The moment of reckoning has finally come for Magnum TPI, our 1988 Firebird Formula. We've spent the last two and a half years planning and building our 396-cid tuned-port motor to prove a point: it is possible to run 11s with a fully-optioned smog-legal third-gen at full weight, using pump gas without a power-adder. We made some unpopular compromises in the process. These compromises run the gamut from using shorty headers with a full exhaust and retaining our stock 3.27 gears, to keeping our catalytic converters and a full complement of accessories. We also elected to maintain the stump-pulling torque of a TPI set-up by using an ACCEL SuperRam--thereby insuring loads of fun on the street in normal driving, but also limiting top-end power and drag strip performance.
In all, we figure we left 40 to 50 horsepower on the table, but that's the nature of compromise. We've had fire-breathing street/strip cars before, and none of them has had the comfort, reliability and driveability of Magnum TPI. In fact, Magnum is as comfortable idling in rush-hour traffic with the a/c on as it is stretching its legs on the freeway on a long trip.
The "Crack Pipe"
When we last left you, we fabricated a 4-inch custom air inlet out of mandrel-bent pipe ("Breathe, Puppy, Breathe!" March 2003). We have subsequently dubbed this device the "crack pipe" due to the comprehensive drubbing we recently received at the hands of our favorite critics at the www.thirdgen.org message board. (For the record, we do not condone the smoking of "crack," however we do have a sense of humor and know a good gag when we see one. At any rate, we do not smoke crack at GMHTP, as some have intimated.)
The crack pipe was designed to open up the flow of air into the SuperRam intake. Although not as unrestricted as an open throttle body, we did discover in dyno testing that the larger inlet was worth approximately 14 horsepower over our previous set-up (323 hp) which incorporated part of the stock inlet elbow, a non-functioning stock MAF meter and a 3-inch diameter PCV pipe from Home Depot. Given the amount of work we put into building the crack pipe, we were somewhat underwhelmed with the dyno results, which netted 337 rearwheel horsepower on the Dynojet. We figured we would come closer to the full 354 horsepower generated by the open throttle body dyno test (another 17 hp), but as we were to discover, dyno horsepower doesn't always equal drag strip performance!
The Drag Strip
We scheduled a track test day at Englishtown Raceway Park at the end of the season knowing that it was going to be a tight fit into the 11s. On paper, we had 337 rearwheel horsepower, 3,625 pounds of mass, and a 3.27 gear ratio. On the other hand, we had our Centerline Telstars, Mickey Thompson skinnies and ET Streets, and over 445 lb.-ft. of torque coming on at just 2,900 rpm. Another one of the secret weapons we planned on using was the datalogging feature of our Gen 7 DFI. This turned out to be a real eye-opener and at the end of the day we can point to the DFI's datalogging feature as being the piece of the puzzle which made our "11" happen.
We also came armed with the chassis dyno information from our previous two sessions. During these, we found the most power came with the open throttle body. We wouldn't dare race with an open throttle body, so we brought along a K&N RC-5000 filter. A favorite of street rodders, this piece fits right on the standard GM twin throttle body flange and could be swapped for the crack pipe at a moment's notice. If push came to shove, we figured we could pop this filter on to get back another approximately 17 hp--just enough to get our 11 if we found ourselves short by a tenth or so.
At the track, we got off to a great start, running a 12.006 at 112.54. Due to a problem with the timers, no 60-ft. was recorded, but Magnum felt very strong off the line. Based on this, Rick Jensen and I felt confident the next run would result in an 11.90. We had the laptop running the DFI datalogging program and initially had difficulty figuring out how to configure the recording parameters. Unable to get it working this first run, we gave it another shot for run two, hoping to get some useable data.
The second run with the crack pipe in place netted us a 12.173 at 112.08. Incipient wheelspin produced a 1.728 60-ft. time, well off our previous best of 1.67 which came this past summer during a 12.30/109 run. A check of the tire pressure afterward revealed it had gone back up to 15 psi, probably a result of being heated in the burnbox two runs. For the third run, we adjusted the pressure back down to 12 psi and were rewarded with a 12.001/112.13 with a 1.645 50-ft. time.
