How To Determine the best SCR to hit the "Target SCR" When Planning a Motor ???
03-03-2014, 05:28 PM
#1
TECH Enthusiast
Thread Starter
How To Determine the best SCR to hit the "Target SCR" When Planning a Motor ??? Please forgive what might be a dumb question . . .
This pertains to LS motors only, in a "Sleeper/Stealth" daily-driven, full-weight ( 3900 lb w/Driver ), 2000 Z28 with an A4 transmission. Idle quality, OBD-II, and MPG are important.
I'm looking at two different stroker combinations ( 408 - 4.030" Bore x 4.000" Stroke w/ 68cc chamber and 225cc intake runners or 406 - 4.070" Bore x 3.900" w/ 68cc chamber and 225cc intake runners ). Valves are 2.06" / 1.60".
QUESTION :
I'd like to know how to be able to pick the correct SCR to arrive at a "Target DCR" of 8.25 - 8.5 : 1, based on each combination and desired RPM range ( 6000 RPM Redline +/- ), for 93 Octane pump gas.
Then, I want to get a custom cam designed and made to compliment those specs.
Most of the time, people build their engines and then get the cam spec'd to match, which seems like a "compromise" to me.
I'd like to be able to optimize the compression of the motor for 93 Octane, beforehand, and then have the camshaft made to let it "be the best it can be".
Thanks, in advance, for your help !
This pertains to LS motors only, in a "Sleeper/Stealth" daily-driven, full-weight ( 3900 lb w/Driver ), 2000 Z28 with an A4 transmission. Idle quality, OBD-II, and MPG are important.
I'm looking at two different stroker combinations ( 408 - 4.030" Bore x 4.000" Stroke w/ 68cc chamber and 225cc intake runners or 406 - 4.070" Bore x 3.900" w/ 68cc chamber and 225cc intake runners ). Valves are 2.06" / 1.60".
QUESTION :
I'd like to know how to be able to pick the correct SCR to arrive at a "Target DCR" of 8.25 - 8.5 : 1, based on each combination and desired RPM range ( 6000 RPM Redline +/- ), for 93 Octane pump gas.
Then, I want to get a custom cam designed and made to compliment those specs.
Most of the time, people build their engines and then get the cam spec'd to match, which seems like a "compromise" to me.
I'd like to be able to optimize the compression of the motor for 93 Octane, beforehand, and then have the camshaft made to let it "be the best it can be".
Thanks, in advance, for your help !
Last edited by ez2cdave; 03-08-2014 at 06:29 PM.
03-04-2014, 03:03 PM
#2
Your best bet would be to call any of the site vendors for this. Telling them everything you typed would give them a good idea on what kind of cam to give you.
Like you, I am also "up in the air" about how to come up with a cam for a specific motor package. To me you can have a CR in mind then start factoring in head combustion volume, piston volume (dome or dish), head gasket thickness, stroke of the piston etc.
Then you will STILL need to determine the pushrod length and cam lift with the RR ratio which will get you an idea how much overlap and lift you get from the valves. Doing this would be more pertaining to DCR (Dynamic Compression Ratio) which would be what the REAL compression ratio is of the motor when it is running IMO. When you know the stroke, deck height and piston design you start to get limited for valve lift (otherwise the valve would hit the piston). Then that could be back tracked to find RR ratio then PR length then cam lobe design.
I get my head wrapped around things up to a certain point and then I get fuzzy on things and what to factor in next.
Like you, I am also "up in the air" about how to come up with a cam for a specific motor package. To me you can have a CR in mind then start factoring in head combustion volume, piston volume (dome or dish), head gasket thickness, stroke of the piston etc.
Then you will STILL need to determine the pushrod length and cam lift with the RR ratio which will get you an idea how much overlap and lift you get from the valves. Doing this would be more pertaining to DCR (Dynamic Compression Ratio) which would be what the REAL compression ratio is of the motor when it is running IMO. When you know the stroke, deck height and piston design you start to get limited for valve lift (otherwise the valve would hit the piston). Then that could be back tracked to find RR ratio then PR length then cam lobe design.
I get my head wrapped around things up to a certain point and then I get fuzzy on things and what to factor in next.
03-04-2014, 04:19 PM
#3
TECH Enthusiast
Thread Starter
Smitty,
What I'm after is knowing what SCR to shoot for, so that the cam isn't a "compromise" or that has to have too much duration to "kill off" cylinder pressure, in order to reach a DCR of 8.25 - 8.5:1.
In my combo's, they all come out right at 11:1 +/- SCR ( with -3cc flat-top pistons ) . . . I'm trying to avoid running dished pistons if possible, because I'm worried about detonation from loss of quench.
So, if my SCR is unnecessarily high, the camshaft profile would have to more radical, with unwanted results, on my part.
My goal is a smooth-idling, daily-driver, with reasonable economy and "stealth".
What I'm after is knowing what SCR to shoot for, so that the cam isn't a "compromise" or that has to have too much duration to "kill off" cylinder pressure, in order to reach a DCR of 8.25 - 8.5:1.
In my combo's, they all come out right at 11:1 +/- SCR ( with -3cc flat-top pistons ) . . . I'm trying to avoid running dished pistons if possible, because I'm worried about detonation from loss of quench.
So, if my SCR is unnecessarily high, the camshaft profile would have to more radical, with unwanted results, on my part.
My goal is a smooth-idling, daily-driver, with reasonable economy and "stealth".
Last edited by ez2cdave; 03-04-2014 at 06:06 PM.
