any benefit to swapping heads?

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AJ/FormS said:
For a streeter, and with no other changes, I ,personally, wouldn't spend the time, or the cash, for new FellPros.
You should already have enough power to spin street tires thru two gears;but at 8.5 Scr, I bet you really have to rev it up to break the tires loose.I hated that. I hated it because it sounded so Mustang.
There are two versions of that Mopar single pattern cam, and neither one is for an 8.5 street engine; and neither one is for 3.55s.
If you have an issue at low rpm, the X-heads won't fix that. IMHO, you asked the wrong question first.
If you really have an 8.5Scr engine, and you really want to keep that cam, and those 3.55s, and can't find or afford the 3.09 lowgear Commando trans, then ............ well;
I could tell you about my 292/.508 experiences in my 11.3 Scr Aluminum headed 367. The short version is I swapped it out in a hurry, for a 270/276/110 cam with lifts of .538/.549, and lowered the compression a tad, and would still be driving it like that today,18 years later, (because it had monster torque), except it began dropping lobes in 2004.Well, that's as short as I could make it.
Click to expand...
Would swapping the 355's to 391's help low end torque?
 
sure- look for some 3:91s if this is not a daily driver it's a mechanical change- you can calculate the difference- and then drive and pretend where your new shift points would be
but for the cost of gears you could replace the high compression bracket racer with headers cam you have with something appropriate
advancing the cam 6 degrees works getting the intake closed earlier but does nothing about overlap and hurts your power expansion on the combustion stroke and gas mileage, if that's a concern
That said do a compression check and try it and do another compression check
you can then calculate your intake closing points and see where you want to go
how's the top end, passing etc now?
 
Wyrmrider said:
sure- look for some 3:91s if this is not a daily driver it's a mechanical change- you can calculate the difference- and then drive and pretend where your new shift points would be
but for the cost of gears you could replace the high compression bracket racer with headers cam you have with something appropriate
advancing the cam 6 degrees works getting the intake closed earlier but does nothing about overlap and hurts your power expansion on the combustion stroke and gas mileage, if that's a concern
That said do a compression check and try it and do another compression check
you can then calculate your intake closing points and see where you want to go
how's the top end, passing etc now?
Click to expand...

That's what I've been saying for a long time, too.
And I've proved it with my installs.
There are only so many degrees to go around, and when you close the intake earlier, you're stealing from Peter to pay Paul and overlap gets a kick in the head. Of course with log manifolds............ that don't mean all that much
Nevertheless, I keep hitting a wall when preaching it.
 
Here's some numbers OP to help you understand the low-rpm issue, with a 340 and a 284/114 cam in an 8.2Scr 340.
I inputted your 284 cam as a 114LSA, so in at 4* advanced, the ICA would be 72*, and I inputted 800ft elevation.
Static compression ratio of 8.2:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 6.17:1 .
Your dynamic cranking pressure is 111.76 PSI.
V/P (Volume to Pressure Index) is 82VP
Notice the cylinder pressure and VP, are both very low.
read about VP here; V/P Index Calculation

Here is a stock 225slanty, at the same compression ratio, but with an ICA of 48*due to it's much smaller cam
Static compression ratio of 8.2:1.
Effective stroke is 3.51 inches.
Your dynamic compression ratio is 7.32:1 .
Your dynamic cranking pressure is 141.33 PSI.
V/P (Volume to Pressure Index) is 93VP .
Notice the pressure is up,partly cuz of the earlier closing intake, and notice also the significantly larger VP. The slanty should actually feel more powerful,car for car, in the lower sub-3000 rpm area.

SO VP is the thing you need to do something about.

Here is YRs proposal of retiming the cam to 102. This would get you an ICA of 64*, so
Static compression ratio of 8.2:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 6.58:1 .
Your dynamic cranking pressure is 122.19 PSI.
V/P (Volume to Pressure Index) is 97VP .
Notice your engine picked up 11psi and 15 points of VP.This is a very significant improvement of 18%. This is about as good as it gets with the parts you currently have.

Ok so lets go back to the original install, and boost the stinking compression up
Static compression ratio of 10.5:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 7.82:1 .
Your dynamic cranking pressure is 154.50 PSI.
V/P (Volume to Pressure Index) is 113 .
Ok now you got some pressure, and can still burn 87/89. This is about as good as it gets with that cam and iron heads.
Notice the VP jumps to 113. From the original 82 this is 113/82=38% improvement. So now it's taking off like a 318.

