LS7 Yella Terra's
 

Interested in the Yella Terra 6670's (LS7 1.8) on bronze guides but can't find any weight info (YT has not returned my email). Would appreciate any info on:

1. Overall weight increase over the OEM rockers.

2. Over the nose weight increase.

3. Estimate/guesstimate how much extra spring pressure would be required (OEM LS7 valves) to compensate for the overall weight increase as well as the over-the-nose weight increase.

With regards to #3, it appears that
a) perhaps up to 5 grams could be saved (gained) by going from the OEM steel retainer to a titanium retainer, and
b) perhaps more than that could be saved/gained by going from the OEM beehive spring (which I weighed at roughly 88 grams) to a PSI 1511 beehive (which reportedly weighs in around 65 grams). Going by a rule of thumb I read somewhere, that would be a rough reciprocating savings about about 23/3=7.5 grams.

Or would the weight savings from a retainer change along offset the increased rocker weight (I'm thinking not quite)?

LS7, stock cam and engine, no plans to change/mod.

I did try to check the over-the-nose weight of an OEM LS7 rocker and got, very crudely, about 7 grams or so (probably +/- 2g or more). Do not have a YT 6670 for comparison.

Just upgrade the stock rockers and go with the titanium retainer and PSI 1511's, or PAC 1211X valve springs.

Hi Mark200,

Yella Terra can answer question 1...

I am not sure you will get any accurate answer to your question 2 here...

Question 3 may bring some activity to your thread...

And can you explain the procedure you used to measure the over the nose "weight" please?

Christian

weight of the spring is not of consequence - because it isnt being controlled by itself as it is the tensile material.

You will need dual springs. Depending on cam, I would be looking for 150closed and 400+open.

why don't you just swap the guides to powdered metal and run the stock rocker?

I'm trying to address the side load on the valve stem.

That is an option but for some reason in the LS7 that has not been working too well, at least on OEM assembled heads. But again, side load on the valve stem is what I'm trying to address, regardless of guide material.

Hi Christian,

YT has not yet been forthcoming on #1. I can try calling them again, I suppose. Edit: just got off phone with their MS office; they don't know but said will contact AU and email any info they get....

Don't laugh, but I did say crude on the nose weight... I simply rested the bottom of the rocker on the table with the rocker pad resting on a digital scale. Shimmed a little bit to get what looked like a typical contact point between the scale and the rocker pad (compared to typical contact between valve stem tip and rocker pad), I looked at the weight and concluded that would be the weight of the nose of the rocker in a level plane (for comparative purposes; the head of course does not sit in a level plane).

Hey -- I asked you not to laugh ;) http://i1114.photobucket.com/albums/...es/lol-049.gif

Ouch. If that's the case then I'll have to stick with the stock rockers. That's far too excessive for my setup (stock cam).

Hey Mark, you know you made my day...and it can be a long one!!!

Thank you.

Other of that if you need Yella Terra AUS contact, send me a PM.

Christian

With stock cam I would be using stock rockers.

That would be ideal if that combination did not produce egg-shaped guides in many instances, for reasons exactly unknown (therefore these shots in the dark to lessen side load on the stems).

FWIW I dug up some internet posts elsewhere (grain of salt: Texas medium) regarding nose weights:
OEM rocker: 9 grams
Jessel shaft: 10 grams (second source: 10.5 grams)
Crower shaft: 11 grams (second source: 11.25 grams)
Harland Sharp: 19 grams
YT LS7: 21 grams (ouch)
.

You are missing the (second source:... grams) for the Harland and the YT...that's all.

Christian

That sounds reasonable on the surface but I have two conflicting sources (one is a non-automotive engineer acquaintance), and since I am insuffuciently schooled in the subject to make an independent determination I'll leave the floor open to whomever else may wish to opine.

The other source (both are in agreement):

Ask yourself where the force is being exerted on the spring? The very top where it connects with the retainer. As this is the point for contraction/extension of the spring and the kinetic energy's focal point, it's only logical to assume that weight on the other side of the spring is what matters as far as lifter and valve stability. While the spring's mass is known to the spring, and expressed as such while the spring contracts under pressure, and extends outwards, that mass is never seen, or burdened by the lifter, as it is literally inside the spring itself, which is what is creating the kinetic energy in the first place, and as such, cannot possibly contribute to or detract from stability of the valve or the lifter, because neither will shoulder the weight of the spring itself as a moving object, but rather as a compressable plane.

WOOOOHHHHH getting over my head quick in here LOL. very good info keep this going im learning a lot.

The valve spring itself most certianly must be taken into account for valve train weight. Even though the spring is controlling everything, it also has mass and must control itself too.

On pro NHRA stuff, we are able to run smaller lighter springs with less load than a heavier spring with more load. this is due to the springs ability to control itself easier.

There are many other factors that contribute the the springs ability to control itself other than its mass, but it does matter. Here we have a basic rule of thumb. All the weight after the rocker arm fulcrum accounts for 80% of the effected mass on a valve train. This means if you add up all the weight in the valve train, 80% of the mass contibuting to the dynamics of the system as a whole is after the rocker fulcrum point. The spring is also included in the wieghts.

Stock GM LS7 cam (.594 lift, 210°/230°). 7000 redline, 7100 fuel cutoff, but I'd like it stable to 7500 as a safety margin. Ti retainer (5.5g). 74g valve. I can set up PAC 1519's @ 1.825 for 141# seat, 344# open (approx). Not enough?

Stock retainer is 11.3g, stock spring is 92g (115# seat, 314# open @ OEM height of 1.945).

TIA for suggestions/insight.

I am a big fan of the OE rockers. GM really did thier homework there. I would look into getting the tips DLC coated to alleviate some of the scrubbing friction.

The OE rockers are quite possibly wearing out the guides on the LS7. Now if I wanted to wear out new guides, then the OE rocker might be the hot ticket.

Other than that, I can't be a fan in this particular application. Anyhoo, I have plenty of info on them; the YT 6670's, not so much. Therefore, this thread.