Cosworth Big Bore Head Gaskets for Sleeved Blocks

Even though Cosworth doesn't subscribe to cutting away a ton of aluminum and then inserting thick ass iron sleeves in production aluminum cylinder blocks, we still have big bore gaskets for Subaru, Nissan, and Honda engines. This way even customers and engine builders who use sleeves can still benefit from Cosworth's superior head gasket sealing. I wrote a blog post a while back on this: Should You Change Your SR20DET Head Gasket?

Here are some of the features of the Cosworth FSL metal head gaskets:

  • Individual die cut layers of stainless steel with superior consistency compared to laser cut gaskets.
  • Pre-coated stainless steel with a 0.25 micron layer of nitrile rubber ensures consistent distribution of coating with no high or low areas.
  • Manufacturing dimensional tolerance of 0.002″.
  • Die cut manufacturing process ensures smooth edges, unlike laser cut gaskets.
  • Cosworth gaskets feature a “folded stopper” sealing layer for additional torque around each cylinder. The width of sealing area is specific for each application thereby providing ultimate sealing properties.

Here's a profile of the folded stopper layer:

The Cosworth FSL metal head gaskets massively increase sealing force around the cylinder over factory type and other brands of basic metal head gaskets that have a little curve indented into them around the cylinders (which is damn near pointless if you ask me). For a visual comparison scroll to toward the bottom of this post.

Aside from the near stock bore gaskets, we have recently expanded the head gasket product line to include big bore Honda K20/K24, Honda F20C, but we also have had big bore gaskets for Nissan VQ35DE and Subaru EJ255/257. Check them out here:

Nissan VQ35DE 98mm, 0.6mm thick

Nissan VQ35DE 100mm, 0.6mm thick

Subaru EJ255/257 04-07 101.3mm, 0.78mm thick

Subaru EJ255/257 04-07 101.3mm, 1.1mm thick

Subaru EJ255/257 04-07 101.3mm, 1.5mm thick

Subaru EJ255/257 2008+ 101.3mm, 0.78mm thick

Subaru EJ255/257 2008+ 101.3mm, 1.1mm thick

Subaru EJ255/257 2008+ 101.3mm, 1.5mm thick

Honda K20A/K24 PRB style 90mm, 1.1mm thick

Honda K20/K24 RAA style 90mm, 1.1mm thick

Honda F20C 90mm, 1.1mm thick

Actually the Subaru EJ255/257 gaskets will work with all years, but throughout the model years Subaru has attempted to direct water flow for quicker warm in an attempt to lower cold start emissions. Engine builders and tuners like to use what they like to use so we decided to manufacture a 2008+ head gasket to have something for everyone.

Big bore Nissan VR38DETT and Mitsubishi 4B11T gaskets are coming soon.

The reason why the Honda gaskets are all 1.1mm thick is because it seems most machine shops deck the crap out of the blocks after installing sleeves. I'm not sure why, but it could be excessive deck distortion after cutting away a ton of aluminum and ramming in 4 giant iron sleeves that didn't belong there in the first place.

If you would like gaskets for other engines or other bore and thicknesses, let me know below in the comment box. If I feel there's some potential business, we'll design a gasket.

Below are comparisons of 4G63, EJ25, and SR20DET sealing force tests. All test were conducted with brand new factory cylinder block and cylinder head castings, ARP studs using ARP's recommended torque. The only changes between each test were the gaskets.

The more defined the sealing lines around the cylinder, the more defined the clamping area is. So as you can imagine, a very clean line is best. Assuming the red imprint is solid (and not blotched or clouded with white), the brighter the red, the higher the clamping force. If the red is dark colored or blotched or clouded with white, the clamping force is lower. One trend that is extermely clear in this testing is that the OE gaskets do an OK job, but their clamping areas are not perfect. This probably isn't a problem at factory horsepower levels. With the other brand (we'll call them COM) metal head gaskets, you'll notice in many cases the colors are a dull red and that the clamping area isn't very defined. All I can say is that it sucks to be you if you're running a brand COM in your big horsepower engine.

You can see in these small images how much more defined and bright red the Cosworth FSL head gaskets are:  (Click to see full size images)

EVO 4G63


 Nissan SR20DET


Subaru EJ25

The thing to look out for on the EJ gasket is in between the cylinders. It's all about the details if you want to make a Subaru live at 600+hp without sleeves.

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