Ok but say 318 take-off sucks to you. Lets put a proper IMO, street cam in there and a matching compression. I like the 268/276/110, in at 108
Static compression ratio of 9.8:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 7.93:1 .
Your dynamic cranking pressure is 157.42 PSI.
V/P (Volume to Pressure Index) is 126
Ok this will burn 87 most of the time, but might want 89/91 at WOT.
Notice the VP is now up to 126; a 54% improvement.This is IMO a real nice balance of low-rpm torque , a fat midrange and reasonably good top-end... for a streeter with 3.55s

Ok one more, if your pockets are deep and you can afford some aluminum heads. This is still with the 268/276/110 cam, but with the Scr pumped up for the new heads . I have burned 87E10 in my 367 with this pressure,
Static compression ratio of 11.3:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 9.11:1 .
Your dynamic cranking pressure is 189.24 PSI.
V/P (Volume to Pressure Index) is 152
Notice the VP is up to 152 now,an 85% improvement, in low-rpm operation, where you probably are some 80% of the time, up to about 3500rpm. The 268 pulls strong to about 5400,then levels off, and with the Eddies I got, I force her to 7000 all the time.
I know, I know, I just included the last one for comparison.
A 152VP is about what a stock 1969 440 Magnum pulled, just so you know.

Edit, added for comparison, see also post #76
here is your 8.2/340 with a 252/112 cam;still at 800ft. This is a stock 360 2bbl type cam.

Static compression ratio of 8.2:1.
Effective stroke is 2.78 inches.
Your dynamic compression ratio is 7.04:1 .
Your dynamic cranking pressure is 134.04 PSI.
V/P (Volume to Pressure Index) is 115 .

Look at the VP jump, this is very significant, and 40% better than the 82VP originally estimated. Remember this is a measurement of performance that is only relevant up to in the range of 3000 to 3500 rpm.
 
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Read the first page... skiped to the third
and noticed people were missing things about the small valves and velocity potential... hell I can have a 1.92 flowing 255 cfm easily , what's that worth against the X 2.02 that's only does 218- 228cfm as cast "given the best casting you can find". More mixing after the carb.

I know if it were me I would probably Port the X and swap them on. You can get about 265 to almost 270 cfm with a 3/8 valve stem and conservative porting, no major guide work.
 
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djais1801 said:
Would swapping the 355's to 391's help low end torque?
Click to expand...

No. It will feel quicker because the more gear gives you more multiplication. It will help the car use what you're making. Not make more torque. A small syntax difference but significant.
 
AJ
could you run both the what he has compression and 9:1 with this cam
265 @.004
256° @.006 (comp 256 cam closes intake at 54 ABDC @.006- should be the same at same ICL but this one has more intensity below .006
246 @.008 (about the same as the slant 6 cam you profiled
202° @.050
120 @ 200
64 @ 275
305 lobe lift

DC 260 is 42 at .275 and about same seat duration as the Comp 268 HE comp 256HE has hardly any at .275
comp 268 has about the same lift but takes 12 more degrees to get there
I'm running this cam in a true 9:1 tight quench 440 HP exhaust 2 1/2 " TQ

moper would he not have more torque at the wheel :)
 
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OP
I know your head hurts but take a crack at this
Cam Timing vs. Compression Analysis
I don't agree with all of it- hell I don't agree with lots of anything but the basics are there
important is is that most tech guys deal with many SBC and SBF and few MOPAR
and there is a big difference between long rod MOPARS and short rod Chevy/ Ford
the bottom line on what he is saying is that intake close and exhaust upon is much more critical on a MOPAR than on a short rod where you have a wider latitude
you want to close the intake earlier and open the exhaust later- a few degrees makes a big difference on the intake close as far as dynamic compression and on the exhaust to get all the power out of the power stroke- especially on a low compression motor
on overlap the fact that the piston dwells longer around TDC means that you have to open the intake later and close the exhaust earlier than a short rod
there is more TIME, DWELL, with the valves open at the same timing than a short rod
so squeezing the lobe centers- well on a MOPAR not so much and a short rod and overlap it's easier to flow your intake right out your exhaust = heat and dilution of the intake charge by the exhaust
If you do not have a clue you end up with a cam that does not do what you wanted eventhough the same cam might work just fine in a chevy or ford

