Part numbers for 1970 LT1 cam
Looking fo the part numbers, GM, Sealed Power, Crane, etc for 1970 LT1 camshaft and lifters.
Thank you.
Thank you.
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Re: Part numbers for 1970 LT1 cam
The GM assembly of finished LT-1 camshaft and indexing pin is 3972178, which is what was sold over the counter. The ...182 is the finished camshaft part number without the pin, which was not sold over the counter. All or the last several digits of the finished camshaft are part of the casting mold on most Chevrolet camshafts. It is often referred to as the "casting number", but this is a misnomer. The P&A catalog lists the finished camshaft part number as the "ID number".
The only available OE-type mechanical lifters are the piddle valve type used on big blocks. which allow more overhead oiling. The F-M number is AT-992 and the cam and 16 lifters may be available together under a single number. Typing the part number into the NAPA home page part number/cross reference box should answer the question.
Most aftermarket cam companies also sell mechanical lifters, but I'm not sure of their design. My understanding is that only one company manufactures mechanical lifters, and all cam marketers purchase and then sell under their own brand/part number.
The original small block type "edge orifice" lifters, 5231585, were also sold by F-M under part number AT840R. Both are long discontinued, but sometimes a NOS set pops up. Small blocks don't need as much overhead oiling as big blocks, and the less overhead oiling is an advantage in restricted oil pan applications.
DukeComment
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Re: Part numbers for 1970 LT1 cam
Thanks Joe, those are insanely cheap. RockAuto has them for $2.11 each.
Duke,
It's probably been asked several times but valve springs and rocker arms work best with this cam? I will be using it with some ported 461 castings that will have screw in studs installed.
MikeComment
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Re: Part numbers for 1970 LT1 cam
The OE LT-1 engine used the same valve train parts, other than lifters, as your grandmothers '67 283 2bbl, and they all work just fine with the LT-1 cam.
With careful valve spring height setup to allow .090-.100" coil bind clearance the valve train will go to 7200, and if you did the heads right it will still be making usable power as long as you use a decent aftermarket connecting rod like the Eagle SIR5700. If not the engine might go BANG! long before anything internal wears out.
As long as pressed in studs have no history of pulling, they really don't need to be changed to screw-in, but it will certainly do no harm.
DukeComment
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Re: Part numbers for 1970 LT1 cam
Duke, Mike,
I got the cam and lifters from Rock Auto.
$2.11 eqch for the lifters and $116 for the cam. The lifters are listed as a clearance item so if anyone is planning anything, time is of the essence...
JohnComment
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Re: Part numbers for 1970 LT1 cam
IIRC, John, you shimmed the valve springs to .090-.100" coil bind margin for the Special 300 HP cam. That's why it revved to 6800 before lifter pump up set in.
Since the LT-1 cam has somewhat greater lift, you need to reshim the 3911068 (Sealed Power VS677) springs to the following heights to allow sufficient coil bind clearance with the LT-1 cam.
Inlet: 1.15 + (.306-.012)1.44 + .090/.100 = 1.656/1.666"
Exhaust: 1.15 + (.323-.017)1.44 + .090/.100 = 1.681/1.691"
1.15" is the coil bind height specified in the GMPP catalog for the ...068 spring, and 1.44:1 is the actual maximum rocker ratio achieved at full lift. The decimal numbers in parentheses are the gross lobe heights and clearance ramp heights above the LT-1 cam's base circle.
This will provide sufficient coil bind margin with the valves set at 1.37(.012) = .016" and 1.37(.017) = .023"; 1.37:1 is the initial rocker ratio at low lift.
If you set valve spring heights at .090-.100" margin above coil bind to achieve maximum valve train limiting speed I strongly recommend that coil bind clearance be measured on the engine stand before firing up the engine to ensure that there are no tolerance issues with the installed parts.
DukeComment
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Re: Part numbers for 1970 LT1 cam
Duke, You must have read my mind because I remember doing a fair amount of work to get those spring compressions correct and was wondering what this cam would do. I didn't even need to contact you.
I'll have fun doing it if IF I don't have to remove the heads. Hopefully it will just be a matter of removing one shim or removing and replacing with a comination. I have a lot of extra shims/sizes and I'll need one of those special tools.
Do you have the special cam specs handy to get the differences?
JohnComment
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Re: Part numbers for 1970 LT1 cam
Just went to Rock Auto and AT840R doesn't seem to be listed any longer.Comment
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Re: Part numbers for 1970 LT1 cam
Son of a gun. I hope my order is on it's way, they took the money!Comment
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Re: Part numbers for 1970 LT1 cam
The Special 300 HP cam max lift, inlet/exhaust, is .2981/.2733", and since it's hydraulic you don't have to subtract clearance ramp heights. Just plug these numbers into the same formula. It looks like you can leave the inlets alone, or add a .010" shim, but you'll have to remove about .050" worth of shims from the exhaust side
You also need to install a B28 VAC.
DukeComment
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Re: Part numbers for 1970 LT1 cam
Hi Joe,
I bought a 63 driver and this engine will be going in it for a while I search for a correct block so I thought I'd try the LT-1 cam configuration.
The car was a 340 HP but the engine is long gone.
JohnComment
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