Chris,
One thing you should remember is that higher compression (all other
things being equal) equals a greater tendency to detonate (spark knock),
thus requiring a higher grade of fuel (ie. 93 octane vs 87)
Having said that, I'll open myself up to flames by saying that the
greatest increase will come with the initial step from "stock" to the
first generally availible increase in ratio. In the case of the MG, it's
from about 8:1 increased to about 9:1, which roughly approximates the
difference between the factory low and high compression engines.
Given the state of gasoline readily availible today, much more than 9;1
would result in a car that is so close to detonation when under the least
load (accelerating, etc) that either copious amounts of octane booster
would be required at each fill up (adding dollars to the already high
cost of fuel), running a mixture of racing fuel and pump gasoline (see
above) or retarding the timing (negating a goodly portion of the power
gains.
Now, I'm sure that somebody out there is going to tell about the 12:1
engine he's running on 87 octane gas that goes like a stripped A** haint.
Maybe. But my BGT, with a 9:1 compression, is only happy running on 93
octane, and a good name brand at that. Some of the convience store 93's
will spark knock.
just my HO, but YMMV
Rick Morrison
72 MGBGT
74 Midget
On Mon, 27 Oct 1997 21:39:43 -0500 Chris Delling <saschris@flash.net>
writes:
>Looking for some subjective opinions here. I am sure that all would
>agree
>that an increase in compression ratio will yield an increase in H.P.
>output. My question regards bang for the buck. Given an engine with
>an
>8.0 to 1 compression ratio, vs. the same engine with a 9.0 to 1 ratio,
>what
>% of increase would be expected. I am laying out my plans (and
>budget) for
>my winter project, namely extracting more from a stock 77 B mill (sans
>emissions, add Weber DGV). Trying to weigh the relative gain to be
>had by
>swapping to higher comp. pistons vs. stock (without any other mods,
>for
>comparison sake). I have confidence that many have opinions, and
>potentially similar experience, so please pass along your ideas.
>
>Regards,
>
>Chris
>
>
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