Thanks AJ Controlled Induction can do it and I did it with an earlier version 20 years ago
if you are serious I could buy you a copy
 
That's very generous, but my time on FABO is sortof winding down.And there has appeared a new group of men, far smarter than me, in addition to those that were here before I came.
My other favorite thing to do involves Bible study, because you know; I believe we are living in the end-times, and I believe we are almost all gonna be going thru it. So I gotta get my chit together.I gotta make sure I'm not still believing lies.
I would count it a blessing if I didn't wake up in the morning, but my gift is good health; so I don't see that happening naturally any time soon.
 
AJ/FormS said:
Here's some numbers OP to help you understand the low-rpm issue, with a 340 and a 284/114 cam in an 8.2Scr 340.
I inputted your 284 cam as a 114LSA, so in at 4* advanced, the ICA would be 72*, and I inputted 800ft elevation.
Static compression ratio of 8.2:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 6.17:1 .
Your dynamic cranking pressure is 111.76 PSI.
V/P (Volume to Pressure Index) is 82VP
Notice the cylinder pressure and VP, are both very low.
read about VP here; V/P Index Calculation

Here is a stock 225slanty, at the same compression ratio, but with an ICA of 48*due to it's much smaller cam
Static compression ratio of 8.2:1.
Effective stroke is 3.51 inches.
Your dynamic compression ratio is 7.32:1 .
Your dynamic cranking pressure is 141.33 PSI.
V/P (Volume to Pressure Index) is 93VP .
Notice the pressure is up,partly cuz of the earlier closing intake, and notice also the significantly larger VP. The slanty should actually feel more powerful,car for car, in the lower sub-3000 rpm area.

SO VP is the thing you need to do something about.

Here is YRs proposal of retiming the cam to 102. This would get you an ICA of 64*, so
Static compression ratio of 8.2:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 6.58:1 .
Your dynamic cranking pressure is 122.19 PSI.
V/P (Volume to Pressure Index) is 97VP .
Notice your engine picked up 11psi and 15 points of VP.This is a very significant improvement of 18%. This is about as good as it gets with the parts you currently have.

Ok so lets go back to the original install, and boost the stinking compression up
Static compression ratio of 10.5:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 7.82:1 .
Your dynamic cranking pressure is 154.50 PSI.
V/P (Volume to Pressure Index) is 113 .
Ok now you got some pressure, and can still burn 87/89. This is about as good as it gets with that cam and iron heads.
Notice the VP jumps to 113. From the original 82 this is 113/82=38% improvement. So now it's taking off like a 318.

Ok but say 318 take-off sucks to you. Lets put a proper IMO, street cam in there and a matching compression. I like the 268/276/110, in at 108
Static compression ratio of 9.8:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 7.93:1 .
Your dynamic cranking pressure is 157.42 PSI.
V/P (Volume to Pressure Index) is 126
Ok this will burn 87 most of the time, but might want 89/91 at WOT.
Notice the VP is now up to 126; a 54% improvement.This is IMO a real nice balance of low-rpm torque , a fat midrange and reasonably good top-end... for a streeter with 3.55s

Ok one more, if your pockets are deep and you can afford some aluminum heads. This is still with the 268/276/110 cam, but with the Scr pumped up for the new heads . I have burned 87E10 in my 367 with this pressure,
Static compression ratio of 11.3:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 9.11:1 .
Your dynamic cranking pressure is 189.24 PSI.
V/P (Volume to Pressure Index) is 152
Notice the VP is up to 152 now,an 85% improvement, in low-rpm operation, where you probably are some 80% of the time, up to about 3500rpm. The 268 pulls strong to about 5400,then levels off, and with the Eddies I got, I force her to 7000 all the time.
I know, I know, I just included the last one for comparison.
A 152VP is about what a stock 1969 440 Magnum pulled, just so you know.
Click to expand...
Amazing...thank you all for taking the time to share your knowledge... I agree that maybe the best bet is to sell the X heads and swap the cam. I just love how lopey it sounds lol... but I love burnouts more than lopey!!
 
