This is an open post and I am hoping experienced guys will add to what I have said here. Because there is a million variables to the questions this will be in general terms for what makes sense for most folks looking to buy or build a V8 Miata.

How much?
For the conversion cost the key is really your ability as a builder. For example all the kit makers have the same type transmission mounts which is a couple feet of 1x2 with a pipe cut in half welded in the middle. They are priced around $400 but anyone with basic DIY skills and tools can build a better mount for 45 bucks in steel, paint and a new rubber mount. If welding upside down in not your thing can you follow a string and tell colors apart? Purchasing a ready made wiring harness can run from $500 to $1000 but if your donor came with a wiring harness for a Saturdays worth of work you can convert it yourself for nothing.

Now you can go to Monster Miata, Boss Frog or Flyin Miatas site and come up with numbers yourself on the kit parts, then subtract what you can make yourself as I mentioned above and come up with a number. What I am going to tell you here is what most people grossly underestimate that number by doing that. The killer to any build is the hundred trips to autozone for 30 bucks in whatever. By the time you add that up your estimate will raise easily 30%. I know you doubt that and I did too but go read build threads and you will see it over and over again.

So in very general terms to build a car with ALL kit parts and a good Mustang donor a Ford will run you from $10,000 for bare bones stock to $20,000 with aluminum heads and similar upgrades - just in parts.
To build an LS using all Flyin Miata kit parts and a good F body donor will run from $18,000 to $30,000 depending on options - just in parts.

Again that is all kit parts. I have seen a Ford build done under $2500 with no kit parts plenty of all DIY LS builds under $10,000 and less than that with iron blocks. It just depends on what you can make or scrounge and what you have to buy in kit parts.

How long?
For how long the build takes the key is really your ability as a builder. For example if you buy your trans mount it will take you about 20 minutes to measure, drill and mount it. If you make it, depending on your skill level, it could take all day easily. Ditto with the wiring, the plug and play harness goes in fast but the DIY takes many many hours to convert and install. Also it depends on how much you do to the car in the build. Seam welding and restoring are very time consuming processes that can add a truck load of time. Some guys can work for weeks non stop and others do better to take a weekend off here and there.

I would say the average for a guy with a full time job and some sort of life out side the garage is 6 months to build a car. I have seen it done in 6 weeks and there is one on LS1tech going on 6 years...

How hard?
For how difficult the build is totally depends on your ability as a builder. You may be surprised to hear the hardest thing is usually not the assembly of the car. No the hardest thing is usually what I call builders fatigue. If you get frustrated by set backs and unexpected problems or you are the sort that is bothered by working on something for many hours and not seeing any progress the build will be difficult for you. There is a video that shows what I am talking about much better than I can explain it in video # 10 HERE.

One thing most first timers don't expect is they tend to build the entire car about 3 times. For example you install X, Y and Z and are feeling quite good about the progress only to realize you needed to install W before Y so now Z and Y have to come off and you ding the flange on X doing taking it back apart so now....

To be sure building one of these cars is beyond what some guys can do but I will tell you this, I never dreamed I could do it when I started and had I not been handed a rusty dead Miata never would have tried it. You are probably more capable than you think you are and to be sure no matter where you are at when you start you will be a lot more talented and experienced when you finish!

 

Jim,
I love this post and will throw my 2% in:
If you are using all Kit Bought parts you can do the entire conversion very quickly. I did my rear diff mount in a day including the welding of the mount tabs and the mods to the lower plate. The engine cradle was another weekend and that included the transfer of suspension parts and engine bay mods. The kits are very well though out so they have become fairly bolt in.

Installing my Painless harness was a full weekend. I started on a Saturday morning and took my time. Laying it all out on the living room floor a few days before going after the car was a big help as I now had a very good idea of what went where.

You mentioned the trans mount and I will say this. Once the engine and trans were on the motor mounts it was very simple to install the trans mount and slide the cross member under it. Then I just drilled the holes and pushed the bolts through the mount...done, no tape measure involved.
Basically my car went from a pile of parts and boxes to running in 34 days.....THAT IS NOT TYPICAL! I made my radiator mount, used a coat hanger to create a shape of my rad hoses then match sizes and bends to what I needed at a friendly NAPA. Some things I did all on my own. There were other things that I wanted to pull my hair out over and that is where friends came in. My local Miata club was a great source of info even though I was the first in the club to have a V8.

Let me say that the single biggest mistake I have seen with any swap regardless of model or brand has been that folks find a used engine at a "Fantastic price!" and think the hard part is done. You have just scratched the surface and many times actually started your project under water right off the bat. These end up being the "Project car: just needs finishing" ads you see on Craigslist.
Don't be that guy.

You are going to buy things that you think are perfect that don't fit at all (for me it was the stainless radiator hoses from Summit that couldn't bend to the angles I needed) and the little things that you never thought of (Posi-loc wire connectors are expensive) that push your cost up little by little. I tried to keep a log but then remembered what would happen if my wife ever found out what it really cost for "Just another engine swap". If you think you can do it for $5 grand because your buddy can weld, triple that. Friends can be fickle and they have there own stuff to fix.

