97 6speed z

How much valve spring pressure is TOO much pressure for stock LT1 hydraulic roller lifters???

Long story made short:

I recently purchased a set of AFR 210 cylinder heads for a 396 LT1 build that I am currently sourcing parts for. Since the 396 build is probably 1 year to 18 months away from completion; I’m considering putting these AFR heads on my current 350 LT1 motor, (just until I finish the 396 build and then swap the heads over to that motor).

Now, my main concern about doing this, is that the AFR heads have a set of (small “ish”) solid roller valve springs on them. If I put these heads on my current 350 motor, I’ll be seeing valve seat pressures of 220/225 lb’s., and …… “over the nose” spring pressures of 545/550 lb’s.

Soooooooo ………….. my question here is just how much valve spring pressure can stock LT1 hydraulic roller lifters take??? Is anyone here running spring pressures equal to, or greater than these numbers with ........ stock LT1 lifters???

Puck

iTrader: (17)

There are more reasons when just the springs why you probably shouldn't run those heads on your 350. Depending on your cam you may lose low end for a trade off up top that you never see, and slow yourself down. Those are big heads for a 350.

Not to mention all the extra stress on your cam lobes, which if its not billet and a quality core may end up wiping a lobe. What about your pushrods? If they are not quality, larger diameter hardened PRs then they will look like spaghetti at 7,000 RPM with 550lbs of pressure. Which rockers are you running? Cheap extruded aluminum rockers are often not even full roller, and they will not last on a 550lb valvetrain.

Keep the SR springs on the SR cams and vice versa.

96capricemgr

iTrader: (1)

Valvesprings are a wear item with aftermarket cams, you do what you are proposing and if it did work which it probably wont then those springs would be worn out by the time you went to put the heads on the new motor.

97 6speed z

Puck, you raise some valid points in your post, but, believe me I'm way ahead of you and the valvetrain issues you've raised. The "custom" cam in the 350 is indeed ground on a billet core, and, I'm running hardened 4130 chromoly pushrods with a .080" wall, and Comp Cam Pro Magnum roller rockers. The "weak link" in the valvetrain would DEFINITELY be the stock hydraulic roller lifters in this scenario.

You've peaked my curiosity about your comment about "losing low end for a high end tradeoff that may not occur"? You really don't think that swapping JUST cylinder heads with a 188cc intake runner that flow 260 cfm (i.e. at .600" lift ..... just to pick one (1) flow point), for heads with a 207cc intake runner that flow 295cfm (estimated on a 4.000" bore), will hurt low end performance do you?

96 capricemgr, my Z is pretty much a Summer car these days. It sees about 3,000 miles a year with three (3) or four (4) Test-N-Tune nights at the local dragstrip. I'm not at all worried about wearing out those quality AFR PAC solid roller springs before the switch to the 396 motor, (although at that time I will dis-assemble the heads, replace the valve seals, and re-check spring pressures).

nitrous2fast

iTrader: (2)

Puck is referring to port velocity. The larger ports on the Afrs will slow the velocity of the air at lower rpms and allow more reversion. Yes it will hurt low speed performance. How drastically will be determined by the porters of both.

97 6speed z

Nitrous2fast, yes indeed, I also surmised that Puck may have been alluding to the delta (change) in port velocity as the rational for his statement, but ...... I guess we just have to "agree to disagree" on this point.

In the specific example we're discussing here, it's my belief that the delta (change) in over all flow of these two (2) intake ports, will more than offset any loss due to negative delta V at low RPM. Remember at low RPM the velocity in the port is lower than at high RPM, so the delta V between the two heads with also be smaller at low RPM.

In the final analysis it's the amount of cylinder filling Q that determines the power you'll make on any combustion stroke, and, I agree that while the better flowing port will move air at a slower speed than the "tight" port will ....... Q will still increase!

Now, back to the original question, anyone on here running high spring loads on stock LT1 lifters???? How about those newer LS7 "race" hydraulic rollers, are they any better for higher spring loads. At $99 a set might they be worth a try?

96capricemgr

iTrader: (1)

You aren't listening to anything anyone is telling you so why keep asking questions?

Just go prove us all stupid already.

97 6speed z

I'm not asking questions (plural), I've only asked one (1) question, and ......... nobody has answered it yet.

nitrous2fast

iTrader: (2)

I guess you have no idea how valve events work..... The intake valve doesn't shut at bdc before the compression stroke; it actually closes after, quite a bit after on some cams. Cylinder filling also has to do with fill time in seconds not just degrees; thus changing VE along the rpm range. Port velocity determines fill time along with degrees open. As you may very well know at low rpms a tiny port can easily fill a cylinder. but hey use all the Q you want to fill your cylinder heads...

