The tough questions...and my answers Last Update: October 6, 2009 8:33 PM

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Which kit is the best?

Each kit has downsides, the following is my opinion and as such should not be taken as fact. Since Racing Concepts is basically no longer in the miata swap business I will leave them out. I have installed and driven a 1991 Racing Concepts LS1 Miata (mine), 1999 Boss Frog LS6 Miata (David's) and a 1999 V8 Roadsters LS1 Miata (Don's) as well a a Lexus V8 1UZFE 1992 Miata (Wreck Racing's).

The short answer is I like the V8R kit the best. Below are the Pros and Cons of each kit. Remember, this is MY experience with them and your experience may vary.

V8 Roadsters:

Pros: Great fit and finish, quick service, well thought out and tested products, flyin' miata support, stock steering rack location, choice of rear end setup (CTS vs Ford 8.8), more room for radiator/fans with rearward kit, CTS diff creates room for dual exhaust easily

Cons: Requires oil pan modifications (possible source of mistakes/failure), rearward kit requires firewall mods which requires removal of interior/dash, rear end setup requires welding and care to insure proper driveshaft angles

Conclusion: Well put together, thought-out and tested kit that requires a bit more skill and time to install but in the end you get a great setup.

Boss Frog:

Pros: Extremely robust diff mount/subframe bracing, no firewall mods needed, no oil pan modifications needed, amazingly overdone part packaging

Cons: fit not up to V8R standards, relocates steering rack forward about an inch (makes on center steering feel more numb and increases bump steer), very tight clearance for exhaust around diff, parts not tested to the extend that the V8R parts are

Conclusion: Still gets you a very capable LSx Miata but the fine details simply aren't there.

Which LS motor is the best?

Best... that's hard to say. Easiest, cheapest, most powerful, etc individually are easy to point out. The kits use either a stock or modified f-body (98-02 Camaro) oil pan so its easier to grab a motor out of a f-body. Problem is the 98-00 make less power and have an inferior PCM (engine computer) than the 00-02 ones so finding a 00-02 motor with low miles can be difficult. Another issue with the f-body motor is the accessories are not as low profile as the CTS-V setup (ls2 water pump and vetter crank pulley). By the way, don't get a 1st gen CTS-V T56 trans, it won't work in these kits. If you are worried about making more power, the cheapest route is to put aftermarket heads and cam on a ls1, that will surpass the other motors for less money.

New crate motors/trans/wiring/pcm/accessoires, once complete with all the parts you need will will cost about double the price of a junkyard setup. Regardless of what motor you get from a salvage yard, get a complete drop-out that includes every part you need otherwise you will be spending lots of extra time and money to collect all the extras.

The f-body wiring is also the easiest to wire up in my experience. Both the CTS-V and GTO wiring were a little different and the CTS-V wiring harness places the PCM on the driver side where there is no room for it in a miata.

There is a great article detailing all the GM Gen III and IV motors here:

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