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1983 Datsun 280ZX Base 5-speed Coupe
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Discussion Starter · #1 ·
I recently started taking ADHD medication and now that I can actually focus on things I feel confident enough to try to undertake a really crazy project.

I acquired an L28E engine from a 1980 280ZX in good condition with only 67k miles on it to try to build something crazy. After doing a LOT of forum reading about dual overhead cam swaps over the past month I ran into 4 options:

1. Weld two four-cylinder heads together
2. Cast your own head
3. Head off a Mercedes M104 inline 6
4. Head off one cylinder bank of a Mercedes M120 V12.

Welding two heads together or casting something custom are both things I've seen videos of working but aren't possible for me. I have heard tell that the M104 and M120 engines have the same cylinder bore and head bolt pattern, but I haven't been able to 100% verify any of that. The M104 head has the intake coming in on the same side as the stock L28E, but the exhaust comes out on the other side. The passenger side (right) cylinder head off the M120 is the same, but the driver side (left) cylinder head has the exhaust coming out on the same side as the L28 with the intake on the opposite side. This is preferable because I won't have to relocate the oil filter or starter or anything to accommodate the exhaust since it will be in basically the same place, and fitting the intake on the other side shouldn't be too hard, especially with what I'm planning. (More on that later.) With all of that in mind, I am pretty set on using the left side head from an M120.

There are obviously a couple of big issues with sticking a 90s Mercedes head on an 80s Nissan block. I am leaving out cams and timing chain assembly for reasons that I will get to later. The main issues all come from measurement uncertainty in a lot of places. The cylinder bore for the M120 is 89mm and the bore on a stock L28 block is 86mm. That is obviously enough to cause issues. I've heard that boring an L28 block out 3mm is possible but is a lot like playing Russian Roulette. I'm fairly certain that the bolt pattern is the same, but the oil and coolant channels definitely aren't. I considered making a spacer between the block and the head which could make the channels flow into each other, but that would change compression and require two gaskets. I have no machining experience so I have no idea if it is possible to mill the block and the head to get the channels to fit. I know that external oil lines are doable, and I can't think of any reason external coolant lines wouldn't work. I have a set of 6-2 headers and I was thinking that I could probably get a spacer fabricated that would act as an adapter for the presumably different bolt patterns, but full custom headers probably wouldn't be a bad idea. The intake manifold will definitely have to be custom. There's some fuel injection stuff I'll have to figure out with that at some point because there is absolutely no way carbeurators would work for this at all.

Let's assume that the bolt pattern is the same and works, I can bore out the block, and i can run external oil and coolant lines. The head is now bolted on to the block with stock L28 crankshaft and connecting rods but 89mm pistons to fit the bore. I'd have to measure the compression with the new head, but I've heard tell of fairly stock L28s surviving very high compression ratios, so I'm not too worried about that.

By this point, everyone is probably wondering why I haven't talked about camshafts or timing chains, since I've heard those are the hardest parts of a DOHC swap. Here is where my idea goes from simply crazy to quite possibly delusional. I don't plan on having camshafts or timing chains. I'm sure some people here have seen THIS video. With my CAD experience and programming experience, as well as access to Wesley Kagan's files that he used on the Miata build, I believe it will be easier and less expensive for me to build a Freevalve system than it will be to make custom camshafts and a custom timing chain assembly.

All I will have to do for the Freevalve system to work will be to fabricate an adaptor that can bolt on to the Mercedes head, fabricate holders for the valves, figure out where Wesley got solenoids that can fire fast enough to run an engine, and add a bunch of sensors for crank position and some other data the Freevalve system needs to time itself correctly. I can use his file as a guidline and pretty much just adapt it to have the right hole patters and angles and such, in addition to adding two more cylinders. I want to go to a Megasquirt ECU system, and I am curious as to whether or not that could run a Freevalve system or if I would have to run it off an Arduino like Wesley did.

I was thinking that for the intake I would just run carbeurator style velocity stacks with holes for the fuel injectors attached right onto the intake ports of the head. With full programable control over the valves, I should be able to program them to function in place of throttlebodies by only letting in a specific amount of air. It would probably be a lot easier to just have a traditional intake manifold, but this would be very unique and take up very little space so I want to at least try it.


Anyway, I'm 17 and anyone who knows me describes me as being simultaneously the smartest person they've ever met and the dumbest person they've ever met so please feel free to tell me exactly how stupid my ideas are, as long as you throw in your two cents on how to make it better. Specifically I would really appreciate any 3D models of an L28 block, diagrams of a stock head gasket with measurements, and advice on machining since I have no experience with that.

Thanks for reading this excessively long post! I'll be posting pictures of the teardown of my L28 and of the Mercedes head once it arrives. I plan on making all of the CAD files and software for this project completely open source so the community can improve on the design and build their own versions.
 

