Thanks for taking the time to try and explain this. I don’t rightly understand much of what you’re saying initially but my current engine has solid lifters perhaps helping address that weakness of the floating valves. Yet I rearly in fact have never seen another solid lifter 340 personally. I have seen a solid lifter LT1 before.
Looks like there.needs to be a coordinated effort on LSA and timing of events and thats the crux of it?
Am I asking too much to have a relatively flat torque curve from a 340? I don’t think so. Nicks Garage has at least two videos at the dyno that have relatively mild mannered cams in a relatively stock motor showing a nice broad relatively broad torque curve.
If I wanted to drive this on the street with headers and a 3.55:1 rear which I am and not for the strip then this is my goal. I’ve been told I’m crazy because I put a 340 in a Bbody. Originally, I had a 318 in it so I was set up for small block already.
I do know the faster the event timing/ramping the better the scavenging and a solid lifter gets you that. I just have zero feel the numbers for the specs on the cam. But I definitely hear what you’re saying. I should talk to Comm and powered and Edelbrock cough cough. I tried to look at their curves, but there’s a lot of variables.
Whether B or A is not the deal-breaker; weight and aero is.
the early factory 340s were rated at the same torque as the early 318s.... but at 800rpm higher, 3200 versus 2400. That should tell you something.
It tells me that the 340 has traded away bottom-end torque to get top-end power, and that is exactly what happens with a bigger cam .
lets look at ALL the numbers of these engines, first up is the 340, with the cam on split overlap;
268 intake/114 compression/106 power/276 exhaust/44 overlap, 318next
240 intake/130 compression/122 power/248 exhaust/20 overlap
Plugging the numbers into he Wallace Calculator, at their rated Compression ratios, here's what we get;
First the 340,
Scr of 10.5, Dcr of 8/1, pressure of 165, and a V/P of 128
Scr of 9.0, a Dcr of 7.9 , pressure of 156, and a V/P of 129
Now first up, check out the near identical Dcrs, and the near identical V/Ps . This brings credence to the torque numbers being so similar. in spite of the 318s lower pressure. This is why these 318s are so loved cuz below 3200, they have more torque than the early 340s.
In other words, your B will perform just like a 318, below about 30mph. Well hang on, that's not exactly true;
340 ftlbs at 2400rpm is 155horsepower, whereas
340 ftlbs at 3200rpm is 207hp.
The problem is gearing.
the 318 mighta had 2.76 gears so 2400 in 1st is 28.5mph at zero-slip, whereas
the 340 car is sure to have at least 3.23s so, 3200 in 1st, is 32.5mph;
so then, with identical cars, in a race to 30mph, it could be a toss-up.
Ok but lets look at those numbers again;
268 intake/114 compression/106 power/276 exhaust/44 overlap, 318next
240 intake/130 compression/122 power/248 exhaust/20 overlap
You see how the 318 has 130 degrees of compression versus the 340 at just 114; in spite of having just a 9/1 Scr versus the 340 at 10.5.
What do you think might happen if we pumped the 318 up to 10.5"
answer; with no other changes, the pressure jumps to 191 psi, and the V/P to 158. Now that's a torque-monster!
But let's back up, and put the 340 cam into the 9/1 318.
Now the pressure falls to 135 and the V/P to 98; which is barely better than a 225 slanty (87 IIRC)
The point is that for a streeter, that operates almost exclusively way off the power curve, pressure is everything. and I can tell you that 195psi, which I have run (in a 367 mind you, with a 270 cam), is effing nuts. In my opinion, it was well worth swapping away the 292/292/108 cam that I took out.
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on a different note
a lot of performance cams are ground on a 110 Lsa, which for a streeter is a good balance for absolute power and and good street manners. For most of us, we're gunna pick a cam from around 262 to 284 advertised intake duration. (I mean at 292 I was out of the ballpark). this is a range of 22 degrees which is about 4 cam sizes, from mild to "wild".
But what I really want to talk about is "intensity" which is best revealed by the time, in degrees, from when the valves are actually tickled into opening called the advertised duration, and the 050 duration.
Advertised durations can be measured from wherever after the valve opens. Some grinders choose .008 tappet rise, some choose .006, and at least one chooses .001.... so you can't always tell much from the advertised unless you know the grinders history. But for hydros everybody has to be accurate at 050, cuz if you lie and your cam is a flop, that's gunna hurt your business.
Generally, for hydros, I see intensities of 44* to 58*. Obviously a slow cam (58*), should last a long time, or at least longer than one at 44*.
But that's just part of the story. Two cams with identical 050 numbers and polar opposite intensities will push the intake opening/closing points some 7 degrees each way. Opening earlier increases overlap, which we can deal with but the later closing-end has repercussions of reducing cylinder pressure, reducing idle-vacuum, and reducing bottom end torque, none of which make for a good streeter. I mean there are ways of dealing with that after the fact, but right now for this discussion, I'm talking about intensity.
At the other end of intensity, 44*, to keep the valve gear together with increasing rpms, spring pressure has to be increased, and that is never good for the lobes. So, high intensity requires special considerations, such as oil chemistry, and oil-change intervals.
Thus choosing a cam based on intensity is a bit of risk.
Now, when we get to solids, intensity is signalled from a different point of the lobe, after the lash has been taken up. The chosen number is usually 020. and 050 is still where we're going, but now the intensity is between those two, and the number gets pretty small. which means, now you are choosing a solid cam by it's 050 numbers, knowing that you can't buy a higher intensity other style of cam for your LA engine, except maybe a mushroom lifter......
Of course this opens the door to installing a bigger solid, for the same specs of a hydro at advertised. and if you close the LSA, even bigger.
The downside is constantly checking the lash so you don't wear the cam out prematurely, and so you can always be sure the valves are closing, etcetera; and you know, streeters are not particularly fond of all the clatter going on under the hood.
Another thing about solids is, for a given modest 050 cam, that cam is guaranteed to offer better fuel economy over a same 050-sized hydro , in a same spec engine........ because the intake is closing a good two sizes earlier, say about 7 degrees. But it doesn't stop there. Knowing this, if you have enough pressure, you can increase the solid cam size at least one size and probably two if you run a tighter Lsa, without affecting fuel economy, from what the current hydro might be getting. ....
But another thing is that, on the street, yur actully, IMHO, just playing a game of numbers. The truth is that there is a hydro available to suit just about every streeter. I mean once you get to 230 to 235@050, 90% of the time, or more, yur just lugging that bad boy around for bragging rights. It doesn't really show up in your zero to 60mph time trial, unless you car 60fts really strong. and if it ain't there, then it's just spinning, and costing you gas money with every mile it turns. and when the cost of gas goes up, there you are in the que, waiting for your turn at the gas-bowser.
