Corvette Fever - February 2002

Mission Impossible: Part Two The University of Northwestern Ohio sits in the shadow of a huge grain elevator owned by the Cargil Company, the landmark that led us to our judgment day. The adjacent rail yard bustled with activity as a tug locomotive noisily shuffled about rail cars loaded with corn and wheat, drowning out the cacophony of student voices questioning us about the specifics of the shiny red 355. Our emotions were a paradox, stuck somewhere between the jubilation of anticipated success and the disappointment of missed goals. The students attacked the engine with the precision of a SWAT team, attaching it to Dyno Cell 1. This 12x8-foot cell offered no amenities but was filled with the necessities of testing, resembling what one imagines a secret government facility would look like. With the instrumentation attached, the Demon carburetor float bowls filled, and the ignition switch on, the starter button was engaged. The small-block jumped to life with less than a 120-degree turn of the crankshaft, and idled as if it were well broken in. This was certainly a good start to what would turn out to be a long clay. First Things First Now that the engine was running, there were many things to do. A common practice is to allow the engine to warm, having both coolant and oil reach operating temperature. On a dyno, the water temperature without load is controlled by the setting on the dyno water tank, and since the 355 had no thermostat, the water tower keptthe coolant temperature at 160 degrees F. If you remember, in our previous installment last month, the use of the Evans NPG coolant was part of our program. Once we arrived at the university, the decision was made to use the dyno's cooling system with pure water, since it was not equipped at that time to utilize a closed cooling system. It would have required a radiator of sufficient size, a cooling fan, a stand, and hoses. The Evans product will have to wait until the engine is installed in the chassis for final testing. Disappointed that we would not be able to take advantage of the technology during this tier of development, we soldiered on, hoping for the best. Northwestern upper-classman Bill Young would be operating the dyno and doing all the wrenching on Mission Impossible. He's a very bright, competent, polite, and knowledgeable young man. No camshaft break-in was required since a roller hydraulic design was employed, so we used the warm-up time to set the float levels on the carburetor, idle mixture, and base ignition timing. The Demon carburetor features large, clear sight windows, making the float level a snap, without any concern for fuel leakage on the intake manifold. The idle speed was set for 800 rpm and the base timing to 10 degrees BTDC. These settings would be required before tuning the idle mixture screws. Demon states once the best idle quality is achieved, the mixture screws should be between one and two turns rich out Iron) fully seated. Bill adjusted the mixture, and it was quickly discovered that the best idle was obtained with the mixture screws fully seated, and not in the specified range. This is indicative of an excessively rich idle circuit. A unique feature of the Demon line of carburetors is an idle feed restrictor (IFR), a separate orifice that limits the fuel flow to the idle well. This allows for jetting that will meet the demand of the engine under full load without suffering the consequences of an overly rich idle mixture. Since our best idle was with the mixture screws fully seated, this meant that the I FR dimension would have to be made smaller, not a concern for maximum power testing, but something that would need to be addressed if our fuel economy and emissions goals were to be met. With the coolant and oil temperature up, the oil pressure read a steady 40 psi at idle, perfect for our application. The engine sounded beautiful, did not miss a beat, and had no signs of leakage—a testament to the crew at Pro-Motion Engines LLC. During the first 30 minutes of operation, Bill varied the engine speed and made a number of light-load pulls to 4,000 rpm to aid the break-in and set the rings. Mission Impossible sounded strong and had unreal throttle response for a street engine. The next step was to shut it down and let it cool off, do a leakdown and compression test, and change the oil. This is a good procedure before making an all-out assault on power. Pro-Motion Engines installed Valvoline 10W-30 mineral oil for break-in, but we would now pour in 5W-30 Mobil 1. Bill cut the oil filter apart to look for any debris; none was found. The leakdown test showed all bores at 4 percent, while the compression test revealed 225 psi on all holes, with nearly 130 psi on the first puff of the gauge. This meant that not only was the ACCEL roller hydraulic camshaft building cylinder pressure very early, but the cryogenic processing of the engine components afforded excellent ring seal and extremely quick break-in. The speed limiter on the ACCEL 300+ ignition was adjusted to 6,300 rpm, and the timing advance curve was confirmed. Bill discovered that the engine wanted about 17 degrees of base timing, which all but killed any sound of overlap in the exhaust and actually made the idle too smooth. But with that much initial lead, the full advance curve yielded about 42 degrees BTDC, which was well above what we anticipated as maximium timing for the Vortec cylinder heads and the Swain Tech coated pistons and combustion chambers. A temporary fix was to leave the initial timing at 10 degrees BTDC and connect the vacuum advance to manifold vacuum, which then gave a total of 18 degrees at idle. Since the manifold vacuum signal would drop off as the engine load increased, it should be self-regulating. Bill then set the ACCEL billet distributor for a total advance of 24 degrees BTDC for our first pull. Let The Fun Begin With Bill situated at the dyno console, the outside of the dyno cell was filled with students trying