Railroadman

This is getting ahead of the game, as I'm still a LONG way from driving it. But it can't hurt to ask.

'64 327/250. M-20. I will enjoy the driving experience, but will not be planting my foot at every light. What sort of mileage can I expect? The car came with a 3:36, but the replacement chassis has a 3:70. My plan at the moment is to put it together as is, keeping the 3:70's and enjoy the "zip", but if I find either the RPM's stay too high for my liking or if the mileage is too low, maybe swap the 3:36's in.

How much gas am I going to save? Any other thoughts?

65GGvert

Given planting your foot and 3.70, I would think around 13-15 mpg. I can honestly say I haven't checked gas mileage on a C1, C2, or C3 since 1969 when I sold my first 1965 I used as my only transportation while in the Air Force, traveling between Ft Walton Beach and East TN on some weekends. It was a 350hp, so my in town mileage was less.

jim lockwood

Back when I checked fuel economy, my '63 could tickle 20mpg if driven with a steady foot and at moderate hiway speeds.

The car has a 327/300, PG, and probably a 3.36:1 gear.

ChattanoogaJSB

Don, I get about 16/17 at real intereste cruise (75 mph) with my l75 300 and a 3.70.

Railroadman

Great, my F-150 gets about 17 on the highway so I can live with 15 to 20 with the Vette. I seem to recall my '67 got about 10 or 11, if I was a good boy, and much less if I put all 3 carbs to work! Like I say, I sure won't be driving the '64 like when I was 19 years old, but an on-ramp is made for the purpose of accelerating up to safe merging speed, right?

Westlotorn

My Dad had the 327 in his 69 Impalla with a powerglide, I don't know what rear gears it had but I can vouch for the gas mileage. We were on a long family vacation and I remember Dad checking the mileage at each stop.

It was getting upper 19 MPG but I don't remember hitting 20.

In your Vette I would expect at least that on the highway. If I remember Dad cruised 65 MPH most of the time.

tuxnharley

I have a different set up here - ZZ4, TKO 500/.67 5th, 3.36 axle - but just for a point of comparison I can average 22 mpg on a trip at 70 mph which is about 2000 rpm.

Vettegeezer

Can't help with the 250 engine, but when I had my '63 SWC equipped with 300/327, 4-sp. M20 & 3:36 posi. best I got on the highway at a steady 60 mph was 18 mpg.

Frankie the Fink

I have the same drivetrain -- 63 250hp, Muncie, etc -- but, the car had an Eaton posi swapped into it in the mid-70s...

Two owners ago the driver was pretty fanatical about record keeping and I have a small spiral notebook in the glovebox with page after page of copious record keeping. So - if you want some real world measurements; here they are:



I'm only posting two pages (approx 8 years worth of data) but there's a ton more with similar numbers.

So I'm gonna say that 14MPG-16MPG is pretty typical with rare excursions higher to 17MPG-20MPG..

The car was typically driven 100-200 miles per month over the time span. However in December of 2004 the car was driven nearly 1,000 miles in one month so I'm assuming a highway road trip with significantly increased mileage.

As an interesting side note its enlightening to see the cost of gas rising over the 8 years in the data...

Dan Hampton

Judging from the data, it looks like Frankie's car saw most of its duty in the city or a combination of city and highway driving. Those consecutive 20+ mpg entries would suggest to me he was on an extended trip.

As a point of contrast, I knew a person in Indiana who, after being being discharged from the service in '68, went down to the local dealership and purchased a '68 L 71 with 4:11 gears. The best mileage he ever achieved, according to him, was 8 mpg going down the Indiana turnpike at 45 mph.
After that, 14 mpg sounds pretty good to me.

Railroadman

Thanks Frankie, that's perfect. And that was with 3:70's?

I have known a few people who kept records of everything like that. I just don't have the self-discipline. But here's a case where it came in handy 20 years later!

Frankie the Fink

Yes, and, yes...

I keep two logs, a "Restoration Log" of restoration tasks performed and parts replaced, and, a "Tune-Up/Service Log" of oil changes, tire balancing, air filter swaps, etc.. Its very loose and by month and mileage...

But nowhere near the detail this guy did, frankly, I don't know if I'd enjoy the car as much if I felt that much of a compunction to track things to that level...on every fillup.

MikeM

If you're satisfied with a range of 15-20, you'll be happy with the mileage you'll get.

If you're wanting to build enough speed to safely merge coming off the on-ramp with that 250, best get an extra block running start if traffic is fast on the expressway.



PS. The gear ratios in the M 20 work well with a 3.36 rear gear. The 250 has a very limited rpm power range and doesn't like low gears too well unless you enjoy a lot of short shifting.

