How far to rev this 273 commando build

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Yes I did read some of it, I started to gloss over lol
Pretty sure it's factual, Steve. I don't understand all of it myself at all. I will say this......don't tell anybody the new generation Ford Powerstrokes won't rev to 5200. Mine sure did. LOL

Did you read that post I linked to that Del posted the text of? I did and I'm still lost. Although a little less lost. A little.
 
I dont fully understand it, but for example you have a "normal" diesel genset. Any that I've seen rev nowhere near 5200 rpm, but there is hp and torque? So that would mean for this example the 5200 is theoretical?

5252 is a constant, used in the math. It could turn 1 RPM or 1/4 RPM and it would still "figure." You are overthinking this, Steve. Dynos measure TORQUE period. It is that simple. HP is calculated from that, traceable clear back to Watts (the guy Watts) and steam engines and horses.
 
For a drag race, that graph in post #6 tells you to shift just past the hp peak ~5500 - 5700 rpm and operate around peak hp.
It does no good to go too far past peak hp @5200 before shifting. You lose hp and risk hurting the engine. For top speed in 4th, the Commando engine goes easily to 6000 rpm.


Again, max performance would be where the lower gear peak falls off and CROSSES the next peak for the next higher gear "on the way up."
 
5252 is a constant, used in the math. It could turn 1 RPM or 1/4 RPM and it would still "figure." You are overthinking this, Steve. Dynos measure TORQUE period. It is that simple. HP is calculated from that, traceable clear back to Watts (the guy Watts) and steam engines and horses.

Ok so the 5252 is the given, same as .785 in the cubic inch formula.
 
That graph in post #4 is incorrect. Torque and HP always cross at 5250 RPM.
I think you're referring to the graph in post #6. They just made it look goofy by using two different scales(torque on left, hp on right). Notice how 280 is lower down the graph than 235. If you just slide the torque curve up until they intersect it makes sense.
 
I think you're referring to the graph in post #6. They just made it look goofy by using two different scales(torque on left, hp on right). Notice how 280 is lower down the graph than 235. If you just slide the torque curve up until they intersect it makes sense.

No, I said it right.
 
Sorry, I didn't see any graph in post #4. So figured you were referring to post #6.

Well lemmie go back and look. Maybe my stupid *** got it wrong. Again.

Yeah, as usual, I screwed up. It's #6. lol Thanks man.
 
I am definately taking the time to read this over later today . I'm glossing over myself. Interesting stuff guys,thanks
 
I build to rev to the moon, so I can shift whenever I please. If it blows up. I'll take it apart and figure out why it broke, make it better, and start over. That might not be the quickest way to the finishline, but I ain't a dragracer.
I'm just that crazy guy who gets his fix listening to his dual 3's screaming long and loud, on a lonely country road, in the middle of the afternoon.
One thing I learned is this; If your gonna spend significant time over 6000, your heavy-rod SBM engine is gonna want to have the oiling system modified so the rods will live. IDK about the lighter rods in the 273s.
With the mods,and a roadrace pan, mine has been spinning, dare I say it,over 6999lol,since 1999. The oiling mods are cheap and easy, and they work. Ok wait; the hi-capacity pan wasn't cheap, but since the engine has survived this long, maybe it wasn't quite as expensive as I thought.

On another note;
To the guy who might be confused about valve float and lifter pump-up, don't be; the first leads straight to the second and for all practical purposes happen together and almost simultaneously. The valvesprings fail to keep it together, and the lifters do exactly what they were designed to do, which is take up the slack. Lifters are just automatic slack-adjusters.
Unfortunately for some guys, pumped-up lifters send the valves straight into their hi-compression pistons, and that spells catastrophic failure. So the take-aways here are; 1) don't let this happen to you, and 2) cuz it gets really expensive in milliseconds, so 3) get a rev-limiter, or 4) just do what I do,spring the chit out of it,run a minimum lifter preload, and pray the lobes survive. So far, so good.
Ok that's not good advice. The cam grinder will call for the springs, and the spring manufacturer can tell you the limits, so those guys have scienced it out for us. If you go beyond their recommendations, then yur on your own.
As for me, I'm moving the daymn wall. I guess I got enough spring pressure on this engine, cuz there was this one time, back in about 2003 or 4,when I missed a shift, and saw the tach-needle crossing the 8 on it's way back down. I immediately crossed rev-limiter off my wish-list.
That do-what-I-do, spring-the-chit-out-of-it philosophy, saved me probably what 5Gs maybe 6 Canadian. A rev-limiter would be cheaper than replacing a cam-kit tho. But then I would lose my 6999 plus screaming banshees fix; and without my fix, I might not want to go on living,lol.
 
