Cam Question : 300 HP vs SHP

[Steve D.]

The GM Specifications publication lists the following specs for cams for the 300 HP and 340/360 HP (SHP) engines.

300 SHP

Lift Int/Exh .3987/.3987 .39375/.39975

Duration 300 deg 287 deg
(including ramps)

(There is an “excluding ramps” duration of 250 deg. listed for the 300 HP but no spec for the SHP.)

It appears to me that lift is almost identical, and the 300 HP has the longer duration. I would have expected a higher lift and longer duration for the SHP cam. Please enlighten me.

Are the including and excluding ramps designations similar to the duration @ .002” and .05” lift designations that are currently quoted?

Steve

[Clem Z.]

Re: Cam Question : 300 HP vs SHP

the specs i have for the SHP 097 are dur at .050 228 in/230 ex,.382,382 lift, 110 lobe center. the 929 cam dur at .050 195 in/202 ex, lift .390 in/.410 ex, lobe center 112

[Dale Pearman]

Re: Cam Question : 300 HP vs SHP

At what point in the cycle does the intake valve close in both cases?

Dale.

[Duke W.]

Re: Cam Question : 300 HP vs SHP

The actual timing of the Duntov cam (097) is 35-72/76-31 287/287, based on a 1.5 rocker ratio (it's actually 1.37) and .012"/.018" clearance. This is the actual theoretical "seat to seat" timing points - the points where the valve just begins to lift off and set down on the seat, not the current "advertised duration", which is typically the timing at .006"/.006" valve lift at the theoretical rocker ratio and specified clearance.

Chevrolet cam specs are all over the place, and seem to vary depending on the era of the cam. The Duntov has both more EFFECTIVE duration and much more overlap than the 929 cam.

If you want to run a mechanical lifter SHP cam go with the LT-1 cam. It has a very similar inlet lobe with just a bit more duration and is phased two degrees later, but the exhaust is much longer and is phased ten degrees earlier. This is to compensate for the small blocks restrictive exhaust ports, and it was developed with the cast iron manifolds, so it's a tough cam to beat for street high performance unless you have headers. The LT-1 cam also has an asymmetric profile to very gently set the valves back on the seats which is easier on the valvetrain than symmetrical cams

The LT-1 cam was the culmination of 15 years development of high performance cams for small blocks and the results show.

Duke

[Duke W.]

Re: Cam Question : 300 HP vs SHP PS

Duntov designed the cam because he calculated he needed 30 more horsepower to reach 150 MPH on the sand at Daytona Beach.

He knew he couldn't modify the valvetrain, so his theory was to lower acceleration and spread out the duration for more top end power and a higher limiting valvetrain speed.

It was later referred to by Chevrolet as a "high lift cam", but as you can see from the specs this was a misnomer. From a practical standpoint it had abaout as much lift as the base cam.

Duke

[Dale Pearman]

Are You Sure Duntov Designed and Developed That Ca

I don't think so!

Dale.

[Dale Pearman]

PS

In a 350 cu. in. small block the Melling C-80P is AWESOME! I prefer it over the LT-1. (wider power band)

Dale.

[Clem Z.]

what point in the cycle does the intake close

somewhat after it has opened but before the plug fires.

[Duke W.]

Re: Are You Sure Duntov Designed and Developed Tha

So who do you think designed it?

Duke

[Norris W.]

Re: Cam Question : 300 HP vs SHP

Isn't this kind of an apples and oranges comparison anyway, with one being hydraulic lifter and the other mechanical? Dale, what is the C80P Melling camshaft? The number's vaguely familiar, but I can't quite place it in my mind. (along with a lot of other things)

[Dale Pearman]

Re: Are You Sure Duntov Designed and Developed Tha

About fifteen guys in the dyno room working under Harry Barr.

Dale.

[Dale Pearman]

Re: Cam Question : 300 HP vs SHP

It's a solid lifter cam tweaked for 350 cu in and boasts a strong bottom end while allowing for 7000 RPM or more on the top. I ran one in a 350 engine in my 1962 driver for about a year with dual AFBs on an Offenhauser 360 degree intake. I used the GM 292 turbo heads mildly reworked and Harlan-Sharp roller rockers.

I was VERY happy with the performance of this engine.

Dale

[Larry M.]

Re: Cam Question : 300 HP vs SHP

Hi Dale -

OK, so what's your preference for more lower rpm torque in a 350: GM's 327/350 cam (or Melling's version) installed 4 degrees advanced, or the C-80P.

Larry