What Is the SBC Header Bolt Torque? Is There a Sequence?
Headers make it easy for the engine to push exhaust gasses out of the cylinder, thus improving performance. They’re secured by a header bolt, which must be neither too tight nor too loose to work well. When servicing your small block Chevy engine, you might wonder what the correct bolt torque is to tighten the header bolts.
The SBC header bolt torque is 25 ft-lbs in 1st generation engines and 30 ft-lbs. in second-generation engines. The third and modern generation requires 18 ft/lbs. torque to tighten correctly. Use a torque wrench for accuracy and ease.
In this article, you will learn about the header bolt torque for the small block Chevy. Also, you will learn the passes used in the torque sequence.
SBC Header Bolt Torque
While going through the circles, the engine produces a lot of pressure which must run through the exhaust system efficiently. If the header bolts are loose, the exhaust can leak, and eventually, the gasket will blow. To stay safe from this scenario, secure the header bolts in two passes and by following a sequence.
The following table contains the header bolt torque for the small block Chevy engine through the two passes.
Sequence (middle to out) | Torque |
1st Gen SBC engines | |
First pass | 15 ft/lb. |
Final pass | 25 ft/lb. |
2nd Gen SBC engines | |
First Pass | 20 ft/lb. |
Final Pass | 30 ft/lb. |
3rd Gen SBC engines | |
First pass | 11ft/lb. |
Final pass | 18ft/lb. |
Why Is Header Bolt Torque Important for SBC Engines?
One of the crucial aftermarket parts added to the engine is the headers. Headers are bolt-on accessories used to improve an engine’s performance. They can increase the engine’s horsepower by 10 or 20 more horsepower by allowing exhaust gasses to exit the cylinder faster.
However, during replacement, you might face problems when tightening the screws. By not knowing the amount of torque needed, you risk over-tightening or under-tightening them. That means, if you overtighten the bolts, you risk damaging the threads or breaking the bolt.
If you loosely tighten the bolts, the exhaust fumes will escape through the gaps in the gasket. As the engine runs, pressure will build, causing the gaskets to blow. This scenario can cost you more money to buy new parts and repair time.
Important Parts of The SBC Header Bolts
Like any other bolt sealing a vehicle part, header bolts need to be tightened securely. But before that, the header must match your SBC engine exhaust manifold if you replace it. Following are the few things you should check to install the header correctly before you start torquing its bolts:
Length
The headers should be equal in length to the previous or the stock headers. Long tube headers can also be used if there is a room and if it matches the exhaust system.
Bolts
SBC header bolts are 1” 3/8-16, with the one-inch length compatible with thicker gaskets or flanges. You can opt to use the headlock locking header bolts, which have serrated teeth grip to provide a locking action and prevent loosening.
Flanges
The thickness of the header flanges affects the torque and should be 3/8 thick for the SBC engine.
Gaskets
Quality gaskets that are also not too thick, and the recommended thickness is 1/8 inch.
How To Correctly Torque the SBC Header bolts
SBC headers use 12 bolts, six on each side, to connect to the engine. Before tightening them, run chaser taps on the threads to clean them. To tighten the bolts, use a torque wrench for easier and more precise adjustments. Loosen the tightener at the end of the torque wrench and rotate the dial to the required torque.
Tighten the bolt when the engine is cold, then again after running the engine for some time. Adjust one more time after a few more heat cycles to confirm that the bolts aren’t loosening. If you’re comfortable with the screws, you can now check them during the oil change and servicing.
What Is the Sequence for SBC Header Bolt Torque?
Bolts that tighten the header on the SBC engine header follow a sequence. The sequence allows alignments and gives the person torquing a chance to remove any bolts if they get stuck. An expert tip suggests you run and warm the engine if a bolt is stuck after which the expansion will loosen the bolt for easier removal.
At first, use your fingers to tighten the bolts, starting with the difficult ones and then the easier ones. After securing them to a finger-tight position, use your torque wrench and follow the following sequence.
- Adjust your torque wrench to half the final torque for the first pass. This should be at least 15 ft/lbs. for the 1st generation engines. Torque the bolts starting with the ones in the middle and towards the ones at the edges. For the final pass, you should use 25 ft/lbs.
- Then adjust the torque wrench to 20 ft/lbs. if your engine is the second generation LT1, repeat the sequence. The torque should be 30 ft/lbs. for the final pass.
- Thus, adjust the torque wrench to 11 ft/lbs. for the new SBC engines and repeat the sequence. Set the torque to 18 ft/lbs. for the final pass.
Conclusion
Header bolts are responsible for securing the header tightly on the engine. While they’re needed to be tight, too tight can damage them, and too loose can allow exhaust leaks. Hence, learn the correct torque to adjust the header bolts on your small block Chevy engine.
SBC Header Bolt Torque varies across generations, and you must first identify your engine generation. Afterward, you can set the torque wrench accordingly and adjust the header in two passes. Using this article, you can now secure the header safely with fewer chances of an exhaust leak.
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