Is the 2.7 conversion the best way to go?

[jedw7503]

Hi all and a Merry Christmas to you and your cars.

I've got a later 1988 320i cabriolet and I'm planning to do a 2.7 litre conversion by sticking my current 320i head on top of a long stroke 325 eta bottom-end.

I'm told this will give me around 50% more power, a lot more usable torque plus better economy.

It's not a cheap exercise at $3,300, so before I commit , does any recommend anything better or going a different way?

Is there anything I should be looking for or asking about before I hand over my deposit?

[EEE21M]

From what I know the 320i head u should just throw it away. Small ports, wrong cam. Doing the head swap on a 2.5L to a 2.7L is also from what I know a popular misconception. I would research it a bit more, are any of you guys able to recommend a tuning house in Perth? If you get no where over there, pay the STD rates and call ALS here in Sydney and ask Andrew. I will post up a few websites later on for you.

[DTME30ic]

The 325i head on 325e block does not work and the US guys will tell you this. What they never got in their market though was the 320i/323i - This is the head you want to use as the way the chambers are designed gives a higher compression than if u stuck a 325i head on a 325e block.

320i and 323i head are the same except i think the valves on the 320i are slightly smaller - can be changed though.

[MaDhAtTeR]

The bloke you really want to speak to is brandon whitehead. The common conversion overseas is the I head with the super eta bottom end (the super eta uses the same head as the I).

You can modify the chambers if you want to take out the 4mm difference in the bore size to match the head. It isnt that it doesnt work, it's just that it decreases volumetric efficiency. You can run into problems with deck heights if the heads have been shaved a few times before.

You need to modify the B20 or B23 head to match the eta block, the smaller capacity engines are missing two coolant passages. there is quite alot of debate going around as to wether this actually has any effect on the engine (mainly, the problem the M20's have with cracking heads when they get hot). Id say, for our climate, if you want the smaller capacity head for the rebuild, it's a good idea to get the extra coolant flowing through. Anything you can do to keep the M20 cool will keep it happy.

If you want to stick with the eta head and just rebuild the 2.7 for high compression, you will need to drill the extra 3 holes into the head (oil passages) for the extra camshaft journals (unless you use the existing eta cam). The eta uses 4 cam bearings instead of 7 like the rest of the i series heads.

Matching the eta bottom end to the i head creates the drop in comp ratio (appart from the decrease in volumetic efficiency) because of the two miss matching sizes. The easiest way to get around this is to deck the head 40 thou raising the comp ratio (that is before you change pistons, the decking changes the ratio by 1.0:1 - 1.5:1 points)

You can grab brandon on the E21 Group http://groups.yahoo.com/group/BMW_E21_Digest or at his website http://www.e21bmw.net

Edit: Just to clear things up alittle

Eta: Early Eta shares the same head castings as the 323 and 320i. The difference being port and valve sizes
Super Eta: (after 9/87 i think it is) same head castings as the 325i.

You can work out which ones match up perfectly from the above pretty easily. You dont have to have matching chambers and bore sizes in an engine as long as you have enough clearence.

Only place i know of in wa with this sort of experience is bmauto.

Edit2: Just in case there is any interest, for the record, mine was an I head with the later eta bottom end and diesel crank. It wouldnt have mattered much which combo i used, nothing was saved from original, only the block and head. The rest was aftermarket stuff.

[the afro guy]

hey all,
i'm thinking of doing the same thing with my eta. i've been talking to Rubin at BMAutoengineering, he seems to be the best place to head to in Perth for this thing cos hes already done a few, and is actually doing one as we speak to a e30 touring. basically what he has said is that its no where as difficult as we hear from the US and that the parts can be had for about $1500, although it takes some looking as you not only need the complete head from a b25, but you also need the ecu and intake manifold. (might be different for you lot cos you already have all the i stuff instead of eta stuff). you can also use the head off a 525i (e34 i think is the one), apparently that is a lot easier to do with the eta, and gets better results in the hp department. not sure how though.

i know that the big problem with the eta to i head swap is that one has flat headed pistons and the other has domed pistons. they don't match and then you wind up getting bugger all compression, hence bugger all power and would have been better off leaving it all alone. i think that was why the 525i head was better. there are slight differences that make it work but i've got no idea how it works and makes no sense at all to me. i thought they were the same engine in the 325i and 525i.

i've done most of the research but cant be arsed typing it up because i always forget the odd important bit. i'd say go talk to Rubin and get it all sussed. he quoted me for between $2000 and $2300 incl labour. all depends on what parts you can find. probly helps that he's done a fair few of them before.

[MaDhAtTeR]

You still need to change pistons otherwise you end up with a comp ratio of around 8.0:1 The newer head has slightly larger inlet valves.

The package is a pretty good one itself, depending on which route you go (either the smaller chamber or the larger) you can expect around 140-150kw at the crank from pretty much stock parts. If you were to build it with forged pistons (I can reccomend the JE set which are on special at present from Top End performance for only $825 USD, plus they will make them to suit any compression ratio, and any bore size for the 6 cylinder range you want), cam change (i find the 288 works well with 10.6mm lift), crank change, and valves with new springs and retainers, (alpina valve sets are pretty good), the m20 is good for up to 170kw. Mine put out around 150kw at the wheels in our workshop dyno. It had a few extra things added that werent in the above, i probably spent $4000 just on extra parts (aside from stuff needed for the rebuild).

There is alot of power to be extracted from the M20 if you want to spend time fussing about with the little things. There is a step where you go beyond reliable daily driver and turn it into a track car. Using over 20L of premium per 100k's does hurt the hip pocket Tis great on the track though

Back in the start of the year i was thinking about building a few of the strokers on the side, i figured i could do it in my spare time , what spare time There seems to be a bit of a demmand for the engines, now that ive finished training and should be back working full time (yay! no more school) i might give them a go on the weekend. Be easy if you could just purchase a built long motor and drop it in

I wonder what a high comp M20 with triple 45's would be like. Anyone know anyone who could modify / create a manifold for me, i might give it a go