[63pig]

I agree with 4004spdta...

I just spent the entire long weekend driving the guts out of my 1969 Pontiac GTO with a freshly rebuilt YS 400 and 3:55 gears...which gets, at best 14 MPG...that's if I drive it like a grandmother, which I don't.

I put over 300 miles on her, and gas here right now is about $4.91 US a gallon. My wife has a Honda...Honda's are girls cars...

[WCWhitey]

Uneasy, even if you are off by a couple of MPG, anything over 20 is good for these old cars. If you are getting close to 25 you are getting as good miliage as my 2000 Mercury Sable w/only 200 hp. My wife's Mitsu Outlander w/ 4 cyl is only rated at 18/26. I might have to look into a 462 T/A for a comuter vehicle. Efficiency and power are not mutually exclusive. LOL Bill

[uneasyrider]

Originally Posted by WCWhitey

...I might have to look into a 462 T/A for a comuter vehicle. Efficiency and power are not mutually exclusive. LOL Bill

I tell you what, I'm still scratching my head on this one. From an engineering standpoint I agree with the last statement because the more efficient the engine "generally" the better power/cid. BUT dang it there are lots of other factors in the equation and it's out of place/odd/throws me off balance! I drove like a grandma but at the speed limit which was an average of 60mph, as a rough estimate, for the trip and it did take about 2hrs. As I said I only passed once and that was the first time durning the trip the gas gauge dropped from fill up! I bet I used the greatest portion of the gas right there in that pass not the last 50 or so miles! The thing is that it's a simple formula and if you have a good idea of your miles and you know what you put in for gas you just can't go wrong. My 1993 Toyota PU 5-spd gets 31mpg on the highway at 70mph and it weighs 3,500lbs which is a little less than my TA. I would guess the aerodynamics at 70 are not a major factor but the Toyota is something like 132cid and about 120hp and the TA is 330cid bigger and guessing about 380hp more! I'm at a loss but I'm NOT complaning. The only logical answer is that those little primaries combined with the tall gears just make for good mileage if you keep your foot out of it. I really mean this, if any of you are up here we can go for a ride and I'll try it again. I plan on going out and doing another test and having someone follow me so I can get a good odometer reading and also compare the milage between the two vehicals. I jammed the linkage in 1st gear on Sat. so I can't go out and do it right away like I wanted to. That dang stock linkage gave us trouble way back in the '80's when my buddy owned the car. It seemed like every other week the dang thing had him stranded or he was driving home from some place in 1st or 2nd. I need to get a new shifter. It's all just money, right? Will it ever quit spilling out of my pockets and into the car?

[WCWhitey]

Remember the old vacuum guages that would tell you "Economy" or "Performance". I wounder if one actually paid attention to that if a signifigant improvement could be seen. I do not use the 66 as a daily driver so economy is not the biggest concern but for the same reason I went low on the compression is the gas situation does have me concerned. Every few MPG's that is saved on a cruise or short trip is left for when the need to get aggressive arises. Less gas, more money for parts and more time spent driving. Bill

[uneasyrider]

Originally Posted by WCWhitey

Remember the old vacuum guages that would tell you "Economy" or "Performance". I wounder if one actually paid attention to that if a signifigant improvement could be seen. I do not use the 66 as a daily driver so economy is not the biggest concern but for the same reason I went low on the compression is the gas situation does have me concerned. Every few MPG's that is saved on a cruise or short trip is left for when the need to get aggressive arises. Less gas, more money for parts and more time spent driving. Bill

EXACTLY, I sacrifice performance in off the line/quarter mile time but I gain a ton in milage and money saved driving it IF I keep my foot out of it. Even if I don't it still doesn't drop to any worse mileage than the BEST mileage the same car with say 4.11:1 might get. The hard part is not stuffing my foot in it.

P.S. I forgot to say that I think those "Economy" gauges did work. All they really did though was tell you when you had your foot in it and when you didn't off of manifold vacuum. I remember our friends Laguna had one on it. That was a cool car, I really like that body style.

[uneasyrider]

Here's an update. I went out today and got more accurate about the whole process and found I' getting 19-20mpg NOT 28mpg. I found that the point I filled my car to last time WASN'T all it could hould. This time I really made sure I got it topped off. I was also doing 70mph not 60-65mph but I don't think the higher speed was the major factor it was the 2gals of gas I found I could still cram in there. It will look like it's close to as full as it can get and couldn't hold more than a few cups more BUT it will take about two gallons more if you carfully fill it. The first time I filled up on that first run I must have been more careful than on the second fill. Not that 19 or 20 is horrible but it isn't 28-30. Ooops. At least that explains the error. It's a straight forward calc. but the data has to be correct.

[b-man]

Uh huh.

19-20 sounds realisitic, 28 no way.

Same pump.

Same station.

Same top-off technique.

Now it's time to calibrate the odometer.

