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Is this hurting my engine ?

Discussion in 'The Hokey Ass Message Board' started by Jims35, Feb 19, 2013.

  1. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    I don't use OD until i'm at freeway speed, before that it's like most stock auto trany cars in the 60s to 80s era ,only not as heavy.
     
  2. chevyburb
    Joined: Apr 17, 2006
    Posts: 169

    chevyburb
    Member

    Lots of opinions- My setup is a 406/200 4R/3:89 posi/31"tires. I find it to be a great combo. Approx. 70mph @ 2100rpms. Gas milage unknown (it's a hotrod for God's sakes). My 2001 chevy truck 5.3/200 4R/3:73, 80mph 20mpg all day long. Your setup doesn't even sound like it's "on" the cam unless you have an RV cam set up for off idle to 5500rpms. Most people make the mistake of over carburating the 350. An Edelbrock 500cfm is perfect for them. My 2 cents.
     
  3. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    It was a used one from a 84 chev 4x4 ,had a Qaudrajet on it , I changed it to a 600 Edelbrock . So I don't have any idea what cam is in it , may be an RV one. Got it cheap enough so i don't plan to tear it down . Just going to drive it until it starts using oil or making unhappy noise . Then get another one , 350s around here are easy to come by cheap.
     
  4. GREASER815
    Joined: Dec 2, 2008
    Posts: 973

    GREASER815
    Member

    I run a T5 behind my 235, and a 3.08 rear. I only hit 5th gear on the interstate, sometimes it feels sluggish but I love being able to go somewhere far away for the weekend and spend $50 in gas. Not sure if it's harmful or not but at least its cheap.
     
  5. fastcar1953
    Joined: Oct 23, 2009
    Posts: 1,647

    fastcar1953
    Member

  6. norms30a
    Joined: Jul 17, 2008
    Posts: 537

    norms30a
    Member

    Just my opinion but, put the Q jet back on. It's the best carburetor ever built. Put the 373 gears in and you will be a happy camper. Unless you do mostly 80 mph driving.

    Carburetor engines are not like the electronic fuel injected engines we are now used to. They require a little more rpm to reach full vacuum advance. Also a little more rpm to get good fuel atomization and mixing with the incoming air, which the Q jet does really well.

    Also the pump in the od