I've been looking more closely at the LS1 engine's build specs to see what GM did with this engine to improve performance over it's predecessors and where these things might be utilized when building other engines. The point of reference that I'd like to focus on is this engine's RPM redline. I have some ideas about what I THINK might be going on but I want to get the engine gurus' take on it. First, some comparisons:

1996 LT1 Camshaft profile:
duration=205*int./207*exh. @.050
valve lift= .447 int./.459 exh.
LOBE LIFT= .298 int./.306 exh.

2002 LS1 Camshaft profile:
duration=197*int./207*exh. @.050
valve lift=.467 int./.479 exh.
LOBE LIFT=.274 int./281. exh.

1996 LT1 Redline= 5,700RPM
2002 LS1 Redline= 6,200RPM

Head flow numbers aside, what I'd like to know is if there is any correlation between the LS1's increased redline and decreased camshaft lobe lift, vs. that of the LT1?

 

In a simple answer - no. There are many variables that determine redline, you cannot take one difference and say that determined the higher redline, the duration is different on the cams, that has a much more profound effect. You also need to look into lobe seperation/overlap/cam advance/retard etc.

 

Okay, let's simplify this even more. Hydraulic roller lifters will "pump up" full of oil when the cam reaches a certain RPM which results in valve float. What I'm trying to determine is how much the linear range of motion that lifters experience affects what RPM they will begin to
"pump up" at?

What I suspect is that the reason GM didn't just grind in the .20" additional lift the LS1's cam has over the LT1's is because the lifters wouldn't be able to handle that additional range of travel at 6,200RPM's without pumping up. So they split the difference with higher ratio rocker arms.

If I'm off, tell me why.

 

If you are on, tell me why.

Honestly I'd need an explanation on why increased lift would cause what you propose. I'm not saying you're wrong, just that I don't know the engineering/theory behind it.

I agree w/ the post above, there are a LOT of things different in the engineering of the LS1 vs. LT1 valvetrain.

 

Aggressive ramp rates. If you have two cams that both have the same lobe lift, but one has say 240* of duration and the other has 210*, the one with lower duration has a more aggressive ramp rate. This means that even though the lifter on the 210* cam will still ultimately travel the same distance as that of the 240*, the speed at which it goes from 0 lift to max lift and back again will be higher.

Imagine two men airing up bicycle tires. If we assume that both tires need the exact same number of pumps to get full, which man will complete the job first: the man who takes 1.0 seconds to complete a full pump cycle, or the man who takes 0.5 seconds? (Duration.)

To expand on this, let's say that we were going to limit the man who takes 0.5 seconds to complete a pump cycle by only allowing him to use half the range of motion on his pump. (Lift.) What will the man have to do to pump the same amount of air as he was before? (RPM.)

If you look at the specs in my first post, you'll see that the LS1 cam has a lower duration than the LT1 cam. But you'll also notice that the overall valve lift is higher than the LT1 due to use of the higher ratio rockers used in the LS1. We've established that higher lift with lower duration equals more aggressive ramp rates. If GM knew that it needed to get 6,200 RPM's out of the LS1 to make effective use of the head's flow characteristics, was lowering the camshaft lobe lift to soften ramp rate aggressiveness how they got more RPM's out of the hydraulic roller lifters?

 

I wouldn't count beehive springs out of the equation. They are able to control valvetrain motion at higher rpm better than LT1/LT4 (or other cylindrical spring packages) springs with less load. That helps the hydraulic lifter a lot. Applying that technology to other engines (LT1) allows the higher rpm and more aggressive profiles to be used. This is done a lot on some LT1 H/C packages that work well past 6200.

As Machinist said, it's not one thing, it's a combination that makes a valve train work. Rarely are things like this 1-dimensional.

Oh, yeah, how about 7K HR LS7?

 

just to throw this in the pot, dont forget that the ls1 has a greatly increased base circle also. which for a given duration/lift give it more lobe area, which is what getting more rpms out of a "bigger" cam is all about. regular sbc cams vs ls1 cores is apples to oranges wrt to lobe area vs duration/lift. another side effect of the big base is that the cam doesnt try so hard to shove the lifter through the block which causes less deflection in the lifter body and keeps the bleed down rate closer to the engineered level. i also believe thats part of why the ls1 left the factory with 1.7 rockers instead of the traditional 1.5's because they limit the amount of acceleration that the lifter actually has to see. I'm with Oldsstroker on the valve springs you cannot count out a lighter spring/retainer package, ask any race engine builder they'll trade any number of vital body parts to shave a few grams out of the valvetrain.

 

Larger base circles...I had totally forgotten about that. But now that you mention it it makes more sense.

So what you're saying is that if you were to install a large base circle blank cam core into a block and set a lifter into the bore onto one of the unground lobes, the lifter would automatically sit higher in the bore than if you had used a blank standard base circle cam? Then from that point whatever lift and duration you happened to grind into either cam, so long as it was equal for both, the larger base circle cam would always have less aggressive ramp angles while maintaining a lift advantage over the smaller one. Right?

I'm damn curious now to see a side-by-side comparison of the ramp angle measurements in degrees between the LS1 cam and the LT1 cam.

Does anybody happen to know if there is enough tolerance in an LT1 block to allow for the cam tunnel to be bored out to accept a large base circle cam?

 

it hasnt got anything to do with a blank core, or how high the lifter sits in the bore when its on the base circle (heel) of the camshaft. and i doubt you'll ever use it in an lt1 block you'll probably have rod interference with even a stock stroke and with a stroker motor you can just forget it. there are aftermarket small blocks with big block sized cam tunnels in them and raised cam locations to achieve it, but thats beyond the scope of 99% of street builds.

there really isnt too much to glean from the way the ls1 cam is setup unless you own one and in that case the leg work is already done for you. the things that can be used easily from the ls1 already have been adapted over (beehives).

 

I know of one strong LT1 advocate that runs a 55mm cam in his record breaking/holding LT1 Firebird... I ain't sayin his name though

It is interesting that he don't run the longest stroke possible too...

 

now you've done it, you're gonna have to give up a few details on that particular job.

i wasnt even aware a core existed for something like that.

 

not sure if anyone noted this-
but you forgot to factor in rocker ratios. That would throw your lift = rpm theroy into speculation.

In my limited experience, lift has a greater tendancy to effect torque magnitude than powerband placement.

 

Lighter valves with 8mm stems, lighter springs/retainers help to stabilize valvetrain at high rpm. Large journal cams allow use of aggresive profiles.