Yet another 273 build advice thread!
In other words the same cam should work similar in both engines.
At WOT thru the power peak.
From idle to the torque peak, well that's another story.
And if you have 2.76 gears, Oh Lord help you if you don't have compression and/or stall.
here's why.
With the same 280 cam , with an Ica of 66*(.006) and who knows when the intake is actually on the seat and closed, and in a street car;
At Scr of 8.5/Dcr of 6.7/ you get 130psi@
VP81 slanty power down there. for street duty with an automatic, you can't even combo that
At Scr of 9.9/ Dcr7.8/ you get 158 psi@VP of 99 ,still a complete dog off idle. You will need a clutch and big gears, and a very light car..Ok maybe complete dog is a bit of an exaggeration. 99 is still better than a slanty,which comes in at about 140psi@83VP.
The problem with this combo is the "pint-sized" swept area of the 273, for to use that 280*,cam on the street. 562 cc apiece just over a half a liter, barely a Big Gulp's worth.
Let's back the Ica up 2 sizes to 59* and with Scr of 8.5, now you get 139psi@
VP of 92
Increasing the Scr to 9.5 gets you 160psi@
107VP Still pretty low.but the 160psi shows there is no room for more pressure
The 59* Ica comes on a cam of about 2 sizes smaller so 266 advertised. You can bandaid VP of 107 for street use with gears and stall, but it will suck gas. And I wouldn't take it on the hiway much
But hang on, that intake valve isn't actually closed yet at the advertised of 266; it could be an easy
8* later, making the no-longer leaking Ica, to be 67*. And with 8.5Scr you are now down to 128psi@
80VP, ohhhh back into the basement with LESS than slanty power off idle. To compensate for that, the Scr would need to be bumped to 10.1 for 160Psi@99VP, criminy.
Ok so lets take that same 266 cam, and make it a
solid lifter cam.
So that 266..... after lashing might be a 262 and lets make it a 108 cam instead of a 110. The Ica can now be set to exactly 57* and with
Scr of 8.5 you get 141psi @
95VP... and at
Scr of 9.4 you get 160psi@
109VP
Ok so 109 is the highest VP we have seen, and the 160 psi shows the engine is in tip-top form. Oh and the Ica of 57* is still darn good especially since the overlap is now49*, so with headers it will make a nice lil boost thru the midrange and beyond.
This engine package would be the about the nicest it can be in a streeter, from idle to about 3000 rpm.
And good news it will be fairly fuel-thrifty, especially with hiway-type gears.
And one more thing, Scr of 9.4 is fairly easy to get in a closed-chamber 273, requiring a total chamber volume of just 66.6cc.
Also one more; if you don't have the compression ratio, then, around town at lower rpms and throttle settings, then you don't get decent cylinder filling and the effective compression drops even lower, making you constantly drive deeper into the throttle to get adequate performance....... and there goes your fuel economy.
Yeah you can make more power, but it will start costing exponentially more.And not just more dollars. But also more sacrifices; go back and look at the VP of that 280 cam, even at an assumed Ica of 66* the pressure was
158 with a VP of 99 WITH the Scr cranked to 9.9.
But recall that 66* is the rated closing point not the actually fully closed point. If we arbitrarily add just 8* to this as I did to the smaller cam, then the Ica becomes a true 74* and to effectively run that you might need an Scr of 10.75 to get 160psi @92 measly VP; and just see what it will cost to bring your 273 to 10.75; and to extend it's operation to over 6000rpm; and what it will continue to cost you at every single fill-up; and just don't stick it in a fat A-body like mine at 3650 me in it.
Ok but you say the 262 cam is a wussy cam. Oh really... Sure by the numbers it is. But lets install it.
Similarly equipped; this cam,@8.5Scr, I think is gonna outpower the 280 hands-down to 3000 rpm and continue to out pull it, to perhaps 50mph. It makes peak power somewhere around 5000 with a broad power band, and with 2.76s and 26.5s, 5000~55mph
And the 280 might peak at 5600/62 mph, with the power coming up at around 4200/
46mph.
Ok so somewhere after 46mph the 280 cam will begin to eclipse the 262, but up to that point, the 262 is hammering the 280. My guess is the 280 will not catch the 262 until after 50 mph
So the question is ; Why would you put up with a doggie bottom end, or a low-powered bottom-end, just to be shown tail-lites to 50 mph by a smaller combo.
Ima thinking; excluding hi-way cruising; the vast majority of the time. the car will not be hammering on the gas in first gear, so with a 280 cam, everything else gets sacrificed for the pull from 46 to 65mph.Everything.
Ok but unfair you say, nobody would put 2.76s behind a 280 cam. Oh really I bet some people do. And then they realize the mistake and but more gear into it, like 3.91s. Mo-muni
And you say; nobody would saddle that 280 cam with a 1750 stock Tc which with the wussy 280 bottom end might now be a 1680Tc,lol. Oh really?
Ok fair enough lets spend another buncha OPs money and get some 3.91s in there, and a 2800 TC; now yur talking. And of course the 262 doesn't stand a chance.
Of course now things have swung the other way, everything has been sacrificed for the rush to 60 mph. First is now good to 47 mph, and second pulls the rest of the way, ending at 60=4500, just barely past the torque peak.
OK wait
So if OP is willing to sacrifice hiway driving then he might as well put that 262 back in there and go with 4.30s. Now the little 262 is gonna hit 60 at 5000 on the nose having hit the power peak twice on the run, compared to once and change for the 280. And the 262 idles so smooth, pulls so soon and so hard and is such a pleasure to lug around. Oh and the best part, with a 10.54 starter gear, it will be a tire-fryer off the line, maybe a good ways out if a modest TC is installed.
I know what I wouldn't do.
I don't even hardly like my 276/
[email protected] cam in a nearly 11/1 367 cuber.
I said hardly,lol.