As for speaking about; " a bit of a cam";
Each "size" of cam, in the "bit of a cam" range, drives the power peak up about 200rpm. But in these small cam sizes, the peak is broad and flat so hard to pinpoint exactly where it is; And I've never been able to find A 200rpm change by seat of the pants, until Top gear, if at all. As the cams get bigger, and the LSAs get tighter, yes the peak is easier to notice. , but more because the cam falls over harder at the top.
Advancing the cam, one way or the other 4* will only move the power about 100rpm, and IMO, kindof defeats the purpose of the cam.
You'll get way better results with a increase in stall rpm. But
You'll get best results with increasing the Cranking Cylinder Pressure, to plump up the bottom end in the first place..
When you advance a cam, this is exactly what you are doing. You are stealing power duration to get compression duration, and IMO, this is surely not the best way to get pressure.
A typical "bit of a cam" might look like; 262/268/110
This cam would have (262+268)/2 less 2x110= 45* of overlap.... like a 340 cam,lol.
So then the total number of degrees for all events is 45 plus 2x360=765 degrees
Intake and exhaust are 262+268=530, so power plus compression are 765 less 530=235 degrees
If you install this cam on split overlap, the Ica will be 59* leaving 121 for compression.
therefore the power duration will be 235, less 121= 114 degrees, and The ICL for this is 108*.
Advancing this cam 4* from straight up will put the ICL at 110-4= 106*. This will steal 2* from Power extraction and give it to compression. This will pump up the CCP about 3 psi (whoopee)_So on a lo-compression 318, you are looking at from 135 to 138 psi at sealevel.
However the total of Power plus compression is still 235; so, 235 less 123=112 for extraction. IMO this is a bad idea because, almost without exception the burning gasses will still have plenty of useable energy in it, when the exhaust valves open. Energy that could have been used to propel the vehicle. At high rpm in a race car, this is not a big deal. But in a streeter, this is costing you money every time you pull up to the gas-bowser.
Ok lets do an exercise using the Wallace Calculator. Lets use a true Scr of 8.0:1, and 300ft elevation.
With an
Ica of 59* I get 126.8psi and a P/V of 98
(Read about P/V here;
Cam Timing vs. Compression Analysis )
Now lets advance the cam just 3* to an Ica of 56* and no other changes.
At 56*, the pressure climbs to 130.2, and the P/V to 103, a solid increase of 5% P/V
Now lets put some new higher-compression pistons in that 318, put the Ica back at 59* where it belongs, and pump the pressure to the max for 91 gas, say around160psi .
At 9.5 Scr, I get 158.5psi at a P/V of 122
Now, lets talk about P/V.
First the stock cam (240/248/112) . In at plus 4*=108, and at a true 8/1; I get an Ica of 50*, for 136.6psi At P/V of 113 So this is the baseline; and you know what that feels like. And so 113P/V is your target, or should be, so that the engine at least doesn't feel like a pig. And so, for me at least, 98 and 103 are NOT acceptable.
>Next, go back to the first example; Ica of 59*@Scr of 8.0, 127psi@98P/V
The P/V has fallen by 1 less 98/113= 13.3% as compared to the stocker . If you had 160 ftlbs at stall, this will now feel like 139 ftlbs,
a loss of 11ftlbs. To get the torque back, you are gonna need more stall.
>Next, lets look at the hi-Compression 318, namely Ica of
59@9.5Scr= 159psi@122P/V
The P/V has actually climbed by 1 less 122/113=plus 8%, compared to the stocker. Again from 160 ftlbs,
this is an increase of 13ftlbs, at the original stall. AND you still have the 114* of power extraction.
>This is also a one-two punch for fuel-economy, namely adequate power-extraction and additional cruise torque, so you can cruise at less throttle opening or use a smaller rear gear, to additionally, decrease cruise rpm. which would be a Triple-whammy.
>Now, I have been talking about low-rpm (below 3000) with all these numbers. If you go to a 3000stall, then the bottom-end is meaningless , under most conditions except cruising.
However, the boost in CCP will pump up the POWER everywhere. The absolute power increase expected is said to be only ~4% at peak, but the midrange from stall and on, is fatter than that, and the throttle-response gets to be snappier, and the engine becomes more eager to pull.
Just look at the differences;
from a stock of 113P/
V@8.0 Scr, to 122P/
V@9.5 Scr = Plus 8%, and
the pressure increase from 137 to 159 = Plus 16%
At low rpm; this will feel like your 318 grew by Plus 8% = 343 cubes, compared to the stock lo-compression slug. A 262* cam is 3 sizes bigger than the stock cam, so the rpm will move up about 600rpm from 4200 to 4800... about. That 600rpm is worth an easy 25 hp or more, never mind the pressure boost could be another 4%, all other things being equal. Plus 4bbl, plus headers, dual exhaust, etc;
Now, I know your engine is already assembled and looks to be installed. So changing pistons may not look appealing, especially in light of a higher stall TC being a cheaper solution (to power off the line); and especially with your future plans. But I thought it was worth going thru an exercise for the next engine.
In case I didn't mention it, the higher stall is only helpful in getting moving.
Once the TC is "stalled " it's all on gears and engine. And
once she's in top gear, it's all on engine and final-drive ratio.
But I'm sure you knew that.
Btw; I have been referencing HFT cams (Hydraulic Flat Tappet) in all exercises. It is possible to install a Flat tappet cam with similar .050 numbers, but having faster ramps and of less effective advertised duration. Such a cam might give you more cranking cylinder pressure for the same absolute power, because the actual point of intake closing angle could be a tad less.
