Inputs on a home built 318 for red light to red light fun
Rumble said;
For this type of hi-rpm engine and lightweight application I think I would gravitate to a loc-up A518, big rear gears, and a modest stall to prevent runaway tirespin with the smallish rear tires.
the A518 has ratios of 2.45-1.45-1.00-.69od
The loc-up has a ratio of near 1.8 @ zero mph.
With a .69od, and a loc-up, you can run pretty much any rear gear you want.
My thoughts;
>With just 255s and what will probably become a somewhat high ride-height at the back, traction will be a big issue.
>With race gears, it will be only too easy to burn thru first gear..... which is where most street races are won; ie, a 2.4second 60ft is not gonna cut it.
> realizing these things, points to a low-torque bottom end, and a modest stall will help with that. Why an automatic? Because the TC acts as an automatically shifting deep-low gear, eliminating the need for race-gears.
>but the lo-stall is a total hindrance at the shifts... so to overcome that, you need two things; a close ratio transmission, and a cam that covers the rpm-drop. The A904/A727/A518 are the closest-ratio automatics that Mopar gave us to fit our cars.
> how does it work?
> check out the 5.2M power-curve below. This is a beer-keg EFI engine so you won't be able to get this shape of torque-curve, but I can use it to illustrate my point.
Part-1
lets assume for this exercise, that you have a Standard A833(2.66low), 4.10s, and 27" tires. Let's say that you soft-launch at 3000rpm, trying desperately not to spin the tires too badly. At 3000rpm, this 5.2M is making say 298ftlbs. Working thru the trans and gears, this comes to; 298 x 2.66 x 4.10 =3250 ftlbs at WOT, into the axles. Your 255s will light right up at WOT, and your race is history.
On your next try, you launch at 2400/285 ftlbs and into the axles this comes to 3108 ftlbs and again, at WOT, the tires light right up.
On your next try, you launch at 2000/276ftlbs at into the axles this maths to 3010 and yur still getting tirespin at WOT.
The bottom line is that, using this dyno-chart, 4.10s are just too much on the start-line, on the street, for WOT. But you sorta need the 4.10s to compress the run into three gears between stoplights, to maximize the application of your power. For instance, top of third gear with 27s is;
76@5500/83@6000/90@6500/ 97@7000
so already, 4.10s are sorta looking like the wrong gear on the big end.....
Part-2
lets assume for this exercise, that you have a Standard Ratio automatic, 3.73s, 27s, and a 2200stall that manages a 1.6ratio with your low-torque engine. At 2200 this 5.2M is making 280ftlbs. thru the powertrain, this comes to
280 x 1.6 x 2.45 x 3.73 = 4100ftlbs at zero mph. Immediately, the tires start to spin. Just as quickly the TC drops ratio, so, a few feet out, the ratio may have dropped to say 1.3. This automatically reduces the axle torque to 3330ftlbs at WOT. Compare this to 3250 with the Manual trans/4.10s, and Hyup your 255s are still spinning. This is no accident, I chose all the parameters to level the playing field.
Part-3
Now that we have the starting line evened out, lets see what happens when we go thru the gears; first the 4-speed. The ratios are 2.66-1.92-1.40-1.00, and 4.10s.. To the road this is; 10.91-7.87-5.74-4.10.. that 5.74 Third gear will get you 83mph@6000
Now the Auto; say a Standard A904. The ratios are 2.45-1.45-1.00, and 3.73s make the road gears to be 9.14-5.41-3.73.. However, the TC affects all these numbers and differently in each gear, because the TC multiplier is always changing with the input of engine torque versus the roadspeed. You have already seen what 1.6 can do on the starting line, now lets see what happens at speed. 9.14 becomes 14.62 at zero mph, reducing to an estimated 11.88 at shift rpm, so lets record it as 14.62/11.88. That 5.41 may become 6.49 at speed, and 3.73 might be 4.10 at speed. So then, the new estimated ratios are;
14.62/11.88-6.49-4.10. That's a 4-gear automatic isn't it...... and 6.49 will get you 74mph@6000
Part-4
The 4.10 manual-trans will cruise at 65=3350 with the 27s
The 3.73s will cruise at 65=3050 at zero-slip (locked up), perhaps as high as 3170 @4% slip. With a .69 overdrive, this becomes 2100@ zero-slip.
