Frankie the Fink

Well my first decent length trip with the 5 speed in the '61 was 150 mile round trip 80% on the turnpike (from 60mph - 75mph) and 20% around town with a few spirited 'sprints'. The mileage (remember I have 2 4bbls) was 19.7 mpg...I'm pretty happy with that.

I have noticed the car is a little 'rougher' feeling in overdrive from about 60mph-70mph but the roads are SO bad around town lately I can't tell for sure if I have a vibration. It could possibly be (long shot) that the car is just different feeling at lower RPMs at speed (e.g. 1500-1900 RPM at interstate speeds). The flywheel and driveshaft were both balanced and the driveshaft angle is perfect.

Think I'll play with the tire pressure some and see if that solves it....

GCD1962

Frank - don't mean the jibe, but with $70k or so you have invested in the car you're worrying about gas mileage? My '62 with 350 LT-1 and mods gets about 14 1/2 or so at 70 mph, I don't care if it gets half that, I'll still drive it anywhere.

Frankie the Fink

Point taken....

It was a general comment for those considering a swap to a 5 speed.
I'm not worried about gas mileage; every time gas starts to creep up I just buy 500 shares of USO (United States Oil) and just 'rock on'....

MiguelsC2

Well said. A rise in efficiency is always something to be proud of.

AZDoug

What was it before?

Thanks,
Doug

Frankie the Fink

I don't have a clue at the 75-80mph range...never cruised at those speeds for long due to engine RPMs.

I did record 15.6 mpg at one point a year or so back...can't remember the particulars...I think I had to baby the snot out of the car to get that though...

vt65

i get about 12 mpg with my 383 stroker and it's as lean as i dare make it...oh well!

jdk971

1sttexan, looks like you are going to do well this summer. look at the price now of oil. and
the economy is still very slow. if the economy picks up and the dollar goes down watch out.
jim

firstgear

I have a 3.55 rear end and when I am in 5th gear (.68) around 60mph I get a vibration, but in 4th gear I never feel the vibration. If I push to 70-75mph in 5th, then it smooths out a bunch....what rear end do you have?

Frankie the Fink

That's pretty much the same thing I'm experiencing ... I have the 3.70 rear...maybe this is just the nature of the aftermarket overdrive.

I haven't tried pushing in the clutch or going to neutral when I feel this to see if that makes a difference...maybe I'll try that tomorrow...

Sounds like you have the TKO-500 and with a 3.55 rear you must have a crazy first gear, "firstgear"..

62Jeff

Frank search the forum, I thought this problem had come up a bunch on the 5 speeds.

Godholio

I generally get about 13-14 out of my 327/300. What surprised me is I did about a 90 minute cruise at 90-100 mph (did I say that out loud?) and I still got 13. 60 vs 90, same fuel economy.

Dan Hampton

I totally agree. I am always amazed at the extent to which people will strive for gas mileage, especially in specialty cars like older Corvettes. They are what they are. I won't even begin to disucss the cost/benefit analysis either.

I used to ice race a Mazda GTX (turbo/AWD). That car, which was racing at WOT most of the time, got in the neighborhood of 4.2 mpg. A C1/C2 at 12 mpg seemed like econo mileage after that.

Frankie the Fink

Folks...some people asked about the gas mileage with the 5 speed....I am NOT worrying about it. With the cost of the tranny swap I would have to get 152.7 mpg to break even in my lifetime...

wesmigletz

I like to see people improving the efficiency of their rides. For me the ability to cruise at a higher speed, with less engine noise, and greater distances between fuel stops, would be enough to justify the swap. I like to see older cars on the freeway keeping up with traffic.

Our 62 got 19 MPG on a trip from LA to Scottsdale, with the stroked 327 engine, 700R4, 1800-2200 stall, a 3.36 gear, and 235/70/R15 tire... and, with the same tune, managed a 12.14 second 1/4 mile pass on New Years Day.

firstgear

no T600.....maybe I quoted the wrong 5th gear

LT1driver

where did you get the trans from and what do they say?????

nitromainia

Seems there is a pretty constant controversy with overdrive vibration in these Tremecs

Did yours come with "their driveshaft?" Check length and balance... A touch to short in the shaft will "out of center" at the higher rotational velocity encountered as speed increases

I've seem this enough on other forums to say the problem may be internal... Hmmm Anybody else?

stratplus

Well that sounds much better than my 12 MPH.

toddalin

Don't think of it as gas mileage, think of it as "less time lost in the pits."