3972178 Cam

[Herb E.]

Guys, in my 1967 Corvette, I have a 350c.i. stroked to 383 c.i. with Edelbrock RPM Aluminum heads and their RPM Hydraulic Cam. I have installed a 1970 LT1 3972110 Aluminum Intake and a 1970 era 780 cfm Holly Carb with vacuum secondaries. I plan on installing 3991492 Heads with 2.02" valves. The heads received mild porting to match the 1205 Felpro gaskets. I plan on installing a new 1970, 2nd design Z28, 3972178 solid cam. MY question is: This cam has a .435 Lift on the Intake, and .455 Exhaust, with 300 deg duration on Intake, and 312 deg on Exhaust. Do you think this is enough cam for this 383? Do you think it will provide adequate vacuum for everything, including: Power boost brakes, vacuum advanced distributer, vacuum secondaries on the carb, and PCV system. I'm after the "vintage" sound from "solids" and power and looks from the old days. Herb

[Duke W.]

Re: 3972178 Cam

There are so many ways Chevrolet cams are measured it takes a book to sort them out. Don't get hung up on this. From a practical standpoint, the LT-1 cam is comparable to a hydraulic cam with 231 degree inlet duration, which is about as high as one should go for a sensible road engine. The inlet lobe is from the SHP big block cam on a slightly smaller base circle, and the exhaust lobe is from the 30-30 cam, indexed four degrees earlier.

The LT-1 cam will work very well in a 3.75" stroke engine. It's available from NAPA - Speed Pro CS1145R. Search "327 LT-1" for more information on this configuration. Yours is the same other than the longer stroke and the more efficient induction system.

Target a CR of not to exceed 10.5:1, and it will run without detonation on premium fuel depending on how your spark advance map is set up. (See the Fall 2009 Corvette Restorer for more information on managing your CR.)

You should also pocket port the heads and relieve the chambers at the sides. This is particularly important on the exhaust side.(See the Fall 2010 Corvette Restorer for more information about head massaging.)

Peak power should be at around 6000, and the valve float speed will be around 7200 with careful set up of the OE equivalent Sealed Power VS677 springs.

Make sure you have high quality connecting rods.

Use a B28 VAC and expect it to idle okay at about 750-800 with 12" manifold vacuum.

The LT-1 cam is somewhat milder in a long stroke SB than a 327. This means it will have better driveability around town, and the large displacement should ensure adequate low end torque, even with a relatively tall rear gear.

If you prefer hydraulic lifters and limit revs to 6500 the L-46 cam (CS1095R) will yield very similar torque and power curves. The primary advantage of the LT-1 cam is the 500-700 revs additional valvetrain limiting speed, which is necessary on a 327 to take full advantage of massaged heads, but the heads run out of flow at lower revs as stroke is increased, so the L46 cam is a good choice for a 383, which may be limited to 6000-6500 either due to head flow or bottom end stress considerations.

If the heads are massaged correctly and you run close to the NTE CR limit, this configuration with either cam should easily exceed 300 SAE corrected RWHP on a Dynojet chassis dyno with the under-the-car exhaust and make in excess of 80 percent peak torque at 2000, but the OE sidepipes are very restrictive and will loose 15-30 RWHP relative to the 2.5" under the car exhaust.

I see you are a new member. Building "cheater motors" - original looking on the outside but highly massaged on the inside - is a passtime of some NCRS members, and how to do it has been extensively documented on the TDB and Corvette Restorer magazine.

Duke

[Thomas H.]

Re: 3972178 Cam

Duke,
Would you recommend retarding the cam 6 degrees (moving the POMLs from 110/122 to 116/116)
Tom

[John H.]

Re: 3972178 Cam

Do you think it will provide adequate vacuum for everything, including: Power boost brakes, vacuum advanced distributer, vacuum secondaries on the carb, and PCV system.

Herb -

The vacuum secondary diaphragm operation doesn't use manifold vacuum; it uses a venturi vacuum signal generated by air velocity through the primary venturi, further enhanced by another venturi vacuum signal from the secondaries once they start to open.

[Duke W.]

Re: 3972178 Cam

Duke,
Would you recommend retarding the cam 6 degrees (moving the POMLs from 110/122 to 116/116)
Tom

...not unless you plan on spending 90 percent of the time over 6000 revs. With the OE indexing and long stroke it will have plenty of useable low end torque. Top end power is a function of how well you massage the heads.

Duke