JDMopar
Well-Known Member
Yep.... the KB’s for the 318 are $150 cheaper than the Egges for the 273. If I don’t get too wild with a 318, the gas mileage won’t be much worse than the 273 build I had in mind.
273 for early A
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Changing to a 318; for the same power, you can build a much tamer engine, and therefore have waaay more low-end torque, which actually points to more fuel-economy........ You can do a lot with 45 more cubes. That's probably over 2, closer to 3 cam sizes, in a 273.
I will agree! I can't believe I said that! Lol
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I had a hard time deciding if I should say it.
a 273@235 hp is .85hp per cube, and is already getting complicated. But 235 in a 318 is an easy build at .74hp per cube,just bolt-ons.And it makes a lotta low-rpm torque for it's size, at that output.
a 273@235 hp is .85hp per cube, and is already getting complicated. But 235 in a 318 is an easy build at .74hp per cube,just bolt-ons.And it makes a lotta low-rpm torque for it's size, at that output.
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JDMopar
Well-Known Member
Thanks guys. This is exactly the kind of help I was looking for. AJ.... can you dumb it down a little for me? LOL. Of the cams I posted the info for earlier, which one would work best in a 318? The Crane, or the Mopar Performance? Will a set of J heads tame down the compression capabilities of KB167’s enough to be livable in a street motor?
pishta
I know I'm right....
Me know!
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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IMO, the factory had a good idea when they put solid lifters in the 273.
And if I was to build a 318 or smaller, because of the difficulty of making cheap compression, I would for sure use a fast-rate, solid lifter, cam.
Swept volume,if you don't know, is just the volume of one cylinder, that the piston sweeps thru on it's way from the bottom of the cylinder to the top.
A 360 has ~752cc,
a 340 has ~696,
a 318 has ~652,
a 273 has ~559.
AS you can see from 318 to 360 the increases are in about 50cc steps. But from 318 to 273 is a rather large step of nearly double that. This is what makes building a 273 so challenging.
The 360 has a generous amount of swept, and let's you be pretty sloppy with component selection, and still have a pretty good streeter.
How is swept important?
Well, it is the principal player in making cylinder pressure, that makes the heat, that drives the piston down, to make the power. But there is a limit to how much pressure you can make on pumpgas before detonation kills your dreams.
So the more swept you have, the more power you can theoretically make within the constraint of the detonation limit of your fuel.
How is that important?
Well, we have a limited number of players in the compression business, namely total combustion chamber volume (TCV), and the intake closing angle (Ica) of your chosen cam.. With various component selection this TCV can be in the range of ~67cc to~97cc. So,depending on the components chosen, you can make or break your combo.
For instance, on a 318; with 652cc of swept, and a cam-dictated 9.5Scr, you have the target of 652/8.5=76.7cc, which looks like an easy target. But you have 4 ways to get there, namely; chamber volume,gasket,deck-clearance. and eyebrows. So if your flat-top pistons are .057 down in the hole, that chews up ~11.2cc right there, and the gasket will be ~8.8 for the good ones, and that leaves you with 56.7cc for the head, and until recently, for performance, this was tough (expensive) to achieve.
But now with a 360, with a swept of 752cc, to get 9.5Scr, the TCV increases to 752/8.5=88.5cc. Now with flat tops .012 in the hole, the head requirement becomes 72cc, and there are plenty of those out there.
As it happens, a 360 can be built to almost any street Scr relatively cheaply.
But, lets back up to the 273. For an Scr of 9.5, it's TCV comes to 559/8.5=65.8cc. The stock closed chamber heads are spec'ed to be 57 (I haven't measured any) and the .028 gasket comes in at 6.8cc, totaling 63.8..... which leaves just 2cc for deck clearance. This is no big deal for what Mopar built these engines to do, but the 57cc head is a low-performance offering and is gonna need a lot of work to find power with.(read expensive)
Whereas the 72cc heads are a good deal of the way there, and have been used to good results right the way the come from Mopar.(read cheap)
So while I have nothing against a 273, it is however, an expensive project to get power enough to locomote your typical non-early-A streeter,with any semblance of authority.
Now, lets get back to the ICA, Intake Closing Angle.
