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Projects Trying to squeeze a little more gas mileage from a 235

Discussion in 'The Hokey Ass Message Board' started by junkyardjeff, Sep 20, 2018.

  1. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    Anyone know if the car 235 had a different lift and duration on the cam then the truck version.
     
  2. jetnow1
    Joined: Jan 30, 2008
    Posts: 1,575

    jetnow1
    ALLIANCE MEMBER
    from CT
    1. A-D Truckers

    Can't help on the cam specs but I can tell you my last truck with 3.70 gears got better mileage and was much more fun
    than the replacement with 3.25 gears. Same drivetrain. A lugging engine is not happy or efficient.
     
    Cosmo49 likes this.
  3. I think a 261 cam is different.
     
  4. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    I have 3.70 gears for a 9 inch but would be nice if they were for a 8 inch,since I have a 60 235 its time to make it work with the gears I have.
     
  5. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    Now that I got the speedo about where it should be the gas mileage is not looking too bad,have not refilled but it used 3/4 of a tank to go 189 miles and it should be a 15 gallon tank and I am figuring 16.8 so I can live with that and will fill again to get a more accurate figure but I was thinking it was getting a little over 10.
     
  6. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    Speedo started making noises on the trip today,was thinking now that I got it close to being right it is going to quit working but I greased the cable and no more noise.
     
  7. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,244

    6inarow
    Member

    Well you have to look at it all together. In my opinion that 235 with a 3 speed and OD, stock 25-26" tire, 4.11 gears is happiest with the old 55 mph speed limit. Since we dont have that, its going to suck gas. So all you can do is minimize it. 75 mph (or more) today and the 235 isn't going to like it. Its will be happiest (my opinion again) at about 2400-2500 rpm. Get some Carters, mild cam, get the ignition to GMC Bubba, overdrive, 28" tires and look somewhere in the 3.90 gears and I bet you will be a lot happier with the mileage
     
    chop job likes this.
  8. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    A tach is next so I can see where the engine is spinning,its alot more driveable with the 3.55 gears and T-5 but it never got the gas mileage I thought it would by slowing it down. I came to the conclusion they were designed to spin that fast and now its way out of its sweet spot,I have another 235 on the stand and thinking about a custom ground cam to work with the slower RPMs.
     
  9. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,244

    6inarow
    Member

    OD and 355 gears you probably have that thing strangled to death unless you have really small tires
     
    Cosmo49 likes this.
  10. stanlow69
    Joined: Feb 21, 2010
    Posts: 4,534

    stanlow69
    Member
    from red oak

    I work on big trucks (Collector items) too. The owner has a fleet of over 100 near new trucks as well and he has a nitrogen system that he uses in all his trucks. It has improved tire wear and fuel economy as well. When I was 16, my first car had a 427. From that day forward, I have never checked fuel economy on any vehicle I have ever owned. And I have driven a lot of miles.
     
    vtx1800 likes this.
  11. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,267

    stubbsrodandcustom
    Member
    from Spring tx

    Honestly before you go throwing money at rear gear, new carb, etc.... pull a plug see what the motor is doing inside... and note... if you made motor changes, some plugs will run like shit... Heat ranges make a difference too... Float level being too high will make a rich sucking fuel condition... 1 thing changes you have to dial it back in for what you want it to do. 14 combined isn't terrible, 16 combined is about normal in my book. Straight flat highway should net 18-22 on these motors all day long.

    The engine load is different now, its working under more load in certain places and less in others. The drop in city driving will be noticeable from 4.10 to 3.55... working harder off a light. Freeway ride motor working same load, less rpm.
     
    samurai mike likes this.
  12. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,520

    1oldtimer
    ALLIANCE MEMBER

    My panel runs 215/85R16 tires with what I assume is a 4.11 rear and a 3spd with o/d. At about 2000 rpm I’m going 65 mph (backed up by a speedo app on my phone).
     
  13. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    I pulled a plug a couple months ago and looked to be burning good and will check again since I did take it on a road trip yesterday
     
  14. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    It does have tall tires,it only goes in 5th above 55.
     
  15. is it possible that with over drive ,5th gear you are lugging the engine and it can not breath freely?
     
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  16. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    That has crossed my mind,the mufflers are a little loud and I like to put in in 5th around 55 so I can hear myself think.
     
  17. HotRodWorks
    Joined: Dec 6, 2005
    Posts: 258

    HotRodWorks
    Alliance Vendor

    A vacuum gauge will tell you if you are lugging it. Run a hose into the cockpit and tape a gauge to your dash.
     
    Cosmo49, samurai mike and belair like this.
  18. belair
    Joined: Jul 10, 2006
    Posts: 8,504

    belair
    Member

    That vacuumn gauge will tell you a lot of other things too.
     
  19. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    I have a vacumn fan on the steering column and will hook a gauge to it this weekend.
     
  20. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,519

    seb fontana
    Member
    from ct

    Why is it that the factory put 4.11 gears in the rear with 3spd od trans? Think they knew what was best? 28" tire and 4.11 gear equals just shy of 3000 rpm at 60...In od that drops the engine to just shy of 2200...So in od at 75 mph the engine is turning 2750...Now with a 5spd fifth gear of .82 and 4.11 gears at 60 the engine is at 2460 rpm and at 75 mph it would be at 3075 rpm..So to equel stock rpm in od you would need a 3.70 rear gear plus or minus .03.....
     
