trouble understanding compression to octane relationship

[shawnxj]

ok so i've made a deal on a 258 block that was running prior to being taken out of the jeep. so i'm gonna grab the crank and rods and either sell or junk the rest of the block. after reading up on stuff and comparing power to expense i've decided on the 4.5 low buck stroker recipe in the stroker recipe pages. so my question is what octane does that particular recipe require? i'm shooting for an 87 or 91 octane build and i live in south texas so we're fairly close to sea lvl. the faq lists that recipe as having a 9.7 cr and a .081 quench. will this hit the octane rating i'm looking for? also i read somewhere on the site that optimum quench is .040 to .060. with this recipes quench being at .081 should i dish the pistons out more and deck the block to get a better quench or increase the head cc and deck the block?

i'm really....really new to this and still trying to wrap my head around all of this so i'd appreciate any and all help.

oh and after talking to turbotom i'll be running the megasquirt 2 incase that helps at all. oh and it's going in an 88 cherokee with an aw4/242, 4.88 gears and 35" tires

[PolloLoco]

Check out the FAQ section, I've read all the posts and have learned a lot. The one that will answer your question is the Compression Ratio FAQ.

Static Compression Ratio (SCR) doesn't mean much, if any at all, and the 9.7 value you stated is the SCR. It's the real compression, aka Dynamic Compression Ratio (DCR), that really matters. Nothing is being compressed until the cylinder is sealed shut and that's when DCR is measured. SCR measures the geometry of the engine. So yes, your ultimate goal should be a set value for DCR, which from what I've read 8.5 is about as high as you want to go and run on pump gas. I'm shooting for 9.5 but I'll be running E85. You cam choice will also have a significant impact on your DCR.

[rradford9]

If you're looking at doing a 4.5L stroker, take a look at my build for some ideas. Its definately not the "best" build but its running great and can hopefully help you a little. http://www.jeepstrokers.com/forum/viewt ... ?f=8&t=645

It ran fine on 87 octane when it was first cranked up. Although since then I've been running at least 89 in it, and am currently running 93 with a SCT Performance tune. IMO, if you're wanting to stay on regular or mid grade pump gas you're going to need to get the CR down a good bit. The SCR, DCR, and quench stats are in my sig and the build thread. For your build, shoot for a SCR around 9.5, DCR around 8.0 and a quench of .06 or better. I had the piston dish increased to 18cc's in my build to lower the CR.

[shawnxj]

thanks for the info