318 Gas mileage?

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Sinister.

Sinister.

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I'm just curious what kind of gas mileage people are getting, and what I should be getting with my 318.

Std bore, mild cam, aluminum intake, holley 4 bbl (vac 2nds), headers, dual exhaust
727 trans
7 1/4 with 2.76s

I've calculated 6-7mpg time and time again.... Should i be getting more?

Any simple tips to improve mileage?
 
It's hard to say what you SHOULD get. It's more what someone could get. With properly matched parts (you dont really say what size of anything there...) and the geraing I can't see why you should be getting less than 20 on the highway, 12-15 mixed driving. But you need to have it tuned properly and the parts working together.
 
Carb is 650 cfm Holley 4bbl vac secondaries. I think I've got it jetted at 58 front or so. Intake is Edelbrock s2p2. Cam is a Crane 268 cam. I think it's something like 268/268 and .444/.444 or something close to that if I remember right.
 
My 318 consists of near stock compression, XE268 cam (.477/.480 lift), 318 heads, Performer intake, 4160 600 cfm Holley with 70 front jets, headers, dual 2.5" exhaust, 904 with shift kit and 2500 stall, 3.21 gears.

Normally gets 12-14 mixed milage (50/50) and 18-20 on all hwy driving.

Its got to be tuned, jetted, and timed properly.
 
what do you guys think it should be jetted to and what timing?
 
I think you should be getting more MPG's. The cam isn't to large. I'm not a fan of that intake though. I'd perfurr a Performer myself, but that's netier here or there right now is it?

Try moving the intal to 15* and limit the total advance to 32*'s.
How's the plugs? Black?

Mileage getters are;

Headers, but they suck on the first bump, but still help.
Your dual exhaust should be 2-1/4. An H or X pipe would help and muffler choice isn't so critical.
And MSD or equal like the Mallory 6 box or Summit racings multi spark box.
Wide plug ga. You could go to .050.
How tall are your tires?

Oh, my 318 with a Crane 216/228-.454/.480 with headers w/2-1/2 jegs exhaust, LD4B, Carter 625, MP resto unsilenced air cleaner, and a orange box fired ignition is getting 17 - 18 Hwy, 13ish around town.
3.21 gears w/225/70/14 tires. And a 904 lock up tranny.
 
Something is wrong here… I think you would need to be trying to get bad mpgs to pull off only 6-7…

This may sound backwards but you may want a gear change… With the 2.76s you probably need to really lay on it all the time to "feel" any power. Foot to the floor = mpgs in the toilet.

If you changed to a 3 something you would be using much less throttle.
 
Get the engine spinning in the peak torque area where it becomes more efficent.
 
yeah something doesn't sound right

before i parked my 66 charger with a mildly worked 440 and 3.55's?

i got 3-8 mpg strickly city driving and i drove it to enjoy it a little too often :)
 
to the OP:
remember, when i comes to carbs. to lean is often worse then to rich. and will show the same symptoms of a rich running carb.
what do your plugs look like?
 
My guess is two things: timing and jetting. Get as much initial into it as you can, something like 16 degrees, and check the base line jetting in the carb, put in the stock size jets. If its a holley make sure you have the stock value power valve in it. Your mileage with that set up should be at least 18mpg or better.
 
Crane 268 cam.
Click to expand...

Too big for MPG with 2.76 gears, your not making enough vacuum, I bet.
Holley thing too.......
The SP2P should do better than a performer, the best MPG manifold is the Offey dual port tho. I had a magnum, with a 440, with 2.7something gears, it got about 22 HWY with a smooth idling 440, the same car with a 318 I bet would have gotten 14. Gotta lower the gears with the smaller motors.

I had a 69 D200 getting over 20 on the highway, for a box, with 31-12.50's on the back, I thought it was pretty good.

It was a 318, 727, 3.55 D60, Dual port, EB600, stock points igntion, 252 comp cam, decked block, port matched, and I tuned the carb with a O2 sensor.

Sometimes mileage just needs some tuning.

And as said before, lean is worse than rich, I had a friend who thought he was a mechanic, and was running a ol 625afb on his 318, he leaned it to the point it had a lean miss inless it was under slight acceleration........

7mpg at best. LOL
 
Something is definitely wrong. My 360 with a much bigger cam and 750 Holley and 3:55 gears get 10-11 in town and 14 on the road. There are alot of good suggestions here. Dial in the timing curve and make sure you use the vacuum advance. Read the plugs and jet the carb as needed. Also the gears may be loading the teen too much and causing worse gas mileage in town. But usually down the hwy they don't hurt it.
 
Sparkplugs looked pretty good. Not black at all. Initial timing is at 12 degrees last I knew. And I actually think the front jets are closer to 62. I won't get some time to tinker until this weekend, but I'll definitely have somethings to look at!
 
276 gears are OK, I have a set to throw in whenever I take a long trip. Don't like the manifold at all, but the problem is probably the Holley. Is the choke open all the way, and does it stay there?
 
Sinister. said:
Sparkplugs looked pretty good. Not black at all. Initial timing is at 12 degrees last I knew. And I actually think the front jets are closer to 62. I won't get some time to tinker until this weekend, but I'll definitely have somethings to look at!
Click to expand...

Is that for sure a 650 Holley? If so it must be the spread bore model. 62 jets are pretty big for the front of it because of the small front barrels. I had one on a nearly stock engine and had to run 58 jets. Now if your talking about the Holley list 1850 that's a 600 cfm carb and 62 jets are pretty close for it.
 
I think you need to work on the timing curve. Not just initial, but the whole thing. What rpm does it idle at?
 
This has become the least of my concerns....

Unfortunately my tranny went out this afternoon..
 
Bad tranny will kill MPG like nothing else! Hopefully, that was most of your problem.
 
It's weird because it has never acted up....

I've got a post in 'transmission and drivetrain tech' if you guys could help diagnose the problem :)
 
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