Ok how about
some theory, to see how this works.
Say you just want a sharp teener, that gets great hiway mileage, will only run the track long enough to see just how fast she is, and want the automatic to kick down at 30 mph and light up the tires. How does that sound?
OK we already have several parameters written ,some in stone.
#1 is the automatic. The ratios are 2.45-1.45-1.00. The splits are 1.45/2.45, and 1/1.45, these work out to .59 and .69. On a streeter this doesn't mean much yet.
#2 we need torque at 30 mph, and we want to run 3.23s for the hiway, and we are gonna run 255/60-15s at 27inches tall. Sound familiar? Ok so what are the rpms gonna be at 30mph. The math says 1203 in drive.1750 in second and
2950 in first. All are plus TC slip
Ok We are gonna cruise in second and blow off the tires in first. Sounds like a plan,right.
Ok then We need power at 2950.
Where else do we need power? Well to cruise this baby will be 65=
2608 plus slip. So to get great mileage we are gonna need torque at that rpm.
Anything else?Well lets say we put this into a 70Swinger that soaking wet and with driver, weighs in at 3400lbs. Lets say for now, that we will target 250 hp with a little 4bbl and HO manifolds, Sound reasonable? Then 3400/250 gives us a P/W (power to weight ratio) of 13.6. This little number translates to13.6 in the qtr with unlimited suspension, or about 14.1 with the street stuff we are gonna be running. This magic number also translates to about 96 mph. Well we are gonna need power at or slightly earlier than 96mph.But first let's see how those 3.23s are gonna work. 96 mph is 3850 in drive,5590 in second. Both plus slip. Well 5590 @ 5% slip is nearly 5900 going through the traps. This is not the kindof engine we want to build. So how about in drive? 3850 plus slip is about 4050 thru the traps. That sounds better. So that means we need power at 4050 or a little sooner, perhaps as early as
3700.
Now a plan is emerging. We need 250 hp and power at 3700.And torque at 2608, and 2950. Now remember this is for an optimized pkg. Now the question is can it be built.
The answer is yes, And no. The P/W assumes running all three gears, optimized to trap well.
And you are not gonna build a teener to make 250hp at 3700. At least not this one. So, we are gonna have to sacrifice something.
To hit 96 in drive,at a sane for a 250hp teener, 5200, will require a 4.10 rear. Are you gonna sacrifice fuel economy and hiway comfort? Answer no, the 3.23s are staying! Ok now we are getting somewhere, we don't care how fast she is in the qtr.So that rules out the requirement of power at 3700.
So next, lets look at what we have left; the torque requirements at 2608 and 2950. Well the 2608 was for hiway. Let's talk about that one.To cruise this 3400 pound aero-mobile at 65mph,might require about 30 hp. At 2608 this is about 40 ftlbs. Shoot, the teener can do this at idle, so this is a non-issue.
Finally then we need lotsa torque at 30 mph/2950 rpm. Well it's gonna be hard to better the factory cam, which IIRC makes peak torque at 2400rpm, or at least was marketed at that number. Back in the day the old girls were advertised at 340ftlbs@2400, while the 340s were advertised at 340ftlbs at 3200. See, you already have matched a 340s torque at 2400rpm. And pay attention; the 340 took 800 more rpm to match the teener torque. The teener had a 240/112 cam, while the 340 had a 268/114 cam. Are you seeing the pattern? Put the 340 cam into the teener and watch the disappointment on the drivers face, as the torque takes a dump. Even if you pumped the compression to the moon, that little teener will have a hard time recovering from that torque loss. The only thing that will work is to band-aid the teener with a higher stall TC to allow the engine to spin up to a higher rpm, where more torque lives. So this takes us back to cruising the hiway. Earlier we found that the cruise rpm was gonna be 2608 plus slip@ 65mph, or about and up to 2738@5%slip. But more likely is 1 or 2 % slip, so lets call it
2650cruise.Since we are after fuel mileage too, I would consider this to be the maximum stall, for cool running of the tranny-oil.
Ok now we have established the
stall at 2600.
And the
rpm of peak torque required is 2950, just about perfect.
Now we get to choose a cam, finally.
Waitaminute. This has become a one gear car. What about second at least. Well 65mph in second is a tic under 4000slip included, and you better shut down if you value your license. So if we had peak power say at
3600 to 3700, we would be good to go, right?
Are you seeing what I am seeing?
That's right the factory teener cam hits both of those targets just about bang-on!
But you say I need mo-powah.
Well it won't come from the cam.
Oh dear
what then?
Well first, lets analyze this; the 3.23s and 2600TC give us the torque at the right rpm, and those same guys give us the power peak at the rpm that we need it to be at. So...... It's the gears that have established the other parameters!
Ohhhhhhhhhhh.
So if we put say 3.91s in there then the rpms would rise 3.91/3.23 = plus 21%. So then the new rpms at 30 and 65 will also be plus 21% or 3571 and 4420. Now you can choose a new cam for 3.91s!
Of course 4.10s are a new cam, and so on. Also this kills hi-way economy/comfort, so another sacrifice has to be made.
But
getting back to the 3.23s, which were written in stone. Now the cam is also fixed.So how to get more power? Well the secret to power is and has always been airflow. The more air into the engine, the more fuel you can jam into that extra air and the more power you will get. And it works at any rpm.