As for the graphs, the lines always cross at 5250, IF; the same scales are used for both torque and it's derivative horsepower. For compactness, many times different scales and even abbreviated scales are used, and then they can cross anywhere. And sometimes I think they just mess 'em up to screw around. You can see this when you see a small hi-reving engine that makes power after say 8000, but not a lot of torque. Then they re-scale it and scrunch it up to fit in a magazine article, sometimes lopping off all the power below say 3000 or 4000, to make room for the torque numbers. With a lil math you can get the numbers back, so it's no big deal. The graph here discussed from post #6 , is just such a graph with a re-scaled axis on one side or the other, looks like the torque side, which may also have been scrunched, that is to say compressed. I picked three random points, did some math, and the two lines appear to be of the same origin.
 
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ust wondering ...........This is the T-3 custom grind isky cam specs I installed in my 273 commando . what is meant by the 2* advance , does it mean it is at 106* or 110* ? Rpm range is 2000 - 6400. does this cam need to be revved to 6400 to make good power or what? I've taken it up to 5900 rpms so far and it's still pulling hard . is there any need to go to 6400 rpms? 65 barracuda with 4 speed , 3.55's gears , hooker headers , pertronix ignition , cleaned up 920 heads . real stock bore 273 commando engine with dome pistons and .028 head gaskets.
also......... what about the 44* overlap concerns ?what does that mean? this cam has 15"vac at 850 idle .here are the specs of the cam installed .
Has anybody actually answered these questions?
As to the 2* advance
This means the installed centerline has been advanced, or is to be, or is recommended to be, advanced 2 degrees from straight up; which on a 110 cam would be 108, but on a 114 cam would be 112. The cam manufacture has reason to believe that at 2* advanced, it will run the best for you. If you have the time and energy, you can try other installs,but mostly, they will have bugged it out for you.
As to the overlap.
Overlap is or can be, a distinct cycle added to the 4-stroke cycle of your engine. It is a period of time measured in degrees, wherein can be exploited the movement of air into the engine. This time-period really only responds to tuned headers and a free-flowing exhaust. Log manifolds pretty much kills it.
How it works was taught to me to be like this; a slug of exhaust flows down the individual header pipe and comes to a lower pressure area and slows down.The exhaust valve behind it is still open. Think of this slug of exhaust as a syringe. Plug the tiny needle opening and yank it apart. During the yanking you create a partial vacuum in the tube, and when the rubber part comes out, the pop you hear is air rushing in to fill the void. A similar thing occurs in the header, a partial vacuum is created by the fast-moving exhaust slug, and it is at it's highest just before the exhaust valve closes. This means the chamber is now also in a partial vacuum! If we now open the intake valve, and the carb is wide open, then we can fast-track air into that chamber, literally have it be sucked into it. And if we open the intake a lil sooner we can fast-track it, even faster.
So the overlap cycle is like a supercharger, ramming air into the chamber. I said like. And so the more overlap you have, theoretically the more air will be rammed into the engine. But big-number overlap and street engines are not the best of friends, cuz the degrees have to come from somewhere, and if you steal too many from here and there, pretty soon you have a powerhouse engine, but it has to idle at a very high rpm, just to keep running.
So the question is what kindof numbers can we use in a street engine.
Well, IMO the Mopar 292/292/108 cam is too big for most street SBMs, and that's because it has 76* of overlap. I can tell you that this cam makes a boatload of power, but if you don't build your engine to properly use it,and you don't have a matching chassis for it, you are gonna be a very cranky 273 operator.
And, the stock smog teeners had IIRC 20* advance, ran log manifolds, idled dead smooth, and didn't rum much different with headers, cuz 20* is as good as nothing.
So guess what's in between 20 and 76?... 48* is in between.
48* will idle like a 340 . But what you rarely hear about 340s is that headers really woke them up, to the tune of perhaps 30 hp I have regularly heard. So that is a difference strictly traceable to the 44* overlap of the 340 cam, and how it affects power.
 
