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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I am in the middle of a 350 vortec build/swap. I have new vortec heads (062) on an 86' roller block with stock rotating assembly, comp 276HR, stock self aligning rockers, Edelbrock RPM, holley 600cfm vac secondaries. This is my first build so i researched like crazy for about a year on vortec builds (and engine building in general of course).
My question is about the work my local machinist did on the vortec's for more lift. I brought the heads to him with the cam specs and told him i need bigger spring pocket diam. and screw in studs, right? He said he had done many vortec builds and all i needed to do was increase the spring pocket and go with comp 943-16 springs, no need for screw in studs. He also did say he would love to take my money and do it anyways (jokingly). So i trusted him and he did the head work and put the springs on as well.
Have any of you ever had the rocker studs actually pull out/break on a vortec? Will i be safe with this spring combo? Thanks in advance!
Re: valve train combo for vortec heads, too risky?
I have never had a stud pull out BUT I have seen a lot of factory studs snap with roller rockers because they are not long enough to put enough threads in the poly lock. Give him money and make him install screw in studs. It is fairly cheap and safe also at 551lbs /in those springs have some power better safe than sorry. The rest looks good should be an awesome build when you are done. Make sure to put some good headers and Y pipe to match.
Re: valve train combo for vortec heads, too risky?
Originally Posted by TinnMann2
new vortec heads (062) , comp 276HR, ...
He said he had done many vortec builds and all i needed to do was increase the spring pocket and go with comp 943-16 springs, no need for screw in studs. He also did say he would love to take my money and do it anyways (jokingly). So i trusted him and he did the head work and put the springs on as well.
Originally Posted by Orr89RocZ
Solid roller springs? do not run on stock studs! Go arp screw in
I wouldnt run those springs on a hyd roller. Not needed. A 26918 beehive kit for sbc would work for a 276hr
Your machinist should have known what Orr has described above.
No machining required for that matter.
Swap out the springs. Get something suited to the hydraulic roller. The 26918 work very well.
Get the screw-in studs.
Re: valve train combo for vortec heads, too risky?
Yes I've had studs pull out. (ahem...) Got a bunch of coolant in the oil and ate the bearings, necessitated a tear-down and rebuild.
No it wasn't Vortecs. Not that it makes any difference.
I won't build a "performance" motor with pull-out studs, PERIOD. Doesn't matter what cam, what springs, what valves, what what what what. WON'T do it.
943 is for solid rollers; something around 250 lbs on the seat and 550 lbs at .700" when used at BIG BLOCK installed heights, if memory serves. Should work out to near 300 lbs on the seat at 1.750" (stock Vortec) installed height. ALTOGETHER too much.
I'd suggest these springs here. http://www.texas-speed.com/p-4885-pa...e-springs.aspx The 1218 specifically. You'll need the Comp 787 retainers. No cutting of the heads required. Screw-in studs should be used regardless.
Last edited by sofakingdom; 10-14-2016 at 05:36 PM.
Re: valve train combo for vortec heads, too risky?
Jeez! I went to a "pro" because im a noobie and I feel like I got taken. I even asked him about the beehive combos that do not require machining and he said to go with what he recommends. Well I should have listened to what you guys said during my time researching. I do not want to go back there and give him more of my cash. Im thinking of trying the tap and alignment tool from summit SUM-900136, should be alot cheaper than the machinist, and I can order the right springs and a new head gasket because the heads are installed already. Oh well, its part of the learning curve i guess hahaha. Think its safe to tap the studs while installed? I really dont want to get a metal shaving somewhere it doesnt belong.
I have made a few mistakes so far and when I do another build I will know better.
and yes midias, i have hedman shorties and y pipe 3" single, no cat, all mandrel bent to dual exit stock style magnaflow muffler. Should be a mean machine when its done!
Heck now that i think about it, i have spend over 1100$ (CDN), about 1450 american, on these stupid heads already. I should have sprung for an aluminum pair for a few more bucks and shaved 40lb off my front end haha
Re: valve train combo for vortec heads, too risky?
