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Turbo Drag Car - Ask Anything

Street Rat
John Lubinsky; via CarCraft.com: I have a '69 Chevelle SS with a 454-inch Chevy big-block that has been bored 0.030 inch over. It has a stock crank that has been turned 0.010/0.010 on the journals and reconditioned stock rods with ARP bolts. The pistons are TRW L2465 forged domed. All this has been balanced for smooth operation. The cast-iron heads were ported and gasket-matched. The block has been decked and the heads have been shaved to 115 cc to achieve a compression ratio of 10.25:1. The camshaft is a hydraulic flat-tappet Lunati special-purpose grind with 225/235 degrees of duration at 0.050-inch tappet lift using stock rocker arms. The intake is a Weiand Stealth with a Barry Grant 750-cfm Speed Demon carburetor. Hooker Super Comp headers reduced to 2.50-inch exhaust flowing through Flowmaster 40-series mufflers and 2.25-inch tailpipes. The engine has about 15,000 miles on it. This combination has a lot of power, and I am assuming it produces more than 400 hp. But you know how it is—I want more power. This car is a weekend warrior and I usually feed it 110-octane race gas.

I now have the funds for aluminum heads and a complete roller cam and valvetrain. I was considering the Edelbrock RPM Performer aluminum heads (PN 60459) and a Comp Cams roller camshaft. My questions are: 1) Will I have any problems with the Edelbrock heads and the pistons I currently have in the engine? 2) Would you recommend different heads than the ones I have chosen? 3) What camshaft would you recommend? 4) Would a hydraulic roller be better than a solid roller? and 5) What kind of distributor gear should I get for my Accel distributor? I would like to break the 500hp mark with a naturally aspirated engine. This is not a daily driver and fuel economy is not a concern. I have subscribed to your magazine for more than 10 years and enjoy reading all of the tech tips and articles you have about making more horsepower. Any help you can provide me will be greatly appreciated.

Jeff Smith: John, I think your Rat plan has plenty of potential, but, as usual, I have some suggestions on how to over-deliver on your 500 hp goal. I think the pistons that are currently in your engine will work just fine. The Edelbrock aluminum heads are a good choice. But rather than the 315cc rectangular-port versions you mentioned, I'd suggest going with the "roval" port Edelbrock version (PN 60479). These heads use roughly a 10 percent smaller intake port volume (290 cc versus 315 cc). The smaller port will deliver a greater mixture velocity and therefore better throttle response. We've tested five oval-port heads, including a set of factory peanut-port heads ("Big-Block Cylinder Head Test," Mar. '08, pg. 30), using a 496ci stroker big-block Chevy. The heads we tested included Brodix, Dart, Edelbrock, and Trick Flow Specialties. AFR now has an oval-port head, but they were not available at the time of our test. Our engine used a Comp hydraulic roller XE276HR with 224/230 degrees of duration at 0.050-inch tappet lift with 0.510-inch lift on both the intake and exhaust. The Brodix heads made the most power with 597 hp at 5,700 rpm and a scorching 626 lb-ft of torque at 4,000 rpm using an Edelbrock RPM Air-Gap dual-plane intake. The engine made this power with 2 1/4-inch open headers along with very cool water temperature and hot oil, so the numbers are a little better than what you would see in your Chevelle. The Edelbrock heads made a little less power than the Brodix castings (582 hp and 618 lb-ft of torque) but are also the least expensive. For the price, they make an excellent purchase. Since your engine is 36 ci smaller, it makes sense to go with a smaller intake port.

To give us an idea how much power your engine could make, let's whip out the calculator. Our 496ci test engine with the Edelbrock heads made 618 lb-ft of torque (1.24 tq/ci) and 582 hp (1.17 hp/ci). The average torque was 582 lb-ft (1.17 average tq/ci) while average horsepower came out to 515 (1.12 avg. hp/ci). Using the peak hp/ci figure of 1.17 and multiplying it by 460ci (454 with 0.030-inch overbore) equals 538 peak hp with a peak torque estimate of 570 lb-ft.

As for a camshaft, I'd suggest using a hydraulic roller. I found a Lunati hydraulic roller cam (PN 60212) that uses 231/239 degrees at 0.050- and 0.600-inch valve lift specs for both the intake and exhaust, with a 110-degree lobe- separation angle (LSA). This has slightly more duration and 0.100 inch more valve lift on the intake (0.090 inch on the exhaust) compared with the flat- tappet version that would surely bump the power. I would also recommend investing in a set of roller rockers. When you get into the 0.600-inch valve-lift range, the slot on the bottom of the stock rockers will probably hit the rocker stud, causing all kinds of damage. Plus, you will have the advantage of a far more accurate rocker ratio than that with stock rockers. As for the distributor gear, most cam companies now design their hydraulic roller camshafts to use a stock-type iron gear, making a bronze gear unnecessary.

I've received several letters from readers who assume that a solid roller street camshaft will deliver superior power over hydraulic roller lifters. We're about to do a dyno test of some new short-travel lifters that appear to be the hot ticket for street engines. We expect these new lifters will deliver virtually the same power curve as a mechanical roller camshaft without the problems associated with the solid roller cams. Aggressive street big-block Chevys seem to be plagued with solid roller lifter failure problems. It appears these problems are related to excessive valvespring pressure combined with long periods of idling that hurts lubrication. Generally, hydraulic roller lifter cams require lower spring pressures and do not seem to suffer the same kind of durability problems. If these new short-travel hydraulic roller lifters can deliver a similar power curve right up to peak horsepower, why would you bother with mechanical rollers? It's worth considering.

You also mentioned using 2 1/4-inch tailpipes. You might want to consider building a minimum of a true 2 1/2-inch exhaust system (a 3-inch system would actually be better). Flowmaster makes a system specifically for your Chevelle that is well designed and fits even with large mufflers. A 3-inch, mandrel-bent system could be worth 10 or more horsepower over a system with 2 1/4-inch tailpipes, especially considering that compression-bent pipes significantly reduce the inside pipe diameter compared with mandrel-bent pipes.

You also mentioned 110-octane race gas with this 10.25:1 compression engine. With the combination of this compression and a longer-duration cam, I think that 93-octane pump gas can handle the effective cylinder pressure. The best way to ensure good combustion is to control the piston- to-head clearance. A tight quench package (a piston-to-head clearance of between 0.038 inch and 0.045 inch) and a decent chamber design with the Edelbrock head should only require between 34 and 38 degrees of total ignition timing for best power. At these timing numbers, even today's 93-octane fuel should have sufficient antiknock capabilities to prevent detonation. Avoiding detonation is the only real reason to use a higher-octane fuel. Higher octane numbers represent the ability of the fuel to prevent or suppress detonation. To put this another way, there are no power advantages to using a 110-octane race gas. Some oxygenated race fuels may produce minor power gains from exotic chemistry, but that hardly justifies the $12 a gallon cost of the fuel. We used 91- octane for our 700hp big-block Chevy dyno test.

More Info
Edelbrock; Torrance, CA; 310/781-2222; Edelbrock.com
Flowmaster; Santa Rosa, CA; 800/544-4761; FlowmasterMufflers.com
Lunati; Olive Branch, MS; 662/892-1500; LunatiPower.com

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1 comments
The Don-#002
The Don-#002

good article, running a W2A myself as the FMIC was not a option i really considered.theres been heaps of discusion on the various types of recent

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