Light puttering under idle

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Feb 22, 2010 | 03:02 PM

#21

xtremerevolution

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From: New Lenox, IL

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Quote:

Originally Posted by Danthurs

Valves burn when they don't close all the way. They need to seat to give off the heat, if not, they just get hotter until they burn. The valve could have been bent, or dirty causing it to stick. But $150 is a good deal for all the parts.

Right. I just did some more reading and found that even engine overheating could cause a valve to burn, and that 75% of a valve'* heat is dissipated when it touches the seal. If the seal is worn, it would have to be machined, which involves a valve job.

A low mileage pair of heads would be a lot easier than going through all that trouble.

Quick question while we're on the topic. I have 1.8 ratio roller rockers on this engine, and have been using stock valve springs. Should I have used stiffer valve springs?

Feb 22, 2010 | 03:04 PM

#22

Danthurs

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From: Sheboygan Wisconsin

That would be a very wise choice. Because the valves open further then have to move further to close. A weak spring could cause them to float under high RPMs

Feb 22, 2010 | 04:28 PM

#23

xtremerevolution

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From: New Lenox, IL

Quote:

Originally Posted by Danthurs

That would be a very wise choice. Because the valves open further then have to move further to close. A weak spring could cause them to float under high RPMs

Any idea what kind of springs I could use to replace the stock springs on the L27?

Then again, my RPM'* don't really go that high to begin with. 5400 is hardly a high RPM.

Feb 22, 2010 | 04:32 PM

#24

xtremerevolution

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Just found this for the L36/L67:

Quote:

2) - High Ratio Rockers – Thankfully GM made one thing simple…pushrod motors!! Stock GT/GTP cars came with 1.60:1 or 1.66:1 Ratio Rockers from the factory. There are a few choices that you have here to make some more power by letting those valves open more...
a) Modded Stock Rockers – ZZPerformance decided to elaborate on the efficient stock design for those wanting more performance on a budget. ZZP introduced the 1.90:1 Modded Stock Rockers. Basically, these rockers start out as stockers. The seats are welded in and ZZP re-machined them to achieve a ratio of 1.90:1. Great and easy way to add about 20 horsepower without having to change valve springs. As long as you keep your shift points at or below 6,000 RPM you will be fine. Anymore and the stock valve springs tend to float. Cost: $275+