Which head gasket to offset 10:1 pistons

[Joesprocket]

22 minutes ago, Conserv said:

Joe,

Can we start over?

 

Thanks for the investigative questions.

 

Let me start with how I ended up with these 10:1 Mahles:

My block needs a re-bore and is already sitting at second oversize. The next standard oversize is 1mm and a readily available option was a set of 90mm / 10:1  Mahles. I also got a great deal on them from a highly trusted source in the community.

 

When I bought them I also was leaning towards picking up IE's 292 cam to make use of the added compression however my builder has since walked me back from that path expressing concerns over messing with the valve timing and the trickle effect of new/different parts that would be required that we didnt budget for (bigger valves, eccentrics, intake/exhaust mani, bigger carb). He's been good about knowing my goal of wanting a simple driver and not letting me stray off course or cut corners.

 

It's not that my builder and I are trying to achieve or have a goal of achieving 8.5:1 compression. It's more that we want to make sure when we throw these pistons in we don't have a final compression that leads to detonation issues as mentioned above. Our theory is a taller head gasket like 1.80 could help reduce the risk. The 121 head is right at it's full 129 height.

 

My intentions for this rebuild:

Street / road trip usage. I'm totally fine running premium to serve these pistons as it's not a daily driver and will put less than 5K a year on it. I just want something that will last and be reliable.

 

 

 

 

[visionaut]

Sorry, but IMHO, you bought the wrong pistons for what you’re trying to accomplish. No matter how good a price, they’re not what you should have gotten (which would’ve been more like 8.5-9.0:1) for your completely stock engine..

 

Now you’re trying to find ways to ‘fix’ the poor ‘too high compression’ piston choice… why not simply reverse course and sell the 10:1 Mahles and get pistons with the correct compression? 

 

[Mark92131]

IMHO, keep the Malhes, they are a good solution for your block and head.  The compression ratio isn't that high for premium fuel and you indicate that running premium isn't going to an issue.  You shouldn't have any detonation issues with the standard height head gasket, but run a slightly thicker one if it helps you sleep at night.  If your builder is happy, you should be happy!

 

Again, IMHO,

 

Mark92131

[858slider]

I’m interested in these pistons if you decide to sell, otherwise I’m taking a trip up to IE! 🤙🏼