Awright, I need some help here, and will greatly appreciate some knowledgable advice.

Have an '02 Firehawk, and here's what I have to work with:

Heads:
243 Casting
Milled .010"
Rev 2.02/1.57 Valves (+.070")
Manley -1428 Springs, shimmed

Head Gasket:
Cometic, .045" Compressed Thickness

Cam:
Comp XE-R 224/224 .581" .581" 114LSA +2 advance
Base Circle: 1.47"

Rockers / Lifters:
Stock, non-adjustable rockers
OEM hydraulic lifters

Pushrods:
TBD (I have both 7.40" and 7.35" available)


I have a question or two that I haven't been able to answer with the 'search'....

First, with the +.070" longer intake/exhaust valves that are on my heads waiting to be installed, does this not throw-off the valvetrain geometry? That is, won't the tip of my OEM non-adjustable rocker now be sitting .070" higher than it was on the stock setup, and thus now as the rocker goes thru its cam-travel, the tip willl no longer be centered on the valve/retainer? (Ignore the other variable of how deep the valve pocket may/may not have been cut into the head)

Even though a shorter pushrod can be calculated/measured to "work" with the longer valve, is this actually not the RIGHT way to install the valvetrain? Instead, shouldn't the rocker itself be shimmed up .xxx" to compensate for the longer valves, and thus then keep the geometry the same as it was with the stock components?

If this is the correct way (shimming the stock rockers), Why do so many persons just use shorter pushrods instead? (and end up with a biased - not centered - wipe of the rocker on their valve retainer)

I've seen sooo many posts from 'searching' that just say to measure & use a shorter pushrod, but that doesn't seem like its the proper way to do this. Comments??


TIA!!

 

Second, can someone help with my theoretical pushrod length needed? (Yes, I am also going to measure...)

Base Circle of my cam is .080" smaller diameter than stock, so it has .040" radius smaller. (1.55 stock diameter, 1.47 my cam)

My heads are milled .010".

Headgasket thickness is .015" thinner than stock (assuming '02 stock MLS gasket has .060" compressed thickness, which is debatable. I've 'searched' on here to see anywhere from .049 to .060 thickness reported on this MLS gasket)

So, ignoring my longer valves, with the info above I would need a pushrod .015" longer than stock, correct? This would be a 7.395" pushrod.

And, if I factored in the .070" longer valve and the stock 1.6 ratio-rocker, how would this change the pushrod length (since the .070" valvestem increase isn't a 1-to-1 relationship to the pushrod)??

 

First rocker geometry.
If your valves are .070" taller, so you would have to shim by that much at the stand to be centered on the wipe.
Now to P-rod:
-0.040" (base Circle) + .070" valves = +.030 (shorter p-rod)
.030 shorter - .010 mill = .020 (shorter p-rod)
If your gasket is indeed .015 thinner then:
-.020 + .015 = -.005 (shorter p-rod)

So by calc you can run 7.40 p-rods (the +.005 will be absorbed by the lifter in preload)
So just center your rockers and measure the difference of gaskets correctly and that will give you a more aproximate figure)
7.35 will be too short IMO if you are running stock rockers and lifters.

BTW stock roker LS1 ratio is 1.7

 

Predator:

Your calcs look good, but are the pushrod and rocker arm bolt parallel enough to just add in the .070" straight up?

 

This is why you should adjust geometry first and have a center wipe.
I do not recall seing a .070 shim, but I know they come in .060 size.
which if this is the case and he uses 7.40 p-rods, then he will be be .005 under which is even better.

See calcs work to a T, provided the data is 100% correct and accurate but there is no substitute for actual measuring.

 

Not sure how you are shimming, but at the point of putting 0.070 under the rocker stands I would seriously consider the LPE stand that is steel and not aluminum. The steel will be three times stiffer.

 

Will an .060" shim still allow the rockers to fit under the stock valve covers?

