The comprehensive 731 head + eta block Thread

[Arems87e]

I'm curious to know what kind of fuel mileage you're getting, Arems87e?

I'm actually getting tha same, if not better when i drive conservative...but I don't drive conservatively, i go more like 80mph on a 65, so i my mpg is never wat it should.

[E30 Wagen]

well i'm getting ready to refresh my 731 head and i've decided to run a new 325i cam. except i have a dumb question:

what cam gear do i run? i currently have a b25 engine, complete, albiet with broken rocker arms and unknown mileage or condition, so i don't know if it would be smart to use the cam from it. But, can i just grab the gear off this b25 and run it with my eta bottom end? The engine is going into an 87 325is with a 173 motronic unit

i'm a n00b engine rebuilder, so any help is appreciated. thanks!

[morerevsm3]

just completed 731 head on ETA, with 1.3 motronic, M30 maf, 17.5 injectors, 3 bar FPR, 325i inlet and TB etc, had to disconnect 02 sensor as it ran really rough when it warmed up with it plugged in, and tacho doesn't work (would have spent its life off the scale anyway) so will have to fit an ols smiths tacho I have laying around

[Stephen]

bump from a long time ago. When people are saying they run the head and just a chip, what motrnoic 1.0 tune are you guys using?



And, also, when people are swapping to motronic 1.3 with the 731 instead of the 885, are you still swapping all the I accessories, or just harness, ECU, and FPR/injectors?

[lennon]

when i did my eta+731 head, i swapped basically everything from a 325i (other than the head). i dont know if there's a pre-made chip out there for "2.7i" motors for motronic 1.0.

[hotballs]

The most common solution you're going to find is 1.3 motronic swap with i parts. People run the 731 head as opposed to the 885 to maintain a higher compression ratio due to the piston shape and combustion chamber.

That's it. The swap is more about a 1.3 motronic swap and i parts rather than a 731 head swap. The head you use is up to you.

[Pdxseth]

I'm currently putting together a seta bottom and 885 top combo but it's getting spendy and I'm impatient.

In the meantime, since I have all the parts laying aroundI was considerring throwing the 731 head,"I" intake,afm, and throttle body
on my eta and running m1.3 with a 2.7i chip.

I've read somewhere that you may have machine the head a bit or the piston will hit it. None of you guys mentioned this, have you had any issues, or do you run a thicker HG?

[digger]

I'm currently putting together a seta bottom and 885 top combo but it's getting spendy and I'm impatient.

In the meantime, since I have all the parts laying aroundI was considerring throwing the 731 head,"I" intake,afm, and throttle body
on my eta and running m1.3 with a 2.7i chip.

I've read somewhere that you may have machine the head a bit or the piston will hit it. None of you guys mentioned this, have you had any issues, or do you run a thicker HG?

pistons will probably hit the head combustion chamber i would not bother

[Pdxseth]

I can have the machine work done, I can get the head rebuilt and p&p'd for next to nothing I was just curious if I had do have any more work done while I'm at it


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[digger]

find a cheap 885 if anything.

[Pdxseth]

I have a built 885 head but I have to finish the block and put in seta pistons or my compression will be shit. With the 731 I can use a regular eta bottom


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[digger]

I have a built 885 head but I have to finish the block and put in seta pistons or my compression will be shit. With the 731 I can use a regular eta bottom


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yeah a 731 will work with a "regular" eta bottom end, i thought you wanted a 731 on a seta bottom end

compression will be lower with 885 but ive never seen a stock 731 make anypower but if all you want is to slap something together in the interim that will run then fine

[Pdxseth]

yeah a 731 will work with a "regular" eta bottom end, i thought you wanted a 731 on a seta bottom end

compression will be lower with 885 but ive never seen a stock 731 make anypower but if all you want is to slap something together in the interim that will run then fine

Awesome, thanks digger. Not looking for much power but my eta has a flat cam. So I figured why not slap this together while I'm still working on my 885/seta combo


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[MR 325]

Why spend the time and money to put together a temporary engine?

Just put together the engine you've been planning.

[Pdxseth]

Why spend the time and money to put together a temporary engine?

Just put together the engine you've been planning.

Because I can get the 731 head rebuilt and p&p'd for 250 bucks(same price I paid for the 885) a gasket set, timing belt, and water pump will run me like 300 more dollars. 600$ tops into throwing this together.

The other motor(885/seta) I need the bottom end rebuilt(4-700$) I plan on buying one if your 274 cams (250 iirc)
Hd rockers and valve springs, itb's, mega squirt and everything brand new.

I don't even want to do the math, I'm looking at, at least 3k to build a nice proper reliable, quick, low maintenance motor.

The car currently has a 350-500k mile stock eta, with headers. The motor is strong, even compression across the board. I flattened the cam during my learning curve in valve adjustments, so it sucks. Afaik the timing belt hasn't been done since 100k. I can slap this together in a reasonably timely manor, And do all the maintenance that needs done. This will only cost me an extra 250$ to have the head refreshed.

I want to take my time, and build a motor right for it. I could throw together the 885/seta motor but it would be half assed. Once my motors done, I will rebuild the bottom end in the 731/eta motor, and drop it in my girlfriends 528e.


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