any benefit to swapping heads?

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Well that kindof depends on what your current set-up can do at low rpm; but yeah if you don't want to bring the compression up, then I would pull that cam in a hearbeat. I would not be able to stand that low a VP. And swapping out the cam is the quickest,cheapest,easiest fix.

The differences in the first gears of all the A833s by themselves,are not enough bring this combo up to a satisfactory performance level. Your VP is just too low.
The odds that you have a 2.47 low are pretty slim.
The odds that you have a 3.09 Commando are even slimmer.
Leaving you with a 2.66 standard box.
But let's say you did currently have a 2.47, and you went to a 3.09; the advantage would be 25% in the first gear alone.
Then as your VP might be close to 82 as estimated in post #55, totally estimated best guess. Say your 340 was able to put out 150ftlbs at 1800rpm. With a 2.47 low and 3.55s this would be multiplied to 1315ftlbs not enough to break those 275/60s loose, am I right? Ok so the simple solution is to just rev it up until you find enough power. Yeah that works but ..... it ain't impressive. And it doesnt solve driving at low-rpm.
But with a 3.09, this maths out to 1645 ftlbs. So maybe your 340 will bust 'em loose,maybe; but I see more of a chirp and a bog, until you get the hang of it. It certainly will not be impressive. Again just rev it up til you find the power, which will now be at quite a bit lower rpm. And it still does nothing for driving at lower rpm in any gear.Which with a manual trans, happens a lot.
Now the cost factor to get that 25% is ridiculous. I mean that is a complete gear swap.
But the rear gear option is just as bad; it would take the same plus 25% gearing or 4.44 gears to equal that improvement.
To my way of thinking this combo really really really needs cylinder pressure, or a much smaller cam. Did I work that out in post #55? lemmee check. Nope I don't see it,
so here is your 8.2 340 with a 252/112 cam in at 108;still at 800ft. This is a stock 360 2bbl type cam. There are other better 252 type cams.

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 that VP jump! This is very significant 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. So consequently this 252 cam may make less power from about that point on; it will not have a top-end rush. That doesn't mean it will stop reving; mine in a 318 went to 5500 regularly and to 6000 occasionally with appropriate springing. It just means it runs outta power about 800 to 1000rpm sooner than your 284.
But I tell you what, I bet that 252 cam will hit 5000rpm/44 mph, sooner than your current combo,lol.
Oh yeah, 115VP should be enough to smoke 275/60 BFG radial T/As with 3.55s, hyup, once you get them rotating. So for $200 bucks or so in parts, this is a cheap fix.

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And if you do want to be impressive with that 252 cam, swapping to the 3.09 Commando box and say 3.73s, well, Shazzam! you're all set up for 60mph@5150 at the top of second gear; let 'er rip! And this cam might make 25 ftlbs more at 1800 than your current combo, so lets call it 175@1800. (it might even make 200,IDK).And that would get you 175 x 3.09x3.73=2017 ftlbs; more than enough to break the 275s loose and impressively. Now you can put on the line-loc and bring the Rs down closer to an idle, and make the tires moan,howl,wail, or scream..... and that's impressive. Well, it is to me when I do it,lol.
But say you kept the 2.66 box and went to 3.91s. Now your starter gear is 10.40 and times 175@1800=1820ftlbs and still just enough to spin, and now you have the VP to sustain it with the 252 cam. This is also a cost-effective swap...... except of course the hiway rpm jumps to 3050. And the 252 is well able to pull 2.45s to do 65= 1911.
If you are willing to learn to adjust your valves about once a year, you could switch to a solid lifter cam and pick up few horsepower, without a loss in VP, but IMO, with log manifolds, and at this cam-size, it's hardly worth it.