And secondly, why aren't we hearing / seeing more people shim their stock rockers on this site? (do a search, and you'll see most don't even consider/think about shimming, but instead just use shorter pushrods....which I'm not saying is right)

 

A higher lift cam will wipe differently than a low lift. It's not a huge factor to most people. Their car will run a long time even with a not so great wipe, especially with roller tips. Assuring that the wipe is centered for your cam, you know that the roller tip will be shoving nearly straight down on the valve reducing the wear on your valves stems and guides and reducing a little friction in the process. Also, don't 243 castings use a longer valve than 241s or others? Is this the same length valve normally used for these castings?

 

Not having proper geometry will cost you power, valve guides tear, rocker wear, can even lead to lifter wear etc...
Bottom line, do it right or pay the consequences sooner or later.

 

Agreed. But, I'd like to now hear from those people that chose to not shim...and why? Or did most people here never even think of valvetrain geometry, and thus didn't know any better?


Will .060 shims fit under the stock valve covers?

 

Exactly, which means I wouldn't necessarily need a .070" shim, if I understand correctly, but something in-between 0-.070".

I'm still interested in how/what others have done when installing a higher lift cam with ported heads that have longer valves. What sort of shim did you end up with??

 

I bought shims in .010, .015, .031, and .062 in plans of shimming my setup this week.

 

Where did you purchase them from?


Others' thoughts/comments on my q's above??

 

Mcmaster-Carr. Not sure how you shim stock rockers. Mine are HS.

 

Check these Pushrod calcs above. They don't seem correct to me. I think in the two lines above that I have bolded, you should have done the opposite calculation (subtract versus add, or vice-versa).

I think it should read:
.030 shorter + .010 mill = .040 (shorter p-rod)
If your gasket is indeed .015 thinner then:
-.040 - .015 = -.055 (shorter p-rod), aka 7.38-.055 = 7.325


But now I'd like to re-look at the effect of the .070" longer valves, because I also *think* that you neglected to take into account the rocker-ratio:

7.380" Stock PR Length
+.040 for smaller base circle (add'l PR length needed)
-.010 for milled heads (reducing the PR length)
-.015 for thinner HG (reducing the PR length)
=====
7.395" New PR Length, W/out compensating for the .070" longer valve.

Now, knowing that the stock rocker is a 1.7:1 ratio, the .070" longer valve will push the tip of the rocker "up" .070", but using this ratio it will push the PR-end of the rocker "down" by only .041". (.070/1.7) So, to now incorporate this value into my 7.395" PR length from above:

7.395" - .041" = 7.354".

Thus, my calc says, assuming no shimming, to use a 7.35" pushrod.

If/when I shim, say a shim of .040" is needed for optimal wipe, I believe this will affect the PR length NOT with the same 1:1 relationship. Shimming will raise the rocker base, but the tip-contact to the valve will remain in the same location - so the PR-side of the rocker then cantilevers this amount as defined by the rocker-ratio. So using the 1.7 ratio again, a shim of .040" will actually affect the PR-side by an increase of ~.040 + .0235 = .0635" longer PR required.

Thus, using a .040" shim, the PR length required would be: 7.354+.0635 = 7.4175". (Thus, a pushrod of 7.40" length)


Can someone PLEASE confirm that I'm not all wet with my notes above? Predator-Z, this make sense, or what did I miss?

 

You're correct on the rocker ratio effect, but since p-rod length on the market are 7.325-7.350-7.375-7.40- (in brief, increaments of .025), I make the guestimation simpler, and that will keep me on the shorter side.
Like I said, those calcs are only accurate if and only if ALL the parameter data is correct (actal measurements).
That is why I mentionned to center (geometry) rocker wipe first and then take care of p-rod length.
See it is a little confusing but this is how it works:
Rocker stand height affects both pre-load and geometry while p-rod length preload (that is specific to stand non adjustable rocker system like LSX one), while that is not true for stud rocker setup, for exemple.
That is also why a dial with p-rod meter tool is the best way to double check for sure.
Calculators do not take all parameters in accord and are not LSX specific.