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The quality of a build-up is relative.
It depends on the goal attempting to be achieved. What I had in mind was
to build a more powerful, dependable 400 for the street. My plans did not
encompass campaigning the TA at the strip...just wanted a 20 year old Pontiac
that would hold its own against the new muscle coming out of the Detroit.
The car also had to maintain its original appearance since my plans also
included entering it in car shows. As a result of people writing and asking
how the car performs, I decided it was necessary to make a few passes down
the strip to satisfy the curious and answer the mail. After all, if my build-up
looked good to them, and the performance was there, they just might try
to build a similar engine--performance and dependabilty are a great combination. My decision was the right one. Yet, I am positive there are other very
good clutch systems that would deliver the power produced by my 400. I was convinced the new clutch solved the transmission problem, but wasn't convinced that my 20 year old posi unit was up to the challenge. Street tires would also be a factor. Considering my best et of 13.90, achieved many years ago before the rebuild using a Crane "Blazer" camshaft, Hooker headers, and running on street tires, it was possible, if everything was right, to better that et with the stronger motor. Unquestionably, the new motor produces more low end torque and the upper end pulls to a higher rpm than it did before. It was the best of times and it was the worst of times...well not really. My fall '98 visit to Budds Creek was only a partial success. The Centerforce was fantastic. Power was now able to get to the rear wheels. With all that torque finally reaching the posi unit--my street tires, and rear suspension proved to be less then capable of dealing with a launch. Coming off the line was like stopping on ice--wild. With 3.23 gears, you shouldn't expect what was I experienced. At 2500 rpm, the wheels whirred producing excessive wheel hop. Wheel hop! That had never occurred before with the TA. Burnouts on the street were always smooth--not any more! First gear came to its rpm limit quickly, then bam into 2nd. Second gear broke the 255/60VRx15 Gatorbacks loose again, but with no wheel hop. Not until midway through 2nd did the car start to hook. Third and 4th gear seemed strong. The oh-hum 60 foot times of 2.4 and 2.7 seconds reflect the car's total lack of traction. The TA's best et was a paltry, but improved,15.08 at 97 mph. (Improved is also relative). The clutch worked fine. Hooking up is now the next big hurdle. For those interested in other relevant details. Ignition was set at 11 degrees initial. The rear tires contained 28 pounds of pressure in each. More to tell...HEI was critically ill Since then, the distributor was rebuilt and sports a very different (not sure if it's improved) performance advance curve. All mechanical advance is in at 1800 rpm (yes, 1800). Vacuum advance has been virtually eliminated with a scant 3 degrees. This curve is a big departure from the stock settings which were: 0 @ 1000 rpm; 8 @ 1400; max 20 @ 4400 (centrifugal advance); 25 degrees vacuum advance, for a total advance of 63 degrees at 4400 rpm. (18 initial + 20 centrifugal + 25 vacuum = 63 degrees). Under stock conditions this meant the distributor was advancing 46 degrees at WOT with a stock initial of 18 degrees. However, the distributor was set at 11 so in effect 39 degrees at WOT; that's assuming the centrifugal was advancing--and it wasn't. The new advance has not been street tested so the jury is still out on how streetable and effective this experimental curve might be. If gas consumption drops and the engine runs hotter, I'll return to the factory specs or get closer to them. The 1800 quick-in was created by using the stock weights (1103315 HEI distributor) with one stock spring and one lighter one. One more thing...the sluggish advance existed at the strip so optimum power was never realized! Will the TA ever run as quickly as it did before? I'm sure it will. Solving the traction problem and getting the timing right should make a big difference. Now if I can only get to make a few dry runs at the drag strip. Traction Woes...Update--July 11, 1999--Mason Dixon Dragway, Maryland
After months of waiting I made three (3) passes with the new advance curve. My not so great P255/60VR15 Gatorbacks, were inflated to 36 pounds to get a full pattern of rubber on the ground under launch conditions. The track and the prestaging area did not provide sufficient room so that cars equipped with street radials could bypass the water box. There was no getting around it...so I drove through and did 2-3 quick burns to eliminate as much water as could be from the rear tires. My launch approach, remember this is a stick, was to come out of the hole at 2500 rpm. On my first run, my 60' time was an atrocious 2.715 seconds; the second, made at 2000 rpm, was a blistering 2.688 seconds, and the third, made at 1800 rpm, was 2.557 seconds. Perhaps, with a few more runs, I would have discovered the best technique. However, it wasn't going to happen that day. Back into the 14s--finally! August 29, 1999, 75-80 Dragway, Maryland It was time to try something new. Borrowing a friend's G-60 McCreary's mounted on PMD Rally wheels, the TA finally broke into the 14s--high 14s. It took three (3) tries. With 20 pounds of pressure in the tires it was immediately evident that these sticky tires would provide better traction. The question became, how do you launch the car? Backing into the water box and pulling forward a few feet, I smoked the tires as well as I could with my manual transmissioned car. On the first pass, I launched at 1500 rpms, and immediately felt the tires grip the pavement. That was a new experience. There was a slight bog and the car took off. After the run, my