My best advice is to make sure you stay focused. DO something positive everyday. Do not take a day off or store the car where you have to GO to work on it. A day off leads to a weekend and that turns into a month.....it happened to me and that is why it took 3 years to get everything into the garage and running.
Lastly, create a build log and keep it updated. We want to see your progress and we are here to help motivate, clarify, confuse, convince and most of all support you.

 

The cost & time to do this project reflect directly on what your expectations are for your finished project. An experienced builder could slap one of these together in a few weeks. I have no doubt that I could have had mine running & driving in two weeks if I had all of the parts on hand & did not alter some of the kits parts or directions.

The cleaning, bead blasting, re-painting/plating/powdercoating every single part, nut & bolt that comes off of the car or from the junk yard is what takes so long. In my case, I replaced all of the bearings & seals in the doner differential, replace all suspension bushings, ball joints, tie rods, hub bearings, struts, brake hoses, & installed a big brake kit as well as new wheels & tires. The engine, which I already had from a previous Mustang project, was treated to all new seals & gaskets as well as a new starter, water pump, & alternator.

My goal was to make my car as mechanically new as possible. I hope that the end results speak for themselves. Point is, a lot of extra money & time go a long way. Be sure to have a pocket full of cash & a garage full of parts before you dismantle your stock Miata.

 

well - I better throw in my experience here too... my build was a very simple one, and much lower budget than many others here. Basically just doing the conversion with a used 5.0 and T5 with monster miata kit.

As a, pior to my build, newbie to this level of mechanical work I have to say that I do not beleive this can be done in a few weeks by anyone unless they're highly experienced and really know what they're doing (such as tbone heller and Meierznutz which posted before me). But for me, it took me 8 months of giving up as many hours in a week, and as many weekends as I could to finally have everything put together, and that doesn't include all the sorting out afterwards...

If I had all parts ready and layed out, each bolt, nut, each extra tool, exhaust constructed, engine freshned up, harness modified - AND I had done the build once before, and had a few weeks off work to deticate to just this, then yes. I agree it can be done in a few weeks.

But it's the constant obsticles that have to be figured out, all the research you end up having to do along the way, every trip to the autoparts store, all the reasearch online for which part to buy, even many random things you don't think of before like how do you wire the fans? what do you do about the washer fluid tank, where do you mount the coolant container, how do you route the hoses to the radiator, what do you do about all the obsticles preventing the hood to close properly... How do you center the 8.8 diff mount on this awkward subframe before welding it?

I had to reallign the clutch to get the transmition back on, to most guys that is a walk in the park and they've done 100 times. for me? I didn't even know it had to be realligned until I realised that plate was loose in there and started wondering if that was normal just before installing the trans... there's 4 hours of reading and fabricating my own clutch alignment tool!!

So: to me with the knowledge, community, and kit components out there for v8 miatas, It is an awsome build that is acheivable by anyone with pretty good intermediate mechanical experience that is willing to take the leap.... Like i was. But if you're like me, do not think you can do this as fast as the pros, including Martin himself which states in the v8 conversion manual that the swap takes around 50 hours... for me it was more like 250 hours... split up in nights and weekends!

 

Want to clarify that I have yet to complete my SBF conversion but I have many completed hotrod builds. I grew up in a home machine shop and my father was a hobby experi"mental" aircraft builder. I have built 10 classic Stangs, numerous Fox Bodies and Classic F0RDs, the Miata project started after a few beers, serious bench racing and my desire to get rid of my dated SBF go fast goodies along with a '90 MX5 that my friend was selling cheap. I also decided to hone my metal working skilz that I would fab as much as possible for this project, not really to save money but take a real DIY approach to things.

I respect the research that went into the products that are available from the V8Miata vendors and they do make this project manageable for a first time builder, KUDOS to Jim for jumping in B4LLS deep and making this his first Hot Rod Project, Well Done!!, and a LS to boot.

For me the hardest part is sticking to the original build plan, Use as many of the parts I have on hand and fab the rest. Let me say that with this approach you will find a few pricey obstacles in front of you. Drive Axles, prolly the hardest to date for myself, mounting rear end, Front Cross member / K Frame Mods, Headers and Oil Pan. I decided to Cave In on the Front K Member and I purchased a V8 Roadsters Piece, ( Less Engine Mounts), However, this ended up costing me $1400.00 CA by the time the dust settled and I still had to fab in mounts for a 5.0 block.

The build will all come down to your personal experience and expectations, I plan on driving my V8 in the winter so bolt on frame stiffeners / closed frame rails would not do. Just learning to bend up open top frame connectors was fun, was way more complicated than I was expecting but fairly easy once you know how, LOL. Good luck with your build and be prepared to change everything, HEHE.

Keep Moving Forward
Dean0