Valve Train Geometry
Discussion
Anyone no of a schematic for the LS3 head? Is the rocker arm a sweep C pattern, in that the rocker fulcrum in perpendicular to the inlet valve at mid lift? Ie minimal swipe pattern
I see a lot of forum posts dying that it should start on the inlet side and sweep to the exhaust?
Correct shimming on the pedestal should produce a C swipe providing the greatest lift potential and minimum lateral stress on the valve guide, this sounds most logical to me.
By C I mean as in the arc to produce to and fro movement.
I see a lot of forum posts dying that it should start on the inlet side and sweep to the exhaust?
Correct shimming on the pedestal should produce a C swipe providing the greatest lift potential and minimum lateral stress on the valve guide, this sounds most logical to me.
By C I mean as in the arc to produce to and fro movement.
Edited by Gelf VXR on Friday 18th July 05:17
Without going into the geometry details there is a fair bit of info regarding using a checker spring and dye on the stem.
Swipe should be centered on the tip of the valve stem.
See here..
http://www.ls1gto.com/forums/showthread.php?t=3220...
Swipe should be centered on the tip of the valve stem.
See here..
http://www.ls1gto.com/forums/showthread.php?t=3220...
I was going to check the wipe pattern on my 243 heads later. That's if I can get on the crank with a ratchet as the fan shroud is very close in my converted car. I don't have the luxury of shims as I just upgraded the trunnions but I do have 3 lengths of rod to play with.
So I can't answer the question myself unless it's clear later. I assume the geometry is pretty similar?
So I can't answer the question myself unless it's clear later. I assume the geometry is pretty similar?
bimbleuk said:
I was going to check the wipe pattern on my 243 heads later. That's if I can get on the crank with a ratchet as the fan shroud is very close in my converted car. I don't have the luxury of shims as I just upgraded the trunnions but I do have 3 lengths of rod to play with.
So I can't answer the question myself unless it's clear later. I assume the geometry is pretty similar?
problem with those square port heads is having that off-set rocker arm. I cant imagine the sideways thrust on that one doing any good?So I can't answer the question myself unless it's clear later. I assume the geometry is pretty similar?
Cathedral ports heads are all straight on so no side thrust.
Here an article the covers what I'm trying to determine
http://www.aera.org/ep/downloads/ep10/EP04-2010_20...
http://www.aera.org/ep/downloads/ep10/EP04-2010_20...
Finally an answer from google I'm content with, a post from Brian Tooley
http://ls1tech.com/forums/generation-iv-internal-e...
Stock rockers are designed to work in a "half arc" meaning that if you visualize the motion of the rocker tip, it works in the first half of an arc. As lift increases past .600" lift the rocker tip starts arcing back towards the intake side of the valve. For roller rockers this is very desirable, it makes the contact patch more narrow. But for stock rockers it's a disaster because the rocker simply spends more of it's cycle dragging across the valve tip. So shimming up roller rockers makes sense. Shimming up stock rockers is one of the worst things you can do for durability.
Pushrod length on a bolt down LS head has zero effect on rocker geometry.
http://ls1tech.com/forums/generation-iv-internal-e...
Stock rockers are designed to work in a "half arc" meaning that if you visualize the motion of the rocker tip, it works in the first half of an arc. As lift increases past .600" lift the rocker tip starts arcing back towards the intake side of the valve. For roller rockers this is very desirable, it makes the contact patch more narrow. But for stock rockers it's a disaster because the rocker simply spends more of it's cycle dragging across the valve tip. So shimming up roller rockers makes sense. Shimming up stock rockers is one of the worst things you can do for durability.
Pushrod length on a bolt down LS head has zero effect on rocker geometry.
Good thing I've been buying my valve train stuff from Brian Tooley then!
That thread saves me time bothering to check the wipe pattern on my upgraded GM rockers too. So checking the push rod length was all I needed to do really and that's done now. Also I was a bit concerned my dual springs may have been OTT for my cam and rockers but they are very similar to the B.T. springs mentioned in the thread and so I'll stick with them.
That thread saves me time bothering to check the wipe pattern on my upgraded GM rockers too. So checking the push rod length was all I needed to do really and that's done now. Also I was a bit concerned my dual springs may have been OTT for my cam and rockers but they are very similar to the B.T. springs mentioned in the thread and so I'll stick with them.
stigmundfreud said:
so they are saying you shim with roller rockers but not with stock? Surely the RR's are designed to go in without shimming up?
The Y.T. pedestal roller rockers for example are supplied with a single shim that you do a wipe test to see if it's required. Though often people appear to require additional shims or even grind down the supplied shim to optimise their wipe pattern.Seeing as the stock rockers work up till 0.650" lift I'll stick with those for the low hassle factor.
stigmundfreud said:
I suppose you have to account for tollerances but would have made the assumption they were designed in. I presume the shims need checking periodically? Is there a massive benefit for the rollers? I'm sure Rich said he got about 2000bhp by adding them once
No that was by going to a 1.8 to 1 ratio (from the stock 1.7) which effectively gave more valve lift. The fact that it was a roller rocker was that they are all that are available after market.I think Shims are because the rocker mounts and re-use of the stock bolts mean you need them to get back to stock geometry.
Roller tips have less friction and so less side loading on the valve. But as noted with OEM and correct geometry this is minimal anyway up to a point.
For higher performance cams you need firmer springs to keep the roller in contact with the lobe. This increases load, flexes pushrods and strains the stock bolt mounted rockers etc. Hence why shaft mount rollers is the way forward for serious setups.
Same with higher ratio rockers the maths for cams is just silly. Some classes actually throw the valve in the air for more lift. Higher ratio is more duration and lift at 0.050 5% more lift roughly plus more duration depending on the shape of the ramp. I got 360rwhp from my otherwise stock LS2 (including stock exhaust)
Anyway Im staying around 0.600 lift unless I upgrade my valvetrain to a shaft system. Comp do the 1521 IIRC which is bolt on shaft system for about £800.
Its all fun and interesting
Roller tips have less friction and so less side loading on the valve. But as noted with OEM and correct geometry this is minimal anyway up to a point.
For higher performance cams you need firmer springs to keep the roller in contact with the lobe. This increases load, flexes pushrods and strains the stock bolt mounted rockers etc. Hence why shaft mount rollers is the way forward for serious setups.
Same with higher ratio rockers the maths for cams is just silly. Some classes actually throw the valve in the air for more lift. Higher ratio is more duration and lift at 0.050 5% more lift roughly plus more duration depending on the shape of the ramp. I got 360rwhp from my otherwise stock LS2 (including stock exhaust)
Anyway Im staying around 0.600 lift unless I upgrade my valvetrain to a shaft system. Comp do the 1521 IIRC which is bolt on shaft system for about £800.
Its all fun and interesting
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