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^^^^I did the first story but not the second two, good Lord too much to read.
My first thought was--- TO THE MOON ALICE!!!!
 
^^^^I did the first story but not the second two, good Lord too much to read.
My first thought was--- TO THE MOON ALICE!!!!

Who doesn't love AJ's posts.
He never leaves you wanting more info!?:thumbsup:
 
You rev it until the power falls off ON A DYNO.

If you keep your foot in it until you can literally feel the power falling off you are revving it far past where you should be shifting and just beating your engine for no reason.

Advertised cam RPM range MEANS NOTHING. ZERO...


Spend 100$ and see where it makes power. Shift accordingly.
 
I build to rev to the moon, so I can shift whenever I please. If it blows up. I'll take it apart and figure out why it broke, make it better, and start over. That might not be the quickest way to the finishline, but I ain't a dragracer.
I'm just that crazy guy who gets his fix listening to his dual 3's screaming long and loud, on a lonely country road, in the middle of the afternoon.
One thing I learned is this; If your gonna spend significant time over 6000, your heavy-rod SBM engine is gonna want to have the oiling system modified so the rods will live. IDK about the lighter rods in the 273s.
With the mods,and a roadrace pan, mine has been spinning, dare I say it,over 6999lol,since 1999. The oiling mods are cheap and easy, and they work. Ok wait; the hi-capacity pan wasn't cheap, but since the engine has survived this long, maybe it wasn't quite as expensive as I thought.

On another note;
To the guy who might be confused about valve float and lifter pump-up, don't be; the first leads straight to the second and for all practical purposes happen together and almost simultaneously. The valvesprings fail to keep it together, and the lifters do exactly what they were designed to do, which is take up the slack. Lifters are just automatic slack-adjusters.
Unfortunately for some guys, pumped-up lifters send the valves straight into their hi-compression pistons, and that spells catastrophic failure. So the take-aways here are; 1) don't let this happen to you, and 2) cuz it gets really expensive in milliseconds, so 3) get a rev-limiter, or 4) just do what I do,spring the chit out of it,run a minimum lifter preload, and pray the lobes survive. So far, so good.
Ok that's not good advice. The cam grinder will call for the springs, and the spring manufacturer can tell you the limits, so those guys have scienced it out for us. If you go beyond their recommendations, then yur on your own.
As for me, I'm moving the daymn wall. I guess I got enough spring pressure on this engine, cuz there was this one time, back in about 2003 or 4,when I missed a shift, and saw the tach-needle crossing the 8 on it's way back down. I immediately crossed rev-limiter off my wish-list.
That do-what-I-do, spring-the-chit-out-of-it philosophy, saved me probably what 5Gs maybe 6 Canadian. A rev-limiter would be cheaper than replacing a cam-kit tho. But then I would lose my 6999 plus screaming banshees fix; and without my fix, I might not want to go on living,lol.
Well said AJ!
 
