e to i options... new idea?

[hotghias]

Alright... in doing the e to i hybrid/conversion on an 87 325, you can't just bolt on the head because of compression ratio issues.

i've heard of using euro eta pistons, a euro 323 head, supereta pistons, and custom pistons to get the C/R up to a good number, but that's not what i'm asking about.

Swapping pistons out is a lot of work and money, and i had a different idea: could i just shave a lot off the i head and achieve a good C/R that way? has anybody done this? would you have to cut too much to make it possible? Would you run into problems having the timing belt being too long or something?

it's just that this way seems to make a lot of sense right now and i was wondering why nobody does it...

i heard the c/r with an i head on an eta would be around 8.4, while the stock i c/r is 8.8. it doesn't even seem like it would take an incredible ammount of shaving to get it to at least that ratio.

thanks,
evan

[bimmerphile]

in doing that you'll need new valves and valve springs, because so much will have to be taken off the head to get the pistons to avoid contact.

In the end, you'd probably end up spending more than the $800 to get some good, high CR pistons, and you would be running a sketch system.

[hotghias]

why would you need new valves and springs? one would use the valves and springs already in the i head. if they would hit the pistons, that's one thing, but new valves and springs would not help that problem.

please explain how this would be any more sketch than using shaved "i" pistons and i rods.

one concern of mine is how is the overhead cam engine affected by a decent ammt of shaving to the head, with respect to the timing belt lenght. that is, could you simply adjust the cam gear to compensate?

if you have any relevant engine stats, by all means post them. this would benefit a lot of people if it's possible. the deck height of the e piston in the cylinder, along with the volume of any dish or dome on the e piston, and the CC's of the i head combustion chamber would do a lot of good for me figuring this stuff out.

thanks

[rs4pro3]

http://home.netpower.no/pberg/Mahle_m20.html

Shaving the head you'll end up with some timing problems the only way to adjust that easily is with an adjustable cam gear. I believe that with eta pistons and an I head you'll end up with lower then 8.4:1 as 8.5:1 is what you get with super eta pistons. with super eta pistons you can get away with shaving the head easily. If you only want to stick with eta pistons your'e best bet is the 323i head or put a 325i cam and full 325i engine control on the Eta engine. Swapping pistons is not realy any more work then swapping the head. If you've got low milage all you need to do is install new rings.
I think what Bimmerphile ment about the valves and stuff is the machine shop must completly tear down m20 heads to shave them and they will probally tell you the head will need rebuilt then.
Basically you can buy a 323i head for $250 or so.
or Try to find some euro eta pistons from either a pre 85 525e and end up with a 10:1 cr ratio or go for just standard euro eta pistons and end up with a 9:1 cr ratio.
The 525e pistons are vary rare, I purchased my set for $120 but they still have not arrived yet from overseas.
The reg. euro eta pistons I'm sure you could find a set of those(contact JonB on this forum)
Or find super eta pistons which are also rare and would probally run $150-$200 a set
Or shave 325i pistons like you said(I believe Pete McHenrey does that for $250-$300
If you don't have much money to spend I'd say just buy some standard euro eta pistons from any after 85 engine. You can just clean them up install new rings and be done with it. No real shaving needed, and your set to go.

[Stu]

You could shave the head, but you'd run into timing issues, there would be poor atomization of fuel, and you'd want to notch the pistons for valve clearence. Would be easy to bend exhaust valves on a downshift overrev.

[hotghias]

good info, especially that website. i saw that once then lost it. thanks guys.
could someone explain why in particular there would be poor fuel atomization on that setup compared to the other ways? importing a head sounds like such a hassle, but i guess the 323 is a good option.

[ColdAccord]

the head will most likely warp, also

if you're looking for a different way to spend your money to make up for that CR, just slap a turbo and some fuel mods on there lol

[Stu]

good info, especially that website. i saw that once then lost it. thanks guys.
could someone explain why in particular there would be poor fuel atomization on that setup compared to the other ways? importing a head sounds like such a hassle, but i guess the 323 is a good option.

