[Overkillphil]

I agree on the "a lot less fuel". I see posts all over the internet referring to 10% or so fuel savings with an OD yet my experiences have been much higher. A 1/5-1/3 improvement in mileage is not unusual.

[leeklm]

Originally Posted by Overkillphil

I agree on the "a lot less fuel". I see posts all over the internet referring to 10% or so fuel savings with an OD yet my experiences have been much higher. A 1/5-1/3 improvement in mileage is not unusual.

I like fuel savings as much as the next guy, which is good for our wallets and the environment. I also see people getting a little carried away thinking they will recoup their upfront investment on fuel savings alone. This goes for hybrid cars, gear splitters, OD trannies, etc.

Just doing a little basic math, let's say the car gets 12mpg with no OD. We spend roughly $2k for a gear splitter and see a 30% increase in mpg to 15.6mpg. If you put on 5,000 miles per year and pay $4/gal in fuel, your annual savings is about $380, so your gear splitter is paid for in about 4-5 years, assuming the money invested was not gaining dollars in a mutual fund, or was not put towards saving some money on your mortgage, etc.

Obviously there are other advantages towards drivability of turning fewer rpm, but just looking at mpg savings here.

In my case, the savings would only be $200 per year since my annual mileage is very limited during our 3 months of summer. In the meantime, I drive my 4 cyl Malibu that sees a consistent 30mpg.

I was using the MPG numbers to my advantage back in about 2004 when convincing my wife to purchase our new Duramax. At the time, Diesel was cheaper than gas, and with the improved mpg, the annual savings was over $1,000. Seemed like a no-brainer to me, with lots of power to boot!

[spb350]

I guess what I like the most about the 2:56's is that I spend most of my seat time just cruising and the gearing seems to be perfect for that. I built my car as a nice driver to be enjoyed as much as possible and getting 9 -10 mpg is going to limit my driving it to conserve fuel.

[zeebo]

i think its funny that now that the tables have turned and everyone is clamoring for the hi way gears that yesteryear we just pitched for a set of 4.11's--now we all want the 3.23 or numerically higher gears and are pitching the 4.11's...lol years ago you couldnt give for scrap a rear end with anything less that a 3.23 or 3.42 ratio---now even on epay the hi way gears are commanding a big premium over the race gears--especially since many of the ratios have been discontinued. example: i have a 2.23 ring and pinion from a 79 seville and a 2.14 ring and pinion from a mid 80s cutlass that i snagged years ago from a now closed junkyard..thats right..a 2.14..no typo..not a 2.41.....they also had 2.29 ratios in those cars too..with overdrive..lol..you can go 90mph at 1400rpm...hee hee!

[geeteeohguy]

When I put the 2.56 rear in my '67 GTO ragtop (originally 3.36) it changed the car. The car has always been my 'cruiser' car (my '65 hardtop is my hotrod) and now that it cruises effortlessly at obscenely high speeds, it is more fun to drive than ever. Getting over 20mpg at 75-80 mph, I've taken to driving it on long road trips, sometimes 1000 miles in a long weekend out of town. Engine noise is way down, temperatures are way down, and fuel economy and road speed are way up. I can cruise in style and keep up with traffic now. Ideally, with my TH400/400 engine, a 2.93 would be optimum for quickness and top end, but the 2.56 posi was given to me, so that's what I'm running. I can't imagine putting the 3.36 back in, and going down to a 65mph cruise speed at 15mpg.

[spb350]

"and now that it cruises effortlessly at obscenely high speeds, it is more fun to drive than ever. Getting over 20mpg at 75-80 mph, I've taken to driving it on long road trips, sometimes 1000 miles in a long weekend out of town. Engine noise is way down, temperatures are way down, and fuel economy and road speed are way up. I can cruise in style and keep up with traffic now. [/QUOTE]

Today I got on a hwy-on-ramp and I was doing 90 (3000+ rpm's) before I knew it, and, with a completely new suspension it felt pretty good for 1969 technology. I wonder how fast it would go? theoretically any guesses?.

400hp + M20 + 2:56's + ? = *** mph

[The Champ]

^

With 27" tall tires that would be 156.9MPH at 5,000 RPM.

