Okay, I know it's an old grind, slower opening, lower lift, etc...
BUT, it is also a grind that is easier on parts, has a wider LSA for idle vacuum (ie: I want power brakes) but can still pull to high RPM's, and was good for 14.2 1/4's with street tires, stock exhaust and unported heads.
Oh, and I'd plan on using 1.6 rockers to put the valve lift at a good level.

Anyways, here's my question... In the old Z28's, they teamed this cam with 11:1 compression and 100 octane gas. But, nowdays that 100 octane gas is missing, and we have to settle for a mere 92. Now, in the '71 Z28 they ran the same engine, but with 9:1 compression, but I'm sure that was an emissions dog, and could have used more compression...

So, if I were to run the LT1 grind, what compression should I aim for to run on 92 octane?

 

I think octane listing for gas was different back then, so 100 back then is like 95 now. Anyway, I think you should be able to run 10-1 with that cam if your car isn't a heavy weight and you have a decent gear in the diff.

 

That LT-1 cam was a pretty decent sized cam, but I don't know if it was big enough for you to get away with 10.0:1 compression without detonation. The general rule of thumb for an iron headed engine that is running anything short of a huge racing cam is that the maximum compression ratio that is "safe" is about 9.5:1. Aluminum heads you can generally run about a full point higher (10.5:1).

I know you say that cam is easier on parts with its slow valve openings and everything, but I think you're slightly misguided in your quest for a cam. Technology on cams has come a looooong way in the last 33 years, I promise. Have you ever seen the duration figures for an LT-1 cam? It's like 250+ at .050". That's HUGE! You can get a cam now days with MORE lift and LESS duration. If you get the matching springs and pushrods, I promise you will have nothing to worry about as far as reliability and durability. The reason that cam had a wider lobe separation was because the duration was so long and the overlap was so huge, they HAD to widen it out to prevent TOO MUCH overlap and TOO LITTLE vacuum. The newer cams achieve the same lift sooner, allowing less duration (which plays probably the biggest factor on your vacuum) and a lower lobe separation (better scavenging and gives you a little "lope" ) Basically, you will make MORE power, MORE vacuum, get BETTER gas mileage, MUCH better drivability, all while having just as much if not more durability in your drivetrain parts. If you don't trust me, talk to the cam manufacturers. They'll be happy to send you all sorts of information and graphs and charts and pictures to better explain how and why they can do all that. Good luck!

 

Concerning compression:

If you run a fast-burn modern cylinder head like the excellent Vortec heads - which only need a max of 32 degrees total timing to make max power - then you can up the compression on 92-94 octane fuel. I run Vortec heads, 11.1:1 413" small block, and can run on 94 octane on the street. At the track - in the cooler Fall air - I don't need race fuel. But in the hot summer months, the car runs a bit better with 100 octane race gas and 94 pump mix.

Concerning camshaft design:

That old LT-1 cam has the following specs:

PN 3972178

Duration @ 0.050": Valve Lift: Lash:

Intake: 242 .435" .024"

Exhaust: 254 .455" .030"

Lobe Sep Angle: 116 deg.


Although its true newer technology cams make power, the 'old stuff' made power back then, and it can make power today. The reason is the slower-ramp profiles are easier on the valvetrain and do not need as much spring pressure on the seat or open as fast-ramp newer style hydraulics. And really, a lot of the power over the years that has come about is primarily due to vastly improved cylinder head design, like the Vortecs for example.

I run an old-style slow ramp hydraulic flat-tappet cam so I didn't need to cut the spring pad of my Vortecs when I put the engine together over the winter (it was a budget build), and yet at 3800 lbs. I've managed a best so far of 12.15/110.52 in the summer heat on drag radials. Thats about 400.2HP at the tires, or just under 500Hp at the flywheel accounting for a 24% loss of power through the drivetrain using a 3000 converter and TH400 transmission.

In fact, you can use right up the massive GM 2nd design off-road solid lifter cam and still only need a 1.273" diameter valvespring. With 110 lbs on the seat, heck you could even sneak in a set of stock stamped-steel GM rockers and be okay. Perfect for the budget-racer.

I'm not saying the old stuff is optimum; what I am saying is it isn't all that bad either. If all the budget can handle is a moderate-lift cam with a stock diameter valvespring and say, stock stamped steel rocker arms, then there is merit to using the old stuff.

Just another opinion.

 

If you're worried about being easy on engine parts go hydraulic roller. Then you're not having reset the valve lash all the time either.
Ya, it cost more but it'll last a lot longer, you can get a more agressive grind and still be totally streetable and you don't have the constant up keep.

