Written by Bill Heath Thursday, 17 December 2009 11:46
September 2008, Bill Heath raced the Heath Diesel Team’s 6.5L GM Diesel pickup at Bonneville. maxxTORQUE featured the vehicle in our Summer 2008 issue before the event. Now, here is a look at the Bonneville performance and what’s inside that makes this truck – that could pass for a daily driver – fast...
Heath Diesel Power’s 6.5L GM Turbodiesel Land Speed Racing truck ran a solid 153 MPH on its first trip to the Bonneville Salt Flats – that felt pretty darn good. Knowing that she has more speed in her yet – that’s even better. Here’s a look at our experience at Bonneville and the details of the build that got us there...
When we first schemed to build the 6.5 land speed racing truck, we saw it as an opportunity for the Heath Diesel gang to have some fun and to give each member a chance to exercise, and maybe expand, his automotive skills. Someone suggested that if we could manage to go fast enough, it would be a great way to champion the 6.5 diesel engine for customers and fans around the world. From that moment on, our project took on a new and vastly more important meaning. We were now more focused and determined to do our best for 6.5ers everywhere – and maybe even give them some bragging rights.
Early on, we decided that our racer should be a full-sized truck with a near-stock 6.5 engine. Of course we realized that we could run faster if we used the smaller S-10 truck; however, GM never offered the 6.5 in the S-10, so such a vehicle would not accurately represent the trucks our customers drive. While modifications would be necessary to get the needed power, we endeavored to keep these modifications to a minimum and, in every way possible, retain original equipment components.
Heath Diesel 6.5L Land Speed Racing Truck at Bonneville
To our knowledge, no one before us has entered a 6.5 at Bonneville and, while we were excited about giving it a go, we were a little concerned about being able to reach a decent speed. Understandably, when working with an untested combination, there is no way to know for sure how it will perform until you give it a try – but we sure did not want to embarrass ourselves. Our calculations suggested we ought to hit 138 MPH; we would certainly have been happy with that. However, we could not know for sure if the truck would even reach 120 MPH. Those with experience on the salt will tell you: do all the calculations you want, but you will never really know until you turn it loose across the flats. You learn, make changes and try again. But then, isn’t that the fun of it?
With no obstacles on it to bump into, the gleaming white and seemingly endless expanse of the Bonneville Salt Flats is a super neat place to go fast, there is just no doubt about it. However, one cannot ignore its 4400-foot elevation and 95-to-105°F race-day temperatures. These two conditions combine to drive the density altitude up toward 11,000 feet on some days, plenty high enough to hinder the production of power. Not knowing for sure what to expect from our combo – and most especially how it might react to the high density altitude – all we could do is take our best shot and see what would happen.
On the Highway
The racer is a very civilized vehicle. It starts and runs just like any other 6.5. It rides well and is quiet and smooth on the road. With its tilt-power steering, power windows, cruise control, stereo and cup holders, it’s a fine cruiser.
We have taken it on some longer journeys to settle the engine before going to the Salt Flats and found our racer to be a very good highway traveler. At 70 MPH, the truck runs in third gear at around 2,200 RPM where it usually gets better than 30 MPG.
As for acceleration performance, the truck moves away from a stop quite well in normal driving even though it is still a naturally aspirated engine under this low-RPM, low-load condition. The turbos do not really begin to contribute much before 2,000 RPM. You can run around town without any exhaust smoke and more than keep up with traffic, no problem. When you get into the throttle a little further, however, and with the tachometer swinging through 2,500 RPM on its way up the scale, the engine starts to make very good power. By about 3,000 RPM, it is coming alive and pulls strongly from there to our 4,600 RPM limit.
From a stop, if the go pedal is suddenly pushed to the floor, the 5200-pound truck moves out fairly briskly. Then, while still in first gear and as the engine gets up into its happy zone (3,000-plus RPM), the power comes on well enough to squall the tires. However, because the transmission gear-ratio spread is wide, the first-to-second gear change results in a shift recovery RPM that is below this happy zone; so there is a lull in the rate of acceleration until the engine can recover into that 3,000-plus RPM zone once again. The second-to-third shift is a better one as the gear spacing is a bit closer, so the shift recovery RPM is higher and the engine is not pulled quite so far below its power zone. The difference in ratios between third and fourth gears is even less, so the shift recovery RPM on this shift is much better and the engine can continue a good strong pull as it moves into fourth gear. Keeping in mind that the Land Speed Racing Truck was never intended to be a drag racer, the net result is this: the truck’s acceleration is only OK up to about 50 MPH. Because each successive gear change results in more favorable shift recovery RPM, it pulls harder and harder as speed builds. By 80 MPH, it is accelerating quite well. It tops out at 90 MPH in second and reaches 133 MPH in third at which point the third-to-fourth gear shift occurs. On this final upshift, the shift recovery is 3300 RPM which is close to the bottom of the power range and still good enough to pull on out and continue to accelerate well on up to top speed. As you might well imagine, our full-sized truck is up against a pretty tough aerodynamic load at 133 MPH so having a good shift recovery RPM going into fourth is critical to be able to continue the acceleration on up to top speed.
On the Salt
The Bonneville experience is totally unique. I know of nothing which can compare. Everything about being here is so rewarding; however, the real excitement happens when the starting line official has given his signal that the course is yours. That is when all the efforts pay off and when we get to see...
In this article...
- Our First Mistake
- Building the Vehicle
- Cylinder Heads
- Water-Mist Injection
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