Looking at the comp 26986-16 vs 986-16, which one would be the better spring? the 986-16 dual spring is half the price but is it going perform half as well?? Remember I already increased my spring pocket size so I do not need to run a beehive if I dont have to, unless they perform better of course.
Re: valve train combo for vortec heads, too risky?
Well if the heads have already been cut, then we need to know what the new OD of the pocket is, what the new OD of the guide is, what the new height of the guide is, and the new "installed height" (before shims). All of those things will impact the "best" choice, and any/all are now NOT stock. Or at least, potentially not.
Beehives definitely do perform better. Since the individual turns of the spring are all different sizes, and therefore have different natural resonant frequencies, they don't set up harmonics as well; and, the retainers are MUCH lighter. Like half the weight or less.
Re: valve train combo for vortec heads, too risky?
Yeah, the Comp "beehive" 26918 is hard to beat given the application and your Vortec heads.
Get that info So was asking about. Pocket O.D. and guide O.D.
Not sure of pricing comparing your Comp numbers to the 26918. At the very least your'll need retainers as spring locators if you go this route. I've used Comps 4872-16 spring locators. These are used when the guide has been cut down for a traditional positive seal.
As for tapping the studs...there may be a problem if you're intention is to run guide plates. They will require milling the top of the stud boss to accommodate the incorporated nut. If you're going to rely on self-guided rockers, then you can get buy with studs that have no integral nut. Plenty of guys have done this with the heads still on the vehicle. Not sure I would though.
Re: valve train combo for vortec heads, too risky?
I am so sorry for wasting your time guys! I just phoned the machinist and asked him about the choice of the 943 springs on the invoice... He said he did not write the full part number on the invoice. They are RV-943X from Elgin! I just assumed they were comp when I searched 943 springs on google and considering he got me the comp cam too. That explains why he ordered Elgin lifters instead of comp also, although I am sure the lifters are interchangeable with the pushrod length being the variable.
It is a single spring with a damper.
OD 1.260
ID .876
Closed Pos. 110 @ 1.700
Open Pos. 285 @ 1.210
This seems like a better suit for my application now, right? Do any of you have any good write-ups on valve springs handy so i can learn more?
Re: valve train combo for vortec heads, too risky?
Closed Pos. 110 @ 1.700
Open Pos. 285 @ 1.210
That's not enough spring for an aftermarket hyd roller. Note for example that the "open" spec they give is at only .490" of lift.
For comparison, go look at the MINIMUM spring recommendation that Comp gives for that cam, which is the 986. That is a DUAL spring, about 1.45" OD, which gives 130 some-odd pounds on the seat at 1.750" installed height, which would be over 140 lbs if installed at 1.700". Furthermore the 986 will go to about .600" of lift before coil bind when installed at the 1.750" height, whereas the typical 1.25" single spring will only go to around .550" with 1.700" installed height, AT BEST, before coil bind, which you MUST stay at least .050" away from. (your Elgin part doesn't give that spec but I'm just quoting a typical one) In a word, those springs don't fit that cam.
"Valve float" is a MAJOR problem with aggressive modern aftermarket cams such as the XR series. Contrary to what most people think, this is NOT "valve toss", where the lifter and valve and whatnot all just keep on going and fly off out into space as the cam lobe passes through peak lift. Rather, it's the valve bouncing off the seat as it reaches the closing point. If the spring doesn't give enough seat pressure to control the valve, the valve will bounce back, and that just HAMMERS all the parts in the valve train to death, besides causing reduced engine power and RPM capability.
No cutting of the spring pockets is necessary to put that Elgin spring in; it's stock dia for all practical purposes. He may have cut the guide down in some way since a damper won't fit over the stock guides in the Vortec heads.
Lifter brand is totally irrelevant. In fact there's a good chance the Elgin and Comp lifters are actually the same part... AFAIK neither makes their own, and there's a VERY small universe of companies that do, from whom everyone simply buys in bulk and re-packages.
It seems the Elgin have an equivalent open pressure. The seat pressure is off some though.
Check out the recommended maximum lift. That could be a deal breaker right there. .490" is less than the XR276HR lift. Something that needs to measured regardless.
If you examine the other minimum recommended spring in Comps list, it's the 26986.