The pressure building event of your engine cannot start until the valves, specifically the intake valve is closed.Your cam manufacturer specifies (usually) the advertised duration of his cam. But the specified number is not the actual fully closed point, but rather some very small opening point that he considers closed enough. Some manufactures choose .008tappetlift, some .006 and others .004. The actual fully closed point can be 20 or 30 degrees further on down the road. This doesn't matter too much, because once the engine is running, it is small enough,time-wise, not to be a problem. So the spec'ed advertised numbers can be used to determine something called the Dynamic Compression Ratio (Dcr). This is a formula that uses the left-over stroke at the time of advertised closing, to calculate the theoretical compression ratio that the engine will be seeing, and more specifically what your chosen fuel will be seeing. If your fuel can only support a Dcr of 8/1 then you cannot build your engine to make 8.1 Dcr without risk of destroying it. This, going back to the 273, is, or can be, a real handicap for that displacement. Again, for a street 360, you can be pretty sloppy and still have a nice streeter.
In other words, Scr is a means to obtain the maximum Dcr with a chosen ICA, for to use a certain fuel.
So, to recap, the ICA is one of two major players in choosing an Scr for your build. The other is elevation. The Effective Compression Ratio (Ecr), namely the pressure your engine actually has to work with, varies with the air density, which varies principally with elevation; namely the higher you go the thinner or less dense the air becomes.This thinner air makes it more difficult to make power with, and so you have to build to a higher Scr, to re-establish your chosen pressure, that still allows you to run the chosen fuel.
So now you may be really confused.
What is Effective Compression Ratio (Ecr)?
At any given time your throttle valves can be between almost-closed and WOT, and your Rpm can be just about anywhere. Of course this means your engine could be inhaling a minimum amount of air to a maximum. Well at idle, your engine is gonna only be able to ingest a few molecules of air, and they are gonna expand in your cylinder to fill it, but the molecules are gonna be far apart.So up comes the piston and squeezes them all into the same old chamber. But instead of the pressure being 160psi, maybe it's only 80.. So if 160 makes 9.5Scr@sealevel, maybe 80 makes 50% of that or 4.75 Effective Compression Ratio.
And if you drive this car up to 5000ft, and the max-pressure drops to 150 WOT, your Ecr will drop,from the Scr of 9.5, which was 8.0DCr at sealevel, to a Dcr /Rcr of perhaps 7.5 ..This is serious business. So much so, that if you optimize your combo for 5000 ft, with best gas available, then you better be real careful descending to lower altitudes.You have to take altitude into account with every build.
But the question was, which cam.
I personally, would not run a 318 or smaller, with an HFT. The actual on-the-seat-and-closed point of the intake valve is an unknown,until you install the cam and measure it. And I don't like that unknown, because it is a known pressure bleeder,and I cannot compensate for it during the build. Yeah, I like to run on the upper edge for midgrade 89octane gas, so that if I screw up, I don't have a do-over, but if I don't screw up, I have a dynomite engine.
So in your case; it depends on how much money you are willing to spend, and how much band-aiding you are willing to do afterwards.
If you have a pile of parts you wanna use, then prep what you have, cuz it's cheap, then measure the players and compute the Scr. Let that dictate your ICA, and slip in whatever cam you have closest to that, and call it done. Then if the bottom end goes away just slap a hi-stall on it ( bandaid #1). And if she's slow to 60mph, just slap some 4.30s in the back, (bandaid #2). Those are the band-aids. Sometimes the band-aids cost more than just fixing the Scr and run the cam your combo demands.
My 318 combo, if I had to build one, would demand a fast-rate solid-lifter cam, for max duration at .050 which is the actual important power-producing number, while maintaining a high Dcr, so I can run 3.55s or less and still get a modicum of fuel economy, cuz............. when the combo is sharp, I just wanna drive it every where all the time.
If I had to pick from your three listed;
I would not use the 112LSa, unless I specifically wanted the small overlap spec.
That leaves the Whiplash 213/226, the Crane 216/216, and the Mopar 220/224.
For me the Crane Single pattern is out.
Between the Mopar and the Whiplash, it's kindof flip-a-coin, except; the Mopar is a full size bigger at peak power, while the whiplash is a full size bigger at the bottom....... if I estimated the advertised spec correctly. Since I cannot know that, I reject the Whiplash on the those grounds only.
That leaves you with the Mopar 220/224
but wait! Remember the Crane. It is spec'ed at .004 lift. If I estimate the duration down to say 266* for the same .008Tappet lift as the Mopar and Whiplash, Suddenly, in at 106*, it becomes practically the same as the Mopar but with 8* less overlap, so idles smoother, while sacrificing a few horsepower. Here is the comparison, with the Crane sized down to estimate the .008T-lift;
268/272/120/112/54overlap, in at 104, the Mopar
266/266/121/113/46overlap, in at 106, the Crane
As you can see, the Crane at 266 exhaust, is 6* less than the Mopar at 272, and the overlaps are 8* apart. But what you don't see is that at those installed angles, the effective overlaps are actually 38* for the Crane and 48* for the Mopar, so that is a lot smoother idle for the Crane... if that matters to you. The .050s tell the story tho, the Mopar intake is ~4* bigger, so, IDK ~5hp on that, and maybe ~10 on the overlap with headers, for a total of perhaps 15hp with headers/ 5 without, advantage to Mopar. The Icas are within 1* so the rest is a wash. So pick your poison as to smooth idle. Oh wait. the much less overlap of the Crane is also gonna contribute to better city fuel economy; gear for gear.. Now recall that I fudged the crane down to 266 from 272, in an effort to make it an apples to apples comparison.
