My90Iroc

iTrader: (26)

I'm doing some research about dynamic compression and in my searches it seems a dynamic compression of 9.1:1 or lower is needed for pump gas (93). According to the calculator I'm using it seems an F13 with 5.3 heads will yield too high a dynamic compression, yet I see combinations very comparable to this a lot on this board. Tell me if I'm doing or inputting something wrong.
http://www.kb-silvolite.com/calc.php?action=comp

Here are my input values:
Cyl. head cc: 61.15 (stock 5.3?)
piston head cc: 0 (flat top)
gasket: .053 (Fel-Pro MLS per jegs.com)
gask. bore: 3.945 (Fel-Pro MLS per jegs.com)
Cyl. bore: 3.898
Deck Clear.: -.008
Stroke: 3.622
Rod Length: 6.098
IC ABDC: 58 (43 for F13 + 15 per instructions on calculator)

Results: Static Comp. 11.092 Dynamic Comp. 9.267

Let me know what you guys think. Thanks.

MadBill

I think the problem is the calculated IVC spec. DRC is calculated from actual (~'advertised') degrees, and most cams have considerably more than the 30 degree difference between 0.050" and advertised spec implied by the 'add 15 degrees' instruction. I would try to get the actual 0.006" lift/advertised number, or at least look at typical values for the cam company you are using. For example, I just checked a 5 year old CC and 6 year old Crane catalog, and found many hydraulic rollers to have a 50 to 60 degree longer advertised vs. 0.050" duration. Adding say 27 degrees to your 0.050" IVC of 43 would give an IVC of 70, and a DRC of ~8.4:1

DAPSUPRSLO

iTrader: (14)

Ahh, so that's why it asks you to add 15 degrees to your .050" ivc. Wow, if that is trying to account for advertised ivc then that is way way off (unless it's attempting to account for the valve train deflection yadda yadda yadda which will make the valve close a little sooner then advertised I think). I've been spending alot of time looking at comp solid roller lobes on their site and the most agressive solid roller lobes I noticed (I believe it was the tk series) took 28 degrees to get from advertised to .050" (I did not look at any lobes with more then .390 lobe lift cause of my 1.95 rockers). And this is solid roller stuff where the advertised number is at .020" or so to account for lash, most hydraulic stuff is at .006" and makes the length to get from advertised to .050" that much longer.

treyZ28

if you have 9:1 dynamic and 11:1 static it means you IVC happens at 2/11ths of the way up. 2/11*90 = 16.36* ABDC?
is that logical? i dunno, prob not. back to work!

Patrick G

iTrader: (14)

If you use J-Rods calculator (which I've found to be extremely accurate), you will see that your dynamic compression is right at 8.5 to 1. Right where you need to be!

DAPSUPRSLO

iTrader: (14)

Can you post a link to that calculator? Thanks Patrick.

dug

iTrader: (10)

Is there a link to DCR of popular cams with stock engines?

Patrick G

iTrader: (14)

Here it is:
http://users3.ev1.net/~black_ops/cam...calculator.xls
Enjoy

SideStep

that is the one I use....

DAPSUPRSLO

iTrader: (14)

Woops, I'm a dumbass. I've been using that for sometime now but did not see that one of the sheets was a DCR calculator. Thanks a bunch anyway.

My90Iroc

iTrader: (26)

Awesome, thanks for that. I didn't think my numbers were correct.