Swapping in M73 instead of M70

[wokke]

So Wolf... Just reading this post and it has me a little worried. Are you saying that you would recommend the M73 bottom end with M70 heads over the entire M73 swap??

Indeed. It just creates a lot less headaches than going with the M73 heads and having the trouble of adapting the M70 exhaust system.
The last few engines I did were all M70B54S because the rather small mark up on the price is justified by the additional power you get.

[adwebinc]

Ok. Thank you!


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[arvis535]

I'm in the beginning of swaping the m70 with m73. Trying to do this on a low budget. How much € are we talking about if I choose to go for m70 heads instead of m73?

[dragon850]

I'm in the beginning of swaping the m70 with m73. Trying to do this on a low budget. How much € are we talking about if I choose to go for m70 heads instead of m73?

There is absolutely no reason or point to go with M70 heads, I found that with M73 heads engine runs super smooth and has tons of power.

[arvis535]

Dragon850, can you write to me on messenger? My name is Arvydas Grunt-Meeris

[Kamiler]

dragon850,

I read this thread, and I like your comprehensive list. Looks like the thread took a different turn though.

So the list your provided was that all or is there more? I am trying to prep a list of parts to order. So far I got this, I have not hit buy yet:

-M70 engine mounts
-M73 water pump
-M73 thermostat
-M73 rear main seal +mounting bracket gasket
-M73 lower timing cover gaskets
-M70 throttle body gaskets
-M70 Oil Pan Upper and Lower Gaskets

A lot of the "add ons" around the block were pretty new on my M70, so Ill be swapping those over. At least those what I can.

I have a few questions on a few more parts:
-so for the crank bolt, N73 for sure or was that supposed to be M73? (just trying to make sure there isnt a typo). I heard the N43 bolt will work too. (You need to cut that one down)
-for AC compressor the M70 one needed? I read that you need the M73 pully for that though. My M73 has no accessories. Would like to confirm if that is true. If the M73 pully is needed I am SOL. lol
-As for setting timing, I noticed on the M70 there was no marks or anything on the cam shafts. Im sorry If i sound a bit uneducated, but I never had to deal with timing. I just would like not to mess this part up lol.
-the rear coolant pipe, can you use the m73 one? Just curious. If you cannot then Ill just use the M70 one, will need to add gaskets to the list for that.
-If you have any pictures of the modifications that needed to be done (cutting/grinding) that you can share that would be great. I have seen Wokke's thread but 2/3 of the pictures are not showing up for me. I am trying trying to be prepared and be ready to jump into this when the engine arrives tomorrow.

Any additional info would be great, if anything feel free to send me a PM.

[rjjablo]

There is a mark on the Timing cover and the crankshaft pulley to line up your cams, that and the cam alignment tool

[vwleadfoot]

I'm looking to resurrect this thread. I'm doing this swap but in a 92 750iL---um and going manual 420g transmission at the same time. I've tried to email Wolf, but have gotten no response. He had said in his build thread (I can't see the pictures either) that he had chipsets that would change the ignition timing appropriately for the higher compression. I'd like to buy a set but I need to hear from him. I'd also like to buy the longer crank bolt he said he had a bunch of. Anyone know how to get a hold of him? Or know of another source for these things? My 94k mile M73 (non "n") motor will be at my house next week and I'd really like to get started.

[rockytt]

He had said in his build thread (I can't see the pictures either) that he had chipsets that would change the ignition timing appropriately for the higher compression

I have the exact build in his thread (m73 block/m70 heads) and was in communication with him during the process. He doesn't actually have the chips, however can put you in touch with his "guy". The ones that he developed were to take advantage of the Schrick cams as I recall - different timing - rather than compression differences. Not cheap, maybe $1500 with maybe a 15hp bump. I've been driving mine w/o the upgraded chips and haven't been able to talk myself into them yet.

[wokke]

I have the exact build in his thread (m73 block/m70 heads) and was in communication with him during the process. He doesn't actually have the chips, however can put you in touch with his "guy". The ones that he developed were to take advantage of the Schrick cams as I recall - different timing - rather than compression differences. Not cheap, maybe $1500 with maybe a 15hp bump. I've been driving mine w/o the upgraded chips and haven't been able to talk myself into them yet.

You are mixing my standard V2 chip with the special M70B54S.
My standard set is €400,- plus VAT where applicable and includes the optimized EML chip for better throttle response.

