731 head meets eta block

[Junkers]

Hey guys

Just recently picked up my first e28 (woooh). The fellow I bought it from tried to change the cambelt himself and pretty much bent every intake valve after trying to crank it over with the timing wildly out.

My question is, can I use a 731 head on a eta block without much hassle? I am aware of the small differences like single valve springs and 4 bearings on the camshaft, but can I not just use the 731 head complete?

Cheers for any input.

[a]

I dunno what head you are referring to and what eta block.
If your head came from a 323i and you a gonna stick it on a pre- 3/87 eta, it will work. If you have a head from a 325i , it should best go on a post 3/87 engine, AKA, super eta. This is all hearsay , I havent had the occasion to swap a head on my super etas.

[turbodan]

The whole 731 bolts right on. If the cam is in good shape you'd do well to bolt it on complete. I had one on my old car for a little while with a 2.5 cam. Later on I ended up bolting on an 885 head with a reground cam. All things considered, unless you've got a -731 handy, its not worth the trouble. The 885 head works just fine if you want to cut it to bring the compression up. Mine was decked .040" and I had no issues even with the reground cam, which would have made potential valve interference issues more likely.

The other big part of the head swap is the electronics. You'll need to wire in the fuel injection from a 2.5 if you want to make it run right. You can use an 88 528e harness or you can get your balls on and use an e30 harness. The e30 harness will require a little splicing and extensions here and there but it'll work just the same. They are cheap and easy to find as well.

[Lucas_Roehr]

The whole 731 bolts right on. If the cam is in good shape you'd do well to bolt it on complete. I had one on my old car for a little while with a 2.5 cam. Later on I ended up bolting on an 885 head with a reground cam. All things considered, unless you've got a -731 handy, its not worth the trouble. The 885 head works just fine if you want to cut it to bring the compression up. Mine was decked .040" and I had no issues even with the reground cam, which would have made potential valve interference issues more likely.

The other big part of the head swap is the electronics. You'll need to wire in the fuel injection from a 2.5 if you want to make it run right. You can use an 88 528e harness or you can get your balls on and use an e30 harness. The e30 harness will require a little splicing and extensions here and there but it'll work just the same. They are cheap and easy to find as well.

So for a regular old eta (non super-e) you can shave the hell outta the 885 head (.040") use the "i" intake and computer and and super e harness... was this a N/A or F/I build? I'm worried about the CR dropping too low for a N/A. I will very likely help a friend with his new (my old) 87 528e and helping another friend with his new (my other old) 88 528 super e do this swap. I know with the 88 it is MUCH easier.

[bm0p700f]

On your US engines an 885 head on a stock pre 3/87 eta will give you a CR of 8.35:1. This include the volume of a crushed headgasket. So not too low for N/A. Perfect for highish boost though.

[turbodan]

So for a regular old eta (non super-e) you can shave the hell outta the 885 head (.040") use the "i" intake and computer and and super e harness... was this a N/A or F/I build? I'm worried about the CR dropping too low for a N/A. I will very likely help a friend with his new (my old) 87 528e and helping another friend with his new (my other old) 88 528 super e do this swap. I know with the 88 it is MUCH easier.

With .040 off it increases compression quite a bit. It probably ends up over 9:1.

Thats not the most important part though. If you dont wire up the right kind of fuel injection it wont run very well at all.

[Lucas_Roehr]

The right fuel injection? Dont you want motronic 1.3 from a 325i, with the matching fuel injection components (afm, intake w/ injectors and throttle body) and possibly a chip for the .2 liters more?

[turbodan]

That is what you want. Unless you have an 88 528, you have some work to do.

[mooseheadm5]

I did the e2i swap on my E30 using a head/intake/etc. from an 87 325i. Shaved the head 0.040" and there were no problems at all, as Dan said. In fact, I have that whole setup for sale if you are interested. Everything you need, all nicely ported.

