LT1 cam for a 327/350 L79

[Bill M.]

Has anyone done this conversion? I did it back in the late 70s and have forgotten what it took to do it.

[Gene M.]

Re: LT1 cam for a 327/350 L79

Bill,
Better off with the chevy L79 cam for street driving. The LT1 cam will give ya same issues the 365 horse cam does..... no bottom end compared to the L79.

[Larry B.]

Re: LT1 cam for a 327/350 L79

There are alot better grinds available today than something out of a catalogue.Give me all your engine details and what you want it to do and I,ll get one custom ground. Call 541-218-7754

[Duke W.]

Re: LT1 cam for a 327/350 L79

Yes, it's been done and the front-end engineering analysis and test results of the completed engines are on the Web.

https://www.forums.ncrs.org/showthread.php?40888-A-fresh-327-LT-1-is-on-the-road

From the above thread follow the link to The Corvette Forum. McDufford's engine started as a '65 L-79 and Johnson's was a '65 L-76.

There is no "conversion" other than installing the LT-1 cam and a set of mechanical lifters. The remainder of the valve train can be left completely original as long as pushrods, rockers, and balls show no signs of signficant wear, which most won't if the engine was well maintained in its first life. If any valve train parts need to be replaced, they should be replaced with OE equivalent parts. The valve springs on both engines are Sealed Power VS677, which are identical to the "second design" small block valve springs that were used from 1967 to at least 1979 for ALL small blocks including 2-bbl. 283s.

Contrary to what was said in the previous post this is NOT a torque-shy 365 HP engine with the 30-30 cam. There may be slightly less low end torque than with the L-79 cam, but barely enough to notice. Eighty percent peak torque is achieved at 2100 RPM, and 90 percent at 2400! The 30-30 cam of the 365 HP engine doesn't make 80 percent until nearly 3000!

These two "327 LT-1" engines I system engineered also included massaged heads, which are absolutely critical to achieving maximum top end power and a compression ratio optimized to the range of 10.35-10.50:1 to operate detonation-free on pump premium using the Federal Mogul OE replacement forged pistons.

McDufford's engine made about 360 gross HP on a lab dyno with the OE exhaust manifolds (not headers as is the case with most current lab dyno tests). Johnson's made about 290 SAE corrected RWHP at 6500 with a useable rev range to 7200, which is where the beginning of false valve motion started dropping the power pretty fast. (For reference, the GM advertised SAE gross power of these vintage engines was overstated by 10-20 percent and torque by up to ten percent, but proper head work can bring them up to the advertised gross power rating. With the cast iron manifolds, torque is 95 percent a function of displacement and compression ratio with the remainder a function of valve timing.)

Headers improved McDufford's SAE gross torque by about 8 percent, but only increased gross power about 3 percent. Most of these increases would be wiped out in the car due to exhaust system backpresssure negating the useable wave dynamics created by the headers, assuming headers are installed, but both engines have the OE exhaust manifolds since a major boundary condition of the project was to not change external appearance.

Externally both engines have all their originally installed identifiable components. McDufford's car Top Flighted. Johnson is not a NCRS member.

Duke

[Duke W.]

Re: LT1 cam for a 327/350 L79

Here is the link to Dave McDuffords 327 LT-1 lab dyno tests and discussion:

http://forums.corvetteforum.com/c1-and-c2-corvettes/841537-lt-1-dyno-results.html

The links to the graphs in the above thread are dead, but I'll summarize the results as follows.

Numerous runs were accomplished, but there were carb and ignition problems that had to be sorted out. Once these issues were resolved runs were made with both the OE 2.5" exhaust manifolds and headers. All data is corrected to standard temperatue and pressure, so it is equivalent to SAE gross that was advertised by Chevrolet. Back then production engine testing was done with the production exhaust manifold, not headers.

With manifolds the best run was 338 lb-ft @ 4500, 356 HP @ 6400 with 80 percent peak torque at 2000.

With headers 358 lb-ft @ 4500, 362 HP @ 6500.

Note that headers yield a 5.3 percent increase in peak torque, but less than two percent peak power increase. In the car with mufflers much of this will be wiped out because negative pressure generated by the headers is mostly offset by exhaust system backpressure.

Using my data-derived 0.89 net/gross ratio the net torque/power numbers with the OE manifolds are 300/317. Applying a 0.85 drivetrain/tire loss figure the estimated SAE corrected rear wheel torque/power is 255/269, which is a little less than Johnson's rear wheel numbers, but in the ballpark.

Duke