[uneasyrider]

Yep, I had someone follow me this time and used that trip odometer. It was a Subaru Legacy wagon still on stock size tires and original rims and we checked it for 10miles against the mile markers just to be sure the factory wasn't off too much. A bit retentive but that way the error was only in the fill up which can still be a big one if your not careful. That dang fuel tank is strange. You'll fill it up into the neck and it will go back down and set there a few inches down in the neck so you think that's all it will do BUT NO. If you are real careful you can set and add about two more gallons after that and then it sets right in the top of the neck and DOESN'T go down. I got to thinking about it when I was filling up and I did that at the first fill up last time but not at the second thinking it couldn't hold more than a few cups more. I need to get my speed'o fixed, I need to figure out the right gear to put on there. It's 20% off on the button right now.

[marauder]

You guys are getting much better mileage than me even with the 700R4 overdrive tranny I recently installed.

I averaged 9 mpg in town over 8 tankfulls with the turbo 400 and now with the OD I'm seeing about 11.5 mpg for an improvement of around 25% however that mileage still sucks! I'd do backflips for 15mpg!

Now I've got a stock 400, Q-jet, super mild cam and 3:42 gears. I'm planning on going with the P-Dude roller cam and some ported 6X heads and intake however I can't imagine getting worse fuel economy. I know that Q-jet needs a rebuild and I'm hoping its the culprit.

[bobzdar]

Run lots of timing and lean primary jetting.

I get 19-20mpg highway in my '78 t/a. st-10 4 speed, 3.23 gears, 6x-8 headed 400, 744 cam, quadrajet on a Torker 1 intake, 1 5/8" 4 tubes through 2.5" dual exhaust. I run 38 total timing (gives best mph in 1/4) all in by 2400rpm with full manifold vacuum. At 2700rpm cruise (or around 70mph with 255/60/15 tires) I have over 50 degrees of timing and I barely have to press the gas to maintain speed. My carb has stock (lean) primary jetting with the secondary metering rods changed to give best mph in 1/4 (around .050" tip size, maybe CE rods? can't remember). This probably doesn't result in the best mixture distribution, but with the open plenum of the T1 it's probably decent under higher rpm WOT, which is all I really care about. I'm not running enough compression for the lean jetting or timing to cause any sort of heat/detonation problems, so probably get better mileage than what a 9.5 or 10:1 engine would be capable of using pump gas, and can do so on 87 octane.

If you're running an auto with a non-lockup torque converter, even with overdrive I'd say you'd be doing good to get 16-17mpg. With an o/d manual trans (or 2.73 gears) you could see 21-22mpg. Auto with lockup t/c and o/d could probably get similar 19-20mpg as my non o/d manual.

Keep in mind a 4.21" stroke engine will have more internal friction and therefore be less efficient than a 3.75" stroke engine. Probably a 1-2mpg difference even with lower gearing proportional to the displacement increase.

[bobzdar]

Marauder, what are your timing specs (specificall total timing and rpm it comes in at, full manifold or ported vacuum advance and how much)?

[marauder]

You may be on to something with the timing. I have it backed off now because I was concerned I might have too much compression with the lame 204/214 deg (or something like that) cam and stock 62 heads with the decked block. I'll throw a light on it in the next couple days and see.

Oh yeah, I've got a B&M Holeshot 2400 lockup converter. I did the exhaust with the 2-1/2" RARE exhaust manifolds with 2-1/2" pipes and x-pipe so it should be breathing OK.

I've got a '96 Z71 with a Rancho 4" lift and 33" tires that only gets 12 mpg around town as well so gas is just killing me these days!

[455earlybird]

My Firebird is my economy vehicle as it gets around 12 mpg average if I stay out of it. My everyday E-350 5.4 liter 4:10 rearend , weighing 8800 lbs loaded, gets 8.5 mpg (to be honest I don't stay out of it though) however I don't think it matters, as I get the same numbers pulling a trailer. By the way the only way to get an acurrate average mpg is to run at least 2 or 3 tanks of gas through it with an acurate speedometer. There is simply way to much room for error only running a 1/4 tank out.

[birdman87]

my best mileage car is my 68 Lemans. It will get 20-25, whether im nice to it or not. Its a mostly stock 350, 4 barrel, performer intake, th 350 w/ a 2.73 rear...

[Billy177]

a 120 mile drive would use almost my entire tank

[BVR421]

Originally Posted by uneasyrider

The speed'o is off so my odometer isn't correct so I got the milage two ways. I went on line to a site that will calculate the miles between cities AND I got out the map and the dividers and did it the old fashioned way and came up within about 10miles difference so I averaged them.

nice try but no dice, maps calculate city to city beween zip codes and post offices
never the less you are obviously getting great mileage which indicates a great job on the tuneup

[roadrage david]

Uneasy rider good job iven if you where off by a couple of miles it would still be awesome.. de 462 formula video that you saw resendly where we tested the tr2004r transmission. saved 30 liters of fuel on a 250 kilometer trip now i dont know how mutch that is converted in miles and gallons, but overhere our gasoline is 100% more ecspensife then in the usa. the car hase a 3.42 rear ratio and a 0.67 overdrive...............