Ramanstud

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

SloRvette

The 219 number is the duration at .050" lift. To use the dynamic compression calculators you need the advertised durations which are the .005" lift duration numbers.

Ramanstud

Boy, THAT made a difference....


Oops.

Caboboy

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