Yet another 273 build advice thread!

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So far, I’ve got a 273 block that will make a nice .030 over, a NOS set of .030 Speed Pro 8.5 compression pistons, and a set of 273 rods. I still plan to use the 340 crank that I have laying around. It should have to have weight taken out, instead of weight added. I will get that work done for free because I gave a 360 motor to a local race engine builder in trade for balancing my rotating assembly. I still want to use a hydraulic cam, and factory LA non adjustable rockers. I’m leaning towards the 360 2 bbl cam, because it is supposed to perform well down low. Sorry, but I don’t have the specs at hand. If I use the Crane cam kit that I have laying around, it will have a nicer idle, but I suspect it will be like AJ says and be a dog. I don’t really want to use headers, but if I use a bigger rumpity rump cam...I will probably have to pony up for a set of Dougs!
 
So far, I’ve got a 273 block that will make a nice .030 over, a NOS set of .030 Speed Pro 8.5 compression pistons, and a set of 273 rods. I still plan to use the 340 crank that I have laying around. It should have to have weight taken out, instead of weight added. I will get that work done for free because I gave a 360 motor to a local race engine builder in trade for balancing my rotating assembly. I still want to use a hydraulic cam, and factory LA non adjustable rockers. I’m leaning towards the 360 2 bbl cam, because it is supposed to perform well down low. Sorry, but I don’t have the specs at hand. If I use the Crane cam kit that I have laying around, it will have a nicer idle, but I suspect it will be like AJ says and be a dog. I don’t really want to use headers, but if I use a bigger rumpity rump cam...I will probably have to pony up for a set of Dougs!
PERFECT! Just build it using what you have. Juice cam and non adjustables will be "fiddle free" and it will run well. With the effecient 273 heads and the lower compression you can run any gas you choose. It will be a nice running 273. Maximum performance isn't always needed.
 
plug that 360 cam into aj's numbers
I think you will find it lacking, it's the long closing ramp problem but stock torque in a 360, 273 not so much
remember the 360 cam was a smog cam and designed to add to the EGR effect by closing exhaust late

I was off, I was trying to stay away from 268 and 262 cams because I know they do not work in your application and was recommending a 256
seems that might even bee too big but I do not know what AJ was thinking of "two sizes smaller"

the 6 pack pushrods should work with Mopar lifters
what's the ch on those supposedly 8.5 pistons
betcha when you do the math you're in the 7's

so here's what you do
call
Kirk at Bullet (662)893-8022 ext 103 reference 620-3
249/ 254 201/206 432 lift 112 in at 107 (+5) uses .858 of the .904 lifter face so it's not out to the edge and should wear well Hyd (or ask about a solid)
that's one size smaller than the 256 Lunati or Howards
how's that look AJ?

from what I see the shorter seat allows the Lobe centers to be spread out for the log manifolds and still keep the intake closed point reasonable
longer ex is for the heads and log manifolds
However log manifolds do not like a lot of overlap
btw the chevy version is 400/430 lift this one is much fatter so you still get the power
Bullet has quick turn around when you decide to pull the trigger
you could also check with Jim at racer brown
I do not see a shelf grind that would in any way optimize your build
 
273's are usually only .020 in the hole with flat top pistons. Unlike most LA small blocks. Plus he is running closed chamber heads. No matter what you guys' computers say, 273's are not as finicky as you think. I've actually built and ran them on the street in all kinds of configurations for decades in A bodies, from stock 2 barrel cam to a 284 duration solid cam, from original heads, to 675 318 heads, to "72" 340 "J" heads, Automatic and 4 speed. All through the original manifolds and mostly though the 1965 2.5 inch OD straight through single exhaust. None were dogs, although that is very subjective. A Stock 273 Commando with new 2 barrel pistons and Chrysler rings, a small Isky E-4 cam recently made 265 hp on the Dyno. Nothing trick or fancy, just good machining and tuning ability. That's almost 1 hp per cubic inch with a .425 inch lift and 216 degrees duration @ .050 solid cam, probably even a chevy lobe, go figure. My next build will be with a custom Racer Brown Cam. Can't wait.
 