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  21. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    Got vacumn gauge hooked up and got it at 20 at idle,plugs looked slightly rich so it got a slightly smaller jet and will fill the tank again and drive it to the swapmeet saturday and see how it does. Would like to go to 3.70 gears but not in the budget right now,had it timed to factory specs but adjusted it to get the highest vacumn.
     
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  22. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    It ran better tonight but traffic was too heavy to try to pay attention to the vacumn gauge since I had to use a flash light to see it,in 5th the vacumn is quite low sometimes so it probably needs steeper gears and going to find a vintage looking vacumn gauge to mount under the dash and maybe try to change my driving habits to improve the gas mileage too.
     
  23. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,244

    6inarow
    Member


    Ding ding ding We have a winner!!!
     
    samurai mike likes this.
  24. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 4,635

    57JoeFoMoPar
    Member

    I recognize that this comment isn't answering the OP's question, but I'll make it anyway.

    We don't partake in this hobby for the economy of these vehicles. What we're really looking for is acceptably poor when it it come to economy, where we can enjoy our cars and drive them without going broke through cost of ownership (be it gas or otherwise). People, some members of my own family included, are often shortsighted in the mindset of "buy a car for better economy", because they forget that to save money at the pump, they had to spend a whole butt-load of money up front to get the economic car in the first place!

    What you really need to do is look at how many miles you drive your car annually. Then calculate how many gallons of fuel you burn at varying MPG, then multiply by the average price of fuel by you to see how much you're actually saving trying to get an extra 2 mpg out of your rig. If you need to sink $500 into your car for the betterment of the economy, you may need to drive for 3 or 4 years, or more, to break even. That's not worth it, especially if it makes the car perform worse or be less fun to drive.
     
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  25. Truck64
    Joined: Oct 18, 2015
    Posts: 4,123

    Truck64
    Member
    from Ioway

    All very true. But it's important to tune the engine properly. See this all the time, people post pics of dark as a dungeon damp as the dew coal black spark plugs. Poor engine tune wastes impressive amounts of fuel unnecessarily out the tailpipe, and there is absolutely no performance benefit. In fact it will be worse. Tends to wash out piston rings and dilute crankcase oil too.
     
    Last edited: Nov 9, 2018
  26. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    I am not going to spend a bunch of money to get it to get better gas mileage since I do not drive it more then 1500 miles a year usually but I want it to run its best and get the best mileage for what it is,going to drive it to the swapmeet tomorrow (if it does not snow) and fill it up so I can tell exactly what gas mileage its getting. The other day I checked the valves and a few were too tight so got them where they are supposed to be,put a smaller jet in the carb and set the timing with a vacumn gauge and its running better then it had in years. Not expecting econobox gas mileage but I want it to be as efficient as possible for what I have.
     
    Truck64 likes this.
  27. trollst
    Joined: Jan 27, 2012
    Posts: 1,761

    trollst
    ALLIANCE MEMBER

    The thing that hasn't been addressed here is what the motor is pushing, basically a really big brick with a lot of hard edges and sharp corners. If you can get between 16-20 mpg, you're doing pretty well and I would be happy with that. But....who builds a hot rod for mileage? I got a 27 roadster pickup with a 2.3 ford in it that gets I don't know mileage, but has miles of smiles.
     
    Black_Sheep likes this.
  28. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,359

    Mr48chev
    ALLIANCE MEMBER

    Had a 59 ElCamino with a 235 and 3 speed that I doubt got 15 mpg on a good day.
    If you scroll down the page you find the perfomance data for the 57 237 in the truck https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1957-Chevrolet-Truck.pdf It does have a chart that tells you where the power band is for the engine. Most any engine has it's sweet spot where it does best as far as gas mileage and highway cruising go. A road trip in the red ot thing out in the driveway showed me that the 80 mph Idaho and Wyoming speed limit would cost me over 5 mpg over running between 74 and 76. 77 and the mileage dropped faster than the speedometer rose.
    The page for the 60 Chev. Neither has cam specs for the 235 that I can see.
    These engines are where small gains end up being big gains as a 2 mpg gain is a pretty big percentage.
    A carb that is more efficient all around is probably the big thing.
    Add to that a more efficient ignition system.
     
  29. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,495

    junkyardjeff
    Member

    Was hoping to get it out saturday and the tank filled so I could see what it done on the trip last weekend and put some miles on it to see if the timing and jet change made any improvements but it did not happen so this project will probably resume in the spring,heading to Daytona beach very soon and could be snow on the ground by the time I get back or shortly after. A better carb and hotter ignition could do some good.
     
  30. 1-SHOT
    Joined: Sep 23, 2014
    Posts: 1,874

    1-SHOT
    ALLIANCE MEMBER

    It's what we call gear bound, I.E. the motor is not running where it's makeing torque so u are lugging it and it will use more gas. I think you would bo better with 4:11 and t-5 the motor would working in its torque curve not lugging it's easier to change the gear than the cam on a 235.
     

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