[pontiac 455ho]

Blued and painted this 301 is not a slug it has power. Like a 350. Will burn the rubber from a light no water. On primary throttle. What woke it up was the can change. And quicker timing no cat .

[Cliff R]

Posi-traction or one wheel burnouts? I've never seen a 301 that would roast both back tires on the street from a dead stop, that would be impressive.....Cliff

[Blued and Painted]

Originally Posted by Ben M.

My '78 Bonneville with a 400 would get 21 on the freeway and 14 in town.

Looks like im not the only one.

Es car go.

[pontiac 455ho]

Open diff but still not bad for a 301 even does dounts and has a great deep sound. Plus a nice deaccel scavenge gonna go out and rich ing the carb and see if it help.with less throttle

[pontiac 455ho]

OK the I put In a 7hg light blue pp spring. And took out the k. Rods.put in cliff 44 custom rods . it now. Takes even less throttle. And can get 16 hg in the city.

[Cliff R]

Good news. I've found the same thing over the years. Giving the engine more fuel at light part throttle results in less throttle angle to sustain any vehicle speed, so we see a decrease in fuel consumption. 10 to 16 is a big jump, hopefully it woln't hurt fuel economy on the highway, or at least result in better overall fuel economy for combined city/highway driving.....Cliff

[pontiac 455ho]

Less mpg from the richer cruise mixture . and under accel it no longer goes to zero hg but under 7 to 5. Could have used the 5hg spring to keep it down under light throttle. And if I loose mpg what rod would ideal for my 301

[Cliff R]

Where is the APT set at currently?

Where was it set with the 49K metering rods?....Cliff

[pontiac 455ho]

With the k rods apt was set at 2.5 it is still 2.5 turns. Runs flawless .with the krods I got 21 mpg on the highway

[Cliff R]

There wouldn't be much difference in A/F from 49K's 2.5 turns up with the APT and 44 rods at 2.5 turns. The 49K's would be around .045-.046" in the jets, the 44's still on the .044" section as they don't start the taper till further down on the rods.

If it's "flawless", that's what the engine wants for fuel delivery. I'd keep it as it is now, and do some testing over several tanks of fuel. It's really difficult to assess these things unless you drive many miles in various conditions and average everything out.

A slight head wind, slight change in actual MPH, DA, A/C on or off, not filling up at the same station, or not exactly the same stretch of road can effect economy just as easily as where the tune is at.

Way back in my "learning curve" days, I used to make 600mph runs between Ohio and Virginia when I was still on Active duty, filling up at the same stations, driving the same course, as close to the same speeds, etc, to evaluate these things. I did this with several different vehicles, and came up with the same results from all three of them when it comes to mechanical timing, vacuum advance, jet/rod combinations, and APT setting(s).

Anytime I tried to really lean things out at light/part throttle, fuel economy only improved on flat ground at very light load, and if I drove like there was an egg I didn't want to break under the gas pedal. For all driving over various conditions, lean APT settings actual consumed more fuel, as the amount of throttle required to climb slight grades, change speeds frequently, etc, required more throttle angle than they would with a slightly richer A/F setting.

The fuel economy thing is also a product of physics. It is just going to take a given amount of BTU's to accomplish a given task.

These days fuel quality is a BIG contributing factor to fuel economy. With my Duramax diesel and my Tahoe, they see BIG swings in fuel economy different stations, and different seasons, depending on how much they "thin" out the fuel.

The Duramax would drop to as low as 14mpg's on Winter grade, and go up over 20mpg's on summer grade #2 diesel.

The Tahoe will see as much as 2mpg's between different brands of fuel, and nearly that much more going from 87-92 octane. Running the "piss" grade at the "no-name" store actually costs about the same as running 93 octane from a name brand store. Since it's pretty much a "wash" I go for the good stuff and reap the benefits of more power and don't worry about the 20-30 cents cost difference........Cliff

[pontiac 455ho]

Good Info. Used my digital caliper. The rod cameout to .046 wear it was riding. So only 2 points differnce . might put in the 5 hg spring to keep rods down at light accel. And try the .038 idle tubs for leaner idle during slow driving