Part-5
Now lets talk powerband;
>First, the manual trans and shifting at 6000; the rpm drops average around .72, so from 6000, that drops to .72 x 6000 =4320. so a powerband of 6000 less 4320 =1680. Your cam has to cover most of that. Say your peak power occurs at 5700, then drops slowly, you could then recalculate to a powerband of 1380rpm. This is pretty tight, and you could run a pretty big cam on a very tight LSA and get away with it, expecting not much torque on the bottom. The 4.10s will help you there. Or
>Second, with the automatic, the rpm drops are staggered; .59 on the 1-2, and .69 on the 2-3. So again, shifting at 6000, the rpms drop to 3540 and 4140 for powerbands of 2460 and 1860. With a power-peak again around 5700, the requirements are 2160 and 1560. This requires a DIFFERENT cam than the 4-speed does. You cannot run the same tight LSA cam, and expect good results. That means the power of a same duration cam will be less, but powerband is broader. This type of cam also loses cylinder pressure so eats bottom end, requiring more cubes or more cylinder pressure to cover. Or more gearing.... Since we are only at 3.73, this is easy to accomplish, but it will sacrifice cruise-rpm. However, with the very low .69 ratio of the Mopar overdrive, 3.73s is too low anyway. There is no way to give your big-cammed 318 enough ignition timing to satisfy 65=2100. By 2400 is is becoming possible. For 65=2400 in loc-up, your gearing needs to be 4.30s.
Your new road gears with 4.30s are; 16.85/13.70-7.48-4.73-3.26-2.97; wait what? I count 6 gears... That's right; the box has 4 gears, the TC is infinitely variable between about 1.8 and 1.1 which is a full gear ratio, and the loc-up is equivalent to about a half a gear. That totals 5.5 gears! However, that 7.48 will only get you 64mph @6000, while 4.73 will get you 102, so we have a problem here. You will need a bigger cam to stretch 7.48 out to a higher mph, or a smaller cam and shift earlier to bring 4.73 down; else 84mph will come in at 4500ish(in 4.73roadgear); which as already stated by Rumble and others; "makes no sense".
Part-6
Ok so, as previously established with the manual trans and 4.10s, 5.74 roadgear(Third) gave us 6000@84mph, which IMO is a good target. To get a ~5.74 roadgear with an auto would take ~5.38s for third gear, or 3.23s in second. With the 3.23s I get
14.24/10.29-5.62-3.55-3.23 in LU; and 5.62 delivers 6000=86. The 5.38s would get you
23.73/17.08-9.36-5.92-5.38 in LU, and 5.92@6000=81.5 mph
Lets put the ratios side by side so you can see what's going on; First the Manual, then auto;
10.91-7.87-5.74-4.10 and 5.74@6000=84mph
14.24/10.29-5.62-3.55-3.23 in LU; and 5.62@6000=86mph
>As you can see, the 4-speed puts a gear between 10.91 and 5.74, that is missing between 10.29 and 5.62 of the auto, whereas the auto gives a gear under 10.29 that is missing with the 4-speed. But, the auto gives you one to 1.5 more gears at the top
But again, to pull that wide 1-2 split, you need a wider LSA cam.
Part-7
And the wildcard is the A518 with 5.38s; the Roadgears are;
23.73/17.08-9.36-5.92-4.08-3.71in LU, and 5.92@6000=still 81.5 mph but 65 is now 3000.. First gear is gonna be pretty tricky, and you can easily start in second for most of the time, giving you a closer ratio between second and third. Because of all the torque multiplication going on, you could probably use the 4-speed cam, with the tighter LSA. With this combo, you also don't need a hi-stall.
