318 Build.. Zero Deck or Stock Deck Clearance?
actually rpm range could be a close first
HP is torque x rpm so HP gets seductive
Exactly; you gotta look at the whole combo; if the engine is stuck with 2.76s and a stock TC because of budget constraints the powerband is gonna be completely different that with 3.91s and a 2800TC.
Consider 32mph with 2.76s, and downshifted into 2.45 first gear; the rpm will be around 2900... so the engine is gonna need some punch down there to get moving, don't put that into a 4000 pound Chrysler with a 1750TC
Consider 32mph with 3.91s. Downshifting into first, the Rs will rocket to 4150, and KaPow!! you are gone. But if you are not careful, you will be outta revs in a heartbeat.
If you want a tirefryer off the line, listen carefully, the horsepower of the 318 by itself, has nothing to do with it. This is all about TM (Torque Multiplication). The non-stock cam will power-peak somewhere close to 5000. You can't break traction and get there with a 318 and 2.76s and a 1750 TC, it will never happen, and here's why;
Depending on the tires, you are gonna need around 2000 ftpounds to the road to break them loose. Then as the car accelerates, you are gonna need more, to keep them spinning. If you run out too soon, all you will get is a chirp.
Ok so say your teener makes 100 ftpounds at 1750, and you multiply that by the trans and rearend ratios, then correct for tire size and I get;
140x2.45x2.76x24/25.5=891# to the road. Now at zero mph the TC is gonna multiply this some, say times 1.4, and I get 1247# just about 60% of what you need.
So if you want a tire-fryer, you are gonna need to change one or more of these multipliers. The 2.45 low-gear is pretty much fixed. and 3.91s won't get you far enough. Tires don't make a big deal so that leaves the footpounds at the crank; 140 is just too small.
So let's say this is a city car and yur OK with 3.91s; these will get you
140x2.45x3.91x24/26.5=1214 and adding the 1.4TC I get 1700, hey now we're closing the gap. But here is another problem; as soon as the car starts to move, the TC multiplier starts to diminish, ending at perhaps 1.05 about 2 or 3 car lengths out; so with that in mind, your 1700 is gonna drop to ~1275.
So that leaves you with ordering up a hi-stall.
So say you order a 2800 (I love that TC), and say at 2800 your teener makes 220# now.
Ok so
220x2.45x3.91x24/25.5=1985 and The TC pumps that up a lil higher than before, say 1.6 now; and I get 3176, hyup we are frying tires, but can it sustain? Lets say 3 lengths out this has dropped to 2084, just barely sustaining tirespin, but now the rpm is rising so the torque is still increasing for a bit... or is it? IDK, yur engine could be sick. Stock teeners torque-peak pretty early anyway,maybe even 2800, so then no, the torque will not be increasing. but
It doesn't matter that much, because another thing is happening; it takes less power to keep the tires spinning than it does to break them loose. So, this stock-engine combo is now a tire fryer. So if that is all you wanted, say; For the cost of the 3.91s and a 2800TC, yur in business.
Of course the stock cam is gonna power-peak at about 4200 to 4400, but is that a bad thing?
With 3.91s now, and a shift-rpm of say 4500, you will get 35mph in first and 60 in second... so you will be going thru the power peak twice on the way to 60 and then into third. So the cam is pretty much right for 3.91s.
But say you upcam 2 sizes and the power peak moves up 400 rpm and your new shift rpm is 4900. This means in second gear the power peak comes at 60=4540, and you just wasted ~300rpm of pulling power; you need 4.10s now to use it all up. So there is no telling if this now bigger cam is gonna be any quicker to 60 or not. And if it is, will it be worth it.
So what's the answer?
The answer is; more pressure and/or more airflow.
But you have already spent your budget money on the gears and TC.
The thing is, as soon as you open up that 318; it's gonna need gears and a TC anyway, there is no escaping this.
Well there is; To keep the bottom end torque up, you gotta keep the pressure up. And if you really want to keep the bottom end up to run hiway gears, this requires a very careful co-ordination of compression ratio and Intake closing angle, to get full value from the detonation resistance of the gas you have chosen to run.
Or just slam some aluminum heads on it and run 180psi on 87E10; I know a guy who did that on a 367, but there was no budgeting involved there,lol.