Compression Ratio, too high?

[VETDRMS]

I'm in the process of building a 406, and I need to decide on which cc AFR 195 head to use. I will have ~.010 deck, and when I ran the 68cc chambers in a CR calculator I came up with 10.8:1. I'll be at ~10.3:1 with the 74cc chambers.
Should I just not risk it and go with the 74cc's?
The cam is a Comp Xtreme Roller 288 Hydraulic roller (236I/242E@.050;.520/.540)
What is the highest you can run on premium?
Thanks :Beer

 

[Rowdy1]

I Said it Before

In my 62 I have a 327 bored .030 over, 12 1/2 to 1 pistons, a Doug Herbert solid lifter cam, duration int. 286 at .050 255 exhaust 296 at .050 263 with a .504 lift int. & exh. Trick Flow 64cc heads with roller rockers, a 700cfm Holley dbl. pump, complete MSD ignition with 6AL box and I run Sunoco 94 and on occaision on a tripwhere I couldn't get it, used 93 and I've never had a ping or fouled a plug. I have dusted some pretty amazed owners from 350's reworked to a couple BB's. The 4:10 rear helps I normally run the 6000 RPM chip in the 6AL but I have used the 8000 a few times and it's all there. Ya gotta love a screamin SB I know I do:crazy

 

[silver 80]

vetdrms,
beautiful vette, what color is that.

 

[VETDRMS]

Roudy1 I think the amount of cam duration you have helps a lot with the fuel you can use. Have you calculated your dynamic compression ratio? I should be at 500+hp/tq, so I'll probably suprise a few as well....:BOW Your car looks great BTW

silver 80 Thanks! Actually I haven't came up with a name for it. I mixed it myself last year. I took a burgandy color, added brick red, and a lot of violet, a light gold metal flake, with bright white pearl. Its painted on a black base with a violet tinted sealer. The bright white pearl turns the paint a silvery color in the sun, at night it looks kind of purple, in direct sunlight its looks a lot like a Bing Cherry. I have the PPG mix sheet if you want to see what exactly is in it.

 

[Rowdy1]

Nope, I Haven't

I have no idea how to even do that. I went with this combo as a result of knowing what I wanted and having a great friend and "Good 'Ol Hot Rod Engine Builder" sit down and do some figuring. I'm extremely happy with the way it runs, and sounds, I get a lot of "What's under the hood? questions. It rocks when I smash it but I can also feather it all day long, totally streetable. Even he's amazed when I take him out to a cruise night and get loose 3rd to 4th:eek

Thanks for the compliment, I appreciate it and I echo silver 80, I really like your color.

 

[silver 80]

VETDRMS.
yes if you post the PPG mix sheet that would be great. :dance

 

[Vette/Berlina-coupe]

-without question employ the 68cc/Cyl.heads, you can always install a water/alchol-injector activated by a vacume-switch or a throttle-position switch if need be for operation on Regular-petro. To use 74cc's would be silly.... ~Bob vH
:dance

 

[VETDRMS]

Well i'm getting mixed answers...I called comp cams, and they said without question go with the 74cc chambers? I don't need detonation, and a water/alcohol is a little out of the question unless it costs less than $400. The .5 point in compression difference would gain me 2% hp at most (~10), and detonation could cost me a lot more than that. I'll be running SRP Forged Flat tops, so they should be able to withstand the detonation a little better. I'm not quite sure what to do, if you could elaborate on why I would not have any problems with 10.8:1 running 91 octane gas, please do.

 

[Robert N]

Personally, I think you will have some issues with 91 octane and 10.8:1, especially if they use the ethanol mixture part of the year. I have had to retard my timing and fule mixtures to keep her running. Upon the addition of 100 octane race fuel, I saw a noticeable difference.

 

[lytemup]

are those heads aluminum? if so i think i would feel comfortable at 10.8:1.

 

[SwaveDave]

VettDRMS,

In my last engine, i was at 11.1 CR using factory iron Heads with a mild cam . Initial timing was 14 and full advance by 36, and running AMoco 93 octane....did not ping.

WIth my current engine, im at 9.6 CR using EDL Oval Port ALum Heads with a radical Hydr. Roller Cam with initial timing at 20 and full advance by 42 , using Amoco 93....and not pinging.

Both engines are BB. Hope that gives you some clue.

 

[VETDRMS]

Thanks again for the info. I figured my dynamic compression ratio to be 8.32259267850636, they say 8.5 is the limit for premium, so I should be just on the edge. I will be running a crane ignition with a timing retard unit adjustable from inside the car, so if i should have problems or get stuck with bad gas i wont' be high and dry.