355 LE Dyno tune this Friday...Guess my numbers
04-01-2008, 11:30 AM
#181
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So the question is what is primary and secondary when talking about rocker geometry sweep and setup. I am only looking at this from a common sense mechanical standpoint, you guys no more than me.
Primary:
My thinking is having the pattern centered (between the intake and exhaust) so that the valve is not being biased against one side of guide is the desired thing. If the pattern is NOT centered then there must be some biasing or unequal forces being applied by the rocker that can contribute to additional drag and wear. It just makes sense to me that you want to equal out the forces on the sides of the valves where they ride in the guides. This is done by adjusting the push rod length.
Secondary:
Obviously the width of the sweep should be as minimal as possible but that is near impossible to change on stud mount rockers without lengthening or shortening valves or doing something custom.
Maybe I am way off base, I am not an expert.
BTW If Dougs lobe is .381" then my cam has slightly less lift than his. It appears they are close but not the same.
Primary:
My thinking is having the pattern centered (between the intake and exhaust) so that the valve is not being biased against one side of guide is the desired thing. If the pattern is NOT centered then there must be some biasing or unequal forces being applied by the rocker that can contribute to additional drag and wear. It just makes sense to me that you want to equal out the forces on the sides of the valves where they ride in the guides. This is done by adjusting the push rod length.
Secondary:
Obviously the width of the sweep should be as minimal as possible but that is near impossible to change on stud mount rockers without lengthening or shortening valves or doing something custom.
Maybe I am way off base, I am not an expert.
BTW If Dougs lobe is .381" then my cam has slightly less lift than his. It appears they are close but not the same.
04-01-2008, 11:40 AM
#183
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All the talk about longevity even if the springs fix the problem is making me nervous.
Starting to wish I took the LE1 cam which is closer to the CC503. The only ill effects I remember Lloyd telling me was to replace the valve springs every three years.
Hell I could not have researched things back then any more than I did. I had extensive conversations explaining that reliability and street manners trumped performance.
Starting to wish I took the LE1 cam which is closer to the CC503. The only ill effects I remember Lloyd telling me was to replace the valve springs every three years.
Hell I could not have researched things back then any more than I did. I had extensive conversations explaining that reliability and street manners trumped performance.
Last edited by wrd1972; 04-02-2008 at 05:37 AM.
04-01-2008, 11:52 AM
#185
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Location: O'Fallon, MO
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I've been running a .379/.389 lobe lift camshaft with early 918 beehives installed at 1.80" for 2 1/2 years without a problem.
About 6 months ago I had a problem with my heads valve seats, they were ground off center from the original machinist (CNC Cylinder Heads). The machine shop that redid the heads checked the valve springs and were within specs on pressure.
Also, I'm running a .050 longer valve and Imp SS head gaskets. My pushrod length is 7.150.
About 6 months ago I had a problem with my heads valve seats, they were ground off center from the original machinist (CNC Cylinder Heads). The machine shop that redid the heads checked the valve springs and were within specs on pressure.
Also, I'm running a .050 longer valve and Imp SS head gaskets. My pushrod length is 7.150.
Last edited by Stl94LT1; 04-01-2008 at 11:54 AM.
04-01-2008, 12:13 PM
#186
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So the question is what is primary and secondary when talking about rocker geometry sweep and setup. I am only looking at this from a common sense mechanical standpoint, you guys no more than me.
Primary:
My thinking is having the pattern centered (between the intake and exhaust) so that the valve is not being biased against one side of guide is the desired thing. If the pattern is NOT centered then there must be some biasing or unequal forces being applied by the rocker that can contribute to additional drag and wear. It just makes sense to me that you want to equal out the forces on the sides of the valves where they ride in the guides. This is done by adjusting the push rod length.
Secondary:
Obviously the width of the sweep should be as minimal as possible but that is near impossible to change on stud mount rockers without lengthening or shortening valves or doing something custom.
Maybe I am way off base, I am not an expert.
BTW If Dougs lobe is .381" then my cam has slightly less lift than his. It appears they are close but not the same.
Primary:
My thinking is having the pattern centered (between the intake and exhaust) so that the valve is not being biased against one side of guide is the desired thing. If the pattern is NOT centered then there must be some biasing or unequal forces being applied by the rocker that can contribute to additional drag and wear. It just makes sense to me that you want to equal out the forces on the sides of the valves where they ride in the guides. This is done by adjusting the push rod length.
Secondary:
Obviously the width of the sweep should be as minimal as possible but that is near impossible to change on stud mount rockers without lengthening or shortening valves or doing something custom.
Maybe I am way off base, I am not an expert.
BTW If Dougs lobe is .381" then my cam has slightly less lift than his. It appears they are close but not the same.
04-01-2008, 06:17 PM
#187
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I was told by Lloyd to replace my springs every three years on a non daily driver with this cam. I am fine with that.
Now you know that is not at all reasonable. The 921's should coexist with this cam much better than the PAC 1218 beehives. The are LS1 springs made for up to .650 lift and fast ramps and trust me I am barely over .600".
Now you know that is not at all reasonable. The 921's should coexist with this cam much better than the PAC 1218 beehives. The are LS1 springs made for up to .650 lift and fast ramps and trust me I am barely over .600".
For the record, this is the first car I ever modified and I am just a lowly carpenter so I may not have even the vaguest of clues as to what I am talking about.
04-01-2008, 08:36 PM
#188
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Think of it like hitting a 4" speedbump at 5mph or 10mph, at 5mph it will likely be a smooth experiance, at 10mph you test the bumpstops and need your fillings checked.
