Stock Cam Question
What about using a stock 360 2bbl camshaft if you're going with a stock cam...
I had a conversation with Larry Shephard many decades ago and he stated that the stock 360 cam was the best for fuel economy...
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I may be able to scrounge one up...
IDK; I wonder what Mr. Shepard was thinking.
I've run that 252* cam in a stock low-compression 318 and discovered a few things.
1) in at split overlap, the cylinder pressure drops like a stone compared to the stock cam, and
2) if I advanced it to get the pressure back, it sucked gas
3) if I retarded it to get some power extraction, well then the pressure was abysmal.
I did run that 252cam in a 318 , but it needed a 2800stall/minimum 3.23s to get moving, and of course neither of those are conducive to fuel-economy, as compared to the 240cam with a 1800/2000 and 2.76s.
I ran that 252cam with the stock 1973 convertor and 2.76s, but no way that was gonna work.
In the end I installed some 273 valve gear and played the lashing game til I was happy with the 2800/3.23s.
Here are the installed specs using the numbers from the chart, both at split overlap; the 240 cam first, which is in at 107. The 252 cam is in at 110
240int/133comp/125power/248exh/26*o-lap/47* Ica.
252int/124comp/120power/256exh/32*o-lap/56* Ica
The total of compression degrees plus power degrees, cannot be changed.
The 240cam totals 133 +125=258
The 252cam totals 124 +120=244
Let's say we retime the cam to equalize the Power Extraction at 124*, in an attempt to equalize fuel economy;
compression of the 240cam would jump to 134*, whereas compression of the 252 cam would fall to 120*. That 14* is the equivalent of about FOUR cam sizes! and explains exactly where my pressure went.
Let's say we retime the cam again, to balance the compression degrees at 132* for both, to keep the cylinder pressure equalized.
The 240 cam increases the Extraction to 126*, whereas
The 252 drops extraction to 112*, but kills the overlap in so doing.
Yes I admit;
that 126* of extraction is overkill on that 318 cam, and
that 112* is likely adequate for the 360 cam, and
that with log manifolds, overlap is relatively meaningless.
Lets say we retime both cams again to settle the Extraction at 116* which should be plenty .
The 240 cam jumps the compression to 142 degrees/Ica of 38*, whereas
The 252 cam falls to 128 degrees/Ica of 52*
The Wallace predicts the 318 to make
144psi at Ica of 38*, whereas only
131psi at Ica of 52*, again with the 13 psi...........
To make fuel economy, the engine needs BOTH pressure and Extraction. but pressure especially. Does the 318 need 258*?
At a paltry 8/1 Scr, it would seem so.
But at 9.2Scr say, I think it could get away with an awful lot less. In fact, I have proven that a 367 with Compression plus Power-extraction totaling just 227*, can make low 30s mpg with overdrive...... but the CCP was pushing 195psi.... and Power extraction was ~111*
I'm just trying to figure out what Mr. Shephard was thinking, and why whatever it was, it didn't work for me, lol..