JPhil

Greetings, all. I, too, have been quietly watching from the shore for a long time and finally decided to wade into these shark infested waters....I hope I won't become chum!
My car is a 73 L48 coupe. 1 owner, totally original, tired & arthritic, but overall very nice condition. Excellent potential!
Mine for 14 months now, suspension, brakes, & steering all new and upgraded, new exhaust system.
I was planning to stay 350", but my hot rod buddies have me 90% convinced to go 383". I like the idea: I like low end torque, I'm not comfortable with RPM (30 years of old Harleys & straight 6 Chevy trucks). So 383" is a no-brainer, right?
....Sigh...
I now believe $2+/gallon gas is only the beginning. My car is not a racer or sunny Sunday cruiser. Besides touring and late night county road running, 4-5 days a week, 9-10 months a year it'll do the 40+ mile round trip to work. And so fuel economy rears it's ugly head.
I know I know, then why did I buy this car? No doubt my buddies with their 502" Chevelles & Camaros enjoy their cars for the few hours a week they drive them. I'd like to enjoy mine every day. The 13 MPG I get now ( with it's whopping 135 RWHP) tends to lessen my enjoyment. I'm not seeking 30 MPG like my C5 aquaintances claim, but something closer to 20 would sure be nice.
Thus the question I would like to present before the collective experience of this forum:
In a comparison of similarly built engines, stroke being the main difference, would the greater torque of a 383 offset the fewer cubic inches of a 350 for fuel economy in typical street driving, or not?
I have already purchased most of the parts for my engine and believe all except perhaps the cam will work either way. This is what I'm working with: MSD/6A ignition, Edelbrock Pro-Flo RPM MPFI (1000 cfm),
AFR 180 cc / 74 cc chamber heads, CC 268HE cam (218* @ .050, .454", 110* LSA), CC valve train w/ roller chain & 1.5 full roller rockers, 10:1 HE pistons, OEM 5.7" rods, 1 5/8 full length headers into 2 1/2" w/ X-pipe, Magnaflow mufflers.
Car currently has OEM TH400 w/ 3.08 gears, but hopefully by next year will have a 200-4R w/ 3.55 or 3.73.
Apologies for going on so long, but many thanks in advance for your advice and comments, which have already helped me out greatly in my endeavors with my new project. I hope to be able to contribute in a worthwhile manner in the future.

JPhil

74 vert

Welcome to the Forum.

79MakoL82

In my opinion, the thing that is going to do the most for your fuel economy is the fuel injection. That should help the engine to be much more efficient. I also think the 383 is going to suck up more gas, but maybe with the MPFI, less than a carbed 350 but more than a MPFI 350. I'm just guessing on that one as I do not have real numbers to compare. Other things to consider for more fuel efficient driving is lower rear end ratio and OD tranny. The increase in torque of the 383 might help you go to a lower rear end gear, but then you're going to lose the torque you gained. The OD tranny would help at highway speeds to lower the RPM's and increase highway MPG, but would do little for around town. My experience is that my 1979 carb'ed L82 gets about 16 MPG highway. My carb'ed 1984 Z28 with 420HP 383 gets about 8-9 mpg. My guess is, you put MPFI on a 350, and you should be able to reach 20 mpg. I don't see it happening on my 383.

That's my $0.02

PatsLs1vette

welcome to the forum,great year also(73)With overdrive and fuel injection in the works you should be ok for fuel mileage.

stingr69

Welcome to the DB!

I like the combo overall but the cam is probably a little small. How about a Comp 280H Magnum. That would do the trick. You should get better mileage with a 350 but the 383 should not be a lot worse. Your current gas mileage sounds a little low so maybe a rebuild will help in that department.

Hope this helps.

-Mark.

Eddie 70

I love the 383 with MPFI route that you are going. That will be one nice set up when you get it all dialed in. That is the way I am going to take mine when it comes time to do it again. Some of the guys on here got 20+ MPG on BB's when they drove from Texas to Bowling Green Ky using MPFI. So I don't really see any reason you should not get close to that if most of your driving is HWY. Can't wait to hear your results.

bobs77vet

welcome, i'm going with a 350/350, 700r4, and 3.08 in my ride

i think you are right on the money, i did not do a stroker just because of the additional $$$$$ if you have the 3.08 why change it? put the extra $$$ into the stroker with the torque the 3.08 should be no problem and you have a friendly cruising machine.... i think you would even be ok with a nicely built 350 and the OD trans...check out the fuel economy thread theres a real wake up call.... ask me after thanksgiving when my swap is done and i'll give you all the particulars on mpg/hp etc....

bobs77vet

welcome, i'm going with a 350/350, 700r4, and 3.08 in my ride

i think you are right on the money, i did not do a stroker just because of the additional $$$$$ if you have the 3.08 why change it? put the extra $$$ into the stroker with the torque the 3.08 should be no problem and you have a friendly cruising machine.... i think you would even be ok with a nicely built 350 and the OD trans...check out the fuel economy thread theres a real wake up call.... ask me after thanksgiving when my swap is done and i'll give you all the particulars on mpg/hp etc....

vettenoir

Check out my signature for specs. I am using the C950 throttle body kit and got about 17mpg on a 200 mile round trip to the drag strip (Gas for down the track NOT included. )

This was at 3500rpm and ~75mph.

Bob

Solid LT1

You have to feed the incresed displacement with a 12-14:1 air fuel ratio, so a 383 WILL get poorer fuel mileage than a 350 engine (volume is volume, no way around that.) Properly camshafted, a carbed 383 can get 17-18MPG but the 350 will get 20MPG in the same state of tune. I don't think gas will be getting any cheaper, I am in the middle of building a Accel Super Ram 383 right now with a 3.08 and Richmond 5 speed. The cam is a Comp Cams XE hyraulic roller with 218@050 int/224@050 exhaust and lots of valve lift (560int/540exh.) My goal is 18-20MPG cruising mileage and I relly don't care about around town economy. I am fortunate enough to drive a company vehicle and don't have to worry about commute fuel mileage but am trying to convince my wife that she needs to start driving her 20+MPG Z06 to work instead of our 16MPG GMC truck (she won't drive the Z06 in the rain because it's too hard to keep clean if she does that!) I don't think we will see any $1.XX gas again!

73Roadster

Sounds like a good overall setup. I like your AFR heads and the 268H cam, a good combo together. I might check the intake vs. exaust ratio on that AFR head, I think it is at least 70% which, with the split grind cam is going to create some very strong cylinder pressures. If I may suggest going with some gapless rings and backing down on the compression to a 9.5 or 9 to 1 you will then be able to run it on street gas and take advantage of a aggressive timing curve of 20 advance in by 2500 rpms and stay with the 3.08 gears and
TH400 , your torque that you develop will do more than make up for the tall gears and WILL give you over 20 mpg. The TH200 is a really weak trans unless you want to put a few thousand bucks into it. I've done it before and it's alot of fun having the best of both worlds, power, and great gas mileage.