Picking a DCR to Meet My Requirements

[Indycars]

Part of picking a camshaft is knowing what DYNAMIC COMPRESSION RATIO ( DCR ) you are going to use. I need to decide what DCR I can live with on 91 octane max. I see where the suggested DCR is 7.5 to 8.5, but I need to get to a specific number, before I can decide on a camshaft. With the Crower 0471, the Intake closes at 69 degrees ABDC, resulting in a DCR of 8.25.

Below are factors that will effect detonation:

- Aluminum Heads Brodix IK200, 70 cc chambers
- Polish combustion chambers
- Radius and polish piston tops
- Forged Mahle Piston
- Continuous outside air (The engine is open to the outside, see avatar)
- Slightly rich A/F ratio. (The vehicle is for fun only and does not have to get good gas mileage)
- Walker radiator for cooling

I have two questions:
1.) What DCR will work with 91 octane fuel ???
2.) What else can I do to stop detonation ???

 

[grumpyvette]

viewtopic.php?f=53&t=3443&p=9118&hilit=+octane+calculate#p9118

viewtopic.php?f=52&t=4081&p=11104&hilit=quench+squish#p11104

viewtopic.php?f=53&t=726&p=9291&hilit=quench+squish#p9291

read thru these, threads and sub links, (btw) 8.25:1 with that cam should be fine with a decent set of aluminum heads and a decent cooling system if the quench is correct.
keep in mind theres no exact compression ratio point where detonation becomes a sure problem, while there is a compression ratio range or cylinder PSI at a known altitude, at a known air and coolant temperature,where a known octane fuel at a certain known temperature in a known combustion chamber design with a known quench and with a set surface texture or roughness , and of a known diam. and with a known spark plug design and heat range, a set distance from the cylinder center-line where its far more likely to occur, but factors as minor as the valve edge and seat diam. and ignition timing curve,the engines rpm, the effective rate of cylinder exhaust scavenging and the fuel/ air ratio and a dozen or more factors can and do effect the results.
you can easily find that two similar engines will perform quite differently due to minor differences in the engine prep, things like a few spark plug threads exposed in the combustion chamber or a sharp edge on an exhaust valve can easily swing the results noticeably.

 

[Indycars]

(btw) 8.25:1 with that cam should be fine with a decent set of aluminum heads and a decent cooling system if the quench is correct.

I forgot to put the quench in my first post, I'm shooting for 0.040". Piston clearance will be in .0025" to .003" range and Scat forged rods w/ 7/16" ARP bolts.