As for me, it would be the Mopar, because it has some flexibility in the cam-timing that I might want to exploit, if I had the pressure to play with.The Crane has no such flexibility.
Just to throw more confusion at you
This Mopar cam may not seat the intake fully, no longer leaking,until something like~304* just like the Crane. It's really hard to measure the actual point. And this is why I would use a solid lifter, cuz when the lash is set, you know exactly when the valve is fully closed. That means you can calculate the exact Dcr. That means you can target the cylinder pressure pretty accurately. And that means you can build to 91 octane gas, which is about 5 psi higher, than 89. And that means more low-rpm torque, more midrange power, and better fuel-economy.
But further, solids can be designed with faster rates of lift than FTHs, cuz their lighter in weight and follow the lobes better; (well they used to). And that means for the same advertised spec, you might get the next bigger .050 spec. OR more importantly, for the same .050 spec, your intake valve will hit the seat ~3 or 4 degrees sooner on the advertised spec but perhaps 20/30 degrees sooner in real, actually-slammed-shut, no-longer-bleeding-pressure, degrees.
And one more benefit; if the intake is on the seat sooner, so is the exhaust, and that means more cooling time for it, reducing the risk of detonation. But now, knowing that, means you can mess with the overlap cycle and let the headers really earn their keep. Headers are so much more than just an escape route for the hot gasses.
I gotta quit, I'm supposed to be doing other stuff,lol.
And if I was to build a 318 or smaller, because of the difficulty of making cheap compression, I would for sure use a fast-rate, solid lifter, cam.
Swept volume,if you don't know, is just the volume of one cylinder, that the piston sweeps thru on it's way from the bottom of the cylinder to the top.
A 360 has ~752cc,
a 340 has ~696,
a 318 has ~652,
a 273 has ~559.
AS you can see from 318 to 360 the increases are in about 50cc steps. But from 318 to 273 is a rather large step of nearly double that. This is what makes building a 273 so challenging.
The 360 has a generous amount of swept, and let's you be pretty sloppy with component selection, and still have a pretty good streeter.
How is swept important?
Well, it is the principal player in making cylinder pressure, that makes the heat, that drives the piston down, to make the power. But there is a limit to how much pressure you can make on pumpgas before detonation kills your dreams.
So the more swept you have, the more power you can theoretically make within the constraint of the detonation limit of your fuel.
How is that important?
Well, we have a limited number of players in the compression business, namely total combustion chamber volume (TCV), and the intake closing angle (Ica) of your chosen cam.. With various component selection this TCV can be in the range of ~67cc to~97cc. So,depending on the components chosen, you can make or break your combo.
For instance, on a 318; with 652cc of swept, and a cam-dictated 9.5Scr, you have the target of 652/8.5=76.7cc, which looks like an easy target. But you have 4 ways to get there, namely; chamber volume,gasket,deck-clearance. and eyebrows. So if your flat-top pistons are .057 down in the hole, that chews up ~11.2cc right there, and the gasket will be ~8.8 for the good ones, and that leaves you with 56.7cc for the head, and until recently, for performance, this was tough (expensive) to achieve.
But now with a 360, with a swept of 752cc, to get 9.5Scr, the TCV increases to 752/8.5=88.5cc. Now with flat tops .012 in the hole, the head requirement becomes 72cc, and there are plenty of those out there.
As it happens, a 360 can be built to almost any street Scr relatively cheaply.
But, lets back up to the 273. For an Scr of 9.5, it's TCV comes to 559/8.5=65.8cc. The stock closed chamber heads are spec'ed to be 57 (I haven't measured any) and the .028 gasket comes in at 6.8cc, totaling 63.8..... which leaves just 2cc for deck clearance. This is no big deal for what Mopar built these engines to do, but the 57cc head is a low-performance offering and is gonna need a lot of work to find power with.(read expensive)
Whereas the 72cc heads are a good deal of the way there, and have been used to good results right the way the come from Mopar.(read cheap)
So while I have nothing against a 273, it is however, an expensive project to get power enough to locomote your typical non-early-A streeter,with any semblance of authority.
