Header choice is a critical cause in fully exploiting your engine's faculty inherent.
GM Performance's ZZ4 350 small-block is one of the most typical crate engines outside there. The ZZ4 has endeared itself to hot-rodders and mechanics homogenous with its advertised 355 horsepower and 400 pound-feet of torque, premium-gas compatibility and factory-solid reliability. Although most installers Testament install this engine as-delivered with GM's recommended intake and carburettor, exhaust header choice is a bit another bothersome because headers get to rainless the chassis.
A 1-5/8 inch diameter/20 gauge tube has an inner diameter of 1.429-inch, and a thick-wall 1-3/4 inch/14 gauge tube has an inner diameter of 1.418. This makes the narrower-but-thinner 1-5/8 header tube about 0.01-inch larger internally than its wider-but-thicker 1-3/4 inch equivalent.
Head Considerations
The ZZ4's L98 heritage way that it uses angled-plug aluminium cylinder heads. You don't necessarily must to manipulate angle-plug-specific headers, nevertheless provided you poll not to then you'll demand to install phase metal heat shields between the Glimmer plug boots and the header tubes. All the more then there's no warrantly that you won't burn the boots, so L98-specific headers are a ace conclusion.
Popular Header Sizes
For chassis that include the clearance, 1 5/8-inch valuable breadth, full-length relay headers Testament extract the first horsepower from your engine. The 1 3/4-inch leading header is another accepted preference, nevertheless Giant Performance Chevy Periodical create these a bit further doozer for its ZZ4. HPC Periodical's ZZ4 evaluation showed a 6 horsepower and 20 pound-feet loss from the stock engine's advertised horsepower and torque ratings. However, these headers worked well when the magazine installed a Comp Cams 268H hydraulic flat-tappet cam and a Performer RPM intake manifold. The net result: 380 horsepower at 5,400 rpm and 402 pound-feet of torque at 4,100 rpm.
Material Considerations
Material thickness is one very important but often overlooked factor in header selection. Manufacturers rate their headers according to the primary tubes' outside diameter, but not all manufacturers use the same gauge (thickness) of tubing; gauge can vary between 14 (0.166 inch thick) and 18 (0.098 inch thick). On a 1 5/8-inch outside diameter header, the thicker tubes give up about 0.427 inch of cross-sectional surface area to the thinner ones. Assuming about 80 cubic feet of air per minute airflow per inch, the thicker headers lose about 34 cfm per tube. Multiply that by eight (the number of header tubes on the engine), and the thicker tubes can cost you a fairly whopping 273 cfm off of the thinner tubes' 2,871-cfm airflow.
This oft-overlooked discrepancy may help to explain why some ZZ4s work better with 1-3/4 inch tubes and some do better with 1-5/8 tubes.