Now at 109 lbs @ 1.800" and 280 lbs/in." rate, the question is: are these suitable because they're "Beehive" /conical springs? Or is the suitability due to the springs rating?
The issue with these is the 1.800" installed height. It's necessary to use offset valve locks when used on the Vortecs (or other OEM heads with a standard length valve.) This is the method used to install the 26918 on my Vortecs.
Re: valve train combo for vortec heads, too risky?
Those Elgin springs are the classic "Z28" springs; meant for factory cams like the 151, 929, and 962. Not really adequate for any but the mildest aftermarket cams, maybe the smaller "Summit" ones and the like, but CERTAINLY NOT the XE or XR.
The issue with these is the 1.800" installed height.
That's not how it works...
The spec is GIVEN at some particular installed height; doesn't necessarily mean they HAVE TO be installed at that height.
If the 26986 are 109 lbs @ 1.800" and have a 280 lbs/in rate, that means that if installed at 1.700", they'll be 109 lbs PLUS (280 × .1), or about 137 lbs on the seat; right where you want them to be for a hyd roller cam. Of course, compressing them that extra .100" at zero lift, also subtracts .100" from their max lift as well, but that's not an issue here. For example Comp also lists them elsewhere in their catalogs at 1.750" and 123 lbs and .600" max lift... right where the above formula would lead you to expect. (280 × .05 = 14, 109 + 14 = 123... surprise!!) They coil-bind at 1.040", which from a 1.700" installed height would allow something up to the mid .500"s of lift. Maybe .550" or so comfortably. At 1.700" installed, they'll give about 285 or so over the nose with .520" lift. Plenty for the cam in question, in fact, arguably near perfect.
And of course, they'll use a MUCH SMALLER 787 retainer, which in turn is MUCH LIGHTER, further easing the "float" problem.
Improvements in technology are often worth the cost of including them.
Re: valve train combo for vortec heads, too risky?
I should also mention, the 26986 is 1.4x" OD, which WON'T fit in the stock Vortec pocket. The PAC springs I linked to above however, are 1.29" OD, which usually WILL fit.
Avoiding more machine work is always a good thing, if it's something that isn't somehow inherently necessary like screw-in studs are. Especially since enlarging spring pockets isn't always possible or even A Good Idea: uncomfortably often, one hits water. Most of the better machinists will therefore cut the pockets using a radiused cutter, to extend the cut outward as small a distance as possible down at the deeper part of the pocket "wall".
Re: valve train combo for vortec heads, too risky?
The seat pressure spec alone on the Elgin spring is enough to exclude it for use with the 276 cam. Comp specs 132 @ 1.750". Elgin is 118 @ 1.700". No spring rate given. No first experience with them either.
Re: valve train combo for vortec heads, too risky?
I just did the math to find the spring rate on the elgin RV943X which is not given. correct me if i am wrong. using 118 @ 1.700 and 318 @ 1.21 i got a difference of .49 and a difference of 200 lb/in. Which would make the formula 0.49 x ? = 200. Answer is 408 lb/in. I did the same formula on the 26986 which had the spring rate given and it verified my answer. Im just trying to wrap my head around some of the basics on valve springs so this math is good practice, aside from cam manufacturer's recommendations on springs, how do i determine how much spring pressure is ideal for my cam? ( or any cam for that matter). Less pressure is better because it is less weight for the valve train to function? (open and close valves ultimately i guess). When is it better to have a higher spring rate?
Thanks in advance, i really appreciate your guys' knowledge on this. Back to studying valve train tech! haha
Re: valve train combo for vortec heads, too risky?
Yes you got the arithmetic essentially correct: that's about how it works.
"Pressure" is not "weight".
You need "enough" pressure to control the motion of the valve - that is, to make its motion EXACTLY DUPLICATE that of the cam lobe - at all times. You don't want "too much" to where the parts in the valve train are overstressed. Truth to tell, it's REAL HARD to get "too much" in the real world, except by using too little spring for the cam, or by operating the spring too close to coil bind. A "little" spring, like those Elgin ones, will be made of few turns of very thick wire, and their free height is relatively less greater than their installed height compared to "more" spring.
