SuperRam: Dynamic CR and 219 cam
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Melting Slicks
Joined: Oct 2002
Posts: 3,193
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From: Cincinnati Oh
SuperRam: Dynamic CR and 219 cam
I have some questions relating to the Dynamic compression ratio of a 383ci stroker, Superram and the 219 cam which is commonly used and I think regarded as the Be all, End all cam choice for said intake on a 350ci - and a common choice for the stroked version....
Using some on-line calculators I've found an interesting phenomenon that I hope someone can explain to me: The 219 with my 383 and an ideal quench area provides a Dynamic CR of ~8.92!!! My understanding is that the rule of thumb for a street motor is a DCR no greater than ~8.0-8.4 for reliability and no detonation issues.
So what's the deal? Is the 219 a bad choice for the extra stroke? did I fudge my numbers? Is this an exception to the general rule - Or are the 219 SR strokers out there just pulling more timing to avoid issues?
The *only* number I'm iffy on is the cc's of valve relief on my pistons (TBD) - so I used 6 as a ballpark. If someone has a better estimation please share.
Here are my numbers:
4.030" bore x 3.75" stroke = 382.67ci
Aluminum head = 72cc
head gasket = 0.044" thick x 4.166" diameter
Block decked at 9.000" for a quench of 0.044" (ideal?)
Piston Dish = 6cc
Giving a Static CR of ~9.93:1
Cam specs for a LPE 219 cam:
Adv Intake/exhaust duration = 219/219
Lobe Seperation = 112
Intake lobe centerline = 108
Calculated Intake Open/Close = 1.5 / 37.5
Calculated Exhaust Open/Close = 45.5 / -6.5
Calc overlap -5 (at 0.050" I believe)
Cam advance 4 degrees
Calculated Intake close angle = 37.5 (matched cam card)
Dynamic Stroke Length = 3.478" (same physical info as static CR where applicable)
Giving a Dynamic CR of 9.28:1 (high)
Now a 10cc dished piston drops that down to 9.5:1 static and 8.92:1 DCR respectively... but geesh it's still high!
Edit: Here's the link I used... http://members.uia.net/pkelley2/DynamicCR.html
Using some on-line calculators I've found an interesting phenomenon that I hope someone can explain to me: The 219 with my 383 and an ideal quench area provides a Dynamic CR of ~8.92!!! My understanding is that the rule of thumb for a street motor is a DCR no greater than ~8.0-8.4 for reliability and no detonation issues.
So what's the deal? Is the 219 a bad choice for the extra stroke? did I fudge my numbers? Is this an exception to the general rule - Or are the 219 SR strokers out there just pulling more timing to avoid issues?
The *only* number I'm iffy on is the cc's of valve relief on my pistons (TBD) - so I used 6 as a ballpark. If someone has a better estimation please share.
Here are my numbers:
4.030" bore x 3.75" stroke = 382.67ci
Aluminum head = 72cc
head gasket = 0.044" thick x 4.166" diameter
Block decked at 9.000" for a quench of 0.044" (ideal?)
Piston Dish = 6cc
Giving a Static CR of ~9.93:1
Cam specs for a LPE 219 cam:
Adv Intake/exhaust duration = 219/219
Lobe Seperation = 112
Intake lobe centerline = 108
Calculated Intake Open/Close = 1.5 / 37.5
Calculated Exhaust Open/Close = 45.5 / -6.5
Calc overlap -5 (at 0.050" I believe)
Cam advance 4 degrees
Calculated Intake close angle = 37.5 (matched cam card)
Dynamic Stroke Length = 3.478" (same physical info as static CR where applicable)
Giving a Dynamic CR of 9.28:1 (high)
Now a 10cc dished piston drops that down to 9.5:1 static and 8.92:1 DCR respectively... but geesh it's still high!
Edit: Here's the link I used... http://members.uia.net/pkelley2/DynamicCR.html
Last edited by Ramanstud; Mar 26, 2005 at 09:50 PM.
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
You have 4* ground in (112+4), try inputing 112* on your DCR calculator. I had the same problem with my Erson 219 also zero decked at 9". Also, like mentioned, use 280 as your advertised duration 