Because of the shape of the piston tops and combustion chamber.

Don't try to cut so many corners. Just get ahold of an '88 325e engine, put an 'i' head on it, and use full, late-model 'i' motronic. This is a proven method for making a budget, stroker M20.

[hotghias]

but that is a lot more complicated and expensive than bolting on a slightly machined head and electronics. i'm not doubting you, i just want to know the how and why.

according to that website above, the pistons are similar, except the supereta looks like it has a little more dish, and it's .6 mm taller from the wrist pin. it says it has a 3.6 mm crown from the top of the piston plate, but it doesn't look like that in the diagram- don't know what to make of it.

that said, i still don't see why the shape of the combustion chamber would be worst than with supereta pistons- they're both flat with a dish and close to the same height from the wrist pin. if anything, it seems like shaving the i head might improve squish/quench with the flat pistons if the deck height was about nill.

i'm not trying to be a d*ck, i'm just a little frustrated by people who know less than me trying to tell me what to do. that's not the case here, but it certainly was on another popular bimmer forum. i admit my expertise is more in the air cooled VW world. i just want to make sure people don't make me or others give up on an idea that might work, just because you have not heard of it. so when you say "poor atomization" or "bad combustion chamber shape" could you try to explain how, or the way the combustion chamber would be shaped? i've never had the pleasure of being able to look at and measure these things. i'm just trying to learn, and i truly appreciate yall for giving me some real insight.

so, DOES ANYBODY KNOW THE DECK HEIGHT OF EITHER ENGINE? anybody who has taken either engine apart should at least be able say if the piston is sunk, flush, or protruding from the block at TDC for the i or e engine.

[rs4pro3]

On that site the diagram of the super eta pistons is wrong, the super eta pistons look identical to the I pistons but has the wirst pin located in a different spot.
Ok here are some pictures
I pistons
Notice how it has a crown this crown goes up into the cylinder head. The 325i's head has a combustion chamber designed to match the pistons
Picture of I head

The eta pistons are flat but then have a dish.(eta piston on the right)

The eta head has a sort of Loped off combustion chamber which is a lot smaller

I hope this helps you to visualise it.
Also email me and I'll send you a lot of info on the different small six heads and some other info.

[JPbmw]

ok let me see i'va i got this right.

so by using an US eta block with an US I head and Euro eta pistons(after 85) you wouldnt need to shave anything?

sorry if it is a dumb question, im trying to learn some more about this since i plan on doing an E to I swap in the near future

[rs4pro3]

yep, the pre 85 pistons have a 11:1 cr ratio yeilding a 10:1 cr ratio with the I head where as the standard euro after 85 eta pistons have a 1-:1 cr ratio yeilding around 9:1 cr ratio. You could shave if you wanted to but it's not required. With any of the setups shaving is not required but is advised, as if your'e building an engine and it's not going to be forced induction, there is no reason to run a low cr ratio when you can get better throttle response with a higher cr ratio.

[JPbmw]

well i plan plan to turbo it so i'll keep the low cr :twisted:
or i might just shave it and when ever im ready to put the turbo in, get custom pistons :?
i also plan on doing the MAF conversion with the E to I sawp

[hotghias]

awesome. thank you very much for taking the time to post those pics. that helps a lot.

now i'm curious as to the how shaved i pistons work with the i head- shaving the 3mm off the top would eliminate (most of) the crown, so my visualization of that combustion event is a lot like my visualization of a shaved i head on standard eta pistons.

i appologize for riding this dead horse till it disintegrates, i just find this very interesting. yeah, i'm a first year ME student.

[rs4pro3]

I realy have no idea what cr ratio exists with the shaved I pistons. the problem with them is the I piston will extend beyond the block 3mm when installed on an eta crank. so that 3mm must be shave off and valve reliefs cut to avoid the piston destroying the head. 3mm will just shave off the upper part of the highest crown and a little bit of the other crowns. I don't know of any one who has actualy gone this route though.