Does anyone have a chart or has gathered information regarding how much compression a Slant Six can run before having to move up the Octane tree? What's the Highest CR 87 Octane can go? How much until you need race gas? What's a good mid-range CR for 91?

There really isn't a table for this , as each build is a bit different and the only 'real' way to somewhat predict your octane needs is using a dynamic compression ratio calculator.

Very general engine builds running the DCR show that
about up to the mid-8's are ok for regular 87...plus comes
in around 8.7-9, generally after 9 you are using super+

But...this also can be altered by your timing and your carb tuning...
Even a guy with a 9 DCR might be able to get away with using regular,
by custom curving his distributor for less timing...adding water injection,
or dialing his jets richer (unburnt fuel will vaporize and carry excess heat from the chamber)...but that's not the most efficient way to make mileage.

Example I run a 10.3:1 SCR street engine, my cam is the ERson 280/270 with a wide LSA (111)...I have good idle and street drivability...the DCR says I'm in the high 8's (about 8.8:1)...By dropping about 4 degrees of vacc. advance and a little mechanical I can run 87 for weeks...but the mileage isn't the best...plus and super I can run more aggressive timing curves which benefit by increasing a couple of MPG on the long haul...

I just built and engine in the 11.4:1 SCR range... the cam has a narrow LSA and bleeds off pressure at overlap...DCR depending on centerline of the intake lobe is in the 8.9:1-9.2:1 range...(I stuck with 8.9)...Should be able to run plus all day...super if I want to (or during races). with no ill effects...

DCR is a nice tool when planning your engine build, and choosing the cam and what centerline to degree the intake lobe at...you can estimate fairly well if you'll be like a 60's dodge truck (6.9 DCR can run on moose whiz, needs a turbo badly), or a track only car (9.5+DCR...SCR in the 12's...likes to drink 108-112 during test and tunes, on the track or loading on the trailer...)

-D.Idiot

hello everyone, while i ve read and reread tons of posts here, i am new and this is my first post. i m trying to find a good baseline start on my timing and timing curve as my 69 cuda sits on stands. i built the engine over 15 yrs ago, lost the build sheet and what i d done to it and am now LEARNING how important proper timing is so as to NOT destroy a perfectly good engine.
i m including the current data i have gathered and hope someone out there has a similar build and successfully dialed it in for the best results. time is of the essence for me at this point(health) so perfect isn t necessary, just a mechanically sound and safe running car is what i need, i can fine tune it for more power later.
my car is a 69cuda h/t. 225 w/904, 7 1/4 rear with 2.76 and 26" tires. what i recall  of the original build is, and if I m remembering right( I ve had her since 92’): --the engine has 10.5 to 1 stock size arias pistons, the block and head were milled to bring it to that static CR.  --the cam is a MP 268-108 .460 lift with a 52 overlap. Lash on IN @16 and ex @ 20. Recommended c/l @ 104. I had originally adv or ret the cambut had tons of issues with idle and eventually found a lot of black carbon in the intake runners of the offy manifold and so I put the 0 degree camshaft offset in and the cam should now be as though I used the timing marks on the chain set. --the head is a 75 or newer (no drool tubes), stock size valves with the backs cut and a mild cleaning up in the bowls and port matched to the offy. --my biggest concern and the reason I m reaching out is I m hitting 215 psi in the chamber and really don t know how much or when(rpm) this will contribute to knock and ping, my ears aren t what they used to be.
--holley 390 w/58 prim and 61 sec plate. 6.5pv, #28 squirter and an orange pump cam and It s on top of a 1’ phen spacer.
--lash set hot @ 13 In and 19 Ex
--the exhaust is a MP 6 into 1 header
--spark plug is a bocsh hr9bp, however I am installing a ur5 which is 1 colder
--standard electr distrib connected to a msd 6a box. I recently bought and installed the 4secflat plate(original is a 13r)), set it at 16 deg. to allow for 12 to 15 deg of initial timing and a total of 28 to 32 total mech adv. (distrib weights 1889264) I installed one new medium rate spring and left one original that was close but a little less in tension and also it is a bit longer. The vac can is an 8.5 and set to start at 9” and fully adv by 15” (approx.).

i ve done an initial base line no load test to find out when timing starts for both the mech adv with and without the vac can and starting with an initial adv of 14 deg btdc.
all timing checked with a dial timing
--mech adv w/o vac starts with 16 deg @ 1300 rpm with 33 deg showing and all in by 2500.

--mech adv with van can readings taken and starting 10" of port vac is 30 deg @ 1900 rpm(28 deg w/ vac disconnected) and fully in @ 16" port vac is 53 deg @ 2500 rpm(33 deg w/vac disconnected).
Note: just measured slots on 4flat plate and according to an article in MPconnect( ADD 14-HORSEPOWER TO YOUR SLANT 6) the 16 deg slot reacts more like the 18 deg should according to the articles measured and machine tested. the 14 slot measures more to what the 16 should have so i will be installing it on the 14 tomorrow( this cleared up a few questions i had while testing)

when comparing these numbers to ALL the articles HERE and there about all the various builds this timing curve seems to come in way to early. having just looked at emsvitil May 2005 fully documented experiment which shows mech adv starting in at 2k and all by 3500 seems to be a smarter curve for my build IMH and uneducated opinion. in another article i read they used the vac adv can to dial in their cruise timing, this also seems like a good way to go for me as well. these are my just my thoughts in regards to my engine.
i did try one test with initial timing to try and get some pinging to give me some reference as to the sound of it. because of the installed position of my distrib (please don t ask why b/c even i don t know the answer) i have about 7 deg btdc at its furtherest CW postion. by using the vac can to be fully in it allowed me to go as high as 29 deg btdc w/ rpm at 1450; i heard no knocking, but as i stated, my hearing isn t the best. moving on
the carb was adjusted to numerous articles i d read where i concluded running a bit on the richer side would help as far as detonation and can be dialed in at a later time by installing an A/F in the exhaust (again, time is a factor for me right now 3 wks left)
In the past i have run the this engine oh so many years ago (about 15) and did put about 1k miles and got good mpg(22 fwy) and didn t notice knocking or pinging at fwy speeds of 70 mph @ about 2700 rpm (this will be my normal driving habit in the future). if your wondering why i ve come to you for help it because of this: i had a ford bronco with a 400 i built in it. i got horrible gas mileage and had this constant sound that sounded like marbles in a blender. in trying to identify the problem i pulled and replaced the tranny and transfer case and it was still there. one day i started heading out and the engine blew. upon disassembly i found every single piston skirt cracked and ONLY THEN did the light bulb go on as to what the sound was. i m afraid of the responses i ll get from admitting this, but it IS the reason i am coming to you now for help, so please be merciful.
the art. and info from so many including emsvitial, aggress ted, /6dan, and others are very helpful, however i just read one from D idiot about a 10.3 CR built which continued to another build which had 11.4 CR and some timing info which allows him to run the street that makes me believe he may have the info(i m not saying he s the only one) i need for a basic start for timing on my build; however i ve lost it in my searches.

I ve done my best to include the known info on my engine/car and what i m trying to accomplish for now. any and all suggestions will be greatly appreciated by any and all that have gone through the grueling and pain staking task of actually documenting their experiences and results while on their venture for the best running /6 possible. my intentions for the use of my cuda are to be running as a weekend driver for pleasure with the occasional itch to punch it down just for a thrill, but no drag racing of any sort as i don t want to unnecessarily replace the rear end at this time.

Thanks again Mike[/size]

You could run your specs through a DCR calculator and see where you are, and probably answer a lot of your own questions.

_________________
There's no such thing as too much cam....only not enough engine!