Cylinder Head Runner Volume

Although Racing Head Service® offers many different intake runner volumes in its cylinder heads, chances are that only one or two of them are appropriate for your application. When it comes to deciding which cylinder heads to order, it is important that you make a realistic judgment of your intended use for your vehicle.

Remember that velocity produces low rpm torque, and flow produces high rpm horsepower. So that 170cc cylinder head that you’ve been looking at -with its smaller, higher-velocity runners and valves, is going to accelerate well from a stop, produce lots of low speed torque, and be a great performer below 6000 RPM (which covers about 97% of all street-performance scenarios), but it may not reach the peak RPM you’d want in say, a drag race engine. Conversely, that high–flowing 235cc Small Block Chevy cylinder head that your friends tell you is all the rage at the local track is going to help your engine to rev like crazy and produce a ton of upper rpm horsepower, but it won’t build power below 3500 RPM -making it virtually unusable on the street.

Which is the correct way to go? Most experts will tell you that the answer is not “bigger is better”, but rather that you should run the correct heads for your application with components (cam, intake, exhaust system, etc.) that are designed to work with them. So if you’re looking to build an all-out race car that will never see street duty, that 235cc head with compression, cam, induction, and drivetrain to match will have you winning races in no time. If you just want to get an extra 20 or 30 horsepower out of your street vehicle, and you aren’t planning on performing 4000 RPM launches anytime soon, then that 170cc head is probably the best choice.

The tables listed below will offer some general cubic inch and RPM guidelines to consider when selecting the intake runner volume of your new cylinder heads:

Small Block Cylinder Head Application Based On Intake Runner Volume*

Small Bore/Short Stroke
Cubic Inches Intake Runner Volume Approximate RPM Range*
Up to 350 CID 170-180cc ≈ Idle-6000
302-350 CID 200-210cc ≈ 2500-6500
347-400+ CID 215-220cc ≈ 3500-7000+
383-421+ CID 235cc ≈ 4000-7500+
Large Bore/Long Stroke
Cubic Inches Intake Runner Volume Approximate RPM Range*
Up to 350 CID 180cc ≈ Idle-5500
302-350 CID 200-210cc ≈ 2000-6000
347-400+ CID 215-220cc ≈ 3000-6800+
383-421+ CID 235cc ≈ 3800-7200+

Big Block Cylinder Head Application Based On Intake Runner Volume*

Big Block Chevrolet
Cubic Inches Intake Runner Volume Approximate RPM Range*
468-500+ 320cc ≈ 3500-7300+
500-565+ 360cc ≈ 4000-7500+

*Note that this is an approximate RPM range guideline only –there are too many individual engine variables such as: rod length and bore/stroke ratio, rotating assembly weight, valvetrain weight, induction, camshaft characteristics, tuning, and many others that will have a tremendous impact on the RPM range of a given engine to offer more than a general prediction of powerband and upper-rpm capability.