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

NOTE: emissions in some states is a very big deal and you need to know if you are in a good or bad state before choosing an engine or chassis.


Which car to convert is all about condition.
No matter what car you use this is the time to be very fussy in the build! There is no reason to convert a rusty or beat up car when there are so many clean ones out there. Consider that you are putting 4 times more power in the car that it was designed for so use the most solid pristine chassis you can find.

As a general rule of thumb automatic trans cars are better than manuals for conversions. The reason for that is no enthusiast would want an auto so they are usually in better shape and cheaper to get into. More often than not they are female driven garage queens that have not been beat on. It takes about 15 minutes to install a clutch pedal and master cylinder in an auto car so no biggie there...

As to what generation is best there are a few pros and cons to all of them but they all make great V8 builds. Unless you are going for an all out track brawler or have emission issues to worry about it really makes no difference what year or model you use. The car you like the best is the best car for you to convert.


OK now the biggie... Which engine to use? It's all about you!
First up you will never hear any V8 Miata owner talk about how nose heavy these cars are because it's just not true. For the vast majority of situations it makes no difference at all what engine you put in the car. Did you get that? You can analyze the pros and cons and numbers to death when it is all said and done it really doesn't matter if you use a Ford 5.0, an LS any number you pick, a Lexus a Rover or whatever V8 you find in the barn. Unless you are building an all out track car any slight change in balance or weight gain will be so overwhelming obliterated by the increase in HP it will never be noticed.

Now I don't mean to go crazy here and put a 1000 lb diesel in the car but at the end of the day the numbers that matter are 16.1 lbs per HP for the stock Miata and below 7.5 lbs per HP for the average V8 Miata and IT MAKES NO DIFFERENCE WHAT ENGINE YOU USE TO GET THERE!

OK that being said everyone still has an opinion on what is better between the two common swaps so here goes.

Most folks feel the SBF sounds better than the LS does.
SBF T5 is usually from a few to lots of thousands cheaper to build than an LS T56.
You can get by building a Ford without owning a welder.
It takes a bit less surgery and maybe a Saturdays less work to build a SBF than an LS.
Most stock 5.0s are around 225 HP, most stock LS1 engines are around 310 HP.
Because of where they start to go beyond 350HP takes less effort and modifications to the engine with an LS.
However because the cost of the LS is higher the cost to build either to 350 hp is about the same.
The ECU programming of an LS has a 30 year advantage on the mid 80's A9L programming of the Ford.
LS T56 is 6 gears and the 5.0 T5 is 5 gears.

And now what everyone needlessly obsesses over:
A fully dressed stock 5.0 T5 complete pull out from a 89 Mustang including the wiring and engine computer weights 661lbs.
A fully dressed stock LS1 T56 complete pull out from a 2000 Camaro including the wiring and engine computer weights 609 lbs.
The difference is easily offset by using aluminum heads on the 5.0, however it should be noted that the T56 trans weighs 45lbs more than the T5 trans so the 5.0 weight is a slightly forward in the car. I don't care what myths have been spread on this the fact is weight is an inconsequential difference between the 2 platforms. And you can have an awful lot of fun with either one.

As you can see for every pro there is a con to both and the weight thing is not much of a thing at all. So in a nutshell if you have from $15,000 to $25,000 in disposable income lying around and want to go beyond 350 HP then the LS makes sense. If 300 HP is enough for you and want to attempt a build for less than $10,000 then Ford is the way to go.

But what really matters and the most important factor to consider is you. The best way to insure you will love your car when it's done is to go with the engine and car you have a passion for.

 

A thing worth mentioning is that LS1 t56 trans are becoming more and more scarce and you can count on 1500-2000 for a T56 where as T5's can be had for $500 all day. so Ford is certainly the cheaper option when considering transmissions.