Swapping in M73 instead of M70

[dragon850]

OK, so have to edit this Post a bit, I realize that there is an old wokke thread detailing the swap but it stretches to a novel that you need 3 hours to read! Wanted to compile in one place the number of changes needed for the swap.
Will be doing this swap on a 91 850 with a bad M70 motor and retaining 4HP24 transmission.
Without going into complexities of making a hybrid, the added cost of schrick cams, swapping heads and such I am rather interested in a simple swap.
Wanted to verify If I am on the right track.
Have a healthy pre 2000 M73 ready to go. Items that need to be swapped over from an M70 onto M73 (please add if I miss something).
So far:

1) Intake manifolds with DK motors and fuel rails.
2) Valve covers.
3) Rear coolant pipe connector(the one with 3 temp sensors)
4) Use water pump from M73.
5) Lower front timing cover (for crank case sensor brackets), grind the lower rear timing cover to fit the alternator arm.
6) Harmonic Balancer.
7) Use exhaust manifolds from M73 with modified down pipes to fir the stock M70 exhaust flanges.
8) Use power steering pump along with tensioners and belts from M70.
9) Use oil pan, pump with chain and oil sump from M70.
10) Use shortened N73 crank bolt because the M73 crankshaft is shorter than M70.
Missing anything else?

Eprom wise, with slightly larger displacement possibly use 5.0 Alpina software, maybe CSI software? Or just a tuned set of chips like Dinan or Turner? Or even keeping OEM chips and going with 3.5 BAR regulators to give them a bit more fuel at WOT.
Reasonable to expect at least 330HP at the crank?
Thanks!

[dragon850]

100 views and no one has any input? I sometimes feel the forum is starting to get away from technical threads...which is too bad.

[TxGR8White]

WOKKE did an excellent, in depth write-up of this procedure on this forum. It has all the answers you need.

[dragon850]

Not interested in Wokke made hybrid using M70 heads. I am talking about a direct swap including m73 heads.

Never-mind, did some more searching and found wokkes thread of doing exactly what I am trying to do, his hybrid thread is separate.

[cartoonz]

or... you could just throw a Dinan TT motor into it...
hehe

[dragon850]

or... you could just throw a Dinan TT motor into it...
hehe

Well
If you sell it to me and not ask for 1 MILLION DOLLAS

[cartoonz]

...with my little finger to my teeth, right?

[IJustDrive]

After all that, what the overall difference between what your doing and the hybrid? Just the heads?

[dragon850]

If M70 heads are used schirck cams need to be purchased and installed and custom chip for more power.
Sounds like M73 heads and engine can produce 360 HP which is more than enough for my purpose.

[Richard454]

OK, so have to edit this Post a bit, I realize that there is an old wokke thread detailing the swap but it stretches to a novel that you need 3 hours to read! Wanted to compile in one place the number of changes needed for the swap.
Will be doing this swap on a 91 850 with a bad M70 motor and retaining 4HP24 transmission.
Without going into complexities of making a hybrid, the added cost of schrick cams, swapping heads and such I am rather interested in a simple swap.
Wanted to verify If I am on the right track.
Have a healthy pre 2000 M73 ready to go. Items that need to be swapped over from an M70 onto M73 (please add if I miss something).
So far:

1) Intake manifolds with DK motors and fuel rails.
2) Valve covers.
3) Rear coolant pipe connector(the one with 3 temp sensors)
4) Use water pump from M73.
5) Lower front timing cover (for crank case sensor brackets), grind the lower rear timing cover to fit the alternator arm.
6) Harmonic Balancer.
7) Use exhaust manifolds from M73 with modified down pipes to fir the stock M70 exhaust flanges.
8) Use power steering pump along with tensioners and belts from M70.
9) Use oil pan, pump with chain and oil sump from M70.
10) Use shortened N73 crank bolt because the M73 crankshaft is shorter than M70.
Missing anything else?

