I'm about to resurrect my '71 SS454 El Camino project after it's languished for 5 years. I had the engine rebuilt years ago but now I'm thinking about changing the design requirements to include regular to daily driving. My objective is to build an engine that will run on regular fuel and get the BEST possible fuel economy, say greater than 18mpg.

What I'm starting with is a mid-70's 454 block that has flat-top pistons and some early closed chambered heads.

I want to use the stock 3:31 rear with a 700R4 trans and a quadrajet "style" carburetor. Even though I know headers would yield better economy, I prefer to stay with exhaust manifolds.

I'm guessing I need open-chamber heads to lower compression ratio. I know velocity is critical to VE, but don't know whether to seek out "peanut-port" heads or just the standard 781's. I also believe that cam selection is dependent making the head choice.

All opinions and feedback are welcome.

Alan, check out the mpg thread. With flattops, SHAVED closed chamber heads might get you 9.5-9.7:1. For economy, you want some compression, and 9.5 would be fine.

BTW, large port heads DO NOT seem to affect economy, although its not clear. Hopefully the old heads you have are ovals. Use 'em.

Also, you don't need a 'miser' cam to get economy, just a miser foot. Big James runs the old UD 280/88 , now Lunati and get 20 mpg. Jake Shoemake also runs a rat in the 20 mpg range.

Alot of good combos in that thread. IMHO 3.31 or 3.42s and a 700R4 are just a match made in heaven!

Check out BigJames4XL's Big Block El Camino combo. There are lots of Big Block cars getting excellent mileage. The secret is that they already make lots of low-end torque, so they can take advantage of numerically lower rear gears.

I'm getting excellent mileage with my small block, but I've since learned that I could do as well or better with a big block and taller gears.

Who is it with the 12-second car with a 2.73 pegleg? He gets impressive mileage too, as well as many other big block Chevelles.

Build for moderate compression, pick a cam to match, and don't be afraid to use plenty of vacuum advance. My mileage can vary as much as 5 mpg just by freeing up vs. restricting the vacuum advance. Just don't let it detonate and you're fine.

The bone stock big block in our 69 Vette with Q-jet and 3.31 gear gets 16-19 mpg as long as I stay out of the secondaries.

Still runs high 13's in the qrt. even with very conservitive launchs from the tree.

I bet with a modern cam grind and HEI tuning (I'm still running stock points dist.) 20 MPG and high 12's should be doable.

Dwayne

Alan, I sent you an email.

Is 9.5:1 compression is too high for regular fuel, dependent upon cam selection? Would the marginal increase in economy for higher compression offset the increased price per gallon of fuel?

Purs...I apologize for not updating my email address in my profile. Would you send the email again?

Thanks for the replies.

Did you get it this time? graemlins/thumbsup.gif

Originally posted by Alan F:
Is 9.5:1 compression is too high for regular fuel, dependent upon cam selection? Would the marginal increase in economy for higher compression offset the increased price per gallon of fuel? You can run the higher CR's if you can cool the fuel enough to get it that compressed.

Stick with a stock torque convertor if you want mileage...

Chris is the guy who's ride ran 12.XX with 273s. But I don't think you'll duplicate that unless you sport the same high DCR Chris does. And the assumption there is that higher DCR makes more pwoer and has a higher VE which equates to good mpg at a steady , low , rpm. Anyway, engines like Chris's or mine cannot live on 87/89. No way. You will give up mpg by shooting for a 87/89 octane-friendly DCR, like 7.5-7.8. With the better quench of the closed chamber heads, I think I'd shoot for 7.75 dynamic and HOPE its 89 friendly.

I am also interested in this info. It seems like if the 700R4 uses a lockup converter, stall speed would be irrelevant to cruise mpg, as it would be locked. Until high gear is reached, a loose converter wuold perform the same as it would on a TH400. My 427 700R4 with a 2,500 lockup converter, 3.31 gears, Q-jet and headers with an unknown hydraulic cam in the .540 lift range and a set of 236 peanut ports got 18 mpg at 70 mph with the a/c running!

Imho, you will get better gas mileage by ditching the automatic tranny and hunting up an OD four speed stick combo.!!

I say this b/c a Buddy of mine had a slant-6 Duster once that had an automatic with automatic highway gears, so he ditched the 904 auto and put in the old OD four speed conversion they had back then and ended up getting like 30 mpg on the road easy!!

I have thought about this really hard b/c they put the same MOPAR OD four speed stick tranny behind GM diesel truck motors so I think?? the bellhousing will fit our SB and BB motors??

Just food for thought is all...

AND they also made Ford OD four speed Top-Loader "RUG" tranny's too....

I went so far as looked into a custom Lakewood bellhousing conversion for the Top-Loader tranny and all the stuff is available to put one behind our motors and at not all that bad a final price..

pdq67

If you're real serious about gas mileage, put a 396/427 crank in it to reduce the cubes (and/or a 396 block too), peanut port heads, 325 hp 396 cam (REAL mild), low tension rings, Qjet carb, OD trans with lockup conv, and 2.56 rear. Ignition curve must be optimized and electronic trigger with MSD or hot coil. It'll be a slug but a real gas sipper and still look like a stock 454. Also front drum brakes have less drag than discs and put the tailgate down. Set the toe-in at 0 and put 40 psi in the tires. :D Almost forgot, use synthetic 0-W-20 oil and cut the oil pump relief spring to reduce oil pressure and pump resistance (well maybe not).

Note the above post was not entirely in jest. Though that would be taking it to the extreme, any one of the items mentioned would help mileage if also used to a lesser degree such as: 3.07 rear gear, 70 series tires instead of 60 or 50, 32 or 35 psi in tires, synthetic oil and rear lube, mild cam, OD trans, etc.