Not afraid of a solid, just mindset wasn’t there.
With alloy heads and a solid-lifter cam, you can bump the pressure to 185 and still run pump gas. I would willingly run 87E10 .
That pressure is now governed by the co-operation of the Scr (static Compression Ratio) and the Ica( Intake closing angle).
If you have and intend to keep the 2.66 low trans, then you have to keep that in mind when engineering the cranking cylinder pressure. But when the pressure goes over 170ish, a funny thing happens; the First-gear traction goes away. I guarantee you that you will need to fit 295/50-15s, to keep it from spinning out, in aggressive driving, even in Second gear.
So ,IMO, there is not much benefit to a streeter, to go too crazy with a very high cranking cylinder pressure. A better measuring stick for your combo, is the V/P index number, and a combination of the right gearing.
Read about V/P here
V/P Index Calculation
V/P is dependent on pressure and cylinder volume. So, if you target a specific V/P number, you can do it by varying one or both of the pressures or the volume. This how a stock 318LA can make the same VP as a big-cammed 340, or even run with a 440Magnum; With a manual trans at low-rpm, it's all about VP.
Ok so here are the stock V/P numbers of a few engines corrected to 6000ft;
225 @8.0 Scr is 72
273 @8.0 Scr is 78
318 @8.0 Scr is 91
360 @8.0 Scr is 98
[email protected] is 113
[email protected] is 114 ( Like yours will be with a 340 cam)
so that is how they stack up at 6000 ft.
My 367 came in at 163VP with an Ica of 61* at 900 ft, with no other changes , at 6000 the VP drops to 139. At 900ft this was a Monster fun combo, with any gear I tried, 2.76s included. So My conclusion is that 163VP is waaaaaaaay overkill .
IMO, 140 at 900ft would likely have been sufficient ......... but once I had 163 it was too much fun to run less.
Now;
for you, running 163 is out of the question. 140 will be hard enough, depending on how small a cam you are willing to run.
If you can't get up to 140, you will need more TM(Torque Multiplication), to make the engine feel bigger than it is. This works very well in the first two gears, but at the top of Third, the Power will seem flat, and in Fourth, the truth will come out.
So lets target 140@6000ft and see what the Wallace spits out.
At 10.95Scr I get 140@
Ica of 56* , and pressure of 164psi.... so these are the
MINUMUMs to get 140. And you could easily run iron heads at 164psi.
So lets increase the Scr .
At 11.50 Scr I get 140 @
Ica of 60 and the pressure is 170psi
At 11.85 Scr I get 140 @
Ica of 62, and the pressure is 173
I don't know how much more Scr your combo can run at WOT, so I will stop there.
But I didn't buy alloy heads to run iron pressures so lets get the pressure up to in the range of 180 to 185, what's it gonna take.
Ok well,
at 11.8Scr and Ica of 56* the pressure has risen to 183psi with a V/P of, are you ready? 156VP. This is big-block V/P. This is about your
Maximum.
So that means; at the minimum, you can run a hydro, but at the maximum, you would have to run a solid.
Ok now why would you want to run 183 psi?
Well for one thing this has the potential to make fantastic fuel economy. But more importantly, when you step on the gas of a well tuned engine at 183psi......... chit happens right away. There is no lag, no hesitation, no "please massa, not again, bs"; the engine just goes. And it starts so nice; click-vroom. And it will idle right down slooooooow, with minimum timing.
The thing is, with a manual trans, your engine is married to the tires; there is no hydraulic coupling and NO TM in the convertor, so V/P and pressure are suddenly your best friends. The smaller the engine, the more important this becomes. Now, I know a 340 is not generally though of as small, but at 6000ft it is actually tiny, because it just cannot process a lot of air.
So at low-rpm, which is what a streeter is, anything you can do to get your engine to process more air, will help it overcome it's "smallness."
Ok so, in my mind, I have settled on a solid-lifter cam. Because it will have a small Ica for a bigger .050, making the getting of pressure easier. Plus getting 11.8 Scr is gonna be impossible if all your players are already chosen, and I don't wanna send you to the poorhouse. So what is the maximum Scr you can make with your parts using the thinnest reliable gasket that you can find?
Is it just 10.5? Or was that calculated using the ever-popular FelPro .039?
You said your Scr was 10.5. Well, to get that at a bore of 4.06 requires a total chamber volume of 74.2cc. You said your chambers were 60cc, so that leaves 14.2 for everything else. Assuming flat-tops with 5cc eyebrows, that then leaves 9.2 for the gasket and the deck-height. If the gasket is .039(8.8cc) then the deck-height is .4cc or pistons .0014 below deck. Ok so that is making sense. The simplest solution is the
.028 gasket, which is good for 2.5cc so the chamber size would fall to 71.7 and your new
Scr comes to 10.83 lets call that accurate, and the best you are willing to do. Lets plug that into the Wallace. I get 140VP at Ica of 55* and pressure of 163. Not a lot of pressure for alloy heads, but for 140VP, this is what it is with an Ica of 55*
How about we sacrifice a bit of VP and we'll make it up with the 3.91s. This will allow a drop in VP of 10% so now targeting a minimum of 126, no way. I ain't agoing that low. Lets target 135.
Ok at Ica of 57*, Scr of 10.83 the VP falls to 135 with pressure of 160, A V/P of 135 is the very least I would run. and This would then be the
latest Ica (57*) I would run with an Scr of 10.83
So now we have an Ica range of
55 to 57 degrees
Ok lets recap at Scr of 10.83 (.028 gasket at about zero-deck), and a V/P range of 135 to 140, we need an Ica of 55 to 57 Degrees.
see how easy that was? lol.
Sooo final question is; what size cam is this?
Well it turns out that this Ica can be had on a lot of hi-torque hydraulic cams; not hi-power. Here are some;
256/262/110 in at 108, or estimated .050 of 212
262/266/108 in at 105, or estimated .050 of 216
268/276/106 in at 102, ...estimated .050 of 222
All of these hydros will have an Ica of 56* when installed at the listed numbers. Notice how small these hydros have to be, to satisfy the 56* Ica.
What about a solid?
IDK the numbers with those are crazy to try and guess because, they are rated differently because of the lash factor. However you can still run off the .050 numbers if the manufacture will supply it. In that case you can add some arbitrary number representing the opening ramp from the point the lash is actually taken up to zero. When I have seen this done, I have seen ramp lengths of as little as 36* but typically 39/40.
If that is true
then
I suppose, and I'm guessing, that you could subtract this fictional 40 degrees from the cams listed and get NEW theoretical .050s of 216/222/and 228
Ima liking that 222.
But you will HAVE to call a grinder to get the true numbers. I have given you this story so you can at least understand how this all works
because at 6000 ft, and just 10.83Scr, there will not be any off-the-shelf performance-cam to satisfy your build, that will not suffer from a soft bottom end, which, with a manual trans, will be intolerable in just a few hours of around-town driving. And if you install the 3.91s, then hi-way driving will very quickly also become intolerable. That is to say, with 26.7" tires and 3.91s; 65=3200. But maybe your tolerance level is higher than mine,lol.
And for me, having such a BB type VP of 163, there is no way I would go back to a VP of something less than 135. No way at all.
Do you have to run a VP of greater than 135?
No, I have to.... cuz for me, 135 is already pretty soft.
If you are used to sub 120 numbers I suppose it's all relative.
A final point is this; If yur not gonna get into cranking cylinder pressures over 160, then honestly, iron heads will do an excellent job at up to ~165 on pumpgas. So you couldda saved a wheel-barrow of money by slapping on a set of Magnums or any big-port, small-chamber ,iron heads.
Happy HotRodding