Generally, the hardest part of the motion cycle to control, is the instant of closing. The steeper the ramps of the cam, the more the valve will want to bounce off of the seat instead of closing and staying put. When it bounces, parts get slammed into each other at very high velocities. Stuff breaks. Cam lobes get a weird "pounded" place right at that spot. Lifters get their face destroyed. Lobes roll. Push rods break. Springs break.
A flat tappet hydraulic cam will want anywhere from around 90 lbs on the seat (stock) to 125 or so (XE, Voodoo, etc.). Something in the 250 - 275 lbs range over the nose is the usual. Thus if there's let's say 120 lbs on the seat and 270 over the nose, and the max lift is .500", then the spring rate is 300 lbs / in (270-120=150; 300×.5=150)
A modern aggressive flat solid, or roller hydraulic, will usually want about 130 - 140 on the seat, and about the same 275ish or a bit more over the nose. So, roughly the same rate, maybe slightly lower; just, more on the seat, and usually, "over the nose" might be more like .550" - .600" rather than .500". The way to get more seat pressure with a lower rate is to use a spring whose "free" height is taller, and is made of more turns of finer wire. Dual springs like the 986 are another way: you have an outer that's only good for around 2/3 of your total target, and the inner adds the other 1/3.
A racing solid roller might easily need well over 200 lbs on the seat and 600 over the nose.
"Weight" is a whole other matter. The heavier the valve train, the harder it is to control its motion. Think of each time the cam lobe tries to open the valve, as being like a hammer blow to the bottom of the push rod: that's how violent it is at higher RPMs.
The heaviest moving parts of the system are the valve, the push rod, the retainer, and the rocker. The top part of the spring, which moves relatively more than the bottom (bottom is sitting still against the head, top moves with the valve) adds weight too, which is yet another advantage of beehives: they're lighter up at the top, the part that moves, because they're smaller. Like everything, lighter is better, as long as strength is adequate. Valves can be made lighter by using a "tulip" shape on the surface in the cyl instead of the typical flat stock shape. Some valves have hollow stems. Reducing the stem dia is another way to lighten them: for example SBC valves are 11/32" dia (.344"), but LSx ones are 8mm dia (.315"). Push rods can be lightened by using thinner walls of stronger material. Retainers can be lightened by making them smaller: the ones for beehives are 1.055" OD compared to 1.4x" for the 986 spring, and much thinner to boot. Rockers are made lighter as far as their rotating mass, by making the parts that are farther from the trunnion lighter; steel ones, because the material is so much stronger, can actually be made quite a bit lighter effectively, than aluminum ones. Valves and retainers are sometimes made of $$$titanium$$$ to further reduce weight: not usually appropriate for a street build.
Last edited by sofakingdom; 10-19-2016 at 08:21 AM.
Re: valve train combo for vortec heads, too risky?
Want some decent tech material?
Get David Vizard's " How to Build Max-Performance Chevy Small Blocks on a Budget".
Don't let the budget thing fool you. The latest edition (2009) has lots of information regarding the SBC and performance building in general. There's a lengthy piece regarding valvetrain science.
Re: valve train combo for vortec heads, too risky?
To give you an idea of "aggressive" when it comes to cams, here's a couple of examples.
This one is a moderately aggressive hyd roller. I seem to recall it's a Comp XR series but I'm too lazy to look up the lobe #s stamped on it. If it is indeed a XR, then it's reasonably comparable to the one you're wanting to use. I wish I had a photo of a stock cam; it would be IMMEDIATELY obvious why an aftermarket cam needs more spring than ANY stocker.
Compare the slope of the ramps and the duration of max lift on that one, to this.
This one is a mild "street" solid roller. Look how the lobes are almost SQUARE: the "ramp" is more like a "jump". This thing is going to just pop the valve to full open as fast as it can, hold it there as long as possible, and then drop it back onto the seat almost totally unrestrained. It's pretty obvious why, in order to keep the entire valve train all with tension on it and no parts flopping around or trying to fly off into space, as cam "aggressiveness" increases, spring requirements go up QUICKLY.
10-13-2016, 05:39 PM
