Gas mileage on a 235?

I've currently got a 235 in my '51 chevy 2 door. I swapped the 4.11 rear for a 3.55 and I've still got the closed driveline with 3 speed on the column. I'm getting about 10 to the gallon, is that pretty typical? Have those of you who have switched to other setups seen better gas mileage?

Thanks,

Haney

 

Did you install a speedo adapter on the transmission/speedo cable and checked your odometer with mile markers, before calculating mileage ?

I got the same setup on my truck and get 19-20 mpg on the freeways with 28+ diameter tires and Patrick's adapter.

 

Hi I have a stock 235in my 54 with split exhaust, 3spd, Nova rear with 2.73 gears. I drive it everywhere. and get 17MPG (US gal.) with 3.55 powerglide gears you should be getting at least 14 Id guess. Did you bump your timing till it pings on regular gas then back it up a couple deg.? Is your power valve closing? I use a GPS for distance calculation.

 

Seems too low for what I know about them...The trannyswap should have made it better than what you were getting. But, that seems too low a gas mileage for that engine.

 

The guy I bought my 55 from said he got about 9 mpg coming from the valley to Corpus. I thought that was lousy so I rebuilt the carb only to find the floats way off. I haven't had a chance to check the mpg now but my bet is much better mpg with rebuild.

 

Did you install a speedo adapter on the transmission/speedo cable and checked your odometer with mile markers, before calculating mileage ?

I just checked google maps for the length of my daily commute against how many days I can go on a fill up, it's just a rough estimate, but it still seemed low.

Did you bump your timing till it pings on regular gas then back it up a couple deg.? Is your power valve closing?

No, and I don't know, I will look into that.

 

I get about 18 mpg from my 235 3 speed and that's with a 4.11 and the vert is heavier

 

I used to get about 16 mpg in my 46 chevy with a 54 235.

 

When I first got my '62 Belair it had a 235. Got about 17 or so with a 3.36 gear. But it ran pig rich when cold. I wish I could get that 17 now (496 installed)

 

I have a 54 210. 235 with shaved head and decked block, Howard's cam, Hei with vac advance, 2 Model b's on an offy. Fenton headers and duals. four speed Saginaw. 2.93 Nova rear, Radial tires. Synthetic oil. Regular gas.

70 mph highway trips at 2500 rpm get me 25 mpg. A little less on local driving but still not bad.

 

I get roughly 17.5 mpg with my 261 3 speed and 3.90 gears in my truck. That is all city driving. I only have rebuilt my carb, everything else is un touched.

 

Our old Fleetline with a cam , 2 -1 bbls , split exhaust, 4 ;11's would always do at least 15.

 

Dang 25 mpg !!! That would be awesome if I could get something like that in my truck.

 

It's very possible that that's my problem as well, I rebuilt the carb, and it was the first one I had ever rebuilt.

What size tires are you guys who are getting >20mpg running? I've got 17" cragers with low profile tires and they measure about 24" tall, I'm beginning to wonder if that's part of my problem.

 

My '52 235 stick, bone stock, gets a tad over 20 on a Canadian gallon, that's about 16 on a US gallon.

 

I have a 37 p/u with a 57 235 and when I installed the T-5 and modern rear end the gas mileage got worse,those motors are designed to spin fast with the steep gears so some tinkering with the carb is needed. You first will need to put a lighter spring in the power valve since its not spinning as fast as it used to the vacumn is lower and the power valve is opening too soon,you might have to put a smaller jet in the carb. I am still trying to get the 37 figured out and cant do much untill I get rid of the too tall gears,I changed the jet and found a light power valve spring and it helped but the 2.79 gears are way too tall.

 

15-17 on the 54 Chevy I had with a PG.

 

What size tires are you guys who are getting >20mpg running? I've got 17" cragers with low profile tires and they measure about 24" tall, I'm beginning to wonder if that's part of my problem.[/QUOTE]

There's a big part of your problem, get rid of that 17 in and 24" tyres. I run stock 15" wheels with 225/75/15" and they 29.5" tall.
Also run 4speed and 3.08 rear, my 235 has mild cam, Fenton splits, cruises comfortably 75mph and gets about 25 mpg. (if I hold the speed back around 60mph)
First step, TALLER tyres
Rod

 

Ya know the pinging starts before you can hear it. You can still do damage this way.

Oh yeah it is, the mileage is scared of the ugly.

 

This past weekend we drove 350 miles and got 18mpg in my 51 3100.I'm runnin a stock 54 235,T5 trans,3.90 gear and 28" tall tire.Make sure you have no fuel leks ,external or internal.

 

and just to add, I got 16-18mpg in my '59 Fleetside with a 235, saginaw 4 speed, and a 3.08 geared rear end. That was highway or around town didn't matter.

 

Jeff makes a good point about Stovebolts liking a higher RPM. I put a '55 4.11 rear and OD in my '54 hardtop, it got better mileage in Direct than in OD. I liked it, though, I could cruise 15 MPH faster. In the '70's, nobody cared about MPG!

 

I think what Jeff is saying is the low rpm creates a lower intake vacuum and the power valve opens during part throttle reducing fuel mileage.
If your cruising vacuum is above 10 inches you should see a mileage increase with lower rpm's,this is my experience on several 235-261's and a GMC 302.
I take road trips along with a bunch of other guys with old GM trucks,the modified engines,more compression,carb and a 3/4 cam seem to get slightly better mileage than a stock engine.12-20 mpg being the most oftem reported MPG depending on engine , gearing and amount of bullshit slinging..

 

on a stock 53 chevy set up and 3 on the tree..i was getting around 18

 

My 41 chevy, 235 headers, strait duels, 4.11s, and 31 inch white walls I get 21-23 mpg! I miss that damn thing, Gota get back on it!

 

Get the odometer working, make sure it's accurate by driving it over several marked miles. Run several tanks of gas, noting the mileage at each fillup, fill it full every time, then calculate the average mileage over many hundreds of miles.

Then you'll know what mileage you're getting.

10 mpg in heavy traffic is plausible. 20 would be the upper limit, with highway gearing and moderate speeds on the open road. 13-17 is pretty typical.

 

Highway gearing and ease of drivability was my whole reason to go with the 4 speed and rear gears. Made a huge difference even around town.

 

I am beginning to think a modern carb and a RV grind cam might be the solution to better gas mileage on those stovebolt sixes since they were designed around those steep gears back then compared to the more highway friendly gears of lately,if I ever take the front sheetmetal off or find a 261 I will check into another cam but now I am not going to mess with the internals. I am thinking on going back to 4.11 gears since the motor seems to like it better going at those RPMs instead of what its doing now and I have o/d for the highway.

 

A vacuum gauge on the dash is your friend in finding the right rpm, cam, gear and tire size combination.

 

from the little testing I've done, less vacuum equals more efficient operation....high vacuum means the engine is being throttled, so a larger percent of the fuel you give it is being used to overcome internal friction, instead of powering the car.

but I could be wrong. Do you have more vacuum in overdrive or 1:1, at the same speed? which gives better mileage?