249/ 254 201/206 432 lift 112 in at 107 (+5) uses .858 of the .904 lifter face so it's not out to the edge and should wear well Hyd (or ask about a solid)
that's one size smaller than the 256 Lunati or Howards
how's that look AJ?
well I have to trust you that the time from advertised closing to actually closed is faster than most, because the advertised to .050 is not indicating it. 48* is a long ramp, am I right? So this could be another one of those; Yabut from .050 on, it is opening exponentially faster than so-and-so's cam, IDK, I'm not privy to that knowledge.
The thing I see, and am not fond of, is the 112 LSA that, in at 110 installed, generates a 55* Ica, and that is what I was trying to avoid. But again it all depends on what the Scr comes in at. If it was me tho, I would tighten up the LSA to something like 104, and let the meager overlap get lost in the logs. This has the double whammy effect of making 6* more pressure(perhaps 6 psi) with the same Scr, and 6*more more power extraction. This costs you nothing except the cost to move the centerline, if any.
This cam has a split of only 5degrees so you can't move it around much as a tuning tool without negatively affecting the other two durations, namely; the compression and power.
But the 249/254 numbers I think are right in the ballpark.
Your thoughts?

But personally,I wouldn't even bother with a hydro.
I'd shop for a tight-lash solid, and slam the intake closed as fast as possible still with as much .050 intake duration as I could get for this 250/255 net duration size of cam, adjusted for Scr and octane. Boy that's a mouthful of qualifiers.
The point is solids ain't everything and you can still get a crummy solid if yur not careful.
If you have a pair of [email protected] cams, one a hydro and the other a solid, installed in a streeter, chances are they will make similar absolute power. The difference is in the power curves below the peak, and how they will perform in daily running. And that goes straight back to when exactly that pesky intake closes; the solid's actual after lashing, compared to the hydro's gentle landing.
I suppose it would theoretically be possible to find or more likely, have built, a really fast ramp hydraulic cam in this modest size....and
I suppose you could bad luck pick a terrible long-ramp, loose-lash solid from out of a catalog, and
in the end the hydro would run better, stronger,quieter,and be faster.
I suppose. .......But I ain't taking bets.
Cuz
to get a 249/255 solid tight lash, you might have to order a 254/260, which after lashing gets you the 249/255. But with this solid, you know EXACTLY when the intake is closed. Whereas with the hydro,that 249 is probably a .006 or .008 spec..... which means the dog-gone valve could still be off-seat for another 7 to 15 degrees(guessing).
Ok but you say, so what!. And you'd be right once the engine is wound up it matters not one iota. But when you put it into drive and the rpm comes down to 500rpm.... now it matters, to the guy with a DD/cruiser,or small engine. If your pistons are now pushing fuel-charge back into the intake, for 15 extra degrees you hadn't counted on, what is that doing to your cylinder pressure, and how is the engine gonna respond when you hit the throttle? Now it matters.

But here is the bigger picture, with that solid; since you can know the exact closing angle, and it is far less than the hydro, you can get a cam of at least one size bigger at .050, with no low-rpm penalty compared to the hydro.What's one size bigger worth?
IDK, it depends on the pressure, but it's not just about the absolute power, it's about the fatter than the smaller hydro, midrange. The more low-rpm pressure comes in awful handy too, especially with a modest sized engine, and modest rear gears.
 
273's are usually only .020 in the hole with flat top pistons. Unlike most LA small blocks. Plus he is running closed chamber heads. No matter what you guys' computers say, 273's are not as finicky as you think. I've actually built and ran them on the street in all kinds of configurations for decades in A bodies, from stock 2 barrel cam to a 284 duration solid cam, from original heads, to 675 318 heads, to "72" 340 "J" heads, Automatic and 4 speed. All through the original manifolds and mostly though the 1965 2.5 inch OD straight through single exhaust. None were dogs, although that is very subjective. A Stock 273 Commando with new 2 barrel pistons and Chrysler rings, a small Isky E-4 cam recently made 265 hp on the Dyno. Nothing trick or fancy, just good machining and tuning ability. That's almost 1 hp per cubic inch with a .425 inch lift and 216 degrees duration @ .050 solid cam, probably even a chevy lobe, go figure. My next build will be with a custom Racer Brown Cam. Can't wait.


There's been a half dozen or so guys on here over the years that ran 280 plus cams in a 273 most of them with less than ideal combination. Everyone of them said their engine ran strong. Not saying to run a big cam. But don't fear a modest cam upgrade.

340 and 273 have a similar head cfm to cid ratio so in theory it should take the same amount of duration to fill the cylinders at a similar rpm. In other words the same cam should work similar in both engines.
 
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.
 
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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 ?
 
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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 ?
The reason why Ma Mopar used a split camshaft is exactly because of the restrictive exhaust manifolds. Your large chamber heads aren't helping your compression. If you're building a hot rod motor the larger ports will help but they don't help you much on a 318 2 Barrel with very low compression. (Lower than stock with those 360 heads.)
 