slip reflected an improvement in my 60 foot times by .30 seconds from the Gatorbacks. On the second run, I was sleeping at the light while trying to pick a good rpm to come out of the hole. My 60 foot time was a little slower but still almost .30 faster than before. After these two runs I began to think I had not improved upon my rebuild over stock. The first run was 15.1742 @ 93.6259 mph and the second,15.2075 @ 93.2084 mph. Hmmph, I thought. Reaching midday, the track surface was now hot, as was the ambient temperature--close to 90 I think. Looking at yet another disapppointing day, I decided to launch at a higher rpm. On my third and final run, I brought the rpm up between 2500-3000 (not sure). When the last yellow appeared, I let it rip. My.5123 RT was my best of the day as was the much improved 2.2171 60 foot time. This start netted a 14.8467 1/4 mile ET @ 93.2776 mph. My speed was down 3-4 mph and I attibute that to the strip's uphill grade and head wind. The bottom line is that tires make a BIG difference along with driving technique. The two must work in concert. Things are looking better folks. ". . . and I catch rubber in all 4 gears." September 18, 1999. Maryland International Raceway, Budds Creek, Maryland With Hurricane Floyd gone, the skies were blue and the temperature was in the low 70s'. Running the same McCreary tires on the rear at 18 pounds, the TA responded with a first run (10:06 am) of 14.484 @ 95.50 mph, a .4 improvement from the previous best run on August 29th. The 60 foot times also dropped to 2.145 seconds. Subsequent runs were quite experimental. My goal was to improve on the first run of the day by concentrating on the best rpm to launch the car. The second run (10:12 am) yielded an ET of14.666 @ 95.60 mph. The 60 foot was 2.179 seconds. The tires spun, followed by a slight bog--rpm was lower than the first run. The third run (10:55 am) turned out to be the worst of the day...my fault, as they say. The TA leaped and bogged producing a 2.251 60 foot and zipping through the traps at 14.708 @ 95.94 mph. The fourth run (11:00 am) was a little quicker. A 60 foot time of 2.145 seconds and an ET of 14.671 @ 95.40 mph. On the fifth run (12:07pm), I cut my quickest light (.518 RT), and had a 60 foot of 2.245 seconds and an ET of 14.501 @ 96.78 mph. My sixth and final run (12:46 pm) was the best of the day. The TA launched smoothly coming out of the hole at 3000 rpm. No noticable bog. The 60 foot was 2.103 seconds and the ET was 14.443 @ 96.49 mph. Here's what it looks like in a table.
Certainly weather and track conditions made a difference. Yet, driving technique is playing a significant role in getting the car to perform. As you can see in the table, trap speed was quite consistent and similar to the speed profile at 75-80 Dragway from the 29th of August. Most importantly, a technique for launching the car (at least with the McCreary tires) seems to be taking shape. Given the fact that the engine has not been performance tuned, I believe more power will be produced. Thinking and crunching some numbers When my car was stowed away for the winter, there wasn't much to do other than read about cars, surf automotive websites, make some additions to the site, and crunch some numbers for fun. Not having a dyno handy to test the power and really know the numbers about my engine, I resorted to using "car" math to give me some theoretical answers. First of all, I needed to know the weight of my TA with me at the wheel. I settled on a figure of 3,824 pounds. I also selected 5400 rpm as the max rpm limit of the engine. The formula to determine an engine's horsepower based upon weight and mph at the 1/4 mile strip is: HP=(mph/234)3 [cubed) x weight Using 96.78 mph as my fastest mph to date with this engine configuration, the numbers were:
Huh? Just 270 net horsepower! How could that be? That's just 50 net horses above PMD's stock rating. Well, what about elasped time? OK, there's math that will give a good estimate. Get the calculator going again and apply the recognized formula which is: ET=(cubed root) of weight divided by horsepower x 5.825 Using 270 net horsepower and 3,824 pounds of car the numbers were:
A 14.093 ET! Well that's close to 14.0 and that's not far from 13.99 seconds. With this information, gearing, traction, and hitting the right shift points might be the answer to lowering the car's elaspsed time. The TA is equipped with a Super T-10 transmission with the following gears: 2.43/1.61/1.23/1.0 The rear gear is a streetable 3.23 to 1 ratio. Pinpointing the best shift points is a tedious "hit and miss" proposition when an engine has not been tested on a dyno. Shifting at the wrong rpm may result in less acceleration because the engine rpm may fall on the down side of the torque curve. Knowing the different rpm drop between gears is critical to hitting the optimum torque mark. Moreover, shifting at the same rpm in each gear may not be optimum. For example, shifting at 5000 rpm to second drops the rpm to 3300 rpm. Shifting from 2nd to third at 5000 rpm drops the rpm to 3800 rpm. Winding third to 5000 and shifting to 4th causes a drop in rpm to 4050. The table below shows these theoretical shifts made at 5000 rpm in my TA.
If the torque curve is broad and relatively flat like I believe it is between 3300 and 4300 rpm, shifts should fall into that power curve. Here's an example of a shift point at 4600 rpm to 4th gear capitalizing on the mid point of the 3300-4300 torque curve.
Again, all this math stuff is theoretical. It may have some relationship to reality, however, nothing can be proven without trying mathematical theory at the strip. Finding the best shift points for each gear may take some times. Once it's located, driving consistency becomes very critical. |
Comments or ideas--email me: bboyle@boyleworks.com This site created, maintained,
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