[goatwgn]

"Feeling my oats" the other day, I followed a new Mercedes around a curved road (Very long exit/entrance on ramp that joins an Interstate to a limited access highway/bypass). The Mercedes guy was being a little bit of a smart alec, and he gunned it going around the curves, and stayed at 60 mph through the turn. I have a tight front end, hydroboost, and quick ratio power steering, with 70 series 15 inch tires. I have to admit it was a little hairy following the Mercedes around the turns there with their 19 inch wheels and low profilel tires. But when the road straightened out after the end of the ramp, I blew by him like he was standing still, engine didnt break a sweat, because of the gearing. (of course, when I backed off he gave me the "high speed driveby", but I proved my point already lol. I even had the AC on. I am even considering going to a 3.08 gear in the back with my GV, just for even more comfortable cruising. Speed limits (and the speeds people actually travel at) are going up all the time.

[importsmasher]

About 10 years ago, I blew up the original 3.55 posi in my 66 GTO. Needing to get it back on the road, I put in the only axle I had available...a 2.73 out of a 71 Skylark. I HATED it with the 4 speed. The car didn't feel like a muscle car anymore. Sure, it would cruise down the freeway at low rpms, but it felt so sluggish off the line, it just wasn't fun to drive anymore. Fortunately, a couple of months later, I scored a 3.23 open rear from a 66 Cutlass (for free) and that is what is in the car now. Someday I will rebuild the original housing and have a 3.55 posi back in it....

My 67 full size wagon came from the factory with a 2.56 rear. It would rip down the highway. I put a 2.73 out of a GP parts car in it for a while (cause it was free, and gave a little better acceleration than the 2.56), and then I put a 3.23 in it when I converted it to a 4 speed. I wouldn't want to drive one of these cars with a 4 speed and anything numerically lower than a 3.23. I don't have a problem running 3500 rpm down the highway. I don't do a lot of long-distance highway driving, but when I moved to Utah, I drove my GTO 75 mph all the way.

For me, gas mileage is not my biggest concern. These cars were intended to accelerate, and that is what they do best. If I need fuel economy, I'll drive the wife's 05 Mustang. For me, these cars are about smiles per gallon, not miles per gallon.

That said, I would be a big fan of overdrive transmissions, if I could afford them....

Just my opinion....

Importsmasher

[spb350]

I wonder how fast it would go? theoretically any guesses?.

400hp + M20 + 2:56's + 225/70/14's = *** mph

[spb350]

Originally Posted by The Champ

^

With 27" tall tires that would be 156.9MPH at 5,000 RPM.

The suspension feels real good........ but not that good.

[Jerry H.]

If anyone is interested I've got a housing with 2.56 gears that I took out of a 65 GTO about 20 years ago that has been laying in the floor of my shop. Yours FREE as long as you come to Georgia to pick it up.

[Skip Fix]

My old stock 400 in the 78 would only pull 4000 in high gear with the 2.56s. Not sure now much HP to pull to say 5500 or 6000 in a 3800 lbers

[The Champ]

Originally Posted by spb350

I wonder how fast it would go? theoretically any guesses?.

400hp + M20 + 2:56's + 225/70/14's = *** mph

If you can get to 5,000 RPM - 153.5MPH

[spb350]

Originally Posted by The Champ

If you can get to 5,000 RPM - 153.5MPH

I don't think I'll try, I think my BFG's are only rated to about 120 mph. Maybe I'll run it up to 120 one of these days to see how it feels.

[Will]

Originally Posted by spb350

I don't think I'll try, I think my BFG's are only rated to about 120 mph. Maybe I'll run it up to 120 one of these days to see how it feels.

BFG Radial TA? 'S' speed rating? = 112mph.

[chrisp]

Take it to the Salt flats .

[The Champ]

Originally Posted by spb350

I don't think I'll try, I think my BFG's are only rated to about 120 mph. Maybe I'll run it up to 120 one of these days to see how it feels.

Speed rating testing is for 10 minutes at the stated speeds.

Are you planning to drive for more than 10 minutes flat out?

That said, in Germany, they require the tires for a car be rated per the max speed of the vehicle. Why? Because in Germany there is no speed limit on the autobahn.

I grew up when we all were running bias ply tires that didn't even have any speed ratings. Been north of 120MPH many times, but not for extended periods. I did manage 130+MPH for a longer period of time while stationed over in Germany back in the mid 70's.

[1967Tempest]

I made an OK video with the car, but Youtube muted it because apparently Led Zeppellin was on the radio. I will set up a two camera video and reshoot one this weekend.

Dave

[gtofreek]

Originally Posted by 1967Tempest

I made an OK video with the car, but Youtube muted it because apparently Led Zeppellin was on the radio. I will set up a two camera video and reshoot one this weekend.

Dave

Oh, that's ridiculous! They muted it because Zepplin was playing. What next? They delete a video because you can see a Snickers wrapper on the ground?