Eprom wise, with slightly larger displacement possibly use 5.0 Alpina software, maybe CSI software? Or just a tuned set of chips like Dinan or Turner? Or even keeping OEM chips and going with 3.5 BAR regulators to give them a bit more fuel at WOT.
Reasonable to expect at least 330HP at the crank?
Thanks!

I can't think of anything off the top of my head- it's been a while since I hobbled together mine. The Intakes IIRC are the same but for some reason have different numbers. I'd definetly look at the M73's injectors- the blue Lucas ones. They are problematic as the center of the three hole center piece falls out (top one)-and screws up the spray pattern. I'd replace with Bosch ones.

[dragon850]

So use M70 Bosch injectors vs m73 Lucas? I was just thinking it would be nice to find a crashed Alpina B12 E38 750il with a 5.7l m73 and stuff that into an 850 with custom chip!!!

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[8Harry8]

Not interested in Wokke made hybrid using M70 heads....

...just because he knows that M73 heads are a step backwards...

[dragon850]

...just because he knows that M73 heads are a step backwards...

Wokke is running m73 engine with m73 heads in his own car. Just makes that m73/m70 hybrid for clients...

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[8Harry8]

Whats wrong about it? He has learned over the years!

[dragon850]

Whats wrong about it? He has learned over the years!

Not saying anything is wrong, just stating a fact. I don't know, I have seen some high milage m73 that are running great, at least the banjo bolts don't back out on their own...
Don't think roller rockers are a step backwards.

[cartoonz]

...just because he knows that M73 heads are a step backwards...

What weight of milk is being run instead of oil in that engine, 2%, half and half, or heavy cream?
Me thinks that motor has some bigger issues....

[TedBobo]

What weight of milk is being run instead of oil in that engine, 2%, half and half, or heavy cream?
Me thinks that motor has some bigger issues....

My thoughts as well.

[wokke]

Wokke is running m73 engine with m73 heads in his own car. Just makes that m73/m70 hybrid for clients...

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I wish I would. The car is still on the hoist since I have no time to finish it. I don't think the M73 heads are worse than the M70 heads. But I also don't think they are any better and that's why I prefer to use M70 heads because the entire down pipe issue is solved that way.

[peake]

Considering the costs of replacing the engine with a M73 + new cams + labour + what ever, why not buy an N73 and having no problem with worn out cams and also getting 400+ hp!

[72tpik5]

Here is a N73 for 13k. It also has a BMW 760 attached to it.

https://www.carstory.com/detail/2006...HN03596DD98273

Or here is a long block.

http://www.ebay.com/itm/03-04-05-06-...hY8AlK&vxp=mtr

[IJustDrive]

From what I understand the N73 will not fit under the hood, unless you do a Chevelle SS style scoop or something drastic like that. Nice try though, that would be awesome! I wonder what it would really take to get and n73 in there? While Wokke's hybrid is appealing, I like the simplicity of what Dragon is proposing. The only thing I was going to mention was the fuel pressure regulators, but it looks like you've covered that.

[cartoonz]

the N74 is the only one worth putting a dry sump on and stuffing it in there... and not have to mod the hood either.

Too bad Dinan burned through all the remaining S70 blocks from BMW... that was the perfect upgrade

[wokke]

Considering the costs of replacing the engine with a M73 + new cams + labour + what ever, why not buy an N73 and having no problem with worn out cams and also getting 400+ hp!

and how do you want to control the engine? There is more than just mechanical issues like fitting the engine under the hood.
M70B54 or M70B54S is more or less plug&play which is a huge advantage.

[arvis535]

Folowing. Could you post the progress with pictures? I to have a 850 with bad head gaskets and want to swap it to m73.

[adwebinc]

I wish I would. The car is still on the hoist since I have no time to finish it. I don't think the M73 heads are worse than the M70 heads. But I also don't think they are any better and that's why I prefer to use M70 heads because the entire down pipe issue is solved that way.

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??