NickTF
Single turbo turd.
This is a subject i've been interested on as of late given some reports of quicker spool by tightenin the exhaust lash which would add some duration and lift to the valve lift profile. I've been told that lash decreases in a diesel as they warm due to the valves getting hot. This idea is further reinforced by cummins requiring more lash on the exhaust valve which should in theory expand more given it's subject to more heat assuming the intake and exhaust valves are the same material.
For my own curiousity I checked my hot lash vs. my cold lash a few days ago and plan to follow up with additional checks on the rear cylinders (4 and 6) of the motor. This is what I found quoted from a reply I posted in Hammilton's sponsor section of this forum:
"I spot checked number one immediately after a 30 minute drive at 70 mph with multiple runs to 15 psi boost and 1100 max egts (did let truck cool down to 350 or so before shutting off as always). Intake was surprisingly about .002" tighter than the .009" I set it at cold and the exhaust was surprisingly looser at about .002" more than .020" I set it at cold. This suggests to me (would spot check other cylinders before drawing a conclusion) that tightening down the exhaust .010" on a stock cam would be fine."
This was the inverse of what I expected. A few possibilities exist for this observation and one variable I want to rule out is variation across other cylinders. As stated I plan to check more cylinders.
Now, check this out. This is Crane Cam's suggestion for adjusting their provided hot lash spec to cold lash:
CraneCams
Compensating for a Cold Engine when Adjusting Valve Lash
When installing a new cam, the engine will be cold but the lash specifications are for a hot engine. What are you to do? There is a correction factor that can be used to get close. We mentioned that the alloy of the engine parts can be affected by thermal expansion in different ways, therefore the amount of correction factor to the lash setting depends on whether the cylinder heads and block is made out of cast iron or aluminum. You can take the ?hot? setting given to you in the catalog or cam specification card and alter it by the following amount to get a ?cold? lash setting.
Iron Block Iron Heads Add .002"
Iron Block Aluminum Heads Subtract .006"
Aluminum Block Aluminum Heads Subtract .012"
They suggest Iron block and head combinations shrink only a tiny .002" when hot according to the above table. They support the idea that lash shrinks in an iron head/block combination although my findings showed differently (subject to change with additional checks on additional cylinders).
I'm curious, has anyone else bothered to check cold vs. hot lash on their motors?
If we're truly talking such small differences than does anyone have any idea on why they require so much more exhaust lash? Are the factory cam's lash ramps big and slow to promote long valve train life which by tightening the lash past recommended would serve to introduce tons of ultra low lift duration? Do the valves contract and expand alot quicker than my hot lash test revealed?
Thoughts?
For my own curiousity I checked my hot lash vs. my cold lash a few days ago and plan to follow up with additional checks on the rear cylinders (4 and 6) of the motor. This is what I found quoted from a reply I posted in Hammilton's sponsor section of this forum:
"I spot checked number one immediately after a 30 minute drive at 70 mph with multiple runs to 15 psi boost and 1100 max egts (did let truck cool down to 350 or so before shutting off as always). Intake was surprisingly about .002" tighter than the .009" I set it at cold and the exhaust was surprisingly looser at about .002" more than .020" I set it at cold. This suggests to me (would spot check other cylinders before drawing a conclusion) that tightening down the exhaust .010" on a stock cam would be fine."
This was the inverse of what I expected. A few possibilities exist for this observation and one variable I want to rule out is variation across other cylinders. As stated I plan to check more cylinders.
Now, check this out. This is Crane Cam's suggestion for adjusting their provided hot lash spec to cold lash:
CraneCams
Compensating for a Cold Engine when Adjusting Valve Lash
When installing a new cam, the engine will be cold but the lash specifications are for a hot engine. What are you to do? There is a correction factor that can be used to get close. We mentioned that the alloy of the engine parts can be affected by thermal expansion in different ways, therefore the amount of correction factor to the lash setting depends on whether the cylinder heads and block is made out of cast iron or aluminum. You can take the ?hot? setting given to you in the catalog or cam specification card and alter it by the following amount to get a ?cold? lash setting.
Iron Block Iron Heads Add .002"
Iron Block Aluminum Heads Subtract .006"
Aluminum Block Aluminum Heads Subtract .012"
They suggest Iron block and head combinations shrink only a tiny .002" when hot according to the above table. They support the idea that lash shrinks in an iron head/block combination although my findings showed differently (subject to change with additional checks on additional cylinders).
I'm curious, has anyone else bothered to check cold vs. hot lash on their motors?
If we're truly talking such small differences than does anyone have any idea on why they require so much more exhaust lash? Are the factory cam's lash ramps big and slow to promote long valve train life which by tightening the lash past recommended would serve to introduce tons of ultra low lift duration? Do the valves contract and expand alot quicker than my hot lash test revealed?
Thoughts?
