Valve Train Geometry

Valve Train Geometry

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Discussion

Gelf VXR

Original Poster:

713 posts

206 months

Friday 18th July 2014
quotequote all
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.

Edited by Gelf VXR on Friday 18th July 05:17

ringram

14,700 posts

247 months

Friday 18th July 2014
quotequote all
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...

Gelf VXR

Original Poster:

713 posts

206 months

Friday 18th July 2014
quotequote all
Yes, seen this, my question is the swipe pattern in one direction or a to and fro motion on the LS head

bimbleuk

156 posts

224 months

Friday 18th July 2014
quotequote all
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?

Gelf VXR

Original Poster:

713 posts

206 months

Friday 18th July 2014
quotequote all
I think so

ringram

14,700 posts

247 months

Friday 18th July 2014
quotequote all
One direction. There is a comp article which says it goes from intake to exhaust. Their valvetrain geometry article. Mr Google will give it to you.

Gelf VXR

Original Poster:

713 posts

206 months

Friday 18th July 2014
quotequote all
I'd rather see a schematic than believe a thing mr google has to offer lol

ringram

14,700 posts

247 months

Friday 18th July 2014
quotequote all
IIRC there was pretty pictures for you in their doc too smile

MyM8V8

9,456 posts

194 months

Friday 18th July 2014
quotequote all
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?

Cathedral ports heads are all straight on so no side thrust.

bimbleuk

156 posts

224 months

Friday 18th July 2014
quotequote all
I tried to look but the GM rockers are very flat over the tip so it was not very clear. Roller tips would be much clearer.

Gelf VXR

Original Poster:

713 posts

206 months

Saturday 19th July 2014
quotequote all
Here an article the covers what I'm trying to determine



http://www.aera.org/ep/downloads/ep10/EP04-2010_20...

Gelf VXR

Original Poster:

713 posts

206 months

Tuesday 22nd July 2014
quotequote all
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.



bimbleuk

156 posts

224 months

Tuesday 22nd July 2014
quotequote all
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.

stigmundfreud

22,454 posts

209 months

Tuesday 22nd July 2014
quotequote all
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?

bimbleuk

156 posts

224 months

Wednesday 23rd July 2014
quotequote all
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

22,454 posts

209 months

Wednesday 23rd July 2014
quotequote all
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

MyM8V8

9,456 posts

194 months

Wednesday 23rd July 2014
quotequote all
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.

stigmundfreud

22,454 posts

209 months

Wednesday 23rd July 2014
quotequote all
yep so just a by product of the ratio not necessarily a benefit of going roller rockers (though I suppose the two go hand in hand). I take it the extra duration gives a more rounded profile so would this in effect improve component wear?

ringram

14,700 posts

247 months

Wednesday 23rd July 2014
quotequote all
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 smile