Now, lets get back to the ICA, Intake Closing Angle.
The pressure building event of your engine cannot start until the valves, specifically the intake valve is closed.Your cam manufacturer specifies (usually) the advertised duration of his cam. But the specified number is not the actual fully closed point, but rather some very small opening point that he considers closed enough. Some manufactures choose .008tappetlift, some .006 and others .004. The actual fully closed point can be 20 or 30 degrees further on down the road. This doesn't matter too much, because once the engine is running, it is small enough,time-wise, not to be a problem. So the spec'ed advertised numbers can be used to determine something called the Dynamic Compression Ratio (Dcr). This is a formula that uses the left-over stroke at the time of advertised closing, to calculate the theoretical compression ratio that the engine will be seeing, and more specifically what your chosen fuel will be seeing. If your fuel can only support a Dcr of 8/1 then you cannot build your engine to make 8.1 Dcr without risk of destroying it. This, going back to the 273, is, or can be, a real handicap for that displacement. Again, for a street 360, you can be pretty sloppy and still have a nice streeter.
In other words, Scr is a means to obtain the maximum Dcr with a chosen ICA, for to use a certain fuel.
So, to recap, the ICA is one of two major players in choosing an Scr for your build. The other is elevation. The Effective Compression Ratio (Ecr), namely the pressure your engine actually has to work with, varies with the air density, which varies principally with elevation; namely the higher you go the thinner or less dense the air becomes.This thinner air makes it more difficult to make power with, and so you have to build to a higher Scr, to re-establish your chosen pressure, that still allows you to run the chosen fuel.
So now you may be really confused.
What is Effective Compression Ratio (Ecr)?
At any given time your throttle valves can be between almost-closed and WOT, and your Rpm can be just about anywhere. Of course this means your engine could be inhaling a minimum amount of air to a maximum. Well at idle, your engine is gonna only be able to ingest a few molecules of air, and they are gonna expand in your cylinder to fill it, but the molecules are gonna be far apart.So up comes the piston and squeezes them all into the same old chamber. But instead of the pressure being 160psi, maybe it's only 80.. So if 160 makes 9.5Scr@sealevel, maybe 80 makes 50% of that or 4.75 Effective Compression Ratio.
And if you drive this car up to 5000ft, and the max-pressure drops to 150 WOT, your Ecr will drop,from the Scr of 9.5, which was 8.0DCr at sealevel, to a Dcr /Rcr of perhaps 7.5 ..This is serious business. So much so, that if you optimize your combo for 5000 ft, with best gas available, then you better be real careful descending to lower altitudes.You have to take altitude into account with every build.
But the question was, which cam.
I personally, would not run a 318 or smaller, with an HFT. The actual on-the-seat-and-closed point of the intake valve is an unknown,until you install the cam and measure it. And I don't like that unknown, because it is a known pressure bleeder,and I cannot compensate for it during the build. Yeah, I like to run on the upper edge for midgrade 89octane gas, so that if I screw up, I don't have a do-over, but if I don't screw up, I have a dynomite engine.
So in your case; it depends on how much money you are willing to spend, and how much band-aiding you are willing to do afterwards.
If you have a pile of parts you wanna use, then prep what you have, cuz it's cheap, then measure the players and compute the Scr. Let that dictate your ICA, and slip in whatever cam you have closest to that, and call it done. Then if the bottom end goes away just slap a hi-stall on it ( bandaid #1). And if she's slow to 60mph, just slap some 4.30s in the back, (bandaid #2). Those are the band-aids. Sometimes the band-aids cost more than just fixing the Scr and run the cam your combo demands.
My 318 combo, if I had to build one, would demand a fast-rate solid-lifter cam, for max duration at .050 which is the actual important power-producing number, while maintaining a high Dcr, so I can run 3.55s or less and still get a modicum of fuel economy, cuz............. when the combo is sharp, I just wanna drive it every where all the time.
If I had to pick from your three listed;
I would not use the 112LSa, unless I specifically wanted the small overlap spec.
That leaves the Whiplash 213/226, the Crane 216/216, and the Mopar 220/224.
For me the Crane Single pattern is out.
Between the Mopar and the Whiplash, it's kindof flip-a-coin, except; the Mopar is a full size bigger at peak power, while the whiplash is a full size bigger at the bottom....... if I estimated the advertised spec correctly. Since I cannot know that, I reject the Whiplash on the those grounds only.
