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Chevy 454 engine Blue Collar Build - Part 4: Tunnel Ram

How to Make 800 HP with Nitrous and a Tunnel-Ram Blue Collar 454

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Dyno Day
We re-baselined our 454 to come up with the initial numbers in the Power Numbers chart. The Rat did not quite achieve the same power numbers until we added a Wilson 1-inch-tapered pacer under the carburetor. We did not spend much time with this package, as we wanted to get right to the tunnel-ram. It would have been nice to put a nitrous plate under the single four-barrel package, but time constraints stood in the way. We bolted on the tunnel-ram, using a new Fel-Pro intake gasket, and soon we were making noise. As you can see from the graph, the tunnel-ram was worth a significant bump in torque, with as much as a 20-lb-ft improvement below 4,400 rpm, due to the 2x4 manifold's longer intake runners. With that pleasant benefit in our pocket, we switched on the nitrous fuel pump, opened the nitrous bottle, and were poised to squeeze the button and bask in the glory of a quick 800hp hero pull.

That's not what happened.
Instead of a nice, fat boost in power, we gained barely 120 hp, and our wideband air-fuel (A/F) ratio meter reported the engine was dead-rich, with an A/F of 9:1 and the ignition timing retarded 10 degrees back to 26 degrees total. After working through multiple testing sessions that involved squeezing our dyno Rat several more times, we finally arrived at a tune where the engine achieved our 804hp number. NOS' recommendation for all Cheater nitrous plate jetting is to match the fuel-jet size with the nitrous jet using 6-psi fuel pressure and a bottle pressure of 950-1,000 psi. In order to make maximum power with a safe A/F of 12.5:1, we had to substantially reduce the size of the fuel jet. In our testing, we started with both nitrous and fuel jets at 65. We gradually reduced the fuel-jet size, but we did not adjust the fuel pressure nor record that pressure at the time. Later, we duplicated our test and measured 7.0 psi, which is 1.5-2 psi higher than the NOS recommendation. After several tuning runs, we finally arrived at the combination of a 65 nitrous jet with a 40 fuel jet and the timing retarded 8 degrees to 28 degrees total. The Autolite race plugs all looked very good, and there was no evidence of any detonation. We were also using Rockett 110-octane race gasoline on the fuel-enrichment side to be doubly safe, and bottle pressure remained within spec at 950 psi.

We wanted to do some additional tuning runs by substituting E85 as the fuel enrichment for the nitrous, but that was when the Rat decided to lay down, killing the No. 2 main bearing. This likely happened because of the 800 hp, but not specifically because of nitrous. We spoke with a couple of Holley engineers, and they told us they intentionally set the budget Cheater kits on the rich side out of concern that some enthusiasts using the kit may likely have less than 5 psi of fuel pressure. Low-dynamic fuel pressure (with the nitrous engaged) requires a larger jet to supply a safe volume of fuel. We had exactly the opposite situation with an excess of fuel pressure. Our higher fuel pressure and rich A/F ratio built into the system would account for the major difference in the jet size our combination demanded to make the power. The bottom line here is that if you are going to add 200 hp worth of nitrous with an NOS Cheater system, you must accurately set the dynamic fuel pressure at 6 psi, and then evaluate the combination based on your engine's particular requirements and perhaps reduce either the fuel pressure or fuel-jet sizes to create a proper tune.

The main point is that we did make 804 hp from a relatively simple 454 with iron oval-port heads and E85. We have almost as much invested in the induction system as we do in the entire engine, but consider that we have barely $6,000 total invested in this engine. True, we knocked out a main bearing, so it could be that 750 hp would be a safe peak power number that you could run on a regular basis. If we bolted this beast into our Orange Peel '66 Chevelle mule, it's safe to predict that it could push the big orange beast well into the low 10s. Yahoo!

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