Ok it just hit me.
that 252 combo is just begging for the 3.09overdrive box and 4.10s. The starter would be 12.67 and times 175 would be 2217 ftlbs @1800 for massively impressive tirespin,lol. Your hiway rpm would be 65=2334, and 60 would be a tic under 5000 at the top of second....... so we could advance that cam just a tad, say to an ICA of 48*
Static compression ratio of 8.2:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.28:1 .
Your dynamic cranking pressure is 140.29 PSI.
V/P (Volume to Pressure Index) is 125 .
There you go; 140psi/125VP; that's a pretty good number, and that will pull the splits in that od-box reasonably well with 4.10s lol. I would even try it with 3.91s. and the best news is up here I have bought those od boxes for as little as $50C at swap meets.
This is not an ideal situation to be sure, but for the cost of a cam-kit, a swap-meet od box, and a set of gears installed, IMO you will end up with a pretty exciting streeter.
Here is a gear ratio comparison. First
9.44-6.82-4.97-3.55 ..... your most likely current set-up, and then
12.08-6.53-3.91-2.85 ......the od box/3.91s
Notice second gear is practically identical.
Notice the wicked starter gear, that will help your 252 cam roast tires.
Notice the hiway gear, that will get you 65=2226rpm
Notice the crappy third gear that you will almost never use, as a streeter, at WOT, so who cares how crappy it is.
Second gear is the most important gear. You will spend more time in second than in any other gear, not including hiway time.This 6.53 ratio has to pull from 1500/18mph to 3600/40mph. This is it's home, and the 252 cam will pull well in that range,very well. And that same gear will pull all the way to 65=5100..... just about right for that cam,nay,just about perfect.
Well, with that starter gear, I might put the cam back to a 50*ICA, and pick up a little power in that Looooooog pull to 65,lol.
Ok I gotta work tomorrow so TTYL
 
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If you spread the trans gears then you have more rpm drop so have to create a broader torque curve
and if you do not spread the gears out you need a broad torque unless your drop the rear end ratio
best to not overcam
I vividly remember a blown 55 chevy at an early Bakersfield march meet with a T10 and low gears- really hurt the years- super fast speed shifts and he did not break it
we broke Dodge's version of that trans behind the Super Stock Wedge- went 727
 
Small Block Chevy Intake, Carb, Camshaft Testing - Danger Mouse Part Four - Super Chevy Magazine 15 years ago
Test 12: Comp Cams Xe262h Cam
To either prove or disprove our theory on whether or not the engine needed more air to make more power we swapped in the next size larger COMP Cams XE262H Xtreme Energy camshaft (PN 12-238-2). The cam was 6 degrees bigger at 0.050 with 0.015-inch more lift and added a little more top-end power while giving away some low-end grunt.
It was kind of a wash, but we think the motor liked the XE256H cam better, and it would definitely have driven better on the street with the extra low-end power of the 256 cam.

Small Block Chevy Heads Test - Danger Mouse Part 5 - Super Chevy Magazine
And on a low-rpm street motor like DM, bigger is not better.
The large combustion chamber dropped Danger Mouse's compression ratio 1/2 point, putting it just below the 9:1 mark,
and the larger valve sizes, particularly on the intake side, probably reduced charge velocity enough to hamper the cylinder's filling at low speeds.
Note: Charge Velocity is a key

Small-Block Chevy Cam Test - Danger Mouse Part 7 - Super Chevy Magazine
Cam Trade-Off
We found the typical less-torque-for-more-horsepower trade-off when we switched to the next-size-larger COMP Cams Xtreme Energy camshaft.
Before installing it, we had figured that with only 6 degrees more duration at .050 and about .015-inch extra lift over the previous cam we'd ran, the XE268H camshaft would have worked well with the un-ported Vortec heads and dual-plane manifold.
However, after testing with the bigger cam, low-end torque fell off, and the only power gains were at the very top end of the scale (perhaps we should have run DM up higher with this cam).
Ironically, both peak torque and average torque and horsepower with both cams remained almost identical (see Test 18).
But it's low-end torque that moves a street car, and given the choice, we'd always choose the cam that could make higher vacuum and build as much as 13 more lb-ft of torque down low for our engines.
end quote
note: the UB Harold 1977 XE268H comp cam has about the same seat duration as the 260 Mopar Performance cam- The MP cam out torques the comp
 
