Cylinder head decision for 318
Going back to post 47
If you extrapolate the chart down to 2000rpm, you might find say 250ftlbs
so at zero mph, a car with this engine, and with 2.76s would be grossing , at WOT;
250 x2.45 x2.76=1690ftlbs into the rear axles , not enough to spin the pair.
But hang on, there is a hydraulic multiplier in the TC that can automatically vary from 1.8 to 1.1 or so, depending on the torque differential thru it. I have no idea of what your stock TC is capable of, but IMO, I think 1.6 would be generous. So then
250 x2.45 x2.76 X1.6in the TC=2704. This is at zero mph. So the tires will break loose. As soon as they do, the torque differential thru the TC drops towards the low end of the scale. Say in the neighborhood of 1.3, so then
250 x2.45 x2.76 x1.3= 2197 and the spin is grinding to a halt. But hang on the rpm should be rising, so the torque is simultaneously increasing. If she can get to 3000, during that initial spin, then the torque will be up to 298, so
298 x2.45 x2.76 x1.3=2620, and the tires will continue to spin, reluctantly perhaps, but spinning none the less. The car is now accelerating in first gear, and roadspeed at 3000 will get you about 27 mph, but the spinning has long ago stopped. So now, at 27mph/3000 rpm, your engine could be at 170 hp. That 5000rpm peak will come at ~46mph, and with good heads you might be able to stretch that to 5500@51mph
Now comes the 1-2 shift.
And the Rs fall from 5500 to 3250; down to 193hp from 285hp, and no help from the TC so yur fun-run is now on time-lapse. It won't be back until 80/85 mph.
The principle problem is the 2.76s, followed hotly by the 2000stall
convertor.
Lets install a 2800TC and 3.73s;
Now, at zero mph the numbers look like
295ftlbs x2.45 x3.73 x1.7 say in the TC=4580 ftlbs, which is instant tirespin. So now you are controlling tirespin with your right foot, which is a chitload of fun. 5000rpm will now be 34mph, 5500 will be 37.4mph, and at the 1-2 shift the Rs fall to 3250 again, same 285hp to 193, that does not change. But at 3250 the torque is 313, and.....................
313 x1.45 x3.73 x1.4=2370 into the rear axles. There is a possibility that your tires ,now at just 37.4mph, are again spinning. This is partly due to the slightly higher multiplier I gave the TC, but mostly due to the 3.73s, which are a 3fer1 deal; 1) the speed is way down, and 2) the TM is so much higher,and 3) the TC is gonna see a bigger torque differential thru it, so I hiked the ratio to 1.4.
Ok now I gotta tell you another thing;
These same principles hold exactly true for the stock 318. The only things that change are the numbers and speeds. The same 2800, and say 3.91s now, are gonna produce similar results to I'm guessing 3500/4000 rpm, So instead of running to 37.4 mph, you are now gonna run to 5000=30mph. Even if your torque is down 20%, say 260ftlbs, this comes to
260 x2.45 x3.91 x1.4=3487ftlbs at 30 mph with still spinning in first gear. on the 1-2 shift, the Rs fall from 5000 to 2950, and there is a very good chance that your stock 318LA is gonna make at least as much torque as this hopped up post 47 one does. But let's give the hotrod a bit of credit and say your LA is down 10%, that would be 268ftlbs, so
268x 2.45 x3.91 x 1.3=3340 ftlbs and very likely still spinning @30mph in second gear. The nice thing about 3.91s is that they get you 60= about 5000;
Exactly where you want to be with a stock 318LA; 3.91s are the quickest way to 60mph with a stock low-compression 318LA. You go thru the power peak twice on the way there. So even tho the stocker is way down on power compared to the post-47 hotrod, it can still be a chitload of fun, as a streeter.
Now; put a 4bbl and some headers on that stock-cammed 318, and see her fly!.
So compare the buy-ins;
a 2800TC and 3.91s installed, versus
whiplash cam & heads, and yur still gonna need a TC and gears, cuz trapping 60 in second with 2.76s is maybe 3800, (4000 at the highest) with the hotrod post-47 engine. Take a look on the powerchart;3800 is 238hp.................
Lessee. if you both spin thru first gear, then you shift into second at 30(with 3.91s), versus him at 47( with 2.76s); and you blast to 60@5000 versus him at 3800; riddle me this;
will that hotrod squash your stocker?
With a 4bbl and headers, Ima thinking you will squash him, but if not, I imagine a very tight race. It's always about the combo.
