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Discussion Starter · #1 ·
It's been a long day so please forgive me if this post too stupid. I've got a friend who is trying to convince me that I should put a ZZ383 in my Chevelle instead of a ZZ4 because the ZZ383 will get better mileage -- not that I really care. Am I missing something? Is 0.4 less compression really going to make a noticeable mileage difference? Do the 70 extra ponies eat for free? This makes absolutely no sense to me. If anyone can explain this line of thinking I would really appreciate it.
 

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The ZZ383 has a slightly longer stroke, which may give slightly more torque at low rpm and across the power band; the ZZ4 has slightly higher compression. It probably depends more on what type of carburetor and if vacuum advance is tuned right rather than the engine itself. The cost of the engine will take a while to make up for FE, if any; I'd keep what you have and just enjoy it. What was his reasoning behind the better mileage?
 

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The ZZ4 has almost 10% less displacement. It will put out good torque. It should produce better mileage.

If you are really concerned about mileage pay extra attention to carb and ignition tuning, then buy and install a vacuume gauge. Learn how to drive the car to maintain maximum vacuume.

Steve R
 

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Discussion Starter · #6 ·
Thanks guys. My friend seems to believe that lower compression ALWAYS means better mileage. He's trying to convince everyone that the 500 HP (builder's dyno number) 440 that he's putting in his car will deliver better mileage than a ZZ4 because it's running only about 9-1 compression. I'll believe it when I see it. Mileage is not a major concern for me. If it was I'd just keep the 307 that the car came with. I like the ZZ4 because it makes decent torque, makes it early, and I'm not paying for a lot of extra HP that I will almost never use. Plus, it's an easy engine to live with. My Chevelle is a driver and touring car, not an auto-cross or drag car. I know that everyone loves EFI, but I'm going with a carb because I hate computers in my cars. Thanks again for the info and advice.
 

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When the ZZ4 was the popular small block crate motor you would often see them running low-13's and an occasional high-12 at the track, depending on how smart the person was at picking the rest of the drivetrain. They are good engines that tend to be underestimated.

I don't think I'd take advice from your friend.

Steve R
 

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Regardless of compression ratio, wouldn't your pal recognize that more displacement consumes more air/fuel? Wouldn't 383 cubic inches drink more fuel than 350 cubic inches? There are lots and lots of variables to consider but by and large more displacement equates to more fuel consumption.

I do not believe that longer stroke makes more torque, rather I believe the engine only knows it has more displacement which can pump more air/fuel and make more power. I suppose there would be a graphical expression that calculations could show the peak torque of each engine and their respective fuel comsumption to do the same work (move your chevelle), but once compression ratio, ignition curve/tune and octane requirements are factored in, I say the 350" engine drinks less.

YMMV pun intended.
 

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Text book Otto cycle thermodynamics states that spark ignition engines ALWAYS see efficiency INCREASE as compression ratio goes up. It's fact, and it's in every thermodynamics text. What is your friend smoking?

Also, more cubic inches isn't going to equal less fuel consumption all else being equal. Why does your friend think modern cars have gone to cylinder deactivation?




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the 383 may very well get better gas mileage than the ZZ4- if everything else on the car is optimized to work better with it... more low end torque means you can run higher gears, which lowers the cruise rpm. it also means you can run a tighter torque converter, which means less slippage.. it's all about the combo, the tuning, and the driving habits..

but lower compression ratios does not equal better fuel economy- quite the opposite, in fact. more compression means more efficiency- that's just physics..
by his theory, the Mopar motors of the 70's and 80's should have gotten awesome fuel economy since they only actually had something like 7.5:1 compression ratios.. and the new engines of today that are running 10.5:1 or even 11:1 on 87 octane should be getting horrible fuel economy...
 

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Do the distributor mods I have outlined time and time again, to either distributor, and both engines will run cooler, attain better fuel economy, and have more drive-abilty.

Rule of thumb, engines with longer stroke, with smaller bore, usually get slightly worse fuel economy.
 
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