I gotta say you got one sweet ride. boy there are a lot of conflicting opinions here on this post.

so I'll add my 2 cents. you bought this car as it is correct? well the guy that built the motor more than likely matched the components and it does sound like it runs well. I would worry about compression ratio as the pistons were matched to the 360 chamber volume. if you lose compression with a bigger chamber in the head, you will not be happy. if the chambers are the same and you do not lose compression you will pick up some high rpm horsepower with the X heads. your cam will definitely love bigger valves at the same compression.

that is why aftermarket aluminum heads are so popular. they are not rare mopar pieces, you cant devalue them by porting and polishing them. they have hardened valve seats that love unleaded gas and thick deck surfaces that can be milled for any chamber volume without compromising the structural integrity of the casting. they all have big valves, raised intake runners and modern combustion chambers and flow boatloads more than any stock casting ported or not.

sell the x heads to a restorer and buy a pair of aftermarket aluminum heads and add 50 to 80 horsepower.
 
your cam will definitely love bigger valves at the same compression.
maybe- maybe not
many times i Have got a flat spot just going to bigger valves and especially with a bigger cam at the same time
gotta keep the velocity up
 
All this back and forth over Cams, Cr, ICL, valves, port velocity, TM,,blah, blah, blah
While the whole combo is choked by the stock cast iron manifolds.

All the proposed "gains" of the various witches brew of "mods" simply pail in comparison to a decent set of equal length, 1-5/8" headers and take significantly more time and money.
 
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Man, this is a good question. When I was in High school I knew guys that would swap 360 heads on a 318 and swear it was a good setup. years later, as a professional line tech at a dealership, I had an old head mechanic tell me that "compression ratios and chamber size effects all that" when he saw I was going to throw some 360 heads on a 318 build. I did take his advice and stay with the 318 heads on my 318, buy have always wondered how that engine would have ran with the 360 heads on it. as far as the 340? I think I would want the 2.02's myself. I think it will be ok, because basically the later 340's had 360 heads on them . I do think they had lower compression with those 360 heads also.
 
Dartswinger70 said:
Man, this is a good question. When I was in High school I knew guys that would swap 360 heads on a 318 and swear it was a good setup. years later, as a professional line tech at a dealership, I had an old head mechanic tell me that "compression ratios and chamber size effects all that" when he saw I was going to throw some 360 heads on a 318 build. I did take his advice and stay with the 318 heads on my 318, buy have always wondered how that engine would have ran with the 360 heads on it. as far as the 340? I think I would want the 2.02's myself. I think it will be ok, because basically the later 340's had 360 heads on them . I do think they had lower compression with those 360 heads also.
Click to expand...



I take head flow over compression ratio every day of the week. Ideally you want both, but to keep compression ratio at the expense of air flow is wrong.

I can't tell you ho many 1.88 valve heads I put on 318's but it was many.
 
I'm with YR
Vizard says (who wants to hear me say it :)
The better the intake filling is, the higher the pressure achieved on the compression stroke.
I like to pick the cam that runs in the rpm that I'm looking for then pick the intake and exhaust and compression to fill as much as possible- but not too much
 
Wyrmrider said:
your cam will definitely love bigger valves at the same compression.
maybe- maybe not
many times i Have got a flat spot just going to bigger valves and especially with a bigger cam at the same time
gotta keep the velocity up
Click to expand...

maybe? yes it will. that grind is an updated street hemi grind purple shaft. the original was designed to be used with stock valve train in 340 motors without worrying about pushing a pushrod through a stamped steel rocker arm.

velocity tuning is what you do when you are class racing with mandated crappy heads. you have been reading too much chivvey straight 6 magazines.
 
djais1801 said:
I am not knowledgable mechanically so forgive me in advance. I have a 72 demon with a 340 block 69 and 360 heads with a purple cam 282/482. The 360 heads are 1.88 intake 1.62 exhaust.
I have a complete set of X heads with 2.02 intake and 1.60 exhaust...
this is a 4spd street car with a weiand dual plane intake and 2.25 stock exhaust manifolds. 355 rear sure grip.

