Why the hell stop at low number LS engines.
LS7 that thing.
Looked into it more than just about anyone. I'd LOVE the LS7. For right now, my friend plans on keeping his a rotary until it pops, then swapping, so I decided I'm going to drive it as an LS2, save up some more money, then give him the LS2 and upgrade to an LS7 when he's ready. Piecing everything together, it's about $30,000 to get the LS7 in and running, after all the small misc. parts you'll need. While you can find used LS2s all day long for 8-10K w/Tranny and ECU, you have to buy an LS7 new for $13K, which doesn't include accessories, a clutch, tranny, or ECU, or intake, or many of the other things you forget to factor in. For now, I'll be happy being one of the very few LS2 RX7s around.
As for the rotary-V8 debate, there have been very close apples-apples comparisons in weight. A full weight (A/C, PS, etc.) near-stock rotary to a full weight LS1 has added 22-32 pounds in most cases I've seen, depending on the small things. On top of this, it actually IMPROVES weight distribution slightly, especially since most 13B cars run a huge front mount. Now if you're comparing a 20B to an LS1, the LS1 is going to be quite a bit lighter... The LS2 is probably going to be a bit lighter even.
For those uninformed about rotaries, they are actually very comparable to a two-stroke engine. The positives are:
-Smooth acceleration due to more combustion pulses per revolution
-Low center of gravity
-Easier to rebuild out of the car.
-Easier to rev higher in stock form, due to lack of a valvetrain, which is often the limiting factor on piston engines.
The negatives:
-Unreliable (note that this only applies to the turbo cars, which all FDs are. NA 13Bs can go 300K miles)
-Piss-poor gas mileage.
-Sound like **** (personal tastes be damned, this is often an agreement).
-Heat monsters. More frequent pulses means more heat, as well as not having the cooling effect an intake charge has on a piston engine. This goes through turbos and engines faster. A vented hood is considered a reliability mod, not an aesthetic one.
-Poor emissions. The cats on these cars are HIGHLY restrictive due to this, but these restrictive cats also contribute to heat buildup. You may not care, unless you live in an emissions-monitored state.
-Burns oil. Not just when it's bad, but by design, they are expected to go through a quart of oil every 2000 or 3000 miles in perfect, off-the-lot condition.
-Poor reliability. "If you take care of it," "If it's been well-maintained" is crap. The highest I've heard of any FD car going on the stock motor is about 120K miles, and this put everyone on RX7Club in shock and awe. I've seen a handful of cars that are 20K(ish) mile chassis with blown motors. The average life of a "well-maintained" FD motor is about 60K miles on average. That's terrible. Big thing to note here is that this 60K average only applies to OEM engines. Rebuilds/custom builds NEVER, EVER last as long. This is the main factor that drives eevn the rotary heads into swapping for V8s. I remember recently reading about a guy who decided on an LS1 after he went through 3 engines in the same time he went through one set of tires.
-Poor ECU. The stock ECU on these is a little dumb. If you pop a vacuum line off (easy to do), it will go lean, instead of rich, like most ECUs. Also, overboosting (aftermarket exhaust and a cool night is enough) will cause the car to run lean also. Easy to detonate!
-Goes through spark plugs. The system operates on a "waste spark" design, which ignites two of the four spark plugs when unecessary. Complicated to explain why, but cheaper to manufacture. This, in combination with the more frequent combustions of the rotary means you're changing plugs much more often. Also, rotaries use special spark plugs, which cost about $6 each (x4 for a 13B). Thinking of a 3 rotor? Hah, they use a total of 12 plugs. You're looking at about $80 (after tax) just for a set of plugs.
-Hard to find parts/shops for. Enough said, it's a rare car with an engine most people don't know enough about to be touching.
-Blown engine = pull! It's advised to do a compression check twice a year. If you can catch your engine on its way out, instead of before it blows, then you can usually reuse the rotor housings, which will save you money, but... Remember what I said about the engines being easy to rebuild (which many rotary heads argue in favor of)? The difference is, you have to pull the motor out of the car to work on it. You can rebuild a piston engine while it's still in the car. Also, who cares how hard it is to rebuild a piston engine, you don't have to do it every other year!
-Terrible torque. The sequential turbos certainly help, but once you go single (if you can afford it after all the rebuilds), you'll end up having to rev the **** out of the motor to get anywhere.
-Backfires like mad. Some people enjoy shooting flames out of their exhaust, but it's all due to the excessive gas.
-Upgrades are a bit more complicated. Porting the engine, which is similar to cams and some headwork on a piston engine, requires pulling the rotary out. When you blow your motor, you better hope you're financially comfortable, because this is the best time to do some porting and upgrading. Also, these sorts of big upgrades are much more detrimental to daily driveability than than those that occur on piston cars. For example, there are low 9 second Supras, Skylines, Camaros, Mustangs that are daily drivers, but many high 10 second rotaries are seen as a headache to drive on the streets, mainly due to poor idle characteristics.
Hope that clears some things up. The only reason I ever see for keeping the rotary is due to the cult-like passion for the thing, but the V8 swap has all the facts and figures in its favor. Many LS1 FD owners are recording 25-30 MPG, while putting down over 400 at the wheels.
By the way, surprised nobody said anything about my friend's license plate yet.
I got a cute little plate on its way, too.
And lastly, doing a V8 swap will never ruin the "asthetics" of the car because the exterior and interior of the car isn't changed what-so-ever. The only thing that changes is the noise. I'm fine with you being anti-American drivetrain--you're entitled to your opinion. But the facts are getting skewed here--putting in an LS1 improves the RX-7 plain and simple. Hell, you get better gas mileage to boot! All I see is a win-win-win situation. 