That leaves you with the Mopar 220/224
but wait! Remember the Crane. It is spec'ed at .004 lift. If I estimate the duration down to say 266* for the same .008Tappet lift as the Mopar and Whiplash, Suddenly, in at 106*, it becomes practically the same as the Mopar but with 8* less overlap, so idles smoother, while sacrificing a few horsepower. Here is the comparison, with the Crane sized down to estimate the .008T-lift;
268/272/120/112/54overlap, in at 104, the Mopar
266/266/121/113/46overlap, in at 106, the Crane
As you can see, the Crane at 266 exhaust, is 6* less than the Mopar at 272, and the overlaps are 8* apart. But what you don't see is that at those installed angles, the effective overlaps are actually 38* for the Crane and 48* for the Mopar, so that is a lot smoother idle for the Crane... if that matters to you. The .050s tell the story tho, the Mopar intake is ~4* bigger, so, IDK ~5hp on that, and maybe ~10 on the overlap with headers, for a total of perhaps 15hp with headers/ 5 without, advantage to Mopar. The Icas are within 1* so the rest is a wash. So pick your poison as to smooth idle. Oh wait. the much less overlap of the Crane is also gonna contribute to better city fuel economy; gear for gear.. Now recall that I fudged the crane down to 266 from 272, in an effort to make it an apples to apples comparison.
As for me, it would be the Mopar, because it has some flexibility in the cam-timing that I might want to exploit, if I had the pressure to play with.The Crane has no such flexibility.
Just to throw more confusion at you
This Mopar cam may not seat the intake fully, no longer leaking,until something like~304* just like the Crane. It's really hard to measure the actual point. And this is why I would use a solid lifter, cuz when the lash is set, you know exactly when the valve is fully closed. That means you can calculate the exact Dcr. That means you can target the cylinder pressure pretty accurately. And that means you can build to 91 octane gas, which is about 5 psi higher, than 89. And that means more low-rpm torque, more midrange power, and better fuel-economy.
But further, solids can be designed with faster rates of lift than FTHs, cuz their lighter in weight and follow the lobes better; (well they used to). And that means for the same advertised spec, you might get the next bigger .050 spec. OR more importantly, for the same .050 spec, your intake valve will hit the seat ~3 or 4 degrees sooner on the advertised spec but perhaps 20/30 degrees sooner in real, actually-slammed-shut, no-longer-bleeding-pressure, degrees.
And one more benefit; if the intake is on the seat sooner, so is the exhaust, and that means more cooling time for it, reducing the risk of detonation. But now, knowing that, means you can mess with the overlap cycle and let the headers really earn their keep. Headers are so much more than just an escape route for the hot gasses.
I gotta quit, I'm supposed to be doing other stuff,lol.
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AJ/FormS
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As to the Js, at ~72cc, the total chamber size adds up to; 2cc in the decks+5cc in the eyes+6.8 with an .028 gasket required to get .038Q, totals 13.8 so far, and the heads adds to~85.8, which drops your Scr back into the basement at 8.68, so yes they will soften your hit extremely. To run that 58/59 ICA with authority, your Scr will need to be ~9.6@800ft elevation. This will require a TCV of 659/8.6=76.6cc. Subtracting 13.8, leaves 62.8 for the heads. That's a lot of cutting on those Js, which will require more cutting to properly fit the intake.
I think there are no iron heads close to 62.8 , except perhaps the Magnums which I think come in at ~58cc. Those are just too small to work with and still use the 58/59* Ica..
For example;
By swapping in the .039 gasket for a new Q of ~.049 you're still in the ballpark, and that will get you another 2cc; so total now 15.8. Add 58=73.8 ..And your Scr with that would be 9.93, which is predicted to make 165psi, .... at 800ft elevation
But if you are operating at lower than 800ft, then it ain't gonna work. Most guys will say that 165psi is already borderline too much for 91 pump gas
So for example, with the Scr of 9.93 but now at 300ft, your pressure rises to 168psi, and you can't drive that at WOT, no pumpgas will support it..
So whaddya do?
You put a bigger cam in it is what. It's the cheapest solution.
So say with a 64* Ica, the Magnum combo comes in at 160psi@300ft elevation; Badaboom!
So what's a cam look like with a 64* Ica? Well it could be a lotta things but here's a theoretical one ;
276/276/116/112/108 LSA/60 overlap in at 106
That will be a ripper in a teener. With a bottom end still about as strong as the stocker.
Now if you make that a solid-lifter cam, your net after lash could be as much as 238*@.050. That would be a heckuva ripper.
_____________
But in all honesty, I don't think that is what you want.
