Oh, yeah, you can get the SCR that high with the smaller chambers.... and that is where I like to be for snappy low end grunt. But the OP wants this to be on the mild side and not hard to tune, for the missus. So getting the 318 up to a true 9:1 SCR is a definite improvement. That 260 ish cam will get DCR in to the mid 7's and that is an easy spot to tune and run.
I like your heads idea
but, with the 260* cam, you're looking at about ;
Static compression ratio of 9.0:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 149.80 PSI.
V/P (Volume to Pressure Index) is
120
A VP of 120 with 2.76 gears, is gonna be a tad anemic,IMO.
And do you think this combo could make 250hp?; honest question.
First gear will top out at just north of 50/55 mph. So it's gonna take until 25/30 to wake her up. Unless you put a fairly big TC in her. 3.55s would bring it down to maybe 20 mph, and a 2800TC would snappy-up the take-off.
Here's what a stocker looks like
Static compression ratio of 8:1.
Effective stroke is 2.86 inches.
Your dynamic compression ratio is 7.04:1 .
Your dynamic cranking pressure is 135.24 PSI.
V/P (Volume to Pressure Index) is
113
And a stocker with the Scr pumped up to about the limit for pump gas
Static compression ratio of 9.3:1.
Effective stroke is 2.86 inches.
Your dynamic compression ratio is 8.16:1 .
Your dynamic cranking pressure is 164.04 PSI.
V/P (Volume to Pressure Index) is
137
This combo with 2.76s,is gonna need some grunt.
The 9/0-260 cam is only 6% better than the stocker in the lower Rs, while the 9.3-240cam is 21% better there. That's a pretty good return, on money spent.
I like the 260 cam idea, but I'd pump it up.
So, here's a
compromise;
Static compression ratio of 9.8:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 8.27:1 .
Your dynamic cranking pressure is 166.91 PSI.
V/P (Volume to Pressure Index) is
134
So what do you think? A tad too much?
Yeah for 2.76s and a stock TC, I think so too.
But I think those closed chambers with a tightQ will clean up the chambers to run the 9.8;So the first thing to go would be the stock TC, for at least a 2800. The vacuum secondary idea I like too, and I'm big on TQs.This will help some more in keeping away the marbles.
Then a free flowing exhaust is a must.
And finally, If I had to, I'd run a cooler thermostat.
How about now?
And after that;put a switch on the A/C to cut it out when you nail it, and I guess skinny tires. Once the tires spin, the load goes away, the rpm jumps up, and then you can get away with a bit more compression than normal. I mean that's how I once ran 10.9/8.9 Aluminum/185/ Vp of 162; lotsa tirespin.
But if you're gonna run mostly at Part Throttle with a small carb, I'd pump it up no fear.
You already know what 113 feels like. 120 ain't much more. Chit don't happen until 140 and higher. But it's really hard to get there with a teener, and the 2.76s just make it that much harder. Gears are the quickest easiest cheapest way to pick up some performance.
For example; the best you're likely to get is 137/113=plus 21%, and this is gonna cost around $4000 (I'm guessing at US prices) after all is said and done. The same 21% can be had with a rear gear of 3.35, for maybe $300 to $400 installed. But that's not all; the gears will let you put down more average power per unit of time, so the car will be quicker to 65mph, possibly even with the stock engine with just a 4bbl, than the $4000 engine with the 2.76s. Ok so add the cost of a used intake and AVS, maybe another $150 rebuilt; total say $500. Oh wait, make it 3.23s that nobody wants, for say $250 installed,total $400.The 3.23s will reduce your advantage to 17%. Still a whopping big improvement for $500 or less.
