New camshaft design - "Special L-79"

[Duke W.]

In the past I have recommended to L-79 owners who want to maximize the broad range torque/power of their engines, but lose no judging points and pass a PV to either use the OE L-79 cam or the LT-1 cam in conjunction with massaged heads and a properly managed compression ratio.

Some were reluctant to install the LT-1 cam due to the mechanical lifters, and I wasn't sure if a L-79 with LT-1 cam could make it through a PV even with lash adjusted lash to my specifications, which pretty much eliminates valve clatter, but it leaves the engine with a more aggressive idle that might result in a PV failure.

The L-79 cam is a very good design for the OE heads, but is not optimized for massaged heads with their typical E/I flow ratio.

So I began swapping OE lobes around and came up with a design that uses either the L-79 lobe or the L-46/82 inlet lobe on the inlet side and the "300 HP cam" inlet lobe on the exhaust side with the same or slightly less than OE effective overlap and a fairly late inlet POML.

The gains are not dramatic, but both low end torque and top end power are improved with a useable power bandwidth to lifter pump up speed, which should be at least 6500 with properly setup OE valve springs.

If anyone has a L-79 engine restoration planned for the future and you want to consider this new design, get in touch with me.

Duke

[Tim S.]

Re: New camshaft design - "Special L-79"

Duke,

I am assuming you ran this through the Desk Top Dyno. Care to share the results?

Tim

[Duke W.]

Re: New camshaft design - "Special L-79"

No, I quit using Desktop Dyno years ago because it basically only allows computation of SAE gross performance.

I use Engine Analyzer 3.0 and will probaby also run it through EA Pro 3.5, which gives somewhat different results, but I'm not sure if they are necessarily more accurate. Both programs allow computation of SAE net performance, which means I can model the exhaust system restriction and use SAE net air density.

SAE gross assumes open exhaust or very little exhaust backpressure, so it's only really useful for racing engines.

As I said, low end torque is about the same or slightly improved with a significant increase in peak power and peak power range depending on how the cam is indexed. Most is due to the massaged heads, but the Special L-79 cam shows some improvement over the OE L-79 cam through most of the rev range. It works better as overlap is reduced, but I don't want to reduce overlap to the point where it smooths out the typical L-79 idle behavior too much.

As with my other cam designs, this one is specifically tuned to the flow characteristics of massaged heads. It won't work very well with OE machined heads.

Duke

[Larry L.]

Re: New camshaft design - "Special L-79"

Question:
I have been an l79 owner since 66. . In 69 I ported / polished heads, flow matched exhaust and intake manifolds. Polished inside of 2.5" exhaust manifold, use under car factory off road mufflers. Heads were reworked like Smokey Yunik
did for Transam engines. Since this is a late 66 327 it has 462 castings which seem to be more tollerant to fuel and spark advance. The distributor is a TI with a set of 65 FI springs. Back when you could get them from Chevrolet. It was checked on a dist mach. and it checks exactly as service manual indicates. The advance total is a few degrees more advanced than stock 350HP. The head / intake on this setup has to have intake lip removed and head ports to match the new intake ports. The stock gasket fits inake and heads perfectly with out any over hang.

35 years later --

Chssis dyno runs gave me 240 hp @ 4800 and 309 lb ft torque at 3500 at rear wheels. This was with out top of airfilter but base of filter installed. Installing the top cost 5 HP, You could also see a standing plume of fuel vapor above carb. A/.F ratio was 13.7 from 800 to 5800. Stock 600 cfm holly with venturi ridge removed and venturi contour corrected and factory off road under car mufflers.

Very docil and quick. Just roll it out at 1200 rpm put it the floor and away you go.
Nice and smooth. The only thing you notice is that after 4,000 you have to be quick to prevent over reving engine. Orginally it ran up to 4,000 and then took a long time to hit 5600. Never did a power check before redoing engine. When I tore it down in 69 it had a 1/4 inch of carbon around valves and was pretty slow. This was done at 9,000 due to a tick when you started it cold - the tick was due to some factory guy not getting #2 rod bearing in correctly / missed slot for anti rotation tab. It was just polished off and didn't mark crank. It now has 41,000
I may be rebuilding the engine due to a #2 rod journal problem - from factory.

What kind of performance inprovement could I expect if I used your modified cam.
It currently idles with a lot of rump but idles smoothly and I don't want to alter this but am always looking for more power. Anyone run this on a real engine on dyno with instrumentation such as EGT and Volumetric efficiency set up? If anyone is interested in Chassis Dyno run plots I can post them but files are pretty big.

[Duke W.]

Re: New camshaft design - "Special L-79"

email me through the TDB - just a simple email. I'll give you my phone number. We need to discuss in more detail.

Read the "Tale of Two Camshafts" article in the fall 2010 Corvette Restorer and gather every scrap of data you have on your engine.

Duke

[Gene M.]

Re: New camshaft design - "Special L-79"

The original L79 cam is just that an L79 camshaft. To modify in anyway as your "Special L-79" is no different from any custom grind. It is not an L79. There are plenty of custom grinds that produce more grunt than the L79 and run just as smooth. Edelbrock 2102, (for example) is as smooth as a 300 hp 327 and runs as strong as an L79 cam with all stock components including 2" exhaust manifolds and full 2 1/2" exhaust. Im talking street driving, normal spirited fun. (Not reving to seven grand) . The original L79's were never intended for seven grand anyway that's beyond red line.

I've done no computer models, just actual use. Reinventing the wheel is just not necessary. It is already available and it's hydraulic lifter.

[Michael H.]

Re: New camshaft design - "Special L-79"

I love the sound of a 350 HP/L79 cam. Pure music.

[Clem Z.]

Re: New camshaft design - "Special L-79"

all we did back in the day with the 327/350 was install GM #142 springs and zero lash the rockers and it ran like they say "jack the bear"

[Michael H.]

Re: New camshaft design - "Special L-79"

Wanna be cam shaft designers is just that, wanna be's.

That's our mission here at the National Cam Redesigners Society.

[Gene M.]

Re: New camshaft design - "Special L-79"

Mike, I like that, now that is funny...........

[Duke W.]

Re: New camshaft design - "Special L-79"

So I began swapping OE lobes around and came up with a design that uses either the L-79 lobe or the L-46/82 inlet lobe on the inlet side and the "300 HP cam" inlet lobe on the exhaust side with the same or slightly less than OE effective overlap and a fairly late inlet POML.

Duke

Correction: The exhaust lobe is from the exhaust side of the "300HP cam" - 3896929.

Duke