If you extrapolate the chart down to 2000rpm, you might find say 250ftlbs
so at zero mph, a car with this engine, and with 2.76s would be grossing , at WOT;
250 x2.45 x2.76=1690ftlbs into the rear axles , not enough to spin the pair.
But hang on, there is a hydraulic multiplier in the TC that can automatically vary from 1.8 to 1.1 or so, depending on the torque differential thru it. I have no idea of what your stock TC is capable of, but IMO, I think 1.6 would be generous. So then
250 x2.45 x2.76 X1.6in the TC=2704. This is at zero mph. So the tires will break loose. As soon as they do, the torque differential thru the TC drops towards the low end of the scale. Say in the neighborhood of 1.3, so then
250 x2.45 x2.76 x1.3= 2197 and the spin is grinding to a halt. But hang on the rpm should be rising, so the torque is simultaneously increasing. If she can get to 3000, during that initial spin, then the torque will be up to 298, so
298 x2.45 x2.76 x1.3=2620, and the tires will continue to spin, reluctantly perhaps, but spinning none the less. The car is now accelerating in first gear, and roadspeed at 3000 will get you about 27 mph, but the spinning has long ago stopped. So now, at 27mph/3000 rpm, your engine could be at 170 hp. That 5000rpm peak will come at ~46mph, and with good heads you might be able to stretch that to 5500@51mph
Now comes the 1-2 shift.
And the Rs fall from 5500 to 3250; down to 193hp from 285hp, and no help from the TC so yur fun-run is now on time-lapse. It won't be back until 80/85 mph.
The principle problem is the 2.76s, followed hotly by the 2000stall
convertor.
Lets install a 2800TC and 3.73s;
Now, at zero mph the numbers look like
295ftlbs x2.45 x3.73 x1.7 say in the TC=4580 ftlbs, which is instant tirespin. So now you are controlling tirespin with your right foot, which is a chitload of fun. 5000rpm will now be 34mph, 5500 will be 37.4mph, and at the 1-2 shift the Rs fall to 3250 again, same 285hp to 193, that does not change. But at 3250 the torque is 313, and.....................
313 x1.45 x3.73 x1.4=2370 into the rear axles. There is a possibility that your tires ,now at just 37.4mph, are again spinning. This is partly due to the slightly higher multiplier I gave the TC, but mostly due to the 3.73s, which are a 3fer1 deal; 1) the speed is way down, and 2) the TM is so much higher,and 3) the TC is gonna see a bigger torque differential thru it, so I hiked the ratio to 1.4.
Ok now I gotta tell you another thing;
These same principles hold exactly true for the stock 318. The only things that change are the numbers and speeds. The same 2800, and say 3.91s now, are gonna produce similar results to I'm guessing 3500/4000 rpm, So instead of running to 37.4 mph, you are now gonna run to 5000=30mph. Even if your torque is down 20%, say 260ftlbs, this comes to
260 x2.45 x3.91 x1.4=3487ftlbs at 30 mph with still spinning in first gear. on the 1-2 shift, the Rs fall from 5000 to 2950, and there is a very good chance that your stock 318LA is gonna make at least as much torque as this hopped up post 47 one does. But let's give the hotrod a bit of credit and say your LA is down 10%, that would be 268ftlbs, so
268x 2.45 x3.91 x 1.3=3340 ftlbs and very likely still spinning @30mph in second gear. The nice thing about 3.91s is that they get you 60= about 5000;
Exactly where you want to be with a stock 318LA; 3.91s are the quickest way to 60mph with a stock low-compression 318LA. You go thru the power peak twice on the way there. So even tho the stocker is way down on power compared to the post-47 hotrod, it can still be a chitload of fun, as a streeter.
Now; put a 4bbl and some headers on that stock-cammed 318, and see her fly!.
So compare the buy-ins;
a 2800TC and 3.91s installed, versus
whiplash cam & heads, and yur still gonna need a TC and gears, cuz trapping 60 in second with 2.76s is maybe 3800, (4000 at the highest) with the hotrod post-47 engine. Take a look on the powerchart;3800 is 238hp.................
Lessee. if you both spin thru first gear, then you shift into second at 30(with 3.91s), versus him at 47( with 2.76s); and you blast to 60@5000 versus him at 3800; riddle me this;
will that hotrod squash your stocker?
With a 4bbl and headers, Ima thinking you will squash him, but if not, I imagine a very tight race. It's always about the combo.
