Long story short:

My friend and I dyno'd his Z06 Vette this weekend. He made an impressive
439.7 HP @ 6500 RPM Naturally Aspirated.

The power curve looked strong from 3500-6800, with a near flat line from
5000-6500 RPM.

He noted that his pre-load was set to approximately 0.046"!

I don't know anything about the LS1/6 valve train, but he did mention it was
non-adjustable.

My suggestion was to decrease the pre-load amount to roughly 0.015 - 0.020" hot.

He is hesitant to try this setting because of some information given from
other Z06 owners who claim the thermal expansion of the heads and block
will cause slack in the valve train if the pre-load is set less than 0.040"

I find this very difficult to believe because while setting the valve lash hot,
the expansion is taken into consideration.

Another doubt I have is the amount of expansion of the aluminum components
to amount to 0.040".

Does anyone have experience tuning valve trains on LS1/6 engines with some
sort of dyno proven data to prove/discredit any of the above statements?

If not, does anyone have solid information on the typical expansion of aluminum
components at an operating coolant temperature of 200 degrees?

 

Actually that's probably close. In a Hyd Roller preload of about .006 (or -.006 lash) is about perfect.

.015-.020 might be too much preload in a Hyd Roller motor, but it all depends on the springs in the lifter.

As for the thermal expansion........

All you really have to look at is the difference in temp (70-200) 130 degs F and the PR length (7.400) and the difference in the rate of thermal expansion between the steel and the aluminum. Basically at the most it's about .0006" growth so not something you can really measure.

Comp has PR lengths in shorter increments for the LS1 guys and there are adjustable rocker arms (but nobody wants to use them, but they want to run springs that effectively put 700lbs over the nose on the PR so i'll never figure that out).

If he doesn't want to change it then don't worry about it. You could always try it on the dyno, but you would need different length pushrods or adjustable rockers to do it.

Bret

 

Thanks Bret.

Your response is more along the lines of what I have been shown for pre-load (0.006")

I'm wondering if you have misread some of the numbers in my post however?

The current pre-load on his motor is 0.046".

I suggested 0.015-0.020"

You're saying even less at 0.006" (basically zero lash)

Is this correct?

 

You probably couldn't actually get a real preload of only .006 if you have non adjustable rockers and have to use pushrods and shims. Also if you set that cold you would blow your engine most likely.

The lash loosens up a TON on the all-aluminum LS1 at temp. Usual is around .010 more hot than cold. So if you set the lash under .010 cold you are gonna blow the lifter apart most probably.

 

Well he sets it at .046" now and it don't blow up.

.006 hot (with the use of adjustable rockers like I said) would be perfect.

Bret

 

Bret,

Actually having run many many tests I have never seen many gains running lash tight on hydro roller stuff. We have hydro rollers turning 7000 in street cars and making from 500-600 RWHP too. Actually quite a lot you will gain some power when running more preload for various reasons and it depends on the cam and the lifter. We turned 8500 rpm in the NMCA with hydro rollers.

The only thing that light lash does do is make sure if you do float you can't pump up too far and bend the valves or pushrods as easy for the most part. With low spring pressure you don't want tons of preload.

".006 COLD" preload will blow it up is what I was saying. If you wanted around .006-.010 HOT you would need around .016-.020 COLD. He asked how much the lash changes from cold to hot and I answered since I know. I've set valves a lot on these engines and ran the first really successful solid roller combo which was also the first real 10 sec LS1 engine and also later the first 9 sec LS1 engine camaros.

I've seen running regular Ford and LT1 lifters from .010-.100 preload hot with no real difference in power except that the power went slightly up with preload. On the down side if you over revved your engine with that much preload you could have some massive pump up and end up crunching valves and pistons together!

 

Clear as mud now

This may only apply to Crane products, but the expalnation makes sense.

The following write-up, along with other sources have always shown that minor
amounts of pre-load make better power. Even with my flat tappet hydraulic
cam, I'm setting 0.021" using feeler gauge and increased nearly 3 HP at 5800 RPM on a chassis dyno.

Not knowing the LSx valvetrain at all, I'm very surprised to learn that a roller
cam is setting 0.040"+ down on the seat!

The last concern is during the valve overlap period where the piston is near
or at TDC...what if the lifters pump up that additional 0.040" - 0.0100"? There must
be quite a bit of clearance, or valve relief?

http://www.cranecams.com/?show=faq&id=3

If the opposite occurs and the pushrod descends too far (more than .060”), then you have excessive lifter preload. In theory, a hydraulic lifter can pump up whatever preload you put into it, therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat.

 

I know where Eric's coming from on this. I build mild street engines almost exclusively which means a lot of hydraulic cams (usually not even roller cams). Many times (yes, that would be a lot more than just once or twice) I have seen where using almost no lifter preload helps and engine make more power upstairs and effectively extend the RPM ceiling of the motor. And almost every time it's in a motor with marginal or completely inadequate valve springs. By leaving nowhere for the lifter to pump up TO via very small amounts of lash, you mask some of the bad, power-robbing symptoms of the valvesprings starting to "lose control" of the valvetrain in the upper RPMs. i.e. lifters "pumping up." But it's a head-fake. Put in some appropriately matched valve springs designed for the RPMs the motor is actually spun to and suddenly the amount of preload doesn't seem to make much difference AND it will spin higher without power drop-off.

It's tough enough for the weekend wrench like myself to nail down a simple .500" lift, 6500 RPM flat tappet SBC hydraulic lifter valvetrain by playing mix-n-match with 4 different manufacturer's parts. I can't even imagine what it's like for you LS-1 guys with big heavy factory hydraulic rollers, massive 1.7-1.8 ratio rockers, an aftermarket cam with ???factory??? valvesprings..... and then trying to zing it well over 6500 while yanking the valves .600"+ off their seats. That's a LOT of valvetrain movement in a very short period of time. I imagine that engine tells you very quickly if you didn't spec out the valvetrain combo properly (somewhere north of 6500 it shuts off leaving you with a handfull of bent valves and pushrods to show for it).

 

I'm not trying to be a pain, but I really want to get my head around this,
because it's not making sense.

I know my valve springs are matched because that's what Comp Com specifies
for their cam. I had my install height shimmed because it was incorrect.

I also believe that Arun (Z06 owner) has proper springs installed because
he mentioned having the spring pressure checked and shimmed for height.
Whether they are the recommend spring, or not can't be answered at this
time.

If the springs are matched to the cam and installed correctly (as per speed
shop), then will a hot pre-load setting that rests at 0.006-0.010" be sufficient
to overcome the thermal expansion of the heads and block?

Second, if we know that solid cams make more power, shouldn't we setup
the hydraulic lifter to reduce plunger movement at all costs?

Afterall, isn't the purpose of the hydraulic lifter to take up slack in the valve
train as the parts wear down?