The reason why Ma Mopar used a split camshaft is exactly because of the restrictive exhaust manifolds. Your large chamber heads aren't helping your compression. If you're building a hot rod motor the larger ports will help but they don't help you much on a 318 2 Barrel with very low compression. (Lower than stock with those 360 heads.)
I completely understand the limitations of the build I used as an example which is one reason I used it. Even in my example a 260 adv. dur. cam worked REALLY well which made me feel that the 252 cam OP is considering seems a little low. Hmm. Another thing, I fully understand that custom grind IS "The Way To Go" but is there an off-the-shelf grind that has the 108 lobe separation and faster closing ramps that some have suggested the 273 responds well to ?
 
I completely understand the limitations of the build I used as an example which is one reason I used it. Even in my example a 260 adv. dur. cam worked REALLY well which made me feel that the 252 cam OP is considering seems a little low. Hmm. Another thing, I fully understand that custom grind IS "The Way To Go" but is there an off-the-shelf grind that has the 108 lobe separation and faster closing ramps that some have suggested the 273 responds well to ?
It all depends on what you are building. I am a huge 273 fan but I believe in the engine as designed and you can't do much to it without going easily overboard.
 
remember you are comparing MOPAR at roughly .008 with the stock cam
with an aftermarket cam @.006
so the 260 comp is not a lot longer duration than the 252 as far as seat to seat duration -building cylinder pressure- Dynamic compression
more of the difference comes in the closer LCA with the aftermarket cam which build low end but narrows the torque curve
compare the ICL's and figure the intake closed point for both
If you look at the Melling and Elgin catalogs you can get more info on the stock cams
more of the difference is in the "intensity" where the aftermarket cam has it all over the stock cam (which will be more computer and emissions friendly)
X2 you can't do much to it without going easily overboard. (on duration) under 9:1

66 we sold a lot of E4s mostly for Y block Fords, interesting to see the difference with a Racer Brown
 
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..
 
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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..


I don't think anyone is saying the OP should a 280 plus cam. It was brought up to show these engine aren't as cam sensitive as one would imagine.

If i was the OP going with a fairly stock setup I'd go with a comp 255deh, if i was to go with more cr gear stalll and headers and maybe some porting I'd go with xe262h cam. Or similar soild setups.
 
Reading threw this thread in gotta say you guys really know your stuff, and I'm have to really think to follow along so thanks for helping the learning curve. What I can add not sure if it helps but the 273 I pulled out of my 64 had a stock 340 cam installed by my dad in the 80's I don't know what particular 340 cam but I do know that thing idled like it was a huge cam and power was way up in the rpm band.
 
A408 thanks for the info
All stock 340 cams are the same except for the rare 68 stick and power is way up in the rpm band in a 273 or 318 and lower down low especially in a low compression
do you know what your cr was or cranking compression?
A motor like late low compression 340-360 and 2bbl 273 with rebuilder pistons of undetermined compression height- 8.5 advertised
Bottom line
Aj mirrors my thoughts
call Bullet
everything is a compromise but it would be easier to make your combination work with a solid cam as you already have the rockers
273 even a 255 or 256 comp is to big for OP's build without making changes
but if you like 255 use this one or similar Lunati Howards Cams Hydraulic Flat Tappet Camshaft and Lifter Kits CL711381-10
compare that with your Dodge Downgrade - unfortunatly comp makes nothing shorter than a 274 for MOPAR
 
Reading threw this thread in gotta say you guys really know your stuff, and I'm have to really think to follow along so thanks for helping the learning curve. What I can add not sure if it helps but the 273 I pulled out of my 64 had a stock 340 cam installed by my dad in the 80's I don't know what particular 340 cam but I do know that thing idled like it was a huge cam and power was way up in the rpm band.
Oh you can put a big cam in one and it will have power but it won't have very good street manners. Many car guys overbuild/over cam their engines and then are disappointed when it isn't fun to drive unless you wing it 6000 rpm.
 
I
A408 thanks for the info
All stock 340 cams are the same except for the rare 68 stick and power is way up in the rpm band in a 273 or 318 and lower down low especially in a low compression
do you know what your cr was or cranking compression?
A motor like late low compression 340-360 and 2bbl 273 with rebuilder pistons of undetermined compression height- 8.5 advertised
Bottom line
Aj mirrors my thoughts
call Bullet
everything is a compromise but it would be easier to make your combination work with a solid cam as you already have the rockers
273 even a 255 or 256 comp is to big for OP's build without making changes
but if you like 255 use this one or similar Lunati Howards Cams Hydraulic Flat Tappet Camshaft and Lifter Kits CL711381-10
compare that with your Dodge Downgrade - unfortunatly comp makes nothing shorter than a 274 for MOPAR

I don't know what the scr psi is dad always said it was 10 to 1, I still have it, looks like new, I guess I could test it sometime.
 