The low-rpm issue can be eased with a bigger TC and deeper gears........ to the point of being a non-issue; the downside is the car becomes becomes a weekend bomber....... for most of us. But you get to keep the Legitimately lopey idle. And when it gets on the pipe, hang on!! And the truth is; there very much is such a thing as having too much torque on take off, and it all goes to tiresmoke. Personally I'm OK with that,lol.
But more than anything, with a manual trans, I like the dump it and go personality of a high-torque engine, and will gladly sacrifice the top-end rush, to get it. I was a far happier guy with the 270/110 cam than I was with the 292/108.
Yeah sure the 292 was wicked on top, but with 3.55s ... it didn't start until nearly 50 mph in first gear, and was done by 55. Then came the shift, and I didn't see the rush again until 66 to 72, in second, and 90/99 in third which I stretched to 106 in the quarter.
Whereas with the 270, torque was strong right off idle. But there was no top-end rush at all.
Finally I compromised with a 276/286/110, sacrificing a bit off the bottom to get a bit on the top. To reclaim the bottom, I got me a 3.09 commando trans. Dadaboom.

To make your life easier, you could play the TM (Torque Multiplication card). More rear gear, a lower gearset in the trans, and a higher stall TC. Of course more compression would be cheaper.
 
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Does he not have a heavy car and tall gears?
Aj
have you read Racer Browns long article?
specifically on Datsun but universal truths you have to read through and make notes then go back
Racer developed a couple of grinds for our SS Dodge 413>426 wedge suffered through the three speed and non "Super" T 10 BW 4 speed "problems"
He was a legitimate mechanical engineer
Racer Brown Datsun 510 camshafts & valve timing datsport
 
Yes; hence the TM/hi-stall card, and the back-tracking to compression. As you know, a lot can be done with TM, on the bottom end, to cover up a multitude of engine shortfall. Unfortunately the downside is a higher cruise rpm.

and no on the Datsun article, soon to be corrected,lol.
And done.
 
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AJ/FormS said:
Yes; hence the TM/hi-stall card, and the back-tracking to compression. As you know, a lot can be done with TM, on the bottom end, to cover up a multitude of engine shortfall. Unfortunately the downside is a higher cruise rpm.

and no on the Datsun article, soon to be corrected,lol.
Click to expand...
I'll bite, TM?
 
I don't like high stall converters on tall gear street builds in heavy cars
now in a T bucket...high stall will lock up where it will not in a heavy car- and that's death in a non lockup trans on the converter just driving on flatland

From the article you posted Aj
I have a long paper on rod length somewhere
one gripe is posters talking about maximum piston acceleration at 90 degrees when it is at rod tangent to crank throw

"
including cam timing, port efficiency, mixture velocity, manifold runner & port cross-sectional area & volume, resonance, harmonics, exhaust system design, &c. I have no method of applying math to these factors - it’s too complex!"
this is what the Controlled induction software does plus much more If you have not go to Rick Jones website and watch the demo
they can do the intake demand curve and calculate velocities through the closing valve at different rpm's and maybe throttle openings
 
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Sorry guys I guess I was/am/probably always will be; a little confused myself.
But the bottom line is the same, I like the dump-it-and-go combo. And I hate having to rev it up and slip it out, the older Mustang way. I like a blip on the throttle and unload the flywheel into the tires then drive away. I like stomping the go pedal and having instant tire howl. I like downshifting into first at 30/35 and again launching the car.And you can do the math; 30mph with 3.55s and 27s, and the fabulous 3.09 first gear is ~4100 rpm; ready to rock with a street cam and plenty of cylinder pressure,Dcr/VP. And second gear makes about 48MPH at 4100, again perfectly geared to blow by some poor slowpoke in a 50 zone. And third at 4100 makes 66mph, again perfectly geared to pass on the freeway.
The Commando box has really nice splits , you just gotta build an engine to maximize it's potential.
The 2.47low box is real handicap for a streeter. It wants a 4.44 for the same first gear TM. It wants a 3.85 to match second, and a 3.71 to match third. So when YR says he has a 2.47 box and 4.56s that's partly why.
The 2.66 box is the same as the Commando except the low gear is different. The internal gearing is different tho, such that the only gear that will swap between the boxes, is the ms first gear.
Here is the 2.47/4.56 combo, in road gears:
11.26-8.07-6.11-4.56 .................. followed by the 3.09Commando with 4.10s
12.67-7.87-5.74-4.10........................... and the standard 2.66box with 4.30s
11.44-8.26-6.02-4.30 ............... and finally my set-up; Commando and 3.55s
10.97-6.82-4.97-3.55
You can see that the starter gears are all more than adequate for a streeter, and second gears are fairly well matched, and on the street they are all good to 60 mph, which is where most of us shut down most of the time. By the time we get to third gear my box is slightly outclassed. And by fourth my box is history
But as a streeter the only thing I want out of fourth is a good cruizing gear so 3.55s are a winner. The other gearsets really want overdrives to be "streeters".
So if I only need to blast thru two gears, then my combo is pretty ideal.
And if I only need to blast thru two gears, why would I need 450 hp.
Why would I need a 292/508, or a 284/484, or even a 276/286? The answer is I don't; cuz I'm only gonna hit peak horsepower ONCE on the way to 60mph, at the top of first gear; and the tires are gonna be spinning all the way anyhow. So why would I need a 6400 rpm cam, for what is gonna be, a 3500rpm car 95% of the time. The answer is I don't.
But boiling the hides to 50,55,60 and 65mph sure is fun.....lol.
 