So lets back up and see what can be done with the Js and a smaller cam, cuz I want to drive home the solid lifter cam option.
So lets go back to the 13.8 basic plus shave the heads to 68cc for a total chamber volume of 81.8cc, and therefore an Scr of (659+81.8)/81.8=9.06 So..... what can we do with that? Well at 300ft elevation now, with an Ica of 52*, you can make a lower rpm torque monster, perfect for 3.55s and a modest stall TC. These 52* will get you~160psi, and no torque loss compared to the stocker, yet plenty of power for a DD.
What's that cam look like? Well you build a dozen cams around that number, or more but here's a theoretical one;
248/256/128/116/112LSA/28overlap, in at 110. there you go, that's the stock teener cam. But But you say where is the power coming from? Well if I recall this cam peaks around 4800, maybe a lil sooner with the Js.
But the neat thing is this;65mph in 1.45 second gear with 3.55s will get you about 4440rpm, right on the fat part of the power curve. And so, you will be going thru the power peak, or near to it,TWICE on the way to 65. That maximizes your average power on the trip. But lets look at what happens at 30 mph when you stomp on it. This will be ~3500 rpm in low gear, on the fat part of the torque curve now, and first gear will go to 45mph@5200 with those Js.
But say you deck the block to pop the pistons out .005, and use the .028 gasket. You got no Q to speak of with the Js,so this will be fine. .005pop-up is -1cc and the .028s are ~6.8cc and the eyes are still 5cc and 68cc for the head, the new total is 78.8.... and the new Scr is 9.36, and Ta-da the new Ica is 56*. Yeah a bigger cam with a higher operating rpm. Is that a good thing? Maybe, and maybe not... cuz with the smaller one we were trapping 65=4440 very close to the power peak. But now the power peak is moving up ~250rpm to 5050. ..... so what's gonna happen at 4440? Well my guess is the car will not be any faster to 65mph with the bigger cam. But if you want one here is what it might look like
256/262/124/117/110LSA/39overlap in at 108. Hey that looks pretty nice.It will be faster to redline in second ~90mph, but I doubt you would see much difference in the zero to 60.
But hang on a sec, what if we went to a different piston without the stinking 5cc eyes which at this power level you don't need. That's 5 big beautiful ccs. How much did we cut off the Js? Hyup 4cc. Hey this is getting exciting. Ok so lets not deck the block and not mill the heads, and say the pistons come in at .011 in the holes. Ok, I get 2.2cc in the decks, 0 in the eyes, 6.8 in the .028s and back to 72 on the heads, for a TCV of 81cc... and an Scr of 9.14, and with the 256/262/110 cam I see 155psi, good for cheapest gas. A lil down on power on account of 155psi versus the 160 that I have been targeting, but what's not to like about burning 87.
So lets go see in your stash if you have a cam suitable to be installed with an ICA of 56*.
Well no, I don't see it. But remember that Whiplash? She goes in at 55* by the spec........... lol; kidding!
Lots of companies can supply you a 256/262/110 cam; it is a common size.
But here comes the punchline..
The 256 advertised could again be at .008,.006, or even .004 Tappet lift. Do we care? yes we do cuz it affects the idle, and low-speed operation. But more importantly, it plays a big roll in figuring the .050 durations which to you is really really important. So for now lets assume all the calcs I have been doing were with .008 tappet lift cams.
So what .050 will this 256 cam give us?
Well with a hydraulic FT cam this might be from ~216 to as little as 204, so you gotta pay attention cuz those 12*degrees could represent 25hp at this level. But typically you might get a 210@.050
What about a solid? Well that's really tricky, cuz if you order a 256 you can't expect it to be a 256 in your engine, cuz the lashing always takes away some duration. So you gotta start with a bigger cam, lash it, and see what you end up with, hopefully a 256*,lol. So say you ordered the next bigger solid lifter cam which might be a 262/270/110 which after lashing just theoretically* happens to be exactly 256/262/110 so we can compare apples to apples.
Now, this SFT you might be able to get it with 38* ramps and end up with 218* intake degrees. Wow! That is one size bigger than the HFT which was 210* ...
So what you end up with is zero loss in low-rpm torque, an increase in midrange,and perhaps*15 extra horsepower at peak. Oh, and we are still burning skunk-pee 87 @155psi.
EDITs in italics*
I think there are no iron heads close to 62.8 , except perhaps the Magnums which I think come in at ~58cc. Those are just too small to work with and still use the 58/59* Ica..