Will I have any noticeable power/torque swapping the heads?
Click to expand...


what 360 heads? are these 308 heads? were they prepped by someone like Hughes?
if they were I would not change them.
 
had one in my 69 340 swinger. totally changed the character of the motor. it was awesome.
 
you need to talk to the guy that put together that motor to find out exactly what you got or you need to find a motor builder that can tell you what you got. its not easy to find the right motor builder then you can start making changes to have your car perform the way you think it should otherwise your going to be led down wrong paths and end up spending a lot of money.
 
so stock 360 heads with unknown valve job/ guides/ exhaust seat/ springs
how's the compression
then squirt some oil in the cylinders and test again
any smoke when you gt on it , get off, get back on, or at start up ?
 
Wyrmrider said:
so stock 360 heads with unknown valve job/ guides/ exhaust seat/ springs
how's the compression
then squirt some oil in the cylinders and test again
any smoke when you gt on it , get off, get back on, or at start up ?
Click to expand...
no smoke when get on/off it...good oil pressure no leaks. compression was 110psi
 
110 lbs, all cylinders, tells you all you need to know
most 8"1 motors get more than that
we had more than that running in a stock class with stock pistons and big cheater cam
so has to be the cam- really short duration high lift cam
also obviously time for pistons if the budget allows
 
Just out of curiosity, what do you set your static timing and how much mechanical advance do you have? What rpm does your mechanical advance come all in by? I think you may be able to tune some of the bog out by welding your advance slots in distributor for around 18-14 degrees mechanical advance and set the static timing around 16-20 degrees with the mechanical all in at around 2500 rpm by spring setting. I would speculate that with the low compression and high bleed off cam set up that even with those big, lazy open chambers it would probably tolerate around 36 degrees of total advance. Check out the article in tech on ignition curve, I am curious to know what your initial settings are now. I spent a lot of quality time on a kitchen table distributor re-curve. Almost all distributors are set for emission control and not performance. With 10:1 static compression, I am setting on 14 degrees static timing and 20 degrees all in at 2800 by mechanical advance. I run VP Octanium on 93 octane fuel or a seven to one mix of 93 octane to low lead 100 octane av gas. Aside from being outright illegal to use in a motor vehicle, the low lead av gas still has four to eight times the tetra-ethyl lead of the leaded auto gas these cars where meant to run on, plus the high altitude additives are very aggressive to the rubber fuel lines, hence the high dilution ratio. No pinging or spark knock with the 2.76 gears so far... Your combination could probably absorb 20 plus degrees of static timing and 10-12 degrees of mechanical all the way in on the very short end of the stick, like around 2000 rpm on 93 octane and generic octane booster.... Do your X head hardened exhaust seats installed? The induction hardened exhaust seats alone are a great advantage to your 587 heads, unless you just want to have to spend extra $$$ on lead substitute additives and such... Much like everyone else has stated, a good set of 1-5/8 tube headers would help tremendously. I run them with 2-1/4 Thrush turbo mufflers and have a very good exhaust note.
 
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A SINCERE thank you to all that have chimed in with their knowledge and experience. This is now a non-issue. I had a gentleman come up to me at a car show in September and offer me the "give me a number" price...so now she is living elsewhere. It was bittersweet...but I stayed with Mopar, so that's good! Have a 72 RR now with a 451 stroker 4spd 391 rear in EV2.
Not sure if there's a way to close the thread?
 
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