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1983 280ZX Turbo
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I don't think we can provide a lot of help on this.

I wonder if you're making the classic assumption that the Datsun L6 is really a copy of the 50's and 60's Mercedes L6. That has been a base assumption for decades, and I tend to believe it. However, I don't know that it assures that any of the passages in a Mercedes head would align with those in a Datsun block.

One simple thing which occurs to me is to take a head gasket for the Mercedes head in question and lay it on the Datsun block. Seems to me that unless the cooling and oil passages line up, the project won't fly.

It would also be helpful to get a Datsun head gasket for that block, and put it up to the Mercedes head and look for the same problems with cooling and oil passages. If they don't line up, IMO that's the end of the project.
 

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This really seems like a lot of work with very little in return.
Just get yourself an RB25 or 26 or even a 30, and you'll have a strong reliable inline-6 motor with dual overhead cams. Problem solved.

Bon
 

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1983 Datsun 280ZX Base 5-speed Coupe
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Discussion Starter · #5 ·
One simple thing which occurs to me is to take a head gasket for the Mercedes head in question and lay it on the Datsun block. Seems to me that unless the cooling and oil passages line up, the project won't fly.

It would also be helpful to get a Datsun head gasket for that block, and put it up to the Mercedes head and look for the same problems with cooling and oil passages. If they don't line up, IMO that's the end of the project.
I know that Derek from Datsunworks utilized external oil lines on his custom cast Honda-based head. I think external coolant lines could also work, especially because this won't have a traditional valve cover. Your suggestion to lay the head gaskets on the block is definitely something I will do. I really wish I had a 3D model of the Mercedes head. That would make a lot of things much more certain.
 

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1983 Datsun 280ZX Base 5-speed Coupe
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Discussion Starter · #6 ·
This really seems like a lot of work with very little in return.
Just get yourself an RB25 or 26 or even a 30, and you'll have a strong reliable inline-6 motor with dual overhead cams. Problem solved.
For me, the return isn't in performance but in the satisfaction of building something very unique. Switching to a crossflow head will definitely increase performance, but that's not why I'm doing it. A simple engine swap is definitely the most sensible choice if your goal is power, but it's all been done before. Not to mention that RB series engines are expensive! I can pick up all the parts I need for this for a couple hundred bucks, plus a couple hundred more for machine shop work and fabrication
 

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My main caution would be to leave the car intact except for what you're working on (engine in this case). Many perfectly good cars have become parts cars because someone was going to "restore" of "mod" them. The other thing is do you have enough money? You could start down a path, take stuff apart, buy parts and get stuck with piles of stuff that no one else will take the effort to care or finish.

One of my peers' father died back in the mid-80s leaving a 1959 MGA to his son. The car was driving fine when inherited but the son was going to "restore it". He disassembled then got busy with work, wife, kids, paying for college etc. He recently retired and almost finished the car after moving it from house to house over the years. He could have been driving it.

A professor I knew retired and started to restore a 65 Mustang. He converted his garage to a shop and worked on the car like he was going to a job. It took him 2 years because of how much he had to figure out and to source original parts. He sold the car and said "never again".

How much time and money do you have? Enough? How do you know?
Are you considering the project because you want the car or because you want to do the project?
 

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1983 Datsun 280ZX Base 5-speed Coupe
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Discussion Starter · #9 ·
My main caution would be to leave the car intact except for what you're working on (engine in this case)

How much time and money do you have? Enough? How do you know?
Are you considering the project because you want the car or because you want to do the project?
I bought a whole spare engine specifically so that I can leave the running, driving engine that is currently in my car alone! :)

I am 17 and still in school, so money may be lacking sometimes but I've often been able to find the time. I can usually make $4-$5k by working over the summer, so it may take a few years but money isn't an impossible problem since I am lucky enough that my parents saved money to send me to college. With the colleges that I'm looking at, I think this would be a super cool engineering/coding project to talk to professors and peers about to help me puzzle out. The schools also have a lot of resources and tools I definitely don't have access to at home.

I'm optimistic about being able to do this. I can source a head for probably under $400, and from there it'll be a little bit of money to take it to get laser scanned so I have a 3D model to build my designs around. Once I have that 3D modeling my project I will very quickly be able to tell if the project will work or not. If it won't be able to work, I'm out some money for the laser scan but I can probably sell the head and part out the spare engine I got before I spend a ton of money boring out the block, buying new pistons, machining custom parts and buying custom solenoids.
 

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1983 Datsun 280ZX Base 5-speed Coupe
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Discussion Starter · #10 ·
The Mercedes head is finally on its way! I got the head off the engine I have and sold it to the Datsun shop I work for. I bought the whole engine for $200 and sold the head for $300 :) more funds for the project
 
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