Fordnatics List Archive

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Mail From: (email redacted)


I'm rebuilding a '69 351W. It will be built up for a cobra kit. I want
it to be a cruiser with plenty of low end torque. Power at the high rpms
is not as important. It will have the stock 60cc quench chamber heads.

I'd like to hear opinions on how high the compression ratio can go
for 92 octane fuel. Are there street legal additives to improve the
situation?

Paul Franceschini
(email redacted)

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Mail From: (email redacted) (squidlinks)

You wrote:

>I'm rebuilding a '69 351W. It will be built up for a cobra kit. I want
>it to be a cruiser with plenty of low end torque. Power at the high
>rpms
>is not as important. It will have the stock 60cc quench chamber heads.
>
>I'd like to hear opinions on how high the compression ratio can go
>for 92 octane fuel. Are there street legal additives to improve the
>situation?
>
>Paul Franceschini
>

The comp ratio depends on a few factors, one you mentioned the
octane rating of fuel, and the duration of the cam you will be using.
If you want good low end torque, you want a cam with a relatively low
duration, IMHO around 260 deg is strong for low end, and some middle
ground. A 270 is more middle ground, and about the highest you can use
with a stock torque converter if you go with an Auto (c4, or AOD).

As for the actual ratio, I would suggest no more than 10.5:1. Most
street cams, and pump gas can handle this, but anything more and your
pushing for detonation. If you want to run this high, make sure your
cooling system is MORE than adiquate, you want to make the engine run
as cold as possible. This will allow you to run a more aggressive
timing curve without a real concern for detonation. The best way, is
stuff the biggest radiator you can get, but no more than a 4 core. 5,6
need high speeds to push the air through (nascar stock racing). This
also depends on where you live, myself I am in the western states,
where you can litterally cook an egg on the roadside during the peak
summer scorchers.

Even though it maybe more expensive than the others, running the higher
octane also lets you throttle romp it a little harder when things are a
little hotter than normal and still avoid detonation.

I myself have a 65 gal w/ a 390 which is a daily driver (~50 mi).
Unfortunately the gas bill ~$150 a mo (92 oct only). Ouch! But I love
every minute of it.

The Master Squid

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Robert Kirk)

>You wrote:
>
>
[...]

>I myself have a 65 gal w/ a 390 which is a daily driver (~50 mi).
>Unfortunately the gas bill ~$150 a mo (92 oct only). Ouch! But I love
>every minute of it.
>
> The Master Squid


Interesting. Is your engine heavily modded? I have a 69 Galaxie 390
that I also use as a daily driver about 50 miles, but my gas bill is a
lot lower. I monitor my mileage closely and get ~ 14mpg doing mostly
freeway driving. And I've never used the top gas. (I've heard urban
legend that they use alcohol to boost the octane and that that's bad
for the gaskets) but it runs fine on mid-grade here in Maryland. Even
used low test regular a few times ehen mid-grade was out, with no
discernable ill effects. I went back to mid-grade more out of caution
than lack of performance. In fact, the only bad performance I get is
during the Winter this last year with the new "environmental" gas. It
cost me a couple of mpg and seemed to give poorer starts & idle.

I only have a 2bbl carb (hoping to upgrade to 4bbl if I can find one). I
wonder if that helps or hurts the mileage.

Does anyone know if the big 390 really needs anything more than regular
gas?

Bob Kirk