1970's "30mpg" V8 cams, big car, w/14:1 CR on 87oct

[Angel And The Wolf]

Originally Posted by Piotrsko

No to argue, but I always understood higher compression lead to higher engine efficiencies,

Higher compression DOES lead to higher efficiency, (note diesel efficiencies) but will it gain the percentage of MPG that offsets the percentage of higher fuel costs?
$2.59 regular, $2.84 Mid Grade, = 9.65% increase in price.
$2.59 regular, $3.04 Premium, = 17.37% increase in price
On a fifty MPG car, you would need 54.81 MPG, and 58.68 MPG respectively to justify the higher cost fuel.

Originally Posted by Piotrsko

and a slew of drivaeability problems with preignition, lope, and power induced throttle mania.

This is why you must step up to a higher octane rated fuel.

Originally Posted by Piotrsko

Valve clearance can be increased by recessing the seats and using shorter valve lift on shorter stems or a non interference cam

Yes, or leave the head and block alone, and weld something into the head beside the valve heads - think stove bolt heads - and mill those down to clear the piston crown. I don't know how much one would want to mess with valve work. A lot of math would have to go into this, so------Engine Shop.

[Piotrsko]

Back in the day we ran 12:1 compression on 88 octane pump gas no alky. Couldn't advance timing much past stock or it would detonate at low rpm. Made more hp, and at 3 mpg/ 25¢ a gallon, didn't care about efficiencies

Btdt. Recessing the seats is what pretty much any shop can do as part of the rebuild processes. Lets you shave the head as much as .090"

[Angel And The Wolf]

I remember, when I was a teen, a friends pulled into the Texaco where I worked in his 442, and said "We drove all over North Texas this weekend, and I must have burned $5 of gas!"

THOSE were the days!
Oh, and 17 cent gas with a free glass with a fill up!

[Piotrsko]

You also realize that statistically 2 gallons of high octane fuel in a 20 gallon tank raises the entire tank octane to about 1/2 of the high octane difference

[Angel And The Wolf]

Originally Posted by Piotrsko

Back in the day we ran 12:1 compression on 88 octane pump gas no alky.

A friend built a 12.5:1 396 El Camino, then went looking for aviation fuel. The guy on the other side of the airport fence said he could sell him the fuel at $5 a gallon, but he'd have to put it in an airplane.

OOPS!

[Angel And The Wolf]

Originally Posted by Piotrsko

You also realize that statistically 2 gallons of high octane fuel in a 20 gallon tank raises the entire tank octane to about 1/2 of the high octane difference

I get 2 gals of 106 octane and 18 gals of 88 octane = 90.7 octane.

[hayden55]

e85 is 104 octane and only like 2.10 here. From that video I posted i forgot to mention that on their sbc they said 12.5:1 was the limit for their engine to run on e85.

[Taylor95]

Supposedly if you get an aluminum head you can bump compression by a full point and still run regular fuel. It is supposed to dissipate heat better so you don't get engine knock as easily.

I read a source that said you get 4% more power for each point up in compression. I don't know how much more fuel efficiency you would get though.

[Angel And The Wolf]

Originally Posted by Taylor95

I read a source that said you get 4% more power for each point up in compression. I don't know how much more fuel efficiency you would get though.

More power allows the use of a taller final drive ratio, but the only reasonable way to take advantage of that is to use taller drive axle tires.

Still, I'm not sure if the higher cost fuel needed for higher compression will work out to less pennies per mile.

[19bonestock88]

I don’t know if it works out to better cents per mile, but...

To go from 9.5 to 11 to 1 compression would theoretically give me 6% more power, or about 8bhp... more power leads to shorter pulse cycles(compared to glide length), which leads to better overall FE...

Slightly better mileage and more power to play with when I’m not hypermiling, may be worth the higher fuel cost...