Yet another 273 build advice thread!
I looked it up. 360 2brl stock cam 71-74 is a split hydraulic. 410/412 252/256
75 and up is straight hydraulic. 410/410 252/252
I've seen many suggest that split cams do NOT work well with exhaust manifolds.
My 69 Barracuda Notch-Back had a stock 318 bottom end, a pair of regular smog type 1.88 valved 360 2brl heads with no porting, Edelbrock Performer Intake, Edelbrock 500CFM carburetor and exhaust manifolds. The 260 adv dur Comp Cams High Energy Cam I used worked REALLY WELL. 19mpg in town and a car that was FUN to drive ! NORMALLY I tell folks they are aiming too high with their cam choices but I think you are aiming a little low. If it must be an Off-The-Shelf hydraulic cam, I'm sure there are members here who can suggest a 260 adv duration grind with ramp characteristics that would work well in a 273. AJ. I see you hating on a 280 cam for his combination (I agree) but don't you agree that the 252 adv dur cam from stock 360 is aiming a little low ?
Advertised numbers wise;hyup
But ,but, but; you gotta see the big picture; cam specs are like a den of snakes, every spec is hopelessly ethereal. Generally, with a bigger engine, you can get away with a few degrees this way or that, but with this size of engine , you gotta be sharp cuz you just can't afford to give up any torque.
And jus saying; I don't hate a 280 cam at all, it just has no place in OP's combo. You can put half a dozen hydraulic flat tappet 280s on the table, and in a 360 they might all run similarly. But in a 273 the dogs will show up, and there might not be, probably will not be, highly unlikely that even one will be; acceptable in a street 273. The effective stroke just gets too short.
here's what I mean; best scenario;
Static compression ratio of 10.75:1.
Ica of 74*, the most likely actual closing point and not leaking, for a typical 280 cam
Effective stroke is 2.33 inches. check it; 2.33 measly inches. One inch got sucked up by the late-closing intake. And where exactly is the piston? Hyup at 67* ABDC it is more than 1/3 of the way up the cylinder, when it has finally stopped pushing the recently inducted A/F charge back into the intake manifold. This reversion will not stop until maybe 2200 rpm. So a lot of the time, dare I say most of the time, the lil 273 will be operating in a very low efficiency operating range. So expect to be buying lots of gas for it.
Your dynamic compression ratio is 7.85:1 .
Your dynamic cranking pressure is
159.55 PSI. about max pressure for a streeter and tight-Q
V/P (Volume to Pressure Index) is
92VP
Yur outta Scr right here for a streeter. and the VP is in the basement at 92. Even a smoggerteen makes more VP than that:~116 at sealevel. Try and imagine how weak 92 is; just barely 10% stronger than a slanty. and this doesn't improve much until coming up on the torque peak. And with a 280 that is a fair bit up the rpm band, perhaps 4000/4100.. Even with 3.91s this is still 32 mph; to the torque peak mind you. The power peak won't arrive until ~5500/44mph. That might be fine for drag-racing, but in a streeter, IMO that would be really crummy.
But think how yur gonna make 10.75 Scr; this requires a maximum total chamber volume of 57.35cc. With flat tops no eyebrows and Zero decks and closed chambers, you gotta run at least .028 gaskets which are about 6.2cc unless you order customs. That means the heads have to come in at 51.15cc. Doable yes, but now you have spent a ton of money on machining every single machinable surface. So good luck on having it all still fit together, and not have sealing issues. And to what end? You still can't run much lift, nor much in the way of valves to compliment a 280 cam. If you want to pump up the lift, you'll have to put some eyebrows in the pistons, and whatever ccs you put in there, you gotta shrink the head chambers the same amount.
IDK, that's a ridiculous amount of money IMO,to have to spend on an engine, just to have an HFT280* cammed 273, that, until you spend even more money on a TC and gears,will probably be slower to 45/50mph than a whole lotta cheaper 266* solid-lifter equipped 273engine, that you can drive anywhere all the time, even with the stock TC and gears..
