Something to discuss "weight balance" Gen 1,2,3
The rotary engine, support equipment, and exhaust systems are heavier than they look. Typical weight gain for a 1st gen V8 conversion car is only 75-125 lbs.
One of the main engineering goals of the RX-7 was to stay close to the perfect 50/50 chassis balance. When they added the extra weight of a turbo system to the Turbo II model(180-200lbs), they needed to come up with a way to maintain the chassis weight balance as much as possible. Some of the methods they used include...
...They went to an Aluminum hood
...They moved the intercooler rearward to the top of the engine
...They used a heavier spare tire & jack
This just goes to show that the Mazda factory uses the same methods to balance their cars as the regular guy. They reduce the front weight as much as possible, then move components if possible, and finally add weight to the rear if needed, in that order.
This is the biggest reason the added 180-200lbs of the Turbo II option did not ruin the balance and handling of the RX-7. The factory decided that the extra power that the turbo system offered more than offset the added weight.
This is what power-to-weight ratios are all about.
Some weight related numbers...
...An aluminum intake manifold is 28lbs lighter than cast iron.
...Aluminum heads save about 50lbs over iron.
...An aluminum block will lose ya another 55 to 95lbs.
...A 4.3 V-6 is only 11 percent lighter than a V-8.
...An aluminum hood(turbo II)will save you about 30lbs.
...Headers are 20 some lbs lighter than iron manifolds and headpipes.
...The typical RX-7 A/C system weighs 55 lbs.
...The RX-7's layout and structure is well suited to engine conversions. The rotary engine's eccentric shaft centerline is way up in the center of the rotary engine, dictating a much higher transmission location than that of a piston engine. The net result is that Mazda designed the RX-7 with a HUGE transmission tunnel, big enough to fit even the monster T-56 6 spd manual transmission which was used in the Viper and Corvette. The rotary engine's low torque output required Mazda to use a very heavy flywheel and a high rear gear ratio, a combination of factors that combined induce large amounts of stress on the RX-7's rear axles and hubs. Mazda planned accordingly, and designed plenty of strength into the RX-7's rear differential/axles/and hubs. Experience has shown that the stock NA RX-7 components are strong enough to withstand low 10sec 1/4mi passes, a feat that requires around 500hp.
The RX-7 chassis is well suited to V-8 power. It was designed as Mazda's flagship sports car right from the beginning, with many features that address the dreaded chassis flex that plagues other small car V-8 conversion candidates. RX-7 design features include...
1...a very large transmission tunnel. The large tunnel dimensions necessary to accomodate the rotary engine's higher transmission location add considerably to the beam and torsional strength of the RX-7's floor pan. The 3rd gen cars use struts across the bottom of the tunnel to further enhance this effect.
2...deep door sills add even more beam strength.
3...generously rounded door openings add body structure torsional strength.
4...subframe connectors are installed right from the factory. As countless highly abused RX-7's can attest, there is none of the buckled quarter panels or popped out windshields the are common with other V-8 converted small cars that were originally designed with economy in mind.