tho, you could get a DOHC VANOS 2.5 motor for decent cash, with lower miles than an 'e' or SOHC 'i' motor, drop it all in, and not have to cobble anything together ...

  • thi v.

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