Part-8
For those that want to know; For this exercise I used the following TC multipliers; 1.8 diminishing to 1.3 in first, 1.2 in Second and 1.1 in Third. Thus the A904 gears look like;
4.41/3.18-1.74-1.10 and 1.0 in LU. The A518 adds .76/.69LU, and may drop the 1.0
Rumble said;
^My thoughts as well^
For this type of hi-rpm engine and lightweight application I think I would gravitate to a loc-up A518, big rear gears, and a modest stall to prevent runaway tirespin with the smallish rear tires.
the A518 has ratios of 2.45-1.45-1.00-.69od
The loc-up has a ratio of near 1.8 @ zero mph.
With a .69od, and a loc-up, you can run pretty much any rear gear you want.
My thoughts;
>With just 255s and what will probably become a somewhat high ride-height at the back, traction will be a big issue.
>With race gears, it will be only too easy to burn thru first gear..... which is where most street races are won; ie, a 2.4second 60ft is not gonna cut it.
> realizing these things, points to a low-torque bottom end, and a modest stall will help with that. Why an automatic? Because the TC acts as an automatically shifting deep-low gear, eliminating the need for race-gears.
>but the lo-stall is a total hindrance at the shifts... so to overcome that, you need two things; a close ratio transmission, and a cam that covers the rpm-drop. The A904/A727/A518 are the closest-ratio automatics that Mopar gave us to fit our cars.
> how does it work?
> check out the 5.2M power-curve below. This is a beer-keg EFI engine so you won't be able to get this shape of torque-curve, but I can use it to illustrate my point.
Part-1
lets assume for this exercise, that you have a Standard A833(2.66low), 4.10s, and 27" tires. Let's say that you soft-launch at 3000rpm, trying desperately not to spin the tires too badly. At 3000rpm, this 5.2M is making say 298ftlbs. Working thru the trans and gears, this comes to; 298 x 2.66 x 4.10 =3250 ftlbs at WOT, into the axles. Your 255s will light right up at WOT, and your race is history.
On your next try, you launch at 2400/285 ftlbs and into the axles this comes to 3108 ftlbs and again, at WOT, the tires light right up.
On your next try, you launch at 2000/276ftlbs at into the axles this maths to 3010 and yur still getting tirespin at WOT.
The bottom line is that, using this dyno-chart, 4.10s are just too much on the start-line, on the street, for WOT. But you sorta need the 4.10s to compress the run into three gears between stoplights, to maximize the application of your power. For instance, top of third gear with 27s is;
76@5500/83@6000/90@6500/ 97@7000
so already, 4.10s are sorta looking like the wrong gear on the big end.....
Part-2
lets assume for this exercise, that you have a Standard Ratio automatic, 3.73s, 27s, and a 2200stall that manages a 1.6ratio with your low-torque engine. At 2200 this 5.2M is making 280ftlbs. thru the powertrain, this comes to
280 x 1.6 x 2.45 x 3.73 = 4100ftlbs at zero mph. Immediately, the tires start to spin. Just as quickly the TC drops ratio, so, a few feet out, the ratio may have dropped to say 1.3. This automatically reduces the axle torque to 3330ftlbs at WOT. Compare this to 3250 with the Manual trans/4.10s, and Hyup your 255s are still spinning. This is no accident, I chose all the parameters to level the playing field.
Part-3
Now that we have the starting line evened out, lets see what happens when we go thru the gears; first the 4-speed. The ratios are 2.66-1.92-1.40-1.00, and 4.10s.. To the road this is; 10.91-7.87-5.74-4.10.. that 5.74 Third gear will get you 83mph@6000
Now the Auto; say a Standard A904. The ratios are 2.45-1.45-1.00, and 3.73s make the road gears to be 9.14-5.41-3.73.. However, the TC affects all these numbers and differently in each gear, because the TC multiplier is always changing with the input of engine torque versus the roadspeed. You have already seen what 1.6 can do on the starting line, now lets see what happens at speed. 9.14 becomes 14.62 at zero mph, reducing to an estimated 11.88 at shift rpm, so lets record it as 14.62/11.88. That 5.41 may become 6.49 at speed, and 3.73 might be 4.10 at speed. So then, the new estimated ratios are;
14.62/11.88-6.49-4.10. That's a 4-gear automatic isn't it...... and 6.49 will get you 74mph@6000
Part-4
The 4.10 manual-trans will cruise at 65=3350 with the 27s
The 3.73s will cruise at 65=3050 at zero-slip (locked up), perhaps as high as 3170 @4% slip. With a .69 overdrive, this becomes 2100@ zero-slip.