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AJ, I have a newly reconditioned A833 from Passon Performance 4spd, 355's as we said...and 275 60's on the back. I AGREE wholeheartedly that I am looking for off the line torque. So w/out swapping the trans gearset, am I looking back to a cam change?
AJ/FormS said:
Sorry guys I guess I was/am/probably always will be; a little confused myself.
But the bottom line is the same, I like the dump-it-and-go combo. And I hate having to rev it up and slip it out, the older Mustang way. I like a blip on the throttle and unload the flywheel into the tires then drive away. I like stomping the go pedal and having instant tire howl. I like downshifting into first at 30/35 and again launching the car.And you can do the math; 30mph with 3.55s and 27s, and the fabulous 3.09 first gear is ~4100 rpm; ready to rock with a street cam and plenty of cylinder pressure,Dcr/VP. And second gear makes about 48MPH at 4100, again perfectly geared to blow by some poor slowpoke in a 50 zone. And third at 4100 makes 66mph, again perfectly geared to pass on the freeway.
The Commando box has really nice splits , you just gotta build an engine to maximize it's potential.
The 2.47low box is real handicap for a streeter. It wants a 4.44 for the same first gear TM. It wants a 3.85 to match second, and a 3.71 to match third. So when YR says he has a 2.47 box and 4.56s that's partly why.
The 2.66 box is the same as the Commando except the low gear is different. The internal gearing is different tho, such that the only gear that will swap between the boxes, is the ms first gear.
Here is the 2.47/4.56 combo, in road gears:
11.26-8.07-6.11-4.56 .................. followed by the 3.09Commando with 4.10s
12.67-7.87-5.74-4.10........................... and the standard 2.66box with 4.30s
11.44-8.26-6.02-4.30 ............... and finally my set-up; Commando and 3.55s
10.97-6.82-4.97-3.55
You can see that the starter gears are all more than adequate for a streeter, and second gears are fairly well matched, and on the street they are all good to 60 mph, which is where most of us shut down most of the time. By the time we get to third gear my box is slightly outclassed. And by fourth my box is history
But as a streeter the only thing I want out of fourth is a good cruizing gear so 3.55s are a winner. The other gearsets really want overdrives to be "streeters".
So if I only need to blast thru two gears, then my combo is pretty ideal.
And if I only need to blast thru two gears, why would I need 450 hp.
Why would I need a 292/508, or a 284/484, or even a 276/286? The answer is I don't; cuz I'm only gonna hit peak horsepower ONCE on the way to 60mph, at the top of first gear; and the tires are gonna be spinning all the way anyhow. So why would I need a 6400 rpm cam, for what is gonna be, a 3500rpm car 95% of the time. The answer is I don't.
But boiling the hides to 50,55,60 and 65mph sure is fun.....lol.
Click to expand...
 
djais1801 said:
AJ, I have a newly reconditioned A833 from Passon Performance 4spd, 355's as we said...and 275 60's on the back. I AGREE wholeheartedly that I am looking for off the line torque. So w/out swapping the trans gearset, am I looking back to a cam change?
Click to expand...


What is the first gear in the transmission? If you want to make the car move, gear it down.
 
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