For example;
By swapping in the .039 gasket for a new Q of ~.049 you're still in the ballpark, and that will get you another 2cc; so total now 15.8. Add 58=73.8 ..And your Scr with that would be 9.93, which is predicted to make 165psi, .... at 800ft elevation
But if you are operating at lower than 800ft, then it ain't gonna work. Most guys will say that 165psi is already borderline too much for 91 pump gas
So for example, with the Scr of 9.93 but now at 300ft, your pressure rises to 168psi, and you can't drive that at WOT, no pumpgas will support it..
So whaddya do?
You put a bigger cam in it is what. It's the cheapest solution.
So say with a 64* Ica, the Magnum combo comes in at 160psi@300ft elevation; Badaboom!
So what's a cam look like with a 64* Ica? Well it could be a lotta things but here's a theoretical one ;
276/276/116/112/108 LSA/60 overlap in at 106
That will be a ripper in a teener. With a bottom end still about as strong as the stocker.
Now if you make that a solid-lifter cam, your net after lash could be as much as 238*@.050. That would be a heckuva ripper.
_____________
But in all honesty, I don't think that is what you want.
So lets back up and see what can be done with the Js and a smaller cam, cuz I want to drive home the solid lifter cam option.
So lets go back to the 13.8 basic plus shave the heads to 68cc for a total chamber volume of 81.8cc, and therefore an Scr of (659+81.8)/81.8=9.06 So..... what can we do with that? Well at 300ft elevation now, with an Ica of 52*, you can make a lower rpm torque monster, perfect for 3.55s and a modest stall TC. These 52* will get you~160psi, and no torque loss compared to the stocker, yet plenty of power for a DD.
What's that cam look like? Well you build a dozen cams around that number, or more but here's a theoretical one;
248/256/128/116/112LSA/28overlap, in at 110. there you go, that's the stock teener cam. But But you say where is the power coming from? Well if I recall this cam peaks around 4800, maybe a lil sooner with the Js.
But the neat thing is this;65mph in 1.45 second gear with 3.55s will get you about 4440rpm, right on the fat part of the power curve. And so, you will be going thru the power peak, or near to it,TWICE on the way to 65. That maximizes your average power on the trip. But lets look at what happens at 30 mph when you stomp on it. This will be ~3500 rpm in low gear, on the fat part of the torque curve now, and first gear will go to 45mph@5200 with those Js.
But say you deck the block to pop the pistons out .005, and use the .028 gasket. You got no Q to speak of with the Js,so this will be fine. .005pop-up is -1cc and the .028s are ~6.8cc and the eyes are still 5cc and 68cc for the head, the new total is 78.8.... and the new Scr is 9.36, and Ta-da the new Ica is 56*. Yeah a bigger cam with a higher operating rpm. Is that a good thing? Maybe, and maybe not... cuz with the smaller one we were trapping 65=4440 very close to the power peak. But now the power peak is moving up ~250rpm to 5050. ..... so what's gonna happen at 4440? Well my guess is the car will not be any faster to 65mph with the bigger cam. But if you want one here is what it might look like
256/262/124/117/110LSA/39overlap in at 108. Hey that looks pretty nice.It will be faster to redline in second ~90mph, but I doubt you would see much difference in the zero to 60.
But hang on a sec, what if we went to a different piston without the stinking 5cc eyes which at this power level you don't need. That's 5 big beautiful ccs. How much did we cut off the Js? Hyup 4cc. Hey this is getting exciting. Ok so lets not deck the block and not mill the heads, and say the pistons come in at .011 in the holes. Ok, I get 2.2cc in the decks, 0 in the eyes, 6.8 in the .028s and back to 72 on the heads, for a TCV of 81cc... and an Scr of 9.14, and with the 256/262/110 cam I see 155psi, good for cheapest gas. A lil down on power on account of 155psi versus the 160 that I have been targeting, but what's not to like about burning 87.
So lets go see in your stash if you have a cam suitable to be installed with an ICA of 56*.
Well no, I don't see it. But remember that Whiplash? She goes in at 55* by the spec........... lol; kidding!
Lots of companies can supply you a 256/262/110 cam; it is a common size.
But here comes the punchline..
The 256 advertised could again be at .008,.006, or even .004 Tappet lift. Do we care? yes we do cuz it affects the idle, and low-speed operation. But more importantly, it plays a big roll in figuring the .050 durations which to you is really really important. So for now lets assume all the calcs I have been doing were with .008 tappet lift cams.
So what .050 will this 256 cam give us?
