Bob,
I have to agree with you about the effect removing and sharp spots from the
combustion area will have on detonation. The key to avoiding the excessive
pressures is by changing where the Intake valve closes in relation to the
piston traveling up on the compression stroke. What is your cylinder
pressure warm with all of the plugs out ... or have you tested it? The
method I will use on y 302 will be to chose the desired cam profile and then
increase compression (or advance the cam) until I obtain about 195 lbs
cylinder pressure cranking. My experience is similar to yours in that
compression is fine provided that the combination once assembled gives you a
usable cylinder pressure. It may be that the guy who has to run race gas
needs to install a cam with a little more overlap or one that closes the
intake valve a little later reducing the amount of cylinder pressure the
piston can build. I do know that back in the race car days we had an engine
that was 14:1 (remember that car Theo .. it was blue and yellow) it made
over 220 cranking cylinder pressure and we had to run C-14 and methanol in a
15% and 85% ratio respectively or it detonated like crazy.
My 2 cents too,
Tim Ronak
B382000680
PS: It is amazing how a well placed email gets us back on the performance
topic....YEEHaaaww!
-----Original Message-----
From: Bob Palmer [mailto:rpalmer@ames.ucsd.edu]
Sent: Thursday, January 20, 2000 8:17 PM
To: MWood24020@AOL.COM; TSMIT@isotel.com;
rdmallory@earthling.net; Ronak, Timothy P; tigers@autox.team.net
Subject: Re: Performance Tuning the Tiger
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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