Part-5
Now lets talk powerband;
>First, the manual trans and shifting at 6000; the rpm drops average around .72, so from 6000, that drops to .72 x 6000 =4320. so a powerband of 6000 less 4320 =1680. Your cam has to cover most of that. Say your peak power occurs at 5700, then drops slowly, you could then recalculate to a powerband of 1380rpm. This is pretty tight, and you could run a pretty big cam on a very tight LSA and get away with it, expecting not much torque on the bottom. The 4.10s will help you there. Or
>Second, with the automatic, the rpm drops are staggered; .59 on the 1-2, and .69 on the 2-3. So again, shifting at 6000, the rpms drop to 3540 and 4140 for powerbands of 2460 and 1860. With a power-peak again around 5700, the requirements are 2160 and 1560. This requires a DIFFERENT cam than the 4-speed does. You cannot run the same tight LSA cam, and expect good results. That means the power of a same duration cam will be less, but powerband is broader. This type of cam also loses cylinder pressure so eats bottom end, requiring more cubes or more cylinder pressure to cover. Or more gearing.... Since we are only at 3.73, this is easy to accomplish, but it will sacrifice cruise-rpm. However, with the very low .69 ratio of the Mopar overdrive, 3.73s is too low anyway. There is no way to give your big-cammed 318 enough ignition timing to satisfy 65=2100. By 2400 is is becoming possible. For 65=2400 in loc-up, your gearing needs to be 4.30s.
Your new road gears with 4.30s are; 16.85/13.70-7.48-4.73-3.26-2.97; wait what? I count 6 gears... That's right; the box has 4 gears, the TC is infinitely variable between about 1.8 and 1.1 which is a full gear ratio, and the loc-up is equivalent to about a half a gear. That totals 5.5 gears! However, that 7.48 will only get you 64mph @6000, while 4.73 will get you 102, so we have a problem here. You will need a bigger cam to stretch 7.48 out to a higher mph, or a smaller cam and shift earlier to bring 4.73 down; else 84mph will come in at 4500ish(in 4.73roadgear); which as already stated by Rumble and others; "makes no sense".
Part-6
Ok so, as previously established with the manual trans and 4.10s, 5.74 roadgear(Third) gave us 6000@84mph, which IMO is a good target. To get a ~5.74 roadgear with an auto would take ~5.38s for third gear, or 3.23s in second. With the 3.23s I get
14.24/10.29-5.62-3.55-3.23 in LU; and 5.62 delivers 6000=86. The 5.38s would get you
23.73/17.08-9.36-5.92-5.38 in LU, and 5.92@6000=81.5 mph
Lets put the ratios side by side so you can see what's going on; First the Manual, then auto;
10.91-7.87-5.74-4.10 and 5.74@6000=84mph
14.24/10.29-5.62-3.55-3.23 in LU; and 5.62@6000=86mph
>As you can see, the 4-speed puts a gear between 10.91 and 5.74, that is missing between 10.29 and 5.62 of the auto, whereas the auto gives a gear under 10.29 that is missing with the 4-speed. But, the auto gives you one to 1.5 more gears at the top
But again, to pull that wide 1-2 split, you need a wider LSA cam.
Part-7
And the wildcard is the A518 with 5.38s; the Roadgears are;
23.73/17.08-9.36-5.92-4.08-3.71in LU, and 5.92@6000=still 81.5 mph but 65 is now 3000.. First gear is gonna be pretty tricky, and you can easily start in second for most of the time, giving you a closer ratio between second and third. Because of all the torque multiplication going on, you could probably use the 4-speed cam, with the tighter LSA. With this combo, you also don't need a hi-stall.
Part-8
For those that want to know; For this exercise I used the following TC multipliers; 1.8 diminishing to 1.3 in first, 1.2 in Second and 1.1 in Third. Thus the A904 gears look like;
4.41/3.18-1.74-1.10 and 1.0 in LU. The A518 adds .76/.69LU, and may drop the 1.0