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  1. #1
    KevinR
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    braintease-what is the CR of my 2.7 with 2.3 head

    with the original low compression slugs and a ported 2.3 head that has not been shaved? Does the compression go up which i assume it does but does anyone know by how much? Please see my subject "2.5eta with 2.3head want to turbo" posted on 17/3/04. No one has responded to previous posts on this topic probably because it's a FAQ but hey, this is a turbo beemer forum so.... anyway I've been checkin it all out for a few months from Downunder in Byron Bay. I have an E30 with huge plans. It started out as an M323i with a tired 2.3(over 500,000 klms!!)that lived til the 2.7 transplant 6mths ago and used the original 2.3 head but had it heavily ported and the cam reground. It goes hard and i drive it hard with regular visits to redline searching in vane for more power but after 5500rpm it really is squeezing blood out of a stone. Anyway hope someone can read my other post and get back to me. thanks. Also can someone tell how to post pics. Have lots.

  2. #2
    ///ARINUTS...
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    Too many unknown variables.........

    stock euro 2.3L m20 has about 10.5:1 compression. Euro eta has something like that also.I never heard of a M323i so I don't know about that engine. North American eta has 9:1 because of different rods and pistons. Porting, polishing, cam, valve train stuff don't affect Compression.

  3. #3
    KevinR
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    Re: Too many unknown variables.........

    My car is the first of the E30 Motorsport cars which was just a 2 door e30 chrome bumper, 1985 323i with recaros,LSD and close ratio 5spd. It also has extractors (6 branch manifold as the Poms say). The origin of the bottom end is unknown to me so cant say whether it is high compression or not. I thought all eta motors had low compression. Like around 8.5:1. Do you know how strong the crank, rods are etc. On a dyno and with my car leaning out at 5000rpm my car only made around 120rwhp at the motor but has monsters of torque so has led me to believe it is lower than 9.5:1 but when your say a 2.3 has 10:1 then I can safely say the 2.7 has double the power under the foot so its all quite confusing really. Downunder, we have HSV Holdens with the Gen 3 Chev based monster and i keep up with the older models. ITS A FREAK. It does 0-100 in 6.5 seconds and readilly breaks 150mph. After the dyno day I came home and tweaked my airflow meter and then lean out disappeared. I have now got a suspicious tick tick tick coming from somewhere that I;m told is either a valve or piston slap. Sounds like tappet noise in an old small block V8. Anyway I'm not suprised. It was a 100,000klm eta bottom end and I heavily worked my 2.3 head and slapped it on and got what I got. I'm kickin SR20 Turbos (not totally off their head of course) with the stock 2.3 injectors and everything else. Anyway, thanks for your reply. Obviously judging by my reply, there mustn't be many Beemer nuts in Oz for me to talk to all this about. Adios.

  4. #4
    Cacatfish
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    Re: Too many unknown variables.........

    Kevin,
    Im not too savvy on methods of measuring compression ratio, but I can tell you that the 2.3 head and the 2.7 eta head are one and the same as far as combustion chamber volume. The later (1984 and up)2.3 heads have larger ports and flow a bit better than the early 2.3 heads which have the same tiny little ports as the eta head has. If you have an e30, you probably have the newer head. Check the part number on the side of the head. The larer port head will end in 731 or 721 while the old smaller port head ends in 200. Slapping a 2.3 head on an eta motor will not change compression ratio at all. 2.3 does have a hotter cam and different cam bearings and oil holes for the increased revs.

    Why you are running out of power above 5500 rpms is that the 2.3 head, even the later one, cannot flow enough air to supply the 2.7 liter motor at high rpms. It does fine with the 2.3 liters, but the 2.7 will not be a screamer with that head. The head also has the smaller valve setup (exhaust I think) than the newer 2.5, which als has even bigger ports and better flows than the 2.3 and 2.7 heads. (but it cannot be swapped onto your eta block without losing a lot of compression as it has about 43cc combustion chambers).

    So, in essence, going to the 2.7 is a trade of for the torque of the 2.7 vs the high top end rush of the 2.3. I think you only pick up about 25 hp in the swap, but the loads of torque are the main benefit, the 2.3 is pretty soft until about 4k rpms.
    In order to get high rpm performance out of that block, you would want to swap in the larger 2.5 exhaust valves and go to a hotter cam. You may also need bigger injectors, but I dont know abut that.

    One advantage to your setup is that you still have the old l-jet with the adjustable AFM, so you can fiddle with the A/F mixture without having to get a chip made ala Motronic. It is also able to handle a hotter cam without losing it's ability to idle, whereas the Motronic loses it's crap with a hot cam at idle.

    It's a nice setup, there. I love the lightweight Euro e30 and the motor has potential for good power. Have that head ported and swap in some larger valves and a hot cam and you should get the top end to go with the torque. That would be a monster, even though, with that longer stroke crank, it will not be as quick a spinner as the 2.3 or 2.5 M20s. It will produce more punch though.

    If all that gets too pricey (which it does) then Id just try to come by a used Schrick 282/284 (or whatever) cam and drop that in and give it a shot.

    As far as compression, you should be able to find a part number on the side of the block, which would tell you which car that motor came form and what the c:r is.

    Good luck, Colin

  5. #5
    KevinR
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    ThankyouThankyou:head is ported heavily so next st

    step is the valves, throttle body and fuel regulator. My car is 6/85 build date so have later 2.3 head. The ports are now nearly double the size they were so not much else to be done there.
    I have always been told the 2.3 and 2.5 are the same head except for port size though it makes sense that the valves would also be bigger. The cam is mild but was scored badly from 400,000klm on the original 2.3 and is a regrind which I'm told is causing a valve problem. So a little way to go yet. I have just acquired a T3/T4 and cant wait to work out the CR so I could run maybe 8psi with the aforementioned mods.
    Anyway thank you for your reply. You'll have to tell me about your ride sometime.
    Kevin Riddell. Byron Bay Australia

  6. #6
    ///ARINUTS...
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    Ported head or not doesnt affect compression!!!

    the porting has nothing to do with compression. WHY? because compression is how much the air gets compressed when the valves are both shut in a cylinder. Assuming the 2.3 head and the 2.7 head have the same cumbustion chamber then it should have the same ratio as the stock 2.7


    You need to find out what the compression of the 2.7L engine was that you are using. Look for a VIN on the block and look it up.

    If it is from a North American Spec vehicle then it should be 9:1 and you should be able to run around 7lbs. of boost with a properly tunned fuel system.

    Ifthe VIN gives you info stating that it is a Euro spec car, then be very careful because you might have compression of about 11:1 then I don't think you should be using anykind of forced induction with that much compression.

    Most of us in here like to use a compression ratio between 8:1 and 8.8:1 , Not much more than that.

    You might to get some books and read about this stuff

  7. #7
    Cacatfish
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    No change. 2.3 and 2.7 heads same casting 38cc...


  8. #8
    KevinR
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    Re: No change. 2.3 and 2.7 heads same casting 38c

    So does that mean if I can find out the volumn of the bottm end then I can formulate the overall compression without taking the head off?
    Do you have any idea of the formula. Please have a look at my reply to - too many variables. Thanks for your reply.

  9. #9
    Cacatfish
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    Also some of the Euro Etas are very hi C:R

    Up to 11:1. Be careful if you have one of these. ETA does not mean "low compression".

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