72 LT-1 engine advice needed

[Tony 38901]

going with the LT-1 cam, now I need head work?

I've decided to go with the LT-1 cam. I've informed the machine shop where I'm getting my heads rebuilt & sent him the specs for the cam. He said in oder to run that aggresive of a cam I will need new springs, retainers and locks and adding a set of spring seats as well as cut the spring pockets open to accept the larger diameter spring.

He said if I go with a cam with under 450" lift I can use the same style spring with a more aggresive rate on it and reuse all of my retainers and locks over.

Is this sound advice? And is this necessary?

As far as I know, the heads I'm having rebuilt are the original (are at least matching #'s 993 castings). So I'm not sure why I would need all this extra work if my car originally came equipped with a solid lifter cam?

[John H.]

Re: going with the LT-1 cam, now I need head work?

Tony -

STOP! You need a new machine shop that knows something about small-block Chevy engines. The LT-1 solid-lifter cam (as with ALL Chevy factory cams) uses exactly the same grocery-getter springs, retainers and locks as Grandma's 307 Powerglide Chevelle.

[Joe L.]

Re: going with the LT-1 cam, now I need head work?

Tony and John-----

Yup---that's how it is. If you are talking about using the stock configuration LT-1 cam (i.e. GM part #3972178 or the reproduction equivalent thereof), you just need stock valve springs of GM #3911068 or the equivalent thereof. These will fit in your heads PERFECTLY AS-IS since this is what resided there in the first place.

Now, if you're talking about using the "LT-1" SERVICE-only camshaft of GM part #3927140 or equivalent thereof, then that's a different story. However, if you're talking about using that camshaft, you're nuts. That camshaft will make for a VERY poor street performer---very, very poor.

You want to make sure that you're talking about a GM #3972178 and definitely NOT a 3927140. Some folks think that the 3927140 was the LT-1 PRODUCTION camshaft. Those folks are mistaken---evry single one of them. Period.

[Duke W.]

Re: going with the LT-1 cam, now I need head work?

Ditto what John and Joe said. The LT-1 cam uses the same valvetrain parts above the lifter as your grandmother's '67 283, which included the new for '67 3911068 valvesprings that have a slightly higher rate than earlier valvesprings.

To get the most out of that cam, you should pocket port/port match the heads and have multiangle valveseats ground with .060" exhaust seats and .040" inlet seats.

"Pocketporting" is well explained in books like "How to Hotrod Your Small Block Chevy" and David Vizard's book. It involves ONLY blending the as cast port to the valve seat to eliminate the annular ridges formed from the first rough valve pocket machining operation and opening up the ports at the interface to match the manifolds.

These changes will improve inlet port flow efficiency by about ten percent (more on the exhaust side), which will increase top end power up to ten percent without affecting low end torque.

A couple of years ago a L-79 was rebuilt with the LT-1 cam and nicely reworked heads that yielded 360 SAE gross HP @ 6500 on a lab dyno. In OE trim a stock L-79 will only make about an honest 300 SAE gross, so that was an improvement of 20 percent with little loss of low end torque and OE appearance. The car has since earned a Top Flight. With my recommended lash specs, it could probably also pass a PV as the mechanical lifters might not be detectable with proper tight lash.

This was a '65 engine with the early, weak connecting rods, and they were upgraded with Crower Sportsman rods to create a bulletproof bottom end.

Improved rods and head massaging is where you should spend some money. Everything else OE or equivalent.

Duke

[Clare Carpenter]

Which magazine?

Clem, do you remember the magazine and which issue? I'd like to read that article. Thanks.

[Clem Z.]

this refers to what ? *NM*

[Clare Carpenter]

Re: this refers to what ?

Clem,

From the thread on, "72 LT-1 engine advice needed". You posted:

>>there is a article in one of the latest magazine how these new engines can run 11-1 CR on pump gas and the big reason is chamber design and very tight deck clearance.

[Clem Z.]

i will hunt it up if i have not trash canned it *NM*

[Bob Simard]

How do you get the correct LT-1 cam from GM? *NM*

[Scott Marzahl]

Re: How do you get the correct LT-1 cam from GM?

I don't think you do, the last time I checked, about two weeks ago, the Crane Cams manufactured cams for GM were discontinued. You can use the Sealed Power CS-1145R LT-1 cam or the Crane Cams piece.

[Clem Z.]

found it and if anyone want to see it e mail me *NM*