boogerschnot

I am really trying to save some gas here.. I love driving my car everyday, but want to see what I can do to lean it out a little..

-Timing? Im running 12* initial right now and I do seem t have a little harder time starting her up when she is hot.. Im thinking I can drop it down a couple of degrees and then maybe tune it again to get the highest vaccume (that allways makes it run great). Does timing have much effect on the mileage?

-Carb? I still smell a good bit of gas in the exhaust and have tried to tune lean it out a couple of times.. Is that going to come along with higher timing? Just like I asked above?

I drive about 11 miles each way for work on the freeway everyday and thats about it, we take the wife's car everywhere else.. in four days I burn about 1/4th tank.. So thats about 15-16 miles per gallon, Im guessing thats not too bad for a 351w but I think it could be better. Any suggestions?

boogerschnot

I feel bad about posting this now that I just read the other MPG post.. I still want to know more about the timing vs mileage thing though.. Whats better for mileage, more or less timing with regular octane gas?

1971mach1

Actually 15-16mpg for a 351 is pretty good. 11 miles on the hiway is really not much hiway, and you have to warm it up and accelerate to get there, so that's really concidered city milage, not hiway. I'm only getting about 15-16 around town with my 2007 5.7L Hemi Magnum.

MBDiagMan

Very generally speaking, the more timing advance you can add, the more fuel efficient it will be. What you must remember though is that there is a point where engine destroying preignition will occur. You can advance it as much as possible without causing preignition. Using higher octane fuel will let you add more timing, but of course, then the fuel is more expensive.

Also the timing relates to the fuel/air mixture. If the mixture is a little richer it will usually tolerate more advance, but then you have the richer mixture which costs fuel. These variables interact and it can get quite complex. Thtt's why modern cars have EFI which adjusts all this for you while drive.

Also along these lines the vacuum advance is VERY important. It adds timing when you're cruising. When the engine is under a light load, it will tolerate more ignition advance. The vacuum advance is strictly an economy device.

Starfury

Also, you don't set timing with a vacuum gauge. If you try to do that, you'll end up with an absurd amount of advance because more advance (to a point) means better efficiency when the engine isn't under a load. At idle, you can set the advance to 25* and it would idle great, but as soon as you take off it'll ping.

Timing advance should be set as high as you can get it without causing detonation.

Do you have a lopey cam? If so, you may consider plugging your vacuum advance into a manifold vacuum port. It takes a little playing with, but it could potentially help things.

boogerschnot

Im not timing with a vaccume guage, Im tuning the carb with it. I time it with the gun and then hook up my dwell tach and keep the idle at 700 while adjusting the fuel mixture to create the highest manifold vaccume I can. Im running an edlebrock performer cam (pretty mild) and a 2bbl stock intake and carb.. I havent used the vaccume guage since I changed out the broken brake booster.. Before I had tuned it with an unknown leaking booster so I was loosing vaccume causing my reading to make it a little rich..

im picking up a new timing gun and vaccume guage today so I can tune it up tonight.. We will see what happens I guess.

htwheelz67

booger, get rid of that 2v carb and intake and install a performer and small cfm 4bbl, a 600 perfomer or holley will be fine but a 525 road demon (annular boosters) which really flows about 600-625 the annular boosters really add low end and throttle response its like having efi in a carb but more overall power, thats why the 4100 carbs are so good (annular boosters) but not much tunability, timing should be 10-14 initial, you can have your dist recurved as well, if you dont have one a good hi output elec ignition (multispark) will allow you to open plugs to 55-65 which will further improve low end and fuel economy, with your rear gears and the above you should be able to pull 20 mpg's hwy easily. Dont even bother with the cast 4v intake, its no better than your 2v. As far as economy the more low end you can make the better mileage you will get, hence why diesels get such good mileage........add overdive and you will really see an increase. My 500 hp 408 gets 18 mpg hwy BUT if I race it around I get about 8mpg's. adding the perfomer int and 4bbl will make your cam work like it was designed to, its basically a low end/fuel economy cam (great for trucks) and it was designed to be used with the performer intake, if you wanted more power the rpm would work too, the stealth would pobably work better than the others, professional products makes a typhoon intake, a stealth copy that can be had for a little over 100.00, summit racings intake is the same. Adding a good int/carb combo will add 20-30hp/tq over your 2v and more mpg's in normal driving, the biggest problem is when you have all that extra power you will want to push the pedal down more..........

MBDiagMan

And so how many miles will he have to drive to experience enough gas savings to pay for all these mods?

htwheelz67

the mods arent just for mileage.

Carlos Pineiro

This is a well stated point. Assuming that drivers don't wnat to improve MPG for environmental reasons, and are doing it to save cash, the cost of any mods to save gas should be considered. However, if the gas saving mods also improve performance or even cosmetics, then the value would be justified.

htwheelz67: 18 MPG with a 500hp 408? Wow. That's impressive. Tall gears? Tall tires? Drive downhill a lot? LOL, j/k. EFI or carb? How do you get those numbers? I get 15 mpg highway on a stock 302 motor w/650 4v avs and a 3.50 rear. Timing is at 16°, and idle is pretty lean; it never gets cold here.

CP