Reenabling the egr

[80' 427]

Idk what it gets now and I am dumb enough to trade some of the mpg for performance because soon the 2.73s will be swapped for 3.23. once it has plates and I start DDing it I will know for sure. Of course my 20s concern is with a 496. Napa can't get the valve so will have to see what the 350 in the shed at the farm has or just forget it.

 

[dyeager535]

Idk what it gets now and I am dumb enough to trade some of the mpg for performance because soon the 2.73s will be swapped for 3.23. once it has plates and I start DDing it I will know for sure. Of course my 20s concern is with a 496. Napa can't get the valve so will have to see what the 350 in the shed at the farm has or just forget it.

It's not dumb to trade performance for economy. Without things like injection, modern engine design and cylinder deactivation, there is little choice but to give up economy as performance is increased. If you want a happy medium, it's possible, but I approach it as cut and dry with earlier vehicles/drivetrains...better economy/horrid performance, decent economy/decent performance, or poor economy/high performance.

Now that I have a car that gets 40+MPG, I feel more free to build my other car without regard to MPG or grade of fuel it requires. My only nod to economy will be OD, but that will be more about keeping highway RPM's lower, while still being able to run good gears.

Buick GN was probably the first successful large scale attempt at achieving good economy and high performance...but look at how it was done.

I would GUESS that under optimum conditions you could hit 20MPG with a 496 in a car, but if possible, it's only going to come on the strictly highway side, and going to be close.

Even the 40MPG econobox is ~9MPG from a stop up to cruising speeds.

 

[80' 427]

I drive 45 min to work which means 43 min of 65-70 the last 4 min is "city". I know the mpg of the big block will be worse but using small heads like the AFR 265, using a q jet with the top APT and optimising things like quench I hope it will get 25 with a Legend 700 with the .69 OD. Of course like you said it is all a compromise and I am willing to trade this for that on each side. It may get fuel rails and a throttle body some day but I really didn't want to have to buy a forged crank.

 

[dyeager535]

If I'm not mistaken, 25MPG would exceed the economy of anything GM put out with a 350 (gas), prior to OD. I don't mean to sound negative, but I spent thousands building a motor/drivetrain that I expected would get 20MPG, and I get barely better than a bone-stock carbed truck. It was an exercise in futility. Economy comes with less displacement and/or diesel, but even displacement has little effect when the platform requires a lot of power to move at highway speed. From folks that had the 5.7L Olds diesel that worked, 25MPG freeway without OD in a 3500lb car was good.

Vortec heads, roller rockers, retrofit roller cam, EGR, TPI, 3.42/33's, manual trans, 5500lb truck, still 16MPG highway. A 10% increase over an old school 305 or 350 (I ran both) would have been noticeable, and in my eyes expected, but it didn't happen. And that's with similar displacement.

Trying cheap fixes isn't really a waste of money, not like enabling EGR is going to be a real expensive attempt.

 

[80' 427]

I know 25 is unrealistic but a girl can dream.

Eigth now I drive a 8.1 so even 18s is better.

I know I could do it with a small block but I am trying to remove that kind of negative thinking from my fleet.

 

[diesel4me]

Back when engines still had high compression ratios factory,gas mileage and performance both were better...in the 60's many had 10 to 12:1 compression,and we had 100+ octane at the pump...
I recall more than one 375 HP 327's in some muscle cars friends had getting 20 mpg if driven like grandpa--but they could still roast the tires in all 4 gears..

When 1970 came and went,so did high compression ratios,then the fuel went to crap...the dark ages of "emissions" reached a low point around 1975 when they started adding catalitic converters,and all kinds of pollution controls,air pumps,EGR,fu-fu valves and retarted timing,etc.....things improved some since with computers and EFI,but we're still stuck with 8:1 compression ratios...

 

[dyeager535]

things improved some since with computers and EFI,but we're still stuck with 8:1 compression ratios...

What's stuck at 8:1? My car is ~10.5:1 on 87 octane, the truck is 9:1 on 87, and I believe some of the direct injection stuff is even higher on 87 octane. Looks like 2015 5.3L trucks are 11:1.

 

[diesel4me]

I was referring to stock 1970's vintage engines that came in square bodies and cars...I'll admit I'm about clueless when it comes to any engines built after the 90's...