Frankie the Fink

All true, if you look at HP/RPM/Torque charts, you don't have to come close to redlining this combo to hit max torque (IIRC its like 4200 RPM but I might be mis-remembering)

Anyway, typically shifting this setup at 2200-2400 RPM results in the best mileage (IMO) and effortless, baby-butt smooth shifts. I've had passengers remark that they couldn't even feel the shifts doing it this way.

SWCDuke

Given that the 327/250 actually has a bit more low end torque than the 327/300, running a 3.70 axle doesn't make any sense unless you live at high altitude and don't do much, if any, freeway driving. The standard 3.36 axle with the wide ratio four-speed should provide decent performance, but the engine does run out of breathe at about 4500 revs.

This engine has a lazy centrifugal curve, 24 @ 4600 and the OE initial timing recommendation is only 4 degrees, so total WOT advance is only 28 degrees which is waaaaaaaaay below the optimum of about 38.

Search for threads stated by me and download the tuning seminal. Modifying the centrifugal to achieve 30 at no more than 3500 with 8 initial and a 15" VAC will improve both performance and fuel economy.

Of course, the above assumes an OE cam. A high overlap aftermarket cam, which is a common modification will hurt fuel economy and low end torque and not yield significant power increase due to the small ports and valves.

Duke

Railroadman

Mike, you mean the putt-putt-putt isn't going to be enough unless I have a tailwind?

I certainly am not going to sell off the 3:36 rear that came with the car. I think I'll keep the 3:70's on it and worry about all the 10,000 other things I need to do to get it on the road. If the power band seems too narrow, I'll go back to 3:36. The mileage range Frankie shows is certainly something I won't mind.

John BX NY

I agree that the 67 350hp/M20/3.36 combo is just about the best setup for all around driving. My 67 has averaged 12-15 mpg in mixed driving over the past 30 years. Your mileage may vary as the EPA is fond of saying.

SDVette

After following the Lars timing setup, I measured 19 MPG in my '61 (350 LT-1, 3 Speed, 3.36) on a 400 mile highway trip.
It was on the 'hairy edge' of too much advance.. I experienced a few 'stumbles' at light cruise from too much advance during that trip.
Swapped in a vacuum can with adjustable advance limit... problem solved.

My combo average is more like 14-15 MPG.. but these motors can get pretty good mileage at cruise - even without overdrive!

Frankie the Fink

Lars setup my 63 stock distributor and its superbly optimized for the 250hp car....the stock advance map is woefully conservative:


I backed off his 16* initial setup to 14* but everything else is the same...
The more aggressive map makes the base motor definitely more "snappy"..

LouieM

Well, there may be doubters in the Greater Orlando metroplex, but some of us have enjoyed our Sting Rays immensely and kept meticulous records over the decades. Frank-ly, I don’t think I’d have enjoyed my Corvettes as much if I hadn’t kept good records. After all, life is not all in-the-moment fun and games; adults have to be in the room too, to keep track of what happens along the way. As a paleontologist, I enjoy looking back in time, and nothing satisfies a glance back at the past as much as a well-kept record book. For example, my first Sting Ray was a 1967 Goodwood Green over saddle coupe with a 327/300, M20 and 3.36:1 Posi. I bought it in August 1968 for $4,000 (yeah I overpaid, but I finally had a Vette!) and started keeping records about sixty seconds later. Here’s my mileage log book for September 1968.

Looking back, mileage ranged from 9.36 mpg to 17.78. At one point I was buying gas every day and I drove 2,450 miles that month, bought 184.5 gallons of gas for $66.93 (= $2.75/gallon) and averaged 13.23 mpg. What the heck? I even drove 902 miles over the next three days after filling up on Sept. 7. What on Earth kept me on the road so much? I was in geology grad school at USC and memory says I was keeping my nose to the grindstone without let up.

This made no sense at all to my present-day self, until I remembered that I was living in West Los Angeles and dating a girl in Pomona, around 50 miles to the east. I’d drive to Pomona, pick her up, go back 40 miles to Hollywood on a date, spend money there, then drive her back home to Pomona, and spend time there, before returning to West L.A. So, 200 miles of driving for nooky. Spending $50 on gas in ten days was a huge financial drain back then, but definitely a worthwhile investment. Heck, I would have driven just as much under the circumstances if my top mileage had been 9.36! Neglecting the scholarly life probably delayed me getting my PhD by a semester, but a man’s gotta live! Obviously, I was having fun with my Sting Ray and keeping good records. Also, keep in mind that I managed to keep meticulous records while battling exhaustion!

Lou