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Old 02-14-2021, 04:29 AM   #1
anon0mouse
Scooby Newbie
 
Member#: 417103
Join Date: Mar 2015
Default Go boom or no?

I'm trying to figure out what head gasket thickness to make use of on my car- and I think I need a bit of help or a sanity check of my thinking.

I has a typical subaru head gasket issue + overheating ended up in a warped block and my first complete enginge reubuild on my own.

My machinist didn't keep a record of on how much was milled off the block or heads so I determined the depth of cut from the block as being 0,36 mm making use of the calculated piston (201mm - 39.5mm - 130.48mm - 30.71mm = 0.31mm pistons below deck) to deck height using dial indicators so I'm fairly sure its accurate. Im pretty sure 0,1mm was skimmed from the heads (again machinist didn't write it down), but I'm not sure how to determine that other than CCing the heads. Ideally I'd like the quench clearance and the compression ration to be close to stock as this motor will be abused on track, and I want to be able to drive it with the stock map.

I found a spreadsheet (http://www.submariner.org/thepno95/T...0-%202017.xlsx) that calculates CR, quench clearance and a variety of other metrics specifically for an ej 257. With no grinding to the head or the block it gives the following data with a stock 0.51mm gasket cr 8.37:1, quench clearance 0,84mm. The compression ratio of 8.37:1 seems awfully high compared to the quoted 8.2:1 I've seen in the Subaru factory manual. But does that really matter - I'm pretty sure that answer is no.

Essentially I shaved 0.46 mm off the mating surfaces, Most of that off the block (0,36mm). So 0.51mm (stock gasket) + 0.4mm to replace the amount material removed results in a 0.9-1,0 mm gasket.

If I plug that data (amount head and blocked shaved + plus a gasket of 0.9mm ) into the spreadsheet I end up with a CR of 8.4 and a quench clearance of 0.81 mm, Pretty damn close to the stock rating of cr 8.37:1 and quench of 0.84 on the stock motor.

So then finally the questions:
Do I need to 100% know that the head had 0,1mm taken off of it to proceed? - I'm pretty sure this is correct and the heads were in good shape and I asked him to take the minimum off. (deep down I know the answer is yes)

If not:
Am I good to go with this setup 0.9mm gasket?
Will fuel trims in the stock map be able to adjust the now slightly lean running engine due to bumped up CR?
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Last edited by anon0mouse; 02-15-2021 at 10:24 AM. Reason: Clarity
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