AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
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I don't really care what a cam sounds like. I like my 185 psi, and I don't like 300 degrees seat to seat in my DD, cause it gets atrocious fuel mileage, and in my car which used to pull down 12000 miles a year, I couldn't afford to send hydrocarbons straight thru my engine. And that was when gas was cheap. At today's cost of gas this becomes many times more important, and into the future will only get worse.
You can pick 5 or more 268* cams out there and get 5 different .050s. Or, you could pick 5 different 220@.050s and get 5 different advertised, and the advertised can be anything from .008 to .006 to .002 to .001. And those 5 cams could be anything when measured seat to seat. So with so many options, why would I pick a slow-ramp cam? I don't need it and I don't want it, and it costs me cylinder pressure, efficiency, and fuel economy. I'd rather pull the heads every once in a while,for freshening, than to run a cam with so much time devoted to being quiet, or long-lasting, or reducing cylinder pressure, or whatever so-called "reason".
And the heavier the vehicle, the more important this becomes. There's no sense in installing a long-ramp cam in a short stroke engine, in a heavy vehicle, or one stuck with hiway gears and a low-stall TC. No excuse for it I might add.
I'm not pointing fingers at any one, or any cam; just saying.
Heres what I mean;all examples are with a 268 advertised cam, and lets not even toss at what lift into the mix; and 9.8Scr
First a 360
Static compression ratio of 9.8:1.
Ica of 64*
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.86:1 .
Your dynamic cranking pressure is............................. 154.50 PSI.
V/P (Volume to Pressure Index) is .......................130
Next a 340
Static compression ratio of 9.8:1.
Ica of 64*
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 7.82:1 .
Your dynamic cranking pressure is .............................153.44 PSI.
V/P (Volume to Pressure Index) is .......................121
Notice the V/P is 130/121= plus 7.4% stronger for the 360. This is like running 3.47s in the 340 to equal the 360 with 3.23s ... in terms of zero to 3000rpm or so.
But this is not the point.
The point is we use this Wallace calculator running off the advertised intake duration..... which we already know is based on who knows what , cuz the valves are not yet closed.
What if the 340 had one of those looong-ramp cams that didn't actually close the valves until 300*, and the 360cam was slammed shut at 280* ? I mean just what if.
Here are the new numbers; first the 360
Static compression ratio of 9.8:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 7.49:1 .
Your dynamic cranking pressure is ..............................144.74 PSI (10psi gone!)
V/P (Volume to Pressure Index) is .........................115
and the 340
Static compression ratio of 9.8:1.
Effective stroke is 2.17 inches.
Your dynamic compression ratio is 6.76:1 .
Your dynamic cranking pressure is .............................125.78 PSI. (almost 30psi;gone)
V/P (Volume to Pressure Index) is ..........................84
Notice that the VP difference now is 115/84= plus 36.9% in favor of the 360
Ok I know your next question; here is the 340 with the faster-ramped cam
Static compression ratio of 9.8:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.45:1 .
Your dynamic cranking pressure is ..............................143.69 PSI.
V/P (Volume to Pressure Index) is ........................107
So, as you can see, the ramps alone are worth 107/84= plus 27.4%
And so, why would you want to run the slow-ramps? This is affecting your bottom end off idle to about 3000 rpm, which with 3.23s could be up to 30 mph in first gear with 28" tires.
Wait what? This is like the vast majority of your driving. Put it into second and WTH just happened,
Here's what a smogger-teen looks like with that same long-ramp cam
Static compression ratio of 8:1.
Effective stroke is 2.17 inches.
Your dynamic compression ratio is 5.58:1 .
Your dynamic cranking pressure is ..................................... 96.03 PSI.
V/P (Volume to Pressure Index) is ................................. 60!!
no wonder factory 340 cams in smogger-teens are so um lazy at low rpm
You can pick 5 or more 268* cams out there and get 5 different .050s. Or, you could pick 5 different 220@.050s and get 5 different advertised, and the advertised can be anything from .008 to .006 to .002 to .001. And those 5 cams could be anything when measured seat to seat. So with so many options, why would I pick a slow-ramp cam? I don't need it and I don't want it, and it costs me cylinder pressure, efficiency, and fuel economy. I'd rather pull the heads every once in a while,for freshening, than to run a cam with so much time devoted to being quiet, or long-lasting, or reducing cylinder pressure, or whatever so-called "reason".
And the heavier the vehicle, the more important this becomes. There's no sense in installing a long-ramp cam in a short stroke engine, in a heavy vehicle, or one stuck with hiway gears and a low-stall TC. No excuse for it I might add.
I'm not pointing fingers at any one, or any cam; just saying.
Heres what I mean;all examples are with a 268 advertised cam, and lets not even toss at what lift into the mix; and 9.8Scr
First a 360
Static compression ratio of 9.8:1.
Ica of 64*
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.86:1 .
Your dynamic cranking pressure is............................. 154.50 PSI.
V/P (Volume to Pressure Index) is .......................130
Next a 340
Static compression ratio of 9.8:1.
Ica of 64*
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 7.82:1 .
Your dynamic cranking pressure is .............................153.44 PSI.
V/P (Volume to Pressure Index) is .......................121
Notice the V/P is 130/121= plus 7.4% stronger for the 360. This is like running 3.47s in the 340 to equal the 360 with 3.23s ... in terms of zero to 3000rpm or so.
But this is not the point.
The point is we use this Wallace calculator running off the advertised intake duration..... which we already know is based on who knows what , cuz the valves are not yet closed.
What if the 340 had one of those looong-ramp cams that didn't actually close the valves until 300*, and the 360cam was slammed shut at 280* ? I mean just what if.
Here are the new numbers; first the 360
Static compression ratio of 9.8:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 7.49:1 .
Your dynamic cranking pressure is ..............................144.74 PSI (10psi gone!)
V/P (Volume to Pressure Index) is .........................115
and the 340
Static compression ratio of 9.8:1.
Effective stroke is 2.17 inches.
Your dynamic compression ratio is 6.76:1 .
Your dynamic cranking pressure is .............................125.78 PSI. (almost 30psi;gone)
V/P (Volume to Pressure Index) is ..........................84
Notice that the VP difference now is 115/84= plus 36.9% in favor of the 360
Ok I know your next question; here is the 340 with the faster-ramped cam
Static compression ratio of 9.8:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.45:1 .
Your dynamic cranking pressure is ..............................143.69 PSI.
V/P (Volume to Pressure Index) is ........................107
So, as you can see, the ramps alone are worth 107/84= plus 27.4%
And so, why would you want to run the slow-ramps? This is affecting your bottom end off idle to about 3000 rpm, which with 3.23s could be up to 30 mph in first gear with 28" tires.
Wait what? This is like the vast majority of your driving. Put it into second and WTH just happened,
Here's what a smogger-teen looks like with that same long-ramp cam
Static compression ratio of 8:1.
Effective stroke is 2.17 inches.
Your dynamic compression ratio is 5.58:1 .
Your dynamic cranking pressure is ..................................... 96.03 PSI.
V/P (Volume to Pressure Index) is ................................. 60!!
no wonder factory 340 cams in smogger-teens are so um lazy at low rpm
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