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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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Last month, we left our brave iron big-block Chevy 454 snortin' to the tune of 589 hp using little more than a tuned-up set of factory iron oval-port heads, 12.5:1 compression, a mild flat-tappet mechanical cam, a single-plane intake, and a 950-cfm E85 carburetor. Until now, this has been a real budget effort; remember, this Chevy 454 motor spins a stock cast crank, stock rods, and a stock oil pan. Of course, all it takes is one bench-racing session to spice things up a bit. That's when Editor Glad declared our Blue Collar Chevy 454 needed a tunnel-ram and nitrous. The call went out across the land until we found a cast-aluminum Weiand tunnel-ram and matched it with a set of Holley carburetors. Holley has promised an E85 carburetor that should hit your favorite speed emporium sometime soon, but once again, we were too far out in front of demand, so we were directed to Patrick James at Pro Systems, who was happy to oblige us with the 950-cfm carburetor we used last month in the single four-barrel attempt, plus two more 750-cfm fuel mixers for our nitrous attempt. While this represents a significant investment, we helped the budget by adding a twin-plate NOS Cheater system using only two solenoids for the whole system. This limits total power to a max of 250 hp, but that was more than we needed. Our goal was to make 800 hp. It seemed simple enough, and we're happy to report that we did achieve our goal. We also learned that this is might be the upper limit for a two-bolt main 454 with a stock cast crank, as it didn't survive the test unscathed. Our Blue Collar Chevy 454 is not dead, but he is certainly going to have to go on injured reserve for the near future. But look for Blue Collar to return, maybe with some better parts.

The Tunnel Ram
Rat motors just look nasty with a tunnel ram sitting up top. The already massive engine bulks up, and those two big carbs make it all come together. But we're not in this just for the fashion show. It takes some serious horsepower to make those twin carbs become meaningful. Because a sheetmetal tunnel ram intake was just plain out of the question and perhaps more than a little misplaced on iron oval-port heads, we looked into affordable castings. Weiand had just what we were looking for-an oval-port tunnel ram for just a smidge over $350-and with a call to Summit, we were in business. Pro Systems was already on board with the E85 carburetors, offering a pair of 750 fuel mixers fully tuned for that ethanol-based fuel. This is the point at which the budget took a significant hit, as this pair was every bit of $1,390. If you like the idea but just can't swing that much coin for a pair of carbs, there are several companies, including Pro Systems, that can convert your existing carbs or sell you the pieces to do it yourself. The conversion is relatively easy, especially if the carburetor has replaceable air bleeds. With the carbs in hand, we next decided on the basic, twin-plate Cheater nitrous system. We went this route rather than going with a dedicated fogger system mainly to keep the cost down. The 2x4 NOS Cheater system was only $600 (minus the bottle). It was at this point that we realized we would also need a 2x4 sideways linkage kit (thanks, Holley) and a fuel-line kit to connect all four inlets together. After much searching, we decided to let a pro build a fuel-line kit for us. We called Derek Stankowich at DMP Fasteners in Chatsworth, California, who built a fuel-line kit using stainless-steel lines and Earl's fittings that we supplied. The system ties both carburetors into a common inlet, which makes connecting it to a fuel-pressure regulator very easy. With the tunnel-ram system assembled and ready to go, we were one step shy of dyno-ready.

During our planning session, we realized that while we were running the engine on E85, the factory NOS nitrous tuning charts are based on using gasoline. Rather than getting bogged down with finding or creating an E85 tuning chart, we decided to go the safe route and use race gas for our 200hp nitrous adventure. While safe, this demanded building a separate fuel-delivery system for the nitrous. We assembled a somewhat clumsy-looking system from parts we had on hand, including a monster Holley electric fuel pump, -8 Earl's lines and fittings, a return-style regulator, and a Zex nitrous fuel-pressure test kit.

Because the pump was oversized for the task, we had to bypass a large volume of fuel to the tank to set the fuel pressure using a -8 fuel line. The best method is to set nitrous fuel pressure while flowing fuel through the same-size jet as the one used in the fuel side of the system. The Zex tool places a pressure gauge in a T fitting but was designed for a single jet. Since our system used two 0.065-inch-diameter jets, we needed to compensate for the second jet. We employed a little high school math by increasing the area of the single jet to equal the area of two smaller jets. Flow is related to a combination of pressure and area. With pressure constant, we calculated the area of a single 0.065 jet (0.003318 square inches), then doubled it because we have two jets in the system, for a total flow area of 0.006636 square inches. We then determined that a 0.092-inch diameter is very close, at 0.006647 square inches. Our closest drill diameter (332 inch) was 0.09375 inch, so we drilled a spare jet to that diameter and set the dynamic fuel pressure at 6 psi. Now we were ready for the dyno. Later, we discovered our fuel pump was very sensitive to battery voltage and that our fuel pressure may have changed during dyno testing.

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