to get a glimpse of what was going on. University of Northwestern Ohio Dean Bill Sergent stopped by and was very interested in the Corvette Fever project engine. Bill Young and Dean Sergent discussed a game plan, and it was decided that the first pull would be to 4,500 rpm, just enough load to gather some meaningful data while trying to determine the tune-up on the engine. With the controls set, the throttle was slammed wide open and the computer took care of the rest. Mission Impossible sounded beautiful as the rpm climbed steadily against the load. The SuperFlow data acquisition recorded BSFC, horsepower, torque, volumetric efficiency, air/fuel ratio, and exhaust-gas temperatures. At 2,500 rpm there was 356 lb-ft of torque available, already beating our goal of a peak of 350 lb-ft. Horsepower at that rpm was 169.46. At 4,000 rpm, torque and horsepower were 396 and 301.59, respectively. The air/fuel ratio was showing between 12.2:1 and 12.4:1 during the entire run, about 7 to 8 percent too rich. More important was the smooth fuel curve of the Demon carburetor and the completely flat torque curve of the engine. The carburetor would need to be leaned out with a jet change; the Speed Demon came equipped with 70 and 78 jets in the primary and secondary sides, respectively. Bill wanted to jet the carburetor down two jet sizes in both the front and back. Interestingly, even with the rich mixture, the BSFC readings were all below .45, showing the fuel efficiency of the engine. With the new jets installed, the power came up and we felt we were ready to make a lull pull. With the console set to 6,200 rpm, the first of what would be many full pulls was made. The dyno cell was eerily quiet as the printer spit out the results: 363 hp and 426 lb-ft of torque with a BSFC of .41. We bested our goal by 13 hp and 76 lb-ft of torque with unbelievable fuel efficiency. Not bad for 92-octane and pickup-truck cylinder heads. But we were not done. These results were obtained with only 24 degrees of total timing, all in by 2,500 rpm, and the mixture still slightly richer than we wanted. The next step was to leave the carburetor jetting alone and advance the total timing to 26 degrees BTDC. Another pull was made and increased the torque below 3,000 rpm by 7 to 10 lb-ft; peak numbers were up only 2 to 3 for power and torque. On a roll, Bill added two more degrees of advance for a total of 28 degrees BTDC. We retained the bottom-end power but lost 6 hp at 5,000 rpm, where peak power occurred. The engine nosed over quite rapidly after 5,000 rpm, indicating that a breathing problem was the cause. The next change was to jet the carburetor down one size in all four comers. We were disappointed. No real power gain was shown and a slight loss may have occurred. The timing was brought back to 26 degrees BTDC, and we decided to stop and think about our next move. Since an engine is an air pump, the greater the throughput, the more power produced. Discussions revolved around the 650 Speed Demon being too small, with some of the students thinking a 750 would be in order. But we felt that the intake manifold was the limiting factor, and the size of the carburetor was perfect. When we started this project, Edelbrock offered only a single-plane Victor Jr. race intake or the standard Performer series. We chose the latter since the single-plane would not have been a good choice. This decision always haunted us, as we believed it would be hard to meet our power goals with this manifold since neither choice was ideal. Luckily, about a week before we were ready to travel to Ohio, Edelbrock contacted us and said that they had just released a Performer RPM Air Gap intake for the Vortec heads. This design had larger runners and a better entry angle to the cylinder head—just what we needed, so we brought it with us, just in case. With the engine hot and the hour getting late, we hit the hotel and decided to swap the intake manifold in the morning. Day Two The enthusiasm of the staff and students at Northwestern is best represented by the fact that when we arrived at the dyno cell at 7:15 a.m., Bill Young and Dean Sergent already had the intake swapped and were just waiting for the silicone gasket cement to dry for a few hours before starting the engine. Over breakfast we discussed the previous day's results and, though exceeding our original goals, we all felt Mission Impossible had some more left in her. She just sounded too good. In total, we made 72 dyno pulls with both intake manifolds. At the end of the day we recorded 398 hp and 456 lb-ft of torque from our little 355. The new intake manifold did the trick. Interestingly, the carburetor jetting remained at 67 and 75, and the timing was lowered to a total advance of 25 degrees. The BSFC numbers came down to .40, and the air/fuel ratio was a perfect 13.0:1. Mission Impossible beat the LS1 by 48 hp and 106 lb-ft of torque! Analysis At this point, all of the technology and engineering we used had paid off. The theory of using the long 6-inch Power Detroit connecting rod with the short camshaft and high compression ratio was right on the money. The cryogenic processing showed its worth when we leaked and compression-tested the engine after all that abuse. The results were exactly the same as during the first test. The Speed Demon carburetor did its job superbly, while the Swain Tech Coatings and ACCEL ignition made these results possible. Pro-Motion Engines needs to be commended for its excellent machining and assembly skills; the 355 did not do anything wrong from the first time it was fired to the 72nd pull. With a minimum of 400 lb-ft of torque available from 3,000 rpm on up, Rich's '81 Corvette should be able to run low 12s or high 11 s at about 112-115 mph. But it still needs to pass smog and obtain a minimum fuel economy of 20 mpg for us to consider it a success. We will swing the engine into the car and let you know the results in the near future.

 

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