Mike, Theo, Doug,
I'll add my two cents, which of course runs somewhat contrary. I am running
nominal 12:1 TRW pistons with 59 cc 351W heads. Factoring deck height, head
gasket, and 0.030" overbore, it comes out to 10.9:1. The heads have been
ported some, mainly on the exhaust side and the chambers polished and all
edges chamfered, including on the pistons. I have the solid lifter E313
cam, which has basically the same overlap as the E303, but more lift. I
have no problem running 92 octane pump gas. In fact, it's damn hard to get
the engine to ping under any circumstance. If you run higher compression,
then you can and should use a bigger cam (i.e., more overlap & duration) to
help avoid predetonation. It's kind of like a poor man's supercharger. I'm
not sure how much of what I did in the way of porting and polishing has had
on my engine's tolerance for high compression. It sounds like Doug's engine
is basically the same as mine; same pistons (?), etc. Maybe he will tell us
what cam he's running (must be VERY BIG) or point to some other difference
that accounts for his need to run race gas and his very low gas mileage (I
get 15 and still have fun). BTW, Crane has the E303 and E313 equivalents. I
had the Crane version of the 303 in an engine back in '78 and it's a really
nice street cam.
Bob
At 07:22 PM 1/20/00 -0500, MWood24020@aol.com wrote:
>In a message dated 1/20/00 4:19:40 PM Pacific Standard Time, TSMIT@isotel.com
>writes:
>
><< So there's a topic worthy of discussion: Assuming we're using a mildly
>zoomy
> cam (let's say the Ford Motorsport E303 or equivalent), what's the maximum
> compression ratio we can run if we're going to use street gas (91 octane).
> Assume the engine will use 38 degrees max timing advance.
>
> Which heads are more susceptible to detonation?
>
> Comments? >>
>
>Common rule of thumb that I've heard from those that "know" (mostly by their
>mistakes) is 9.5 to 1 with iron heads, 10.5 to 1 with aluminum heads. Sounds
>a little high to me, but I guess that's what thicker head gaskets are good
>for...
>Mike
And, from Doug Mallory
>The only problem you will have is the same as my Tiger ...
>
>
>Getting gas. I am running 12:1 popups with 351 heads (Don't Tell) getting
>2-4mpg
>at $4.25 a gal.
>
>
>Doug
Robert L. Palmer
UCSD, Dept. of AMES
619-822-1037 (o)
760-599-9927 (h)
rpalmer@ucsd.edu
rpalmer@cts.com
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