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

[racprops]

Great Cats that is a 496 BIG BLOCK...sorry but a OLDs 350/403 is the total limit to fit into my vans firewall and doghouse.

Interesting reading: Horsepower: 330 hp @ 4200 RPM
Torque: 450 lb.-ft. @ 3200 RPM

In fact, the primary complaint is the gas mileage, which most state is in the 8-10 mpg range, but that is to be expected with an 8.1 liter gasoline engine. The 8.1L Vortec was the final big block gas engine from GM to date. This engine was primarily created for work purposes and was very popular among people who needed that kind of power. The massive size led to high fuel consumption, which was likely one of the key contributors to this engine being replaced by the small block 6.0 liter.

Of course your mileage may be different...I know because my Mercury is on record for getting 25MPH Highway.

Thanks anyway.

PS I do not plan on doing any towing.

Also look at the gears of the 8L90: 1st. A super Granny 4.56 2nd low 2.97, 3rd 2.08 4th. 1.69 5th.1.27 6th. 1.00 7th. .85 OD 8th. .65OD.

Compared to my stock 4L60: 1st. 2.48 2nd. 1.48 3 rd. 1.00 and 4th. .75OD.

[Taylor95]

Going back to the original topic does anyone have input on doing something more reasonable such as running a 9:1 ratio on regular gas? I think doing that is fairly easy if I get the right cam. Right now my vehicle is at 8.7:1. Under normal circumstances 9:1 would require midgrade.

[Ecky]

Sure. Go back just a few years and cars were running over 10:1 on pump gas. Compression dropped in the 70's due to emissions.

[racprops]

My understanding was that was possible with Leaded Gasoline and not with today's unleaded fuel.

Rich

[Ecky]

I'm not sure how much compression you can have with older engines, but some of Mazda's newest designs have a static 14:1 compression and run happily on 87.

[Angel And The Wolf]

The delayed closing has not been thrown away. Modern Prius engines use it to give a longer power stroke to a shorter intake "stroke" to extract more of the energy from the burning gases. (Think of the energy still available for driving a turbocharger.) The delayed intake closing effectively creates a smaller engine's intake charge while giving a larger engine's exhaust stroke. The quoted "Compression Ratio" is actually the "Expansion Ratio". The true compression ratio is close to an ordinary low octane engine's.
Why does Toyota use Atkinson cycle engines? - Toyota

[hayden55]

Originally Posted by Taylor95

Going back to the original topic does anyone have input on doing something more reasonable such as running a 9:1 ratio on regular gas? I think doing that is fairly easy if I get the right cam. Right now my vehicle is at 8.7:1. Under normal circumstances 9:1 would require midgrade.

Talk to an engine builder. If they know your engine platform well they will pretty much tell you what will run on xx octane or even e85 (cheap race gas). Oops they talk about what the max comp you can run on each fuel is with the pay to play video.

https://www.youtube.com/watch?v=bKSLXV1SlbQ

I'm a Ford/Chevy guy so LS limit for 87 octane is 10:1. Ford limit for 87 on the 2011+ Coyote is 11:1. I typically won't really mess with 93 though because it cost like 20% more in my area and if you run the thermodynamic formula bumping up the comp up one point (say... 10 to 11) to run 93 is only going to get you 2.5% gain (in efficiency) (The bump in comp and 6 points of octane would be around 6% gain power) .

https://www.youtube.com/watch?v=wYWMi0O0UB4&t=304s

[Taylor95]

Now that I think of it I'm not sure if I really want to experiment with that at the moment. However, what kind of difference in compression would a thinner head gasket make?

[Angel And The Wolf]

It would depend on your TDC clearance with the OEM gasket, and what percentage smaller the thinner gasket would achieve. (Check your stock valve clearance) More could be achieved by milling the deck, but, again, be careful not to mill so much that you begin slapping your open valves. Alternatively, you could fill in the combustion chamber in your heads without causing valve -piston interference. Find your Combustion Chamber Volume, and work from there - it shouldn't take much fill. Avoid sharp edges that might lead to pre-ignition. But Hayden is right, Higher compression will get you higher HP, but the fuel required will more than wipe out any financial advantage of higher MPG.

[Piotrsko]

No to argue, but I always understood higher compression lead to higher engine efficiencies, and a slew of drivaeability problems with preignition, lope, and power induced throttle mania.

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