We see regular comments on the internet saying you need to upgrade the head studs on the L15T engine. Is that true? Well..

A little 101 before we dive into the meat and potatoes of this blog. What is a head gasket and what are head studs and what do they have to do with the engine in your Civic?

Almost every motor (maybe even every single motor) in an automotive application these days utilizes these two parts.

At the most basic level, your L15 engine has a top end and a bottom end that need to be joined together. Those are the cylinder head(top) and the engine block (bottom).

In between these two parts lies the head gasket and it is secured or clamped down with head studs aka head bolts. This gasket and bolts combo play a critical role as they seal combustion gasses within the cylinders and allow circulating oil and coolant to flow uninterrupted without spilling over into unwanted areas.

Ok, got it now? Good. 

Let’s move on to what happens if we encounter a problem with the ‘seal”. Two things can occur. 1) the engine oil and coolant mix, and 2) the engine loses power as the combustion gasses now have a way to escape. We don’t want either of these things to occur!

For all intents and purposes, the gasket on the L15 engine found in your Civic Sedan or Hatch is not the issue.

It is perfectly able to seal these 2 engine components together. However, the head studs/bolts that secure the cylinder head to the engine block are rated for a specific amount of clamping force. That is, they clamp down on the cylinder head and squeeze the gasket for a proper seal.

Why would they not squeeze and provide adequate sealing? Well, they do! In fact most L15 owners never have any issues with the gasket or head studs.

So when might a problem start? When you drastically increase the power generated by a motor the risk increases. As we increase power (via increased boost pressure or other means) we also increase the pressures in the cylinder head. At some point, when you increase power too much, the clamping force is no longer high enough to keep the gasket sealing. This usually happens over time where you “lift the head” every so often little by little until it allows coolant and or oil to escape their passages. The cylinder head literally starts lifting off the block as it’s not being secured by the head studs sufficiently.

How do you mitigate the chance of the head lifting? Well that’s not too hard. If you’re going to be tuning your car for more power, make sure you are doing so safely. Pick a proper tune and/or pick a well respected and experienced tuning shop.

Remember, excess combustion pressures lead to a higher likelihood of lifting the cylinder head. Maintaining proper pressure in the cylinder head when upping the power is crucial. Push it too far and you know what can happen. 

We recommend you do a bit of research on the various tunes out there or directly speak with your tuning shop about your power goals and choose a route that you’re comfortable with. If you want to minimize risk and the cost isn’t too big a concern for you then upgrade your head studs/bolts when you start going for big power.

Just like this sounds, a stronger or thicker bolt can put more pressure on the cylinder head and gasket to keep it from lifting when exposed to higher cylinder pressures. There are kits out there for the L15 engine that are not too expensive and can be installed in just a few hours.

Now hopefully there is a little less confusion on what happens and what can be done about these pesky little head stud situations we sometimes encounter.

In our experience, a properly built and tuned bolted Civic will be fine without upgraded head studs. When we build a motor for big power, we upgrade. For a Civic running around 300WHP we’ve had good reliability on the OE studs. We push our cars hard, but we also tune them using expert shops and maintain them properly. 

Need any advice on keeping your stock head studs vs upgrading? Just post a comment or shoot us an email and we’ll give you all the info you need. 

REDEFINE the Aftermarket

-Vlad