[derrith]

Duggi on the board did this swap on his 84 528e. Used 1.3 motronic with a stock 325i chip for now. Car runs great and still gets good mileage. I helped out a little bit. I'd recommend updating to the super eta exhaust manifolds and downpipes (same as the m20b25) as Duggi's car feels a little strangled above 5500 or so.

[12valves]

I'm running a franken-eta (325i head, etc.) with the original Motronic 1.0 and it runs OK (custom chip is definately needed however). I did change the FPR to the 3.0bar version also. Tuning WOT is the easy part. Part throttle is not perfect, though it seems like it never was, even before the swap. I plan to get on a dyno to work on that a bit later. If one is too cheap/lazy to get the newer electronics the swap can still be done.

[Junkers]

I should have probably said that I am from New Zealand. We get the euro market of E28's over here so I believe I have a 525ee with a 11:1 compression ratio motor.

I already have a 731 head, I would like to know whether it will improve the power of my motor or just cost more to run. The intake ports are larger than those of the intake plenum. It's not as if it's going to be getting any extra air, just losing velocity. Has anyone had experience with this? I'd like it to still knock out a reasonable fuel efficiency if I can.

[turbodan]

I'm running a franken-eta (325i head, etc.) with the original Motronic 1.0 and it runs OK (custom chip is definately needed however). I did change the FPR to the 3.0bar version also. Tuning WOT is the easy part. Part throttle is not perfect, though it seems like it never was, even before the swap. I plan to get on a dyno to work on that a bit later. If one is too cheap/lazy to get the newer electronics the swap can still be done.

How custom is the chip?

I had one made that revved to 6000 but the maps were still way wrong. It was missing the low-mid torque and it didn't do much on the top end either. That was with the -731, a 2.5i cam and intake with the eta fuel injection. It was a major improvement getting 1.1 wired in.

[bm0p700f]

Well my e2i is "finished" as well. An 885 head bolted directly to a euro 10.2:1 eta engine giving a 9.35:1 CR. I also use motronic 1.3, 325i injectors, 325i AFM and a 325i inlet manifold. Like Turbodan my chip has the fuelling all over the show. It is rich low down and gets richer as the rpm's build (getting as low as 11.5:1). The car feels strangled over 5500 rpm as well. I still use the stock eta exhaust so that mat be part of the problem but it would no explain the overfueling before 4000 rpm. So I need an exhaust and I have found someone who can remap motronic 1.3 properly. The other altnerative is I go for a piggyback system like unichip. I just need the money now. My RR power and torque curves are posted in the dynodatabase sticky on this site.

Like you my car has the euro engine. 11:1 compression ratio was only available before 09/85. After that al euro engines had 10.2: CR like mine.

I am not positve that a 731 head works on an 11:1 CR engine. I have never tried it but I do remember a conversation with Ant Woodjets of A-Tech (here in sunny England who has built several 2.7i M20's), where I am sure he said using a 731 head on an 11:1 CR engine is sucide for said engine.

Also if you do use a 731 head be aware that the oil pathway for the spray bar is not cut into the M20B27/25 head gasket. They need to be added seperatley. I found this out after the 731 head was fitted drove it work and clattered like hell. Got home and took it to my local garage to find no oil getting to the cam. Hense I went for an 885 head.

[turbodan]

The stock eta exhaust will hold up quite a bit of power. It could also cause the rich condition by creating excessive backpressure. Motronic 1.3 and a 2.5i chip should run alright with a suitable exhaust.

The oil spray bar is fed by the rocker arm shafts through the journals in either end of the head. Theres a groove cast into the cam that aligns the spray bar feed with the rocker shaft oil supply once every revolution. If the cam and rockers and the rest of the head is getting oil, the spray bar is too. As far as I know all of the oil and coolant passages at the head gasket are the same for all M20's.

I'm not sure about the 11:1 euro eta's, but I believe the 731 would retain that compression ratio. The combustion chambers in the 731 are identical to the 200 head. The same shape, volume and design. You would have to use decent quality fuel and get a chip made specifically for the high compression high rev motor but theres no reason a guy couldn't do it.

