Dear gearheads and fellow diesel freaks,
It’s mid-May 2008, and we are now at a power level with the Banks Sidewinder S-10 that is reminding me of all the nitromethane-burning engines I raced back in the day. We are using up pistons like a good thing. We’re not changing them every run like I did with my nitro-burning rails and drag boats, but we’re changing them too damn often for a diesel. We’ve been doing it for a while, and it’s only gotten more problematic as we’ve made more power and gotten down into the 7.70s. Now we are too close to “running on kill” for my liking.
The culprit is injector on-time as measured in crank angle degrees. As we have gained engine speed (now 5,800 rpm at times) and increased fuel rate, our piston position at injector closing has gone down the hole. The truck weighs 2,930 pounds, we’re in the low 7.70s, and we’re making good power (1,280 bhp). Of course there’s more power to come, but first we need to address getting more fuel in and using less crank angle to do it.
Right now, at 1,280 bhp, the thermal energy from the injected fuel is gradually drilling 7 holes in each piston right at the top edge of the firing cup. We have not killed an engine, but this is not good for long-term piston life. We have gotten to this level using a single Bosch 3.3 pump that we have modified for proper fuel control at the flow and pump speed (same as engine speed) that we are demanding. Honestly, with this engine combination, 1,200 bhp is probably the safe limit. Beyond that, we begin to have demanded rail pressure problems.
It works like this: You demand torque with the throttle. The EDC-16 controller commands the rail pressure and injector on-time necessary to produce the desired torque at that rpm. If the pump can’t supply the necessary rail pressure, the software extends the injector on-time to allow the required fuel amount to be delivered to the cylinder. That is just what occurs when we go beyond a nominal 1,200 bhp while turning in the 5,500 rpm range. The extended injector on-time leads to piston crown erosion, and then we need to change the pistons.
That occurred while we were testing last week at Speedworld Dragstrip over in Arizona in preparation for the Alabama meet this weekend. We are now freshening that motor but will not be able to finish it in time to make the tow and be there Saturday…and that bums me out, Big Time.
When the motor goes back in the truck, we are going to back it down so it can make a reasonable number of laps between rebuilds. Based on our records, that should be a 7.80s setup and capable of doing that lap after lap. Then we will begin our next engine build using a new combination of pieces.
Our new engine combination involves a lot of revisions to piston design, rings, fuel supply, injectors, camshaft and high-swirl cylinder heads, all of which are being manufactured now. Also, we’re building a new Spitzer-based “Top Dragster,” and we plan to start working that car with a clutch as opposed to the torque converter setup in the S-10. Mike Spitzer is another “senior citizen” who hasn’t realized it…just like me. And he’s got a thing for Bonneville…just like me. I wonder where this is going? Time will tell; both of us have miles to go before we rest.
So best regards to you all, especially the new friends I’ve made the last few months at Famoso and Beech Bend.
I’ll see you soon,