Not an exact example but is a easy comparison about how the same "lift" at different speeds(rates) is harder to control.
Not an exact example but is a easy comparison about how the same "lift" at different speeds(rates) is harder to control.
I saw almost that exact metaphor on the net yesterday! Just the numbers were different.
04-01-2008, 08:51 PM
#189
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This just in from lloyd Elliot regarding the Comp 921's only:
I just checked the pressure on these and make sure you are getting them set up at 1.720.
They call for a 1.750-1.770 set up ht BUT they only have 143 lbs of seat pressure at 1.750. This is not much more than the bee hives are and the bee hive is able to work witha lower pressure. make sure and increase the seat pressure to fix the problem.
1.720 set up ht still gets you .080 travel before coil bind with the .600 lift of your cam (1.040 is coil bind) and you only need .030-.040 so you are still safe.
Heck, you could set them up at 1.700 but there is really no need.
1.720 should get you about 155 lbs on seat and 395 lbs open. This will control the valves and eliminate any problem you are having if it is spring related.
Most of your problem is the 1.800 set up ht and the rest is due to the rocker adjustment. Add about 20 lbs of seat pressure and 50 lbs of open pressure along with the proper lifter pre load (rocker adjustment) and you will be fine.
I just checked the pressure on these and make sure you are getting them set up at 1.720.
They call for a 1.750-1.770 set up ht BUT they only have 143 lbs of seat pressure at 1.750. This is not much more than the bee hives are and the bee hive is able to work witha lower pressure. make sure and increase the seat pressure to fix the problem.
1.720 set up ht still gets you .080 travel before coil bind with the .600 lift of your cam (1.040 is coil bind) and you only need .030-.040 so you are still safe.
Heck, you could set them up at 1.700 but there is really no need.
1.720 should get you about 155 lbs on seat and 395 lbs open. This will control the valves and eliminate any problem you are having if it is spring related.
Most of your problem is the 1.800 set up ht and the rest is due to the rocker adjustment. Add about 20 lbs of seat pressure and 50 lbs of open pressure along with the proper lifter pre load (rocker adjustment) and you will be fine.
The bolded part is EXACTLY what I'd do! You want to run springs close to the coil bind height to prevent spring surging. I don't know how much .020" would help surge, but it'll definitely help out on your pressures. It's a win-win situation.
04-01-2008, 09:07 PM
#190
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Narrowest PR sweep is king over centered tip. As long as the tip stays within 25% of the stem diameter from the edge, you'll be ok. You want your rocker pushing the valve DOWN, not across.
My engine has a .015" decked block and GM847(I guess the base circle is same as stock?) and it really could use a 7.300" PR, but it gets a little closer to the edge than I am comfortable with, so I'm just gonna leave the 7.200" PRs in it. If I installed longer valves, or even lash caps, I could run the longer PR and have it centered AND the narrowest sweep, but it's not worth all that to me. Especially when it'll be fine .080" from the edge of the stem(at the closest point).
You want your rocker pushing the valve DOWN, not across.My engine has a .015" decked block and GM847(I guess the base circle is same as stock?) and it really could use a 7.300" PR, but it gets a little closer to the edge than I am comfortable with, so I'm just gonna leave the 7.200" PRs in it. If I installed longer valves, or even lash caps, I could run the longer PR and have it centered AND the narrowest sweep, but it's not worth all that to me. Especially when it'll be fine .080" from the edge of the stem(at the closest point).
04-02-2008, 05:51 AM
#191
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Here is a link that backs up what you guys are saying.
http://www.circletrack.com/techartic...try/index.html
When I stated my opinion on what is primary and secondary, I was looking at it from more of a reliability angle rather than MAX performance angle and. It makes a bit more sense now after hearing from you guys.
I will revisit this when I install my new springs.
BTW click this link for a insanely long LT1 related discussion on rocker geometry not to mention the biggest pissing contest on the subject ever. After a few pages my head was about ready to explode. And I thought you guys were obsessed.
http://speedtalk.com/forum/viewtopic...er=asc&start=0
http://www.circletrack.com/techartic...try/index.html
When I stated my opinion on what is primary and secondary, I was looking at it from more of a reliability angle rather than MAX performance angle and. It makes a bit more sense now after hearing from you guys.
I will revisit this when I install my new springs.
BTW click this link for a insanely long LT1 related discussion on rocker geometry not to mention the biggest pissing contest on the subject ever. After a few pages my head was about ready to explode. And I thought you guys were obsessed.
http://speedtalk.com/forum/viewtopic...er=asc&start=0
Last edited by wrd1972; 04-02-2008 at 07:23 AM.
04-02-2008, 11:46 AM
#193
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04-02-2008, 11:50 AM
#195
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Its obvious from that thread alone that opinions on the matter are all over the place.
So what length did you settle on? I though the 7.000" or 7.050" looked the best. But again I aint no expert.
All I know for sure is when I ran 7.200" pushrods with Comp Pro mags the first time, every single GM bowtie guideplate showed an average of .070" slot wear with one slot opening up nearly 1/8" to the point a rocker fell off the valve in less than 2K miles. The roller pouneed the hell out of the retainer and rounded over the stem. Mine looked just like yours from the first page of that thread in terms of setup which clearly did not work.
Moved to 7.050" on those same heads and rockers (focused more on center) and not even a hint of wear with over 3X the miles compared to the first time. I may have given up a tad of duration and lift but by God it went the distance and did not trash the guide plates.
Oh my frigging head.
Last edited by wrd1972; 04-02-2008 at 12:25 PM.