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

[Angel And The Wolf]

How does that help MPG in real world driving? I think the cheapest way to take advantage of the higher HP is to increase the diameter of your tires (when you need to buy new tires, of course).

[hayden55]

Originally Posted by 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...

Honestly, if you don't have at least a cheap source of e85 if you're considering any fuel except 87 you will be disappointed. The real world price of regular and premium in my location right now is $2.47 and $2.90. That for me is a 17% increase in price. If your car was power limited the power thing would come into play more, but its a v8 car so just throw that out and focus on efficiency numbers using the thermal efficiency equation. Check you're valve clearances and quench... have the head decked and buy a thinner head gasket which still allows the engine to function and have a reliable seal.
Make the changes you can while running 87 octane (timing, leaner afr's, decked head, thinner head gasket), and find a good double overdrive transmission and work on aerodynamics. Your car is realistically making too much horsepower for the rpm it's spinning to go x speed so follow Chevrolet's mark and skip shift (1-4) under 2000 rpm with high load and have your car geared to spin about 1500 rpm at 70 mph.
Also, the head cooling is true. Real world numbers I do not know but aluminum engine blocks cool better than iron blocks, and I recently saw a company talking about their better integrated cooling circuit into their heads on the car which allowed them to decrease knock because of cooler cylinder head temperatures.
If you wanna play with numbers this a good video too:

https://www.youtube.com/watch?v=wYWM...o6RHE2rcjGAHRg

On point three he uses the equation normalize thermodynamic efficiency numbers from compression ratios. It's a logarithmic curve though so don't expect a ton.

Also, another point to consider is the bar is probably already so low you'll never even reach the efficiency numbers of an LS drivetrain. Thats why a ton of people don't even mess with rebuilding 350s that came in their car anymore unless they want to be concours original.
That and the reason why LS's are so cheap is because you can buy an aluminum block ls based 5.3 from the junkyard for cheeeeep.

[Angel And The Wolf]

you might consider the Prius simulated Atkinson cycle engine. The Prius engine is an 1800 CC 13:1 four cylinder, but it's only 13:1 on the power, exhaust, and intake strokes. On the compression stroke, it pushes air back out the delayed closing intake valve, so that the effective compression stroke is 10:1. this allows the engine to act like a 1384 cc engine, (346 cc per cylinder) with an extra 103.75 cc of expansion stroke per cylinder, salvaging the heat energy that would normally waste itself out the exhaust manifold.

Raise your compression to 13:1, and install intake cams that will hold your intake valves open 41.54 degrees past BDC. Use 87 Octane regular.
You need port fuel injection, so you can delaying injecting the fuel until after the intake valve closes.

Using your 350 as an example, this would effectively give you a 269 Cu In V8 with the mechanical efficiency on par with the Prius engine.

[Angel And The Wolf]

Of course, this could be applied to ANY gas guzzler you may have.

[19bonestock88]

The thing is, I don’t have a V8, nor do I have easy access to E85... I figured that my engine makes 140bhp/150lb/ft stock and a few extra wouldn’t hurt...

I considered dabbling in Miller cycle since I have the blower that’s compatible with my engine, but without standalone engine management to tune it with I’m kinda limited on what I can do...

Was honestly hoping that I could maybe get away with 87octane in winter and 89 in summer... my logic is that the different Ecotec engines use different compression ratios but they all run on regular unleaded... for example, my L61(2.2L) runs 9.5 to 1 but the LE5(2.4L) runs 10.5 to 1... the only major difference is VVT but GM made no claims of simulated Atkinson cycle to offset the compression... leads me to think a higher compression L61 might live on regular

[hayden55]

Originally Posted by 19bonestock88

The thing is, I don’t have a V8...

Hmm.....
Thread Title: "1970's "30mpg" V8 cams, big car, w/14:1 CR on 87oct"
But yeah what we said still applies.