Now let’s move onto the top end of your engine. You have a little problem using your camel-back heads as they have a 64cc combustion chamber. The Vortecs also have this small combustion chamber. With your 350 being punched out 0.060-inch over, and using the flat-top pistons, your compression is just a tick over 10.2:1. This is not a happy number for pump gas, iron heads, a carbureted engine, and a short camshaft. This is a recipe for pinging and detonation. You want to limit your compression to the 9:1 range so this puppy can run on 87-octane fuel. You’ll need to either swap out your pistons for buckets with a 12-16cc dish or go with cylinder heads with larger combustion chambers. If you swap out your cylinder heads, the 72cc combustion chambers will come in at 9.38:1, and 76cc chambers will yield 9.0:1. If you decide to change out the heads, give the Dart Iron Eagle S/S cylinder heads a look. They feature a 72cc combustion chamber, 165cc inlet runners, and come dressed with 1.250-inch valvesprings with 110 pounds on the seat and will accept up to 0.520 inches of lift. This spring package will work perfectly with the Chevrolet Performance roller listed above. These are a great set of affordable replacement cylinder heads, sold under PN 10021171. If you decide to go with the piston change we’d recommend the Vortec heads as they will give you better performance and mileage than the early fuelie heads.
Topping off the engine we’d recommend the Edelbrock Performer intake manifold; PN 2101 will fit standard Gen 1 heads, and the PN 2716 for the Vortec heads. These manifolds, with their dual-plane design, are also incorporated in two sized intake runners to give you a very broad torque curve. These manifolds will also accommodate your Quadrajet, which is a great selection for sipping fuel and making great power.
Any of these combinations will meet your 300-plus horsepower bogey, with a couple making upwards of 325. The main thing is that they will build great slow-speed torque and when dressed with 15/8-inch headers and a free-flowing dual exhaust will knock down 20-plus mpg if you keep your foot out of the throttle. Back in the day, we knocked down over 21 mpg on the Hot Rod Power Tour with a ’67 Camaro equipped with 3.08s, a 700-R4, and a ZZ4 with a Holley 750 double-pumper. The bottom line is to get everything right and mind your right foot. Good luck on your mileage quest!
Sources: edelbrock.com, dartheads.com, chevroletperformance.com
LS for Torque
I read the information about the big-block torque engines and found it interesting. The dynamics of building an engine to produce low-end power are somewhat confusing to me, especially in the cam selection area. I want to build an LS3 block with a stroker for maximum torque. I’m not really concerned about the top end horsepower numbers, just getting a lot of down-low power.
My plan is to stroke an LS3 to 415 ci and use LS1/LS6 heads to keep high velocity at low to mid rpm. Since my engine would never see high rpm, the range where someone would drive normally is where I want to concentrate a search for torque, say, 1,800/3,000 rpm.
Do you have any suggestions on the camshaft? Also, I plan to keep the compression ratio at 10:1 or less so I don’t need to burn premium fuel. Keep up the great magazine.
This is the second question in the many months as far back as the Aug. ’12 issue, where we addressed the same type of question. In that answer we recommended going with LS3 rectangular ports, as most of the dyno sessions we’ve reviewed reported higher torque levels with the larger LS3-type inlet port. Well, what you see on the dyno at wide-open throttle and what you feel at transient engine speeds and part-throttle torque can be completely different. Let’s review building another Torque Monster from LS1 and 2 parts.