Ok but you can't afford super charging or are afraid of it. Fair enough. What are some other alternatives?Well the first option is compression. 8 point OH has got to GOH. My references say that from 8.0 to 11.0 is about 5.2% power and about double in economy. Well plus 10.4% economy translates to an easy 1.5 to 2..0 mpgs, not too shabby. And plus 5.2% on top of 250hp is 13 horsepower. But that number doesn't tell you about the torque increase at stall. But the economy number sure does. If economy at 65mph goes up 10.4%, you can bet it's because the torque has risen, also, by very near to that amount.Earlier we figured out that it takes about 40 ftlbs to cruise at 65. So now perhaps we will get 42 ftlbs at the same throttle setting. No big deal you say. True that, but if those extra 2ftlbs are with the throttle nearly closed, what's happening at peak torque? Well, plus 10% say at a peak torque of 340ftlbs is 34 ftlbs.That's not much you say. Oh yee of little comprehension. It would take about 3.55s to match this in road torque; are you awake now?
But you may say that is impossible!
Fair enough lets run the numbers. Say you have that 3400 ftlb engine now plus 34 ftlbs, and 3.23s and a 2.45 low gear. The math says (340+34) x 3.23x 2.45 =
2960ftlbs into the rear axles. So lets go back to the 340 ftlb engine, and swap to 3.55s. Here is that math; 340 x 2.45 x 3.55 =
2957ftlbs. So, we see that the jump from 8/1 to 11/1 is equal to one rear gear upsize in terms of added torque output.
Ok now how about the A999 gear swap. Well I'll tell you another secret, this stuff is all math. The 2.74 low is 2.74/2.45=11.8% torque increase! 11.8% you say? Hyup this is the equivalent of going from 3.23s to 3.23x 1.118=3.61s. You can also multiply the original 340 ftlbs by that same 1.118 to get the equivalent feeling as 40 extra ftlbs. Forty! By now you are seeing that these little numbers mean big increases. By the same token, you can trade them around.
Say you picked those 3.23s to keep the rpm down on the hiway, but they were a compromise for torque to turn tires. Well since we know the teener can make enough torque to cruise 65mph at idle, why are we spinning it to 2700ish. If we bumped the compression, and swapped in the A999, we could reduce the hiway rpm and not lose any road torque at 2400 rpm. How would that work?
Well, earlier we figured out the roadtorque to be 340 x 3.23 x 2.45 in low=2690 ftlbs to the axles,right? ? Lets say we were happy with that but wanted a lower cruise rpm. So we are gonna add the compression first, then divide it by the new low gear to get a new equivalent rear gear.
So then; 2690/{ (340x1.10) x 2.74}= the new gear ratio of 2.625, and these would cruise 65=2140slip included.. And first gear would still make 2690ftlbs to the rear axles. That is a hiway rpm reduction of 2700 less 2140=559rpm. Imagine what that will do to your fuel consumption!
Okay but let's say you'd be willing to trade away some of that economy for a bit more go power. Remember we found out that little numbers mean a lot? And we saw that 34 ftlbs was worth 1 gear change? Well, lets go to the other extreme and leave the cruise at 2700slip included.
Ok so the 3.23s have to stay. And we'll keep the A999, and the compression to, cuz it's worth about 2 mpgs. Now then what kind of road torque increase might we see? 340x 1.10 x2.74x3.23=3310. And we earlier had 2690. This is an increase of 3310/2690= 23% Are you kidding? 23%? Hyup. this is about the same as increasing the size of that teener 23% or to 391 cubes, This is rather simplistic, but you get the idea. We are still on the stock cam,iron log manifolds and a 2bbl, cuz that is how the factory rated them in up to 1972, when the 340 ftlb number was published. Plus 23% is pure math. It doesn't care how many actual ftlbs your engine is making, Just add 23% to it.
So what have we learned? Fun with math! You can take a stock slow-poke teener, dress it up with compression and a lower gear ratio, and go out and have a blast. And if you do it right, you can get better fuel mileage too.
Oh, we didn't go there did we? Well, what was I thinking? There is no reason to go from one extreme to the other.
Lets try it with 2.94s. The rpm at 65 is 2400, and first gear road torque could be 3013ftlbs, an increase of 3013/2690=12% , making your teener feel like a 356 cuber.
Or with 2.76s. 65=2250. And the roadtorque to the axles is 2828; an increase of 2828/2690=5.1%, making your teener feel like a 334cuber.
A one up-size in cams might equal 4% or 14ftlbs. making your teener feel like a 331.
Now what are we spending to get all this mythical increase? It ain't cheap. 11/1 compression is pistons for sure, and total chamber volumes down to 65cc; totally doable. Then there is the A999. And gaskets,Badaboom! Plus gears if you want to strike a balance. The fuel mileage savings will take years to pay for this, so forget that. But say you went with the 2.94s, and between the 300rpm cruise reduction and the 10 % increase in economy, your mpgs might climb from what?, 18 to 22. Because you find the new cruise rpm of 2400 so much more comfortable, you are eager to drive it everywhere, all the time. Suddenly your annual mileage is climbing to 12000 miles. At 18 mpgs this would cost you 667 gallons. At 22mpg,just 545 gallons. Simple math I know but it illustrates the point,right? So what's a gallon of gas cost you? say 4 bucks. That would be an annual savings of 4 x (667 less 545) =$448 bucks. Ima thinking you can do a lot with $448. But let's say a gallon costs just 3.50 today. That's still an annual savings of $427. But what if it goes to $5 a gallon? The savings then would be $610.
So,
let's recap;
We left the engine completely alone except for bumping the compression. We installed an A999, and maybe swapped in some 2.94s. We are gonna expect 10% more torque, everywhere cuz that is what compression does. And we are gonna expect 2% more torque multiplication from the gear swapping, and the fuel economy might rise 22%; Hey, it's just math. And you can expect a performance increase similar to adding 38 cubic inches, IN FIRST GEAR, which with proper valve springs and the 2.94s might rev to 5400, and take you to 54mph. Kicking the tranny down at 30mph will get you about 3150rpm slip included.
And we never put a steengkeeng cam in in it yet.
Now I just gotta say this to protect my AZZ;
your results may vary