The engine with the set for the M70B54S has 375HP on the dyno. It also includes the optimzed EML chip of course.

[rockytt]

Ahh - found what I was looking for:
"Yes, I have a special mapping for the M70B54S. The engine runs with the V2 set but to take full advantage of the engine’s capabilities the special mapping is needed. Attached a dyno graph for your info.
I do have to purchase each chip separately from the tuner because due to expected volume it made no sense to me to buy a copy license as with the V2 chip set. The guy is charging €xxx,- excl. VAT (which won’t apply to you) so you my want to check what a local remapping may cost you."

I may have to find some budget for those now that the (M70B54S) car is running with the Schricks -

[HeinrichG]

Hi guys,

Sorry for hijacking the thread, but I think the question is in good hands here.

Do the M73 cylinder heads fit on the M70 block? If the M70 heads fit on the M73 block, then it should also work vice versa?
What compression you have at the end?

[wokke]

Hi guys,

Sorry for hijacking the thread, but I think the question is in good hands here.

Do the M73 cylinder heads fit on the M70 block? If the M70 heads fit on the M73 block, then it should also work vice versa?
What compression you have at the end?

M73 heads fit the M70 heads, But....
1. you lose power because the cams are much milder than M70 cams
2. your M70 exhaust wont fit anymore due to different exhaust manifolds (no, M70 ones don't fit)
3. Compression doesn't change. The higher M73 compression is due to different pistons in the M73 engine
4. overall IMO a senseless modification

Cheers
Wolf

[HeinrichG]

Hello Wolf,


thank you very much for the detailed answer.

Then also fit the intake manifolds and valve covers from the M70 on the heads from the M73?

[wokke]

Yes, they both do fit.

[HeinrichG]

Thank you Wolf

[BMSman]

compared to standard M70 setup (91 850i), do you get any more power running M73 bottom with stock M70 heads and standard (or Wokke's V2) ECU chips? Do you need a custom tune to make this conversion worthwhile?

[dragon850]

You can now use M73 block and M73 heads and order Soara headers to bolt up to the original M70 downpipes.
With M73 heads you get a benefit of roller cams and quicker revving engine.
I have gotten about 360hp out of this set up without the headers, with headers I imagine another 10hp is there.

[adwebinc]

Hey all. I’m back! Unfortunately after 3 1/2 years of having my car in a shop to do the M70B54S conversion, it’s back on my loft at home not running right. Shop gave up so she’s back and I can’t even enjoy it.

It starts right up, but is popping and even back firing on occasion. Sounds horrible and is way under powered. Any advice?

[LappingLuke]

Cam timing is off?

[Hyper]

...Any advice?

General...

• Start a thread for your specific situation.
• Be patient and methodical. Confirm assumptions. Keep a record.
• Engine basics: compression, fuel, spark. First Go-noGo, then qualitative.

[Hyper]

...Confirm assumptions...spark...

Here's an example, from just now...

Following extended down time, got a CEL.
OBD says random misfire with trouble on cylinders x & y.
I have a spare (M62) engine so I swapped COPs and experienced plugs, but still no good.
Then, for mere $50, I defended the dreaded Double Fault, bought a fresh set of spark plugs.
Well...whadaya know. A DF.



Did I really prove the previous sets were bad?
No, that would require repetitive A-B swapping, observing that the CEL OBD fault is tagged to the set.

[adwebinc]

Hyper - while I appreciate the feedback, the car was in a shop for 3.5 years. Mechanic tells me they tried EVERYTHING. This is the M73 block swap and this is a specific thread for that.

So, there are a couple of guys here who are experts on that swap, so I thought I would share my very unusual symptom to see if the experts had a step one for me to try.


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[adwebinc]

Cam timing is off?

Shop said they set and checked multiple times. While the shop isn’t experienced in this swap, they are a legit BMW service center.

But if that’s the most likely culprit, then a may have a different shop check.

Wokke - no problems running your chips in this set up correct?


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[dragon850]

Shop said they set and checked multiple times. While the shop isn’t experienced in this swap, they are a legit BMW service center.

But if that’s the most likely culprit, then a may have a different shop check.

Wokke - no problems running your chips in this set up correct?


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I will be ready for you in a few months, will be interesting to investigate and find the issue...
Diagnosing via forums is not a good idea with something custom like this.
There are only 2 people I know capable of figuring out complex problems and are willing to work on cars, myself and Cartoonz down in so cal.
You need a specialized shop that just does E31.... nothing else.