Duramax Diesels Forum Truck of the Week
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Old 01-16-2015, 12:19 PM
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Default Lobe lift vs valve reliefs

Let me start off by saying I don't know enough about this topic to know what I'm getting Into.. so I don't want anyone to think Iim trying to prove anyone wrong here. I'm simply making sure I won't run into issues when my engine gets assembled.

I've got a set of 16:1 .020" over oval bowl pistons with no valve reliefs for my build.

I picked up a "stage 1" alternate firing cam as well that states no valve reliefs are needed to run this cam. I got looking at the spec sheet that came with my cam vs what a stock cam measures and it appears this cam has .066" more lift on the intake than a stock cam. I just want to be sure my combination will work together without issue.

Measuring a stock lbz piston to my oval bowl, it appears the oval bowls are roughly .010" shorter from the top of the wrist pin hole to the top of the piston (1.271") and the lbz pistons measures 1.281". I would assume a stock lly piston is the same height wise as the lbz piston..

At how much additional lift over stock are valve reliefs needed?

From what I can tell, I should be good to go..right?
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Last edited by mike diesel; 01-16-2015 at 12:24 PM.
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Old 01-16-2015, 01:26 PM
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lift doesnt necessarily dictate the need for reliefs, the duration and when the valves open and close does. fingers pistons may be decked to simplify in case the block is decked as well.
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Old 01-16-2015, 02:30 PM
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Double stack your head gaskets lol!
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Old 01-16-2015, 02:38 PM
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Quote:
Originally Posted by Bonestock View Post
Double stack your head gaskets lol!
Put the new ones on top of the old ones
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Old 01-16-2015, 02:52 PM
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Yeah only way to know is get some putty out or a you could put finger light weight springs on and spin the engine by hand. Timing and duration play the biggest part
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Old 01-16-2015, 02:59 PM
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Well i have no reason to believe I'll have an issue since I'm sure they have sold hundreds of these cams to guys in my same situation/build. I mainly wanted to learn more about the products I'm putting in my engine.
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Old 01-16-2015, 06:11 PM
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Quote:
Originally Posted by mike diesel View Post
Put the new ones on top of the old ones
No. The old ones go in between the new ones. Everyone knows that.

But yeah, it depends where the valve is when the piston is tdc

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Old 01-16-2015, 06:15 PM
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Mike, I have a set of LLY pistons I can measure for you to double check to see if they're the same thickness if you need those measurements.
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Old 01-16-2015, 07:23 PM
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You'll be fine if you put a washer between the gasket an the head at each bolt hole for spacers.
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Old 01-19-2015, 07:03 AM
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Poor man's clearance check:

Putty the top of your pistons.

Use your old gasket.

Bolt the head to the block.

Lash your valves +0.1

Spin the engine two revolutions.

Check the putty thickness. Keep in mind the putty is 0.1" thicker now than the real clearance.

You can do this with your old pistons to find out your clearance before you order the new ones. Especially important if you are going to get the new ones coated.
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Old 01-19-2015, 07:13 AM
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Quote:
Originally Posted by Fingers View Post
Poor man's clearance check:

Putty the top of your pistons.

Use your old gasket.

Bolt the head to the block.

Lash your valves +0.1

Spin the engine two revolutions.

Check the putty thickness. Keep in mind the putty is 0.1" thicker now than the real clearance.

You can do this with your old pistons to find out your clearance before you order the new ones. Especially important if you are going to get the new ones coated.
Well i already have my oval bowl pistons and i already have my cam. Pistons will not be coated. Empires says no valve reliefs are needed. I'd just hate to have an issue after the short block is assembled. I think im just being paranoid about it.
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