 

Dirt - I like your cam choice - I've actually looked at the Crane solid that has about those specs, but a wide 114LSA. Thing is they call for dual valvesprings, 130# seat, 400# open! $$$
Maybe I'll ask for Vortechs for X-mas...
Right now I've got a set of #601 305HO heads I'm working with. The stock flow numbers I've seen already put them flowing better than stock camel humps (the intake port is bigger by a few cc's) and they can be ported out pretty well with some work - about to where vortechs flow.
Of course, they've got those small chambers... I'll be polishing them which will add a few cc's, but I'd still like a cam that is less detonation prone - hence the wide LSA, long duration plan to prolong the intake valve closing and keep dynamic compression in check...

I'd love to go hyd roller, there are some sweet-looking grinds out there. The problem is that an entire hyd roller setup (cam, lifters, pushrods, springs, cam retainer) would cost about 1/2 of my entire budget...
With the LT1 cam, I can get cam and lifters for $150 and Z28 springs are cheap - probably not much over $200 for the valvetrain.
Yeah, budget is a major factor!

I know with faster ramps, you can get more vacuum and all, but every cam I see with 6500+ rpm potential is down at 110 or 112 LSA and having vacuum for power brakes is questionable - some say it's OK, some say not enough... I figure if GM put it in a production car, power brakes have to work pretty well.
Also, the valve lash takes out some of that duration, so it's not quite as big as a 242* hydraulic...

 

The problem with hydraulic rollers is that they don't RPM very well. Under their duration curve - and below peak RPM - they do make good power and are efficient compared to a flat-tappet. But hyd roller lifters are heavy suckers, and even the biggest Comp grinds are relatively low RPM cams due to valve float issues. Some guys run a rev kit to combat this so they dont have to run a valvespring with so much open pressure it drastically shortens the life of the lifter, but many of those kits dont actually work, according to Dave Vizard.

A solid-flat tappet cam has a secret weapon few are aware of, but is used to great effect by Winston Cup cars which must use a flat-tappet cam - valve 'lofting'. Valve lofting is used to get the last 40HP out of a WC car, and in fact Lunati has now created a series of solid cams called their 'Launcher' series to take advantage of this phenomena. What happens in a nutshell, is the solid lifter will literally loft the valve higher at high RPM's, which allows the head to take in more airflow, but yet the valve is under control whe whole time. This is not the same as valve float, which is uncontrolled harmonics. The solid-lifter gets away with this because it is light, and well, solid. (A solid roller cannot do this because of the weight of the roller follower.)

In any case, I kind of got away from the topic a bit, but I'd say you know what you are doing by the sounds of it. The wide lobe sep aspect is correct, if you want to run higher compression on the street. Some guys think tighteing up the LSA allows for more compresson but this is not so - it actually increases cylinder pressure where you dont want or need it. My cam has 114 LSA and is probably one reason I get away with the 11:1+ CR on the street with steel heads using 94 octane (along with the fast burn Vortec chambers).

Its tough to beat the Generals' cam grinds for power on a budget. Crane is the company that actually grinds GM's repro 'musclecar' cams for them, so if you buy Crane its the same as buying from Chevrolet. I'm looking at installing the 2nd design offroad cam as a winter project.

Also, if you want to quicken up the valve action, theres always using a 1.6 rocker on the intakes.

 

Tightening the LSA reduces cylinder pressure. Think about it, the duration of the cam is a set number of degrees of rotation. The close you put the intake and exhaust cams together, the more overlap there will be, which will bleed off a little cylinder pressure.

 

Tightening the LSA closes the intake valve sooner.

This means, as the piston travels up the bore at lower RPM it is trapping more cylinder pressure. Widening the LSA traps less pressure, as the piston is further up the bore before the intake valve closes.

So - if you have a high dynamic compression ratio and couple this with a tight LSA cam, the cylinder pressure increases and detonation becomes more likely, especially at low and mid-range RPM.

 

also, overlap is occurring right around TDC, and berfore the intake stroke. So, there's no cylinder pressure yet to be bled off.

Of course, the tighter LSA does allow some exhaust reversion. This is responsible for the lope, but also accomplishes some EGR, which should help some. Of course, I might (*gasp* horror!) decide to run EGR. This will likely go in an '84 trans-am, so technically it has emissions regs, and the EGR shuts off at WOT anyways...
But, considering the Z06 'vette is running 10.5:1 and LSA near that is the LT1 grind, there's gotta be something there to that wide LSA...