[12valves]

I had one made that revved to 6000 but the maps were still way wrong. It was missing the low-mid torque and it didn't do much on the top end either. That was with the -731, a 2.5i cam and intake with the eta fuel injection. It was a major improvement getting 1.1 wired in.

The stock eta chips have very little spark advance under 3K RPM, so the larger cam and intake will lose a lot of torque until that is fixed. At the top end I believe they run 21 deg. (except the early chips which have 26 deg.) which might have been a little weak for the 731 head. My high RPM feel pretty good after installing headers and a 2.5" exhaust. I tweaked my own EPROM with the help of some other M20 spark advance tables I found online for comparison.

[bm0p700f]

Turbondan, you misunderstand/I didnot explain clearly enough. I tried the 731 head on a eta block with a stock head gasket and no oil came out of the spraybar. Took the head off and holes where drilled in the head gasket for the oil feed and then the cam was well oiled, in fact oil sprayed everywhere. I don't understand it myself but there you go. However the damage was done by this point. Scoring marks on the cam, that and the rocker shafts where installed back to front. So the head was changed.

I was warned that a 2.5i chip in a 2.7i will run but will be far from optimum. Best drive it glenty I was told by someone who builds these engines. The comment was the fuelling will be fine but the ignition timing will be out.

Comparing a 731 and 200 combustion chambers the 731 ones looked a little smaller. I know they are meant to be same volume but the diameter seemed to be less about; 80mm which makes sense as the bore on the M20B20 and M20B23 is 80mm. This could be the cause of the problem with 11:1 eta piton and 731 head. A conflict may result. To be sure put the head and try manually craking the engine (is this possible) to see if there is any interference between piston and head. Its just a nagging doubt.

Seeing as I have got both heads (731 another head I threw the one that I wrecked away and a 200) in the shed, if our guy has a 11:1 CR motor I pull both out and use a pair of calipers to check dimensions.

[turbodan]

Turbondan, you misunderstand/I didnot explain clearly enough. I tried the 731 head on a eta block with a stock head gasket and no oil came out of the spraybar. Took the head off and holes where drilled in the head gasket for the oil feed and then the cam was well oiled, in fact oil sprayed everywhere. I don't understand it myself but there you go. However the damage was done by this point. Scoring marks on the cam, that and the rocker shafts where installed back to front. So the head was changed.

I had no problems with my 731. Bolted on and ran it. The head gasket can be put on wrong, which would cause this. If all you had to do was drill a hole in the gasket, that tells me the passages in the head and block were in the right place. That means either it was the wrong gasket or the right gasket installed incorrectly. I'm 99% sure that all M20's use the same coolant and oil passages, except for the steam holes which the 2.0/2.3 blocks didn't have.

I was warned that a 2.5i chip in a 2.7i will run but will be far from optimum. Best drive it glenty I was told by someone who builds these engines. The comment was the fuelling will be fine but the ignition timing will be out.

I had tested a generic performance chip for a 2.5 as well as a chip from an Alpina B3 2.7. The difference was noticeable but not extreme. I could have run the 2.5 chip without any problems. It wont be right but it'll be close enough.

Comparing a 731 and 200 combustion chambers the 731 ones looked a little smaller. I know they are meant to be same volume but the diameter seemed to be less about; 80mm which makes sense as the bore on the M20B20 and M20B23 is 80mm. This could be the cause of the problem with 11:1 eta piton and 731 head. A conflict may result. To be sure put the head and try manually craking the engine (is this possible) to see if there is any interference between piston and head. Its just a nagging doubt.

Seeing as I have got both heads (731 another head I threw the one that I wrecked away and a 200) in the shed, if our guy has a 11:1 CR motor I pull both out and use a pair of calipers to check dimensions.

The 731 and 200 heads are designed to be used with flat topped or dished pistons. Unless you bolt either head onto a B25 motor with the dome/offset dish piston to head contact isn't possible. Any motor that runs with a 731 will run with a 200 head, and vice versa. They're identical except for the intake porting.

[bm0p700f]

OK I'm mistaken.