292/508 question
After reading all this it looks like I need to ditch the .509 an go to something differant.
Here's my take on the 292/292/108, for a 360streeter
If you don't have the compression to support it nor the combo,( Deep starter gear/big rear gears), then you're going to want to advance it. So then you close the intake sooner........ and that means you also open it sooner.......messing up the very reason you have this cam, for the 76* of overlap. Sure;now you have trapped more of the intake charge, and brought up the bottom end, but you gave away a bunch of effective overlap, and along with that a bunch of power. So now you end up with a wicked sounding cam with a modicum of torque, that seems to make power, but is horribly wasteful of fuel.
At 8* advanced, you might as well install a cam 1 or maybe 2 sizes smaller, and get the torque you want/need, and have a more balanced set of events. If you need more power, tighten up the LSA for a bit more overlap, and get the power there.
That's what I did, And I have never missed that cam.
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>Say you had that 292 in at 100, for an ICA of 66*.
The intake and exhaust durations we know are each 292*
the compression duration will be
114*,
and power extraction will be
98*, count 'em 98*
The overlap is mathematically 76*, but because the intake is now opening 8* earlier, and the exhaust is also closing 8* earlier, you will have an effective overlap of just
60*. You gave up 16*. This is a big fat deal if you are running long-tubes.
>You could run a 276/284/110 cam in at 108, and have the same ICA (66*), and therefore the same compression period of
114*. Your extraction period would jump to
106*, much better on the street, and your overlap period would still be
60*! No it won't make the same power,but how many streeters need power at 6500 plus rpm? I mean with street-friendly 3.55s;7000 is about 60mph in 2.66 low gear,and I don't know why you would put an automatic behind this cam, but if you did, 7000 would be 62mph@5% slip.
But here's the deal, the smaller cam is likely to make more power sooner, and I'm guessing if you shorten the race to where the 276 cam runs out,I bet it wins.
> But say you took this 276 cam and tightened the LSA to 104, and installed it at 102 for an ICA of 60* , This would now have
120* of compression, and
112* of extraction, and it would have
72* of overlap. The extra 12* of overlap would make a nice boost in power. The extra 6* of compression is usually a good thing. and the extra 6* of extraction means a few less cents per mile in fuel useage. Say it's only a nickle, that's still $250 in 5000 miles,a typical summer.
> now get this, the factory 360 2bbl cam was a 256/260/112 IIRC. It has a compression event of
124* and extraction of
116*, and overlap of just
32*. So this 276/284/104 is within a few percentage points of the compression/extraction events, yet the overlap has more than doubled. The 276 cam is about 3.5 sizes bigger and so the power-peak will have moved up about 700rpm. and that might generate X-amount of hp, if the compression and bolt-ons kept pace. But the overlap period might boost that another 7% or more. Say you were up to 300 and the overlap added 21 more. That's a nice boost I'd say.
> so now you are within a stone's throw of the power that 292 was making, but you got it several hundred rpm sooner, and it's a way fatter powerband. The compression ratio is easier to achieve, and the extraction event is saving you money with every mile you drive. And it likes those 3.55s, something you will never get from the 292.
Well, my 292* wasn't happy, even with pressure up over 180 psi(aluminum heads) and the 3.55x2.66=9.44 starter gear sucked. And the 3.55s had to stay...... so the cam had to go.
>your results may vary.
