I have a 1986 series 4 rx7 with a 1989 series 5 turbo engine. Everything is stock except for a microtech LTX-8 computer and exhaust upgrade.
What turbo would give me the biggest increase in power without having to modify the engine? What other modifications to the car would be necessary?
How much would fuel economy decrease, and to what degree can this be overcome by installing a boost controller?

 

I've heard great things about the GT35R on stock-port engines. You'll need a T4-flanged exhaust manifold, and a beefed up fuel system with larger injectors. The Microtech should be good for your goals. And, most importantly, a good tune on a dyno from a pro tuner.

 

depends on what your goals are, you can crank out 800 wheel horsepower from a basically stock engine if you slap a big enough turbo on it. the engine isn't the weak point, it is the tuning and setup.

 

The BNR turbo upgrade is the simplest bolt-on option. Otherwise, you will need an aftermarket turbo manifold, external wastegate, intercooler plumbing and maybe a new intercooler, oil/water lines, and an appropriate downpipe for any full aftermarket turbo upgrade. The GT35R is well-sized for the 13B engine, but otherwise you will want at least a T4 size. You can use up to a TS04 (T58) sized turbo with decent results on a stock engine. Most people choose the slightly smaller 60-1 or T04E 60, and those with more money tend to go with the more advanced GT35R.
http://www.bnrturbos.com/2ndGen.htm

Your car will require the appropriate fuel and cooling system upgrades in order to support whatever horsepower goals that you have.

The fuel economy depends on your right foot and the quality of the engine's tune. Simply upgrading the turbo will not have a significant effect on fuel economy if the car is driven in the same manner. If you race the car you can expect as little as 8 miles per gallon.

The stock S5 engine is only good for about 500hp before it starts to have issues.

 

for 380HP at the wheels would i need to upgrade the fuel pump and injectors?
If so, what sort should I get?

 

Lol


You are not even going to reach 300rwhp with stock fuel setup..

 

I'm just wondering but was your 7 a turbo car before this? Did you upgrade the radiator or anything else than the motor/exhaust?

Thanks