97 6speed z

Nitrous2fast, yeah I guess I just have NO idea how valve events work, so take me to school here. Just where does that btd valve timing event occur with respect to say ........ bottom dead center BDC ?

And, about those seconds it takes to fill that cylinder, see again I always, thought that at 6,000RPM that intake valve was opening 50 times a second, silly me.

BALLSS

OP

looks like you have 2 ?'s

regarding the second one, mu $02 is if you use the heads with the solid lifter springs...that is a butt load more seat & open pressure from springs your current hydraulic roller cam needs and I assume will put unnecessary spring pressure on the current cam & lifters.

Not going to comment on putting those heads on a 350...others have expressed their points on that

maybe just put some springs on the AFR heads more suitable to your current cam and keep the others until you go solid on the 396 build...

Puck

iTrader: (17)

Some people ask questions without really wanting help.

What are your cam specs? AFR 210s are definitely on the big side for a 350 limited by the LT1 PCM. Huge ports that want a lot of cam to fill them up...which then gets you in trouble with our stock PCM. The cam that wants AFR210s on a 350 doesn't want a 7,000 RPM limit.

The power you gain, depending on your cam, will be primarily on the top end. Unless its a pure drag car don't want to gain 15 more hp in a very narrow power band at the expense of 10 from idle. You will slow yourself down. In my experience, I would either swap to HR springs and step your cam up and deal with a top end heavy strip car (which wont be THAT bad if its not a DD), or just hold off completely until your stroker is done.

As for your question, do not do it without swapping springs. The plungers of stock HR lifters will not be happy with 550lbs seat pressure. Your .080 wall PRs and Pro Mags will be fine.

speed_demon24

iTrader: (6)

Why won't your old spring go work on the afr heads?

nitrous2fast

iTrader: (2)

wow I had a typo... good thing you are here to correct me. .05 sec in still considered in seconds. but hey if you want, put that in milliseconds if it makes you feel smarter. Hey im glad you can do some form of math, but at 6000 rpms the intake valve open's only 25 times per second.

97 6speed z

Puck, from the level of detail you're providing in your reply's I truly believe you're sincerely "looking out for my best interests" here, but, maybe what you didn't pick up in my brief description of why I'm looking at putting those AFR's on my current 350 motor this Summer is this: I know those new AFR heads were not bought for my current motor. They were bought for my 396 engine that is 18 months away from being built.

My "grand idea" here was ........ other than a set of head, intake and header gaskets, what would be preventing me from just "slapping" these heads on my current motor, to try them out for a year? Everything you've said in your most recent post would be true if I were trying to "optimize" my 350's performance with these heads, but ........ I'm not looking to do that. Those AFR 210's were chosen for the 396 motor, and will definitely be "optimized" for that motor!

Speed_Demon24, you're on the right track here. My initial question pertained to just "slapping" the new heads on my current engine, the easiest way possible. Since I've gotten some direct experience now from a similar post I made on another LTX board, I'm getting first hand reports that even the LS7 "race" HR lifters are failing at seat pressures around 165-180 lbs., so that 220 lb. seat pressure from those SR springs is just waaaaaaay to much.

And, since, as you suggested, I'd be changing out the valve springs to use the AFR's anyway...... I'll just pick up a new set of hydraulic roller valve springs, and put those on.

Nitrous2fast, hey you're the one who told me I knew nothing about valve timing events, sooooooo ......... I didn't know if I'd truly missed understanding that btd event. Now typo's not withstanding ....... let's review your second comment about that "some form" of math I can do.

6,000 RPM/60 seconds per minute = 100 rps (revs per second)

Now on a four (4) stroke engine, the intake valve only opens and closes once every two (2) crankshaft revolutions, so at 100 revs per second/2 crankshaft revs per intake event ......... I get 50 intake events per second ......... at least by my "form" of math.

nitrous2fast

iTrader: (2)

Well **** I cant add. lol oh well. im having a bit of a bad day... back to topic- What size valves are in the afr's? 1.94, 2.02? having larger valves will require a bit stiffer spring than what comp has recommended. The stock lifters have taken a beating from quite a few people. a double/triple spring setup would give enough over the nose spring pressure to control the larger valves. Seeing that your not concerned about low end stuff or optimizing the "for a little while" setup those heads will work fine. Idk if anyone has an answer for the too much pressure question. Some probably will take 240" some may break the cups at 200. The rpm is probably gonna be the worst on them with large stiff springs.