Hey guys I just had a quick question about building a 408 stroker. When it comes to pistons, how do you know what relieve sizes to get? Is that dictated by what kind of heads you have? or do you determine the size and then get heads to match? Are there any "rules of thumb" to go by when selecting the relief? Thanks in advance.

 

I've asked the same thing with no good answer yet...I pretty sure you need to know what cc chamber on head, cam specs, and desired compression ratio before you can order the pistons. Maybe someone will answer and we'll both know

 

Most dished pistons are set up to establish some specific static compression ratio with a given combustion chamber volume.

The combustion chamber volume used is usually what the factory heads are equipped with, or whatever is most popular for that particular bore size.

Given that the success and/or failure of your engine is pretty much always dictated by the heads you use, I would get pistons to match the heads. Not heads to match your pistons.

Figure out what the best heads you can afford are for your build. Once you have the heads picked out, you should have a known combustion chamber volume. From there, you will be able to pick out the appropriate dish/dome to reach your desired static compression ratio. The cam will be spec'ed to get the correct dynamic compression. After the pistons are installed in your block, you measure for quench and buy the correct thickness head gasket to give you the .035-.045 squish, or whatever the golden standard is these days.

 

When i had my 408 built I bought my pistons with reliefs to match my ls3 heads

 

You have confirmed 2 of my assumptions. Doesn't the lift of the cam play a roll as well?

 

Obviously the overall amount of peak valve lift plays a determining role, but not so much as where/when peak valve lift occurs. The timing of the valve events is a bigger factor than just the max lift value.

 

Note: you need to know what heads you will be using. Different types of heads require different shapes of pistons, as the valves may be located in different places. Cathedral port heads and rectangle port heads have the valves spaced differently, and you want to choose the right piston to match. Trick flow heads, as well as some others, use different valve angles and this also will have an impact on piston selection.

 

Ok that makes since. I have been putting off ordering my pistons. I have the heads already (ported L92 w/71cc), so should I have the cam speced for my goal and let the grinder (BTR and I will be sending him the flow chart) tell me what reliefs I need? Thanks,

 

I'm absolutely sure that the folks at BTR will be able to offer you much more assistance in finding exactly what will work for your combination.