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Has anybody actually answered these questions?
As to the 2* advance
This means the installed centerline has been advanced, or is to be, or is recommended to be, advanced 2 degrees from straight up; which on a 110 cam would be 108, but on a 114 cam would be 112. The cam manufacture has reason to believe that at 2* advanced, it will run the best for you. If you have the time and energy, you can try other installs,but mostly, they will have bugged it out for you.
As to the overlap.
Overlap is or can be, a distinct cycle added to the 4-stroke cycle of your engine. It is a period of time measured in degrees, wherein can be exploited the movement of air into the engine. This time-period really only responds to tuned headers and a free-flowing exhaust. Log manifolds pretty much kills it.
How it works was taught to me to be like this; a slug of exhaust flows down the individual header pipe and comes to a lower pressure area and slows down.The exhaust valve behind it is still open. Think of this slug of exhaust as a syringe. Plug the tiny needle opening and yank it apart. During the yanking you create a partial vacuum in the tube, and when the rubber part comes out, the pop you hear is air rushing in to fill the void. A similar thing occurs in the header, a partial vacuum is created by the fast-moving exhaust slug, and it is at it's highest just before the exhaust valve closes. This means the chamber is now also in a partial vacuum! If we now open the intake valve, and the carb is wide open, then we can fast-track air into that chamber, literally have it be sucked into it. And if we open the intake a lil sooner we can fast-track it, even faster.
So the overlap cycle is like a supercharger, ramming air into the chamber. I said like. And so the more overlap you have, theoretically the more air will be rammed into the engine. But big-number overlap and street engines are not the best of friends, cuz the degrees have to come from somewhere, and if you steal too many from here and there, pretty soon you have a powerhouse engine, but it has to idle at a very high rpm, just to keep running.
So the question is what kindof numbers can we use in a street engine.
Well, IMO the Mopar 292/292/108 cam is too big for most street SBMs, and that's because it has 76* of overlap. I can tell you that this cam makes a boatload of power, but if you don't build your engine to properly use it,and you don't have a matching chassis for it, you are gonna be a very cranky 273 operator.
And, the stock smog teeners had IIRC 20* advance, ran log manifolds, idled dead smooth, and didn't rum much different with headers, cuz 20* is as good as nothing.
So guess what's in between 20 and 76?... 48* is in between.
48* will idle like a 340 . But what you rarely hear about 340s is that headers really woke them up, to the tune of perhaps 30 hp I have regularly heard. So that is a difference strictly traceable to the 44* overlap of the 340 cam, and how it affects power.
AJ ..............Ron at Isky made the cam with 2* advance , giving the 273 more grunt on the bottom end . which it sure does . That is what I specifically asked for . I don't think this cam has that radical of a sound when idling . imo. sooooooooooooso if the cam is advanced 2* then lsa is at 106 is that correct ?
 
Video..................Listen to this dartcharger commando I owned a few years back. This engine revved to 7000 all day long . It was tired and smoking badly with 74K miles . All original 273 except I installed dougs headers ld4b duals dynomax ultra flos x pipe 2.5", pertronix ign with a dist curve . This engine screamed ! at one rev in this video it was at 6500 rpm easy. and fast . trimmed smoking bad reving
 
You rev it until the power falls off ON A DYNO.

If you keep your foot in it until you can literally feel the power falling off you are revving it far past where you should be shifting and just beating your engine for no reason.

You're right, I shoulda mentioned take your foot out of it when the Gs drop, don't wait to see if the Gs will go back up. Lol

I bet there's lotsa folks shifting well above their optimum RPM , as you mention, abusing their engine, simply because they THINK they're still accelerating.

G-meter is a simple avail tool that folks can use, and avoid an expensive Dyno.
 
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You're right, I shoulda mentioned take your foot out of it when the Gs drop, don't wait to see if the Gs will go back up. Lol

Yes, you can certainly play around with shift points to a degree...

So for instance mine makes peak at 5800. At 6200 it only falls off maybe 10hp at most. So I geared to through the traps at 6200 and the timslip was favorable. However push it past that and the time slows. I've short shifted some of my cars before the marked redine only to go faster because it was actually making power and dropping the RPm upon shifting into the tq band.
 
Using a G-meter to establish power drop off, and then experiment initiating the shift at slightly lower RPMs till you got the sweet spot.

Different gears often have different shift points.

I Edited post #46.
 
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Just wondering ...........This is the T-3 custom grind isky cam specs I installed in my 273 commando . what is meant by the 2* advance , does it mean it is at 106* or 110* ? Rpm range is 2000 - 6400. does this cam need to be revved to 6400 to make good power or what? I've taken it up to 5900 rpms so far and it's still pulling hard . is there any need to go to 6400 rpms? 65 barracuda with 4 speed , 3.55's gears , hooker headers , pertronix ignition , cleaned up 920 heads . real stock bore 273 commando engine with dome pistons and .028 head gaskets.
also......... what about the 44* overlap concerns ?what does that mean? this cam has 15"vac at 850 idle .

here are the specs of the cam installed .

my-coammdo-cam-specs-ii-jpg.1715285896


my-commando-cam-specs-jpg.1715285897

What are the full specs on this cam? Duration @ .050, lift, etc.

Sounds very similar to the cam we installed in Jason’s 318
 
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