ME Leigh

Ok everyone i have a set of aluminum Y-body LT1 heads with stock springs that i am converting to run on my 305. I would like to know what the max lift these springs can take is.

I am going to be running a comp XS262 solid lifter cam with 1.6rr. The cam has .477 and .488" lift with 1.5 rockers. So .512" and .520" with the 1.6 rr's.

I am just wondering about breaking in the new cam, what should i do? Should i run the stock springs or should i go with my upgraded springs that i will be running. The upgraded springs i will be running are a dead match to the comp 986 springs.

What should i do for cam break-in?

pasky

believe max lift on stock lt1 springs are .480

Vader

That may be a bit of a stretch, but close. The peak lift with those springs would be about the same as any other stock SBC spring, since it is the same old 85# spring that has been used in SBCs for decades. There is nothing special about the LT1 springs. I hope you didn't pay a lot for them. If you're changing them just because they were from or for an LT1, save the time and forget it - Unless your current 305 springs are cracked or failed.

The LT4 "Hot cam" springs are a bit different, using different wire (ovate) and having a slightly larger diameter. Peak on those is about 0.540", but they're still considered weak by modern standards for roller cams.

EDIT: Oops. I missed the part about the break in. If this is for a roller cam, you don't need any different springs for break in. If anything, break in with 1.5 rockers (if the slots are long enough) then change to the 1.6 rockers.

ME Leigh

Actually i am swapping in a mechanical flat-tappet cam and some modded AL LT1 heads. I bought the heads already rebuilt with the stock springs off ebay. I am going to swap to 986 springs when i put them on.

The thing is i don't have any SA 1.5 rocker only the 1.5's.

What should i do for cam break-in?

ME Leigh

So whats the consensus? Should i score some stock SA rockers and use the stock springs?

Nathan Plemons

Don't even try to get away with the stock LT1 springs, they are CRAP.

A lot of Corvette guys try to get away with swapping 1.6 rockers and keeping the stock springs. Although it technically will "work" they're asking for trouble down the road. The LT1 springs are very weak to start with and are not capable of taking a high lift. .480 is the lift with 1.6 rockers for a standard LT1 cam and that is VERY close to coil bind.

Most people upgrade to LT4 springs which are very cheap and are easily rated to take .525 lift, which is that of the LT4 Hot Cam with 1.6 rockers. Even that though isn't a great choice. LT4 springs are still pretty weak. Although they may be adequate for the LT4, the LT1 valves are heavier than that of the LT4. They'll work but you don't have a very big safety margin built in.

Example, I'm running an LT4 Hot Cam with 1.7 rockers. The car sees 6500 RPM's on a very regular basis. My springs though are 1.440" and will take nearly .700 lift before coil bind. This allowed me to sacrifice some lift capability and shim them up for a higher seat pressure. I've still got plenty of head room, they'll easily take .650 lift and they are strong enough to take any RPM I want to throw at it. Once or twice I've missed shifts and over-reved the engine greatly with no harm done. On stock LT1 springs or even LT4 springs my pistons would have met the valves in a very bad way.

My personal theory is that overkill is a good thing. Run the biggest spring that your camshaft will allow. I'm running about 140# seat pressure on mine, but that's a hydraulic roller so it can handle quite a bit more than your typical flat tappet cam can. Also allow yourself a minimum of AT LEAST .050 inches between your maximum lift and coil bind height. This buys you a safety net should you over-rev it.

ME Leigh

Again i'm not going to use the stock springs. I just want to know if i should use them for breaking in the new cam.

Stekman

The factory springs from an SBC reach coil bind in the very early .500"s (.510"-ish or so), and at that, by that point they are so weak that they cannot control the valve. Now take old aged springs and do that, and they are even weaker. I wouldn't trust them, primarily based on the lift issue (coil bind).

That's my few cents. Whatever it may be worth.

What springs would you run on the alternative side?

ME Leigh

I'm going to eventually run the 986 springs, but i don't know what to do for break-in.

Stekman

I would just get the springs now and, if you are worried, remove the inner spring. Though, it's a solid, so there's really nothing to "collapse" I suppose.

i don't know, don't listen to me.

Streetiron85

I think you ought to do a mock assembly with the shortblock completely assembled and the cam you'll be using in place.
Then bolt a head down with one of the old gaskets and the LT1 springs in there, and find out if they coilbind by slowly turning it through a cycle.
If it seems okay, then do the break in with those lighter springs and then switch them out for the stiffer springs after a half hour or however long it's supposed to take.
If the 1.6 rockers give it too much lift, then maybe 1.5s will work.
It seems like a good idea to play it safe, especially since there is no added cost involved other than your time.
But then... you enjoy changing valve springs anyhow, right?

Nathan Plemons

Mocking up the entire assembly requires a whole lot of time and energy that can be avoided by doing a little bit of math first. Just take one of the LT1 springs off and measure the coil bind height. If you can't do it an local performance shop can.