Project Nissan Sentra Spec-V Part 7: Installing a Turbo System
By Mike Kojima
Some good news for our project is that Redline Track Events has revamped their rules set so our Spec-V is now eligible to run in the less exotic Modified class. Now we have a chance since we no longer have to compete with mega buck efforts like Chris Rado's Scion TC monster. The car was designed to run DOT radials so now we can run in a class where they are required. This will also cut our tire budget. Now that our car has a chance of being competitive we will turn our attention to our turbo system.
|We had started our Project with the intent of using a fast spooling Garrett GT28RS Disco Potato turbo. It became quickly apparent that we would need much more than the DP's 350 hp capability to be competitive in Time Attack so we changed courses in mid stream and decided to run a bigger turbo, a GT30R. The compressor on our GT30R dwarfs the GT28RS.|
|The Turbine discharge is a lot larger for a lot more flow as well. Note the divorced flow path for the internal wastegate.|
Since the long stroke QR25DE does not like high rpm, we have chosen to limit its maximum revs to 7000 rpm and make power by adding turbo boost. Jim Wolf Technology designed our turbo system to produce power over the widest possible range of RPM rather than peak power. The JWT system was also designed for simplicity, lightness and reliability over maximum power.
|It was apparent that our newly built JWT experimental turbo system was going to be massively outgunned on the track even though it would have been wonderful on the street!|
|Goodbye small GT28RS, hello GT30R!|
We had started with a smaller turbo, an uber fast spooling Garrett GT28RS otherwise known as the Disco Potato. This turbo can produce a maximum of 350 hp or so. We quickly realized that this was probably too little horsepower for us to have any hope of being competitive. This lead us to scrap much of our original system and upsize to a Garrett GT30R.
|Burns Stainless supplied us with thin wall 90 degree and straight 321 stainless tubing. With a 3” radius the burns 90 is extremely tight. With exotic 321’s superior properties, you can get away with real thin tubing for less weight. 321 is expensive, more difficult to fabricate and harder to weld but it is a superior material.|
|We also used these stainless steel doughnuts from The Chassis Shop. Doughnuts are made by welding two stampings together to create a tighter longer radius bend than can be made by a mandrel bend. These things can help you package many sorts of things in tight places.|
We could have gone more exotic and designed an equal length tuned header with external wastegates but we jointly decided with JWT that we could easily make more than 500 whp with a very simple system using a log manifold and internal wastegate. In racecars simple is better. A log manifold packages much better, is less likely to crack, can spool faster and is lighter. An internal wastegate makes the exhaust plumbing simpler and more reliable. We also felt that it would be hard to get more than 500 whp to the ground in a FWD car with the technology we could afford. It would also be difficult to get the drivetrain to be reliable with more power than this as well without exotic and expensive technology.
|Mike Smith, Jim Wolf Technologies master fabricator starts by test fitting our new turbo to our old manifold.|
|Once he has an idea of where the new turbo can fit, he gets a rough idea of where the larger T3 size flange has to fit.|