Thinking Small—Sizing Turbos For Both Response And Power
Not too long ago, I was at a photo shoot with a hopped-up Dodge, and the owner suggested he do a burnout. Unfortunately, we were up at about 3,000-ft. altitude, rather than at sea level where the truck’s owner resided. Why was this unfortunate? Well, try as he might, the big turbo on his Cummins engine wouldn’t light at that elevation, or even get the tires spinning at all. Sure, the truck rocked under boost, but from a dead stop he could be beat by a Prius. If this story sounds farfetched, it’s actually not. Most people who talk about how well their truck spools have never been up in high altitudes.
On the same excursion, I also drove a turned-up early Ram, which had the itty-bitty stock turbo on it, along with the super-loose factory torque converter. Guess what? It was great at sea level, and it was great up in higher elevations, which got me to thinking that maybe people are over-turboing their diesels. After all, shouldn’t response and drivability count for something?
When I worked at a diesel shop, one of the most common technical questions we would get was regarding turbo sizing. “I want something that spools like stock, but can make more power,” was…
