If I was doing an LA318, on the factory foundation; I would do everything I could to keep the Dcr up. And that means the ICA at final install needs to be very similar to what the factory ICA was; or else I would be prepared to also purchase a TC and gears.
When you look at a particular manufacturer's line of cams, you will generally see them on a 110 LSA, and therefore see, a steady march of the ICA changing about 3.5 degrees per cam size. When you install those cams at split overlap, you will generally see the cylinder pressure drop about 4 psi per size, and along with it, the same in VP.
The factory LA318,starting at 7.8Scr and at 800 ft, with only a cam change;
with a 240/248/112 cam, ...makes about 130/107VP factory cam
With a 240/248/110 cam, it makes about 131/109VP
With a 248/256/110 cam......................~127/103VP
With a 256/262/110 cam..................... ~123 /97VP
With a 262/268/110 cam..................... ~120/ 93VP
backing up
With a 256/262/108 cam......................~125/100VP
With a 262/268/106 cam...................... ~124/99VP
Pay particular attention to the VP, 5 out of 6 cams will lose bottom end grunt.So, IMO, all these guys are gonna need a TC and gears else the cam will be a disappointment.
Now lets pump the compression up and try that again
With a 240/248/112, factory cam at 9.1Scr ~159/131VP factory cam
With a 262/268/110 cam, at 9.5Scr...................~156/120VP
With a 268/276/108 cam, at 9.5Scr..................~ 155/118VP
Notice the VP, which tells you you can keep the factory TC and gears at least for a while, cuz the new VPs are far superior to the factory 107 number.
So ask yourself; what's a set of pistons worth,installed, to get the Scr up, and nothing else......
versus
leaving the Scr at 7.8, installing that big cam, and the bigger TC, and rear gears....... just to have the same or similar low-rpm performance..... allbeit a peppier top-end, which you might experience just once, on the way to 65 mph.
That's the rub.
Each of these cams will move the rpm of peak power up, about 200 rpm starting with the factory one at about 4000, and the 268 at maybe 5200, not likely with factory heads but let's just say. And lets add 400rpm to get a preliminary shift rpm, but keep the trap to peak power plus 100rpm
Ok so with 2.76 gears 4400 is~ 49mph, and 65 in second gets you ~3500
And with 3.23 gears,4400 is~42mph,and 65 in second is..... ~ 4100
And the go-to 3.55s,. 4400 is~ 37mph, and 65 in second gets you ~4500
But choose 3.91s,...... 4400 is~ 34mph, and 65~4900 if you are brave
So here you can see that the perfect gear to hit 65 at ~4100 would be 3.23s
>>But lets jump to the 262 cam which might peak at 5000 and might like to trap at 65=5100 in second. Now the best gear is 4.10s. Ok sure you can run less gear, say the 3.55s again, and trap 65~4500, fully 600 rpm short of peak. Now if you were still at 7.8 dcr, you would be some ways down on power, and there is a good chance the 9.1 factory-cammed engine, with 3.23s would fly by you, or at least give you a good run. Sometimes less cam is quicker ET. And if you now threw some TC at the 9.1factory cam combo, well then let the SHTFan.
But now, what about a solid lifter custom cam, with a fast rate of lift designed for a .904 lifter. Say a 252/258/106, that after lashing might be 248/254/106, and actually slams the intake shut at 48* ICA, and still at 7.8Scr, this will get you 131psi/109VP. Where have we seen that before, oh, yeah, at the top of the list,with the factory cam! So now you lose nothing on the bottom, compared to the stocker, but have moved the peak power up possibly 200 rpm, and the lift on that cam is gonna add it's shot of power and the 106LSA is gonna double your overlap, so the headers are gonna pump a few more horsepower into the mix. This is the way to exploit your LA318 low-compression engine.
Ok one more, lets do the 268/276/106solid cam, with an after lash of 262/268/106 and lets put it in the 9.5 Scr engine.
I get 161psi/128VP.
This is way more low-rpm performance than the stocker (130/107),and is a really good trade. Plenty more than stock performance with a power peak up about 800 rpm higher, and tons of pressure to rocket the teener at every rpm.