You can't get any closer to the 11s than a 12.001. It was like torture. We were running good trap speed and had a great 60-ft. time, but the ET just wasn't cooperating. Fortunately, the DFI was cooperating, and with Jensen putting in overtime figuring out the "autolog" function, we had some data to go on. The first thing we noticed is that our $900 wide-band O2 sensor was not working at all. It had been turned off during the Second Street Speed dyno tuning sessions because Second Street prefers to use its own wide-band sensor for the sake of consistency. When we toggled the wide-band "on," to run in closed loop operation, it did not begin working either. We suspect the sensor was damaged due to vibration (we have a header pipe rattling on the frame somewhere) but we've not yet had the opportunity to pull it off and inspect it.
This was not good. We were not getting the full advantage of wide-band closed-loop operation and it looked like we weren't going to get it any time soon. Since we did have a good open-loop tune in place from Second Street, we opted to not make any changes in the short time remaining. Instead, we decided to concentrate on simple issues, like our inlet pipe.
For the fourth run, we decided to pull off the crack pipe and install our K&N TPI filter. Other than some slight interference from the thermostat neck (they are somewhat funky on the TPI motors), it fit fine. Making no other changes, we brought Magnum TPI to the line and ran a 12.071/111.93 with a 1.636 60-ft. time. This run had the best launch of the day, but the ET and trap speed were mysteriously off. Why?
The DFI datalogging held the key to this question, but we didn't actually figure it out until we made one more run with the open K&N filter in place. This fifth run resulted in a 12.122/111.20 and a 1.678 60-ft. time. One of the parameters we configured into the DFI autolog was inlet air temperature, which is taken off the air temp sensor installed in the SuperRam intake. With the "crack pipe" in place, this hovered around 60 degrees during the entire run. With the open K&N filter in place, air inlet temperature soared to around 100 degrees, or about 40 degrees more.
This is where chassis dyno power and real drag strip numbers part ways. We had dyno tested the open throttle body with the hood up and fresh cold air being fed to the motor. We theorize that at the track with the hood closed, the advantage of less restriction was countered by the 40 degree increase in air temperature, negating the extra 17 horsepower we thought we'd pick up. Bad news. The K&N throttle body air filter so favored by street rodders wasn't going to give us back anything.
Time was running short. Not wanting to hot-lap the car, we let it cool with ice (our normal routine) for another 40 minutes. In the meantime, we put the crack pipe back on Magnum and looked through the data searching for more clues.
One more thing we discovered was that Magnum was going through the speed traps at only 5,200 rpm. We knew from our dyno testing that peak power was at 5,600 rpm. If we could go through the speed traps at 5,600 or maybe a tad higher, we might be able to eke out another tenth or two, but that would have to be a story for a different day. A switch to 3.70 gears--the next gear size higher in an Australian nine-bolt--will put us through the lights with 13 percent more rpm, somewhere over 5,800 rpm. That might indeed be too high, not to say anything about the added wheelspin in a 3.06-geared (first) trans. Sad to say, but we might be required to change rears altogether in order to get the right gear ratio. We think something in the 3.50 range would be ideal. Be that as it may, we still needed to pull down the big number using our existing 3.27 rear, and we only had one more run before packing it in for the year.
Maybe it was our depleted fuel supply or the slight tailwind (E-town always has a headwind), but on the last run Magnum TPI pulled off an 11.996 at 111.95. The 60-ft. time of 1.643 was our second best recorded launch of the day, which probably also helped. Whatever the case, we finally did it. This by no means ends our drag testing on Magnum TPI. We're not kidding ourselves for a minute that this one run constitutes Magnum TPI being an 11-second car, but at least now we know it can be done. With better gearing, functional wide-band closed-loop DFI operation and some tweaking, we think we're there.
Our next major plan over the winter is to improve the brakes on Magnum, particularly in the rear. Perilously close to failing the state inspection brake test, Magnum has also proven unable to hold more than a token amount of stall speed on the starting line. Plus, we're just tired of having no brakes when we stomp on the pedal (we've already tagged another car from the rear in a traffic jam because of having no brakes). Look for an install and test on a set of Baer Claw brakes next, then when spring comes, we'll head back out to the drags and finish where we left off.
After cooling the intake with ice for 40 minutes, Hunkins took Magnum TPI to the line one final time. It felt really strong in the burnout box, and off the line it hooked like velcro with a 1.643 60-ft. time. | 
The timers don't lie: the run was true and lit the scoreboard with an 11.996/111.95, our best run of the day. Our next big move will be to get the DFI's wide-band closed-loop operation up and running. We'll also upgrade the brakes (our most immediate concern in terms of safety) and look into a change in gear ratio to get the big boat through the traps closer to peak power. | |