Here is the 340 cam in a 273 at 1000 ft elevation, and in at 110. The Ica according to the advertised intake duration would be 64*. Because this cam is known to have long slow ramps, and IIRC Wrmryder may have mentioned close to 300*intake duration at .001. If that is correct, then the difference from 268 to 300 is 32* and half may go to each end or 16*. On the off chance,lol, that I remembered it wrong, I will arbitrarily add just 10* not the 16* or so that is called for. So I'm calling the Ica, 74* so; close to sealed but may still be leaking
Static compression ratio of 10:1.
Ica of 74*
Effective stroke is 2.33 inches.
Your dynamic compression ratio is 7.33:1 .
Your dynamic cranking pressure is ............................140.55
PSI.
V/P (Volume to Pressure Index) is ............................ 81VP

So first notice the pressure is just 141psi, with an Scr of already 10/1. It will take another full point of compression, namely 11.1 to get the pressure to 160
Second; notice the slanty VP. Off idle this combo will pull about as hard as a slanty and continue to get a lil better until around 3000/3500 when the lil 273 will start trapping mixture properly. To combat that, she would need some combination of higher stall and IMO, to be fun, a lotta gear. For best results I would recommend a manual 5-speed, and whatever gear it takes to power peak a couple of hundred rpm below 60 mph in second gear.

I built a combo similar to that, but with a teener and I used the 273 solid lifter kit, yes on the hydro cam. You know, cuz I thought I could get away with that on that looooong-ramp cam. With the lash, I could control the Ica to something a lot lower than 74*. It worked out not bad except the fuel consumption was insane, and it took a 2800TC to get moving with 3.23s. I installed this in a 71 Monaco base model. Between the weight and the low cylinder pressure, it was still a dog until wound up, then it turned into a beast, perfect for downshifting and passing at 65 mph ..... but it wasn't good for much else. I shouldda known better cuz I was already in my late 20s......... but I had this 340 topend looking for a home, and a smogger-teen shortblock, and the 360 in the Mon was burning a lotta lotta oil....... you know the story....


Just for the heckuvit, lets put that cam into a 360
Static compression ratio of 10:1.
Ica of 74*

Effective stroke is 2.53 inches.
Your dynamic compression ratio is 7.36:1 .
Your dynamic cranking pressure is ................................... 141.33 PSI.
V/P (Volume to Pressure Index) is ....................................108VP; still a dog,will need a TC and gears
Check out the 33% VP increase, at roughly the same pressure. .
Lets crank up the pressure

Static compression ratio of 11:1.
Ica of 74*

Effective stroke is 2.53 inches.
Your dynamic compression ratio is 8.07:1 .
Your dynamic cranking pressure is...................................... 160.08 PSI. good for iron heads and best gas
V/P (Volume to Pressure Index) is ..................................... 122VP; This is like a 5.2 Magnum (124VP), TC or gears, but not both

And next lets put some aluminum heads on it and crank up the pressure some more
Static compression ratio of 12:1.
Ica still 74*

Effective stroke is 2.53 inches.
Your dynamic compression ratio is 8.77:1 .
Your dynamic cranking pressure is ..................................178.90 PSI. Good for aluminum heads and 87gas
V/P (Volume to Pressure Index) is ................................... 137VP; OK now the dog is dead and buried. Drop it in and drive
 
After reading all the theoretical opinions about 273’s and cams. My first 273 was in a 1964 Barracuda TRW forged 10.5 pistons, good valve job, milled just enough to flatten the block side, Offy intake, 600 Holley, 284 duration solid cam, Mallory all mechanical dual point distributor, stock exhaust manifolds, 65 Formula S exhaust with a 4 speed and 3.21 8 1/4 rear. Ran strong about the same power to weight as a 383 Road Runner equipped similarly. Next incarnation swapped the 273 heads for .040 milled 72 340 J heads, used 340 hydraulic cam and lifters, 71 340 intake and TQ, 72 340 electronic distributor. What a monster engine. No way to go slow, quick revver, whole new level of performance. A 273 in an early “A”, even an 8.8 to 1, is Not comparable to a 318 in a Monaco. 360? Did anyone ask?
 
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