My truck, a work in progress
Tuesday, January 01, 2002
Part 9: Dyno time (01-01-02)
I'm now zeroing in on the right setup for the street. With Dan Fodge's help, we did a pretty good job of getting the engine tuned, as described in Part 8. Our initial tune was conducted with the cam 2º retarded. After driving that around a bit, I decided that cam timing put the powerband too high up for my gearing and driving taste -- i didn't have as much bottom end torque as i wanted, and the engine would pull like crazy from 80 mph to 100 mph. Surprisingly enough, I don't really want to drive 100 mph all that often, so I advanced the cam 4º from that position (making it run 2º advanced), and drove that around for a bit. We didn't readjust the fuel tables, just took a couple of degrees of ignition advance off the higher cells in the spark table, as the increase in cylinder pressure caused a little pinging. Interestingly enough, the engine still didn't feel right with the cam advanced like this -- it felt like it was fighting itself a bit. So I moved the cam back 2º, so that it was straight up -- no advance/retard -- and this appears to be the winning combination. With the cam installed in this position, I made an appointment to meet Dan at Ralph Gobel's Hot Rod Heaven in Sacramento for some dyno tuning, to see if we could tweak the fuel and spark tables for a bit more power, and to find out what sort of power we were making on paper.
Since I tend to be wordy as hell in these updates, I'll just cut to the chase here: the dyno session was very worthwhile, as we found another 30 hp by increasing the fuel and turning up the boost.
The punch line: 205 hp, 233 ft. lbs. of torque to the rear wheels @ 12 psi
Now, as some of you will note, this isn't a whole lot different than the numbers I pulled back in October.This makes sense, as I'm running the same amount of boost (12 psi) as I was back then. What is different is that this curve is nice and broad, and the engine doesn't ping at all. These numbers were achieved with a 69% duty cycle on the 550 cc/min injectors, running 91 octane gas. The quality of the gas is the real buzz killer here, as I know I could run more boost and timing with better juice. Still, it's important to me that this motor be tuned to run on pump gas -- no race fuel or water/alcohol injection for me. I want to get the most power that I can from fuel that's readily available, without having to resort to additives or other half-measures. Since the max safe duty cycle for the injectors is around 80% - 85%, I still have some room to grow, and I think that a richer mixture and some additional boost will yield another 20 - 40 rwhp. Eventually, I'd like to be able to run 15 psi, which I think will just about max out my injectors.
So that's where things stand now. The engine is running *great* -- I'm seeing 15 mpg in the city, and 17 - 19 mpg on the highway, when I can keep my foot out of it. These are very close to my numbers with the stock CT20 turbo, believe it or not. It starts right up and idles very smoothly. It's a bit loud, as one would expect with a 3" exhaust, but not obnoxiously loud, and it doesn't sound tinny or "ricey" in any way. It sounds like a healthy truck, which is what it is. Oh, and it pulls hard, and is an absolute blast to drive :-)
Now to finish the stereo and get the interior back together. When I get a chance, I'll post copies of my Speed Pro tuning files anmd some screen shots of the fuel and spark tables, as I think people will find them to be of interest. I'll also keep polishing these tables, and edging up the boost. I may not make the 300 rwhp that I had set out to make, but that's just a numerical goal, anyway. The chief purpose of this was to build a rock solid engine that made a bunch of power, and was very fun to drive (while not sacrificing any reliability). It's taken a lot of time to reach this point, but I am pretty happy with the results to this point. Stay tuned as I see if I can take it further.
I'm now zeroing in on the right setup for the street. With Dan Fodge's help, we did a pretty good job of getting the engine tuned, as described in Part 8. Our initial tune was conducted with the cam 2º retarded. After driving that around a bit, I decided that cam timing put the powerband too high up for my gearing and driving taste -- i didn't have as much bottom end torque as i wanted, and the engine would pull like crazy from 80 mph to 100 mph. Surprisingly enough, I don't really want to drive 100 mph all that often, so I advanced the cam 4º from that position (making it run 2º advanced), and drove that around for a bit. We didn't readjust the fuel tables, just took a couple of degrees of ignition advance off the higher cells in the spark table, as the increase in cylinder pressure caused a little pinging. Interestingly enough, the engine still didn't feel right with the cam advanced like this -- it felt like it was fighting itself a bit. So I moved the cam back 2º, so that it was straight up -- no advance/retard -- and this appears to be the winning combination. With the cam installed in this position, I made an appointment to meet Dan at Ralph Gobel's Hot Rod Heaven in Sacramento for some dyno tuning, to see if we could tweak the fuel and spark tables for a bit more power, and to find out what sort of power we were making on paper.
Since I tend to be wordy as hell in these updates, I'll just cut to the chase here: the dyno session was very worthwhile, as we found another 30 hp by increasing the fuel and turning up the boost.
The punch line: 205 hp, 233 ft. lbs. of torque to the rear wheels @ 12 psi
Now, as some of you will note, this isn't a whole lot different than the numbers I pulled back in October.This makes sense, as I'm running the same amount of boost (12 psi) as I was back then. What is different is that this curve is nice and broad, and the engine doesn't ping at all. These numbers were achieved with a 69% duty cycle on the 550 cc/min injectors, running 91 octane gas. The quality of the gas is the real buzz killer here, as I know I could run more boost and timing with better juice. Still, it's important to me that this motor be tuned to run on pump gas -- no race fuel or water/alcohol injection for me. I want to get the most power that I can from fuel that's readily available, without having to resort to additives or other half-measures. Since the max safe duty cycle for the injectors is around 80% - 85%, I still have some room to grow, and I think that a richer mixture and some additional boost will yield another 20 - 40 rwhp. Eventually, I'd like to be able to run 15 psi, which I think will just about max out my injectors.
So that's where things stand now. The engine is running *great* -- I'm seeing 15 mpg in the city, and 17 - 19 mpg on the highway, when I can keep my foot out of it. These are very close to my numbers with the stock CT20 turbo, believe it or not. It starts right up and idles very smoothly. It's a bit loud, as one would expect with a 3" exhaust, but not obnoxiously loud, and it doesn't sound tinny or "ricey" in any way. It sounds like a healthy truck, which is what it is. Oh, and it pulls hard, and is an absolute blast to drive :-)
Now to finish the stereo and get the interior back together. When I get a chance, I'll post copies of my Speed Pro tuning files anmd some screen shots of the fuel and spark tables, as I think people will find them to be of interest. I'll also keep polishing these tables, and edging up the boost. I may not make the 300 rwhp that I had set out to make, but that's just a numerical goal, anyway. The chief purpose of this was to build a rock solid engine that made a bunch of power, and was very fun to drive (while not sacrificing any reliability). It's taken a lot of time to reach this point, but I am pretty happy with the results to this point. Stay tuned as I see if I can take it further.
