The rest of the block is totally stock as is the crankshaft. If you need more power, you need a larger engine usually. There seems to be two types of people preparing turbo race engines for import drag racing. This mod brings the displacement out to 1702cc and drops the compression ratio from 8. Nitrous oxide injection is used quite extensively in drag racing for a substantial power gain.
Stock turbos are usually sized for mid range torque and are undersized even for stock top end power. Since engine life will plummet once you exceed this type of output, it is not a viable option for most people to be rebuilding an engine every 10,000 miles. On most 4 cylinder engines, going with more than 285 degrees of duration at 0 lift will result in truly gutless bottom end power. Install a properly matched core from Spearco. This is not usually a great mod for street use as everything must be just right as far as fuel and nitrous flow goes and of course the major disadvantage is that the tank runs dry after only a few minutes of use and must be refilled. One school uses small, stock based turbos for quick spool up.
Installing a header and free flowing exhaust along with a cold air induction system may free up a few more hp on certain engines. We see more problems and complaints with people fitting race type cams in street type engines. Increasing the compression ratio is another way to increase power. Many high compression street engines must have their timing severely retarded to avoid detonation which reduces the power right back to stock levels. Of course, top end power should be better. Conclusion Use the right tool for the job. These are a bad idea at high boost pressures.
On naturally aspirated engines, the compression ratio is often raised substantially to boost torque and power. The fuel mixture will no longer be correct. To get these characteristics, most street engines have relatively moderate camshaft timing, small turbos, small diameter intake ports with long runners and usually cast pistons. Raising the redline will not make any more power in most cases unless the engine components are modified to efficiently pass that increased airflow. Avoid matching for efficiencies of under 65% at full power and operation near the surge line also.
Bigger turbos don't necessarily mean quicker times. Always go for as many cubes as you can if you have a choice of engines. This engine was used for road racing so the life expectancy had to be about a full season or 15 hours. At some point, the stock injectors and possibly fuel pump will not supply enough fuel. If your engine uses a vane type airflow meter, you are losing a substantial amount of power potential through its restriction. Let's examine the differences in the 2 different worlds: Street A good street engine should have a smooth idle, have lots of low end torque, a wide powerband, long life and good fuel economy. .
It takes 4 times the fuel pressure to double the fuel flow. If the engine is turbocharged, a larger turbo and intercooler along with forged pistons and stronger rods are fitted to handle the loads. On the externals; A custom, equal length header was made using 1. Expecting your 18 second car to do 13 seconds while retaining good idle and fuel economy when modified is unrealistic most of the time. Graph is drawn in real-time while you're flooring it! Turbos need to be properly matched for the application and primary intended usage.
The effective powerband was 5000 up. The stock hp is rated at 70 at 6000 rpm. Because turbo engines usually have lower compression ratios than atmo engines, they do not take kindly to hot cams on the street. Hopefully I have touched on some of the major points here and saved you some money and time on your project. The head was extensively ported on the flow bench taking intake flow from 82 to 122 cfm and the exhaust from 66 to 86 cfm. Raising the redline to achieve higher airflow through the engine is another way of increasing power.
These have poor turbo response and a super narrow powerband. This is usually done by changing to stronger parts such as connecting rods, pistons, crankshafts and valve springs. These engines run super high boost but don't make any power. Secondly, the fuel pump is not designed to do this. Finally, boost pressures can be raised to increase engine airflow and power. Turbocharged Engines for the Street Turbos are a different ball of wax but many of the same mistakes are made when modifying them.
This engine produced 358hp at 7700 rpm at only 15 psi boost. To achieve higher power, ports are opened up for increased flow at high rpm and camshaft timing and lifts are increased, both of which kill off low rpm torque, power, fuel economy and that smooth idle. Porting the head will improve airflow if done correctly. These may boost economy slightly but they almost always lose power. Some companies offer rising rate fuel pressure regulators with their turbo kits to allow increased injector flow rate over stock pressure. Unfortunately, the pump fuel available in most areas limits the compression ratio useable on the street to under 10. A narrow powerband may be acceptable on a race engine because close ratio gearboxes are usually fitted to minimize rpm drop between shifts.