Well with a hydraulic FT cam this might be from ~216 to as little as 204, so you gotta pay attention cuz those 12*degrees could represent 25hp at this level. But typically you might get a 210@.050
What about a solid? Well that's really tricky, cuz if you order a 256 you can't expect it to be a 256 in your engine, cuz the lashing always takes away some duration. So you gotta start with a bigger cam, lash it, and see what you end up with, hopefully a 256*,lol. So say you ordered the next bigger solid lifter cam which might be a 262/270/110 which after lashing just theoretically* happens to be exactly 256/262/110 so we can compare apples to apples.
Now, this SFT you might be able to get it with 38* ramps and end up with 218* intake degrees. Wow! That is one size bigger than the HFT which was 210* ...
So what you end up with is zero loss in low-rpm torque, an increase in midrange,and perhaps*15 extra horsepower at peak. Oh, and we are still burning skunk-pee 87 @155psi.
EDITs in italics*
Last edited:
JDMopar
Well-Known Member
Thanks AJ. 
Detroit Iron
Well-Known Member
Very true, and the 318 is a better fit for a 600 cfm carb. Looks like everyone derailed your 273 plan.
JDMopar
Well-Known Member
I'm about beat into submission....lol. The price of the 273 pistons are what's killer! I've searched in vain for Sealed Power 322NP pistons for a 273. 
Egge pistons cost a war pension. The fact that I have close to a dozen 318's sitting around makes the decision make sense too....lol.
Egge pistons cost a war pension. The fact that I have close to a dozen 318's sitting around makes the decision make sense too....lol.
There are other pistons available. Try the search function. I don't happen to have the brands saved anywhere. Banter comes to mind.I'm about beat into submission....lol. The price of the 273 pistons are what's killer! I've searched in vain for Sealed Power 322NP pistons for a 273.
Kanter and PAW may have affordable pistons for you.I'm about beat into submission....lol. The price of the 273 pistons are what's killer! I've searched in vain for Sealed Power 322NP pistons for a 273.
Mike,,,,,, I thought PAW was long gone. As far as I know they didn't stay up with the times, and the internet(or lack of it) killed them. I was a big customer of theirs.
Dave
Dave
replicaracer43
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PAW has been out of business for years
replicaracer43
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If he builds the 318, no one will know the difference except his wallet.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Put the cast-iron single-plane on it, paint it red, and call it a big-bore 273. Show people go for that. They hated that my S-clone didn't have a 340. But as soon as I called it a 3.58stroker -340 with a standard 4.04 bore, we were all friends again; go figure .
Lots of good pistons for the 318. If you happen to have a Magnum, you'll be ahead of the game in every way. Teeners are so much easier to make compression with, on account of the larger swept volume; 652.27@3.91bore, and 662.32@3.94.
Lots of good pistons for the 318. If you happen to have a Magnum, you'll be ahead of the game in every way. Teeners are so much easier to make compression with, on account of the larger swept volume; 652.27@3.91bore, and 662.32@3.94.
I actually Love 273's. If not a 273 I jump to a 340 or 383. I've had a 340 done for years sitting on a stand, no need to swap out the 273 in an early A yet. I have a set of +.030 #322 pistons for $160 + shipping, or come and pick them up.
273's are capable of excellent performance. My bone stock 273 4 speed '65 Dart ran in the high 14 seconds with 13" cheater slicks in 1966.
Problem is they are more expensive to rebuild than a 318/340/360, so what's the point? I prefer the 340 because of the short stroke with 63 more ci.
Nobody builds Ford 260s or Chevy 265s for the reasons stated above.
Problem is they are more expensive to rebuild than a 318/340/360, so what's the point? I prefer the 340 because of the short stroke with 63 more ci.
Nobody builds Ford 260s or Chevy 265s for the reasons stated above.
BillGrissom
Well-Known Member
Consider Rhoads leak-down lifters. It will make it run better at low rpm, with more vacuum yet give full lift at higher rpm. Better cruising, mileage, and less emissions. Unless you like that stumbling "race car" idle that some seem to like (not me, I'm an engineer). I put a hydraulic cam (RV Torker) in my 65 Dart 273 w/ Rhoads. You can use the stock adjustable rockers if you buy shorter 340 TA pushrods (ball & cup). The adjustments let you set the lifter pre-load perfectly. Unless you have your heart set on a carburetor, I would buy a throttle-body EFI. They are now <$1000 even with self-learning, while carb prices keep rising. You should save just in the better mileage. Good luck.
JDMopar
Well-Known Member
I had a friend who put Rhodes lifters in a 440. They seemed to clatter a lot. Do yours rattle? I had already pretty much planned to run a Holley Sniper EFI on it after I get the cam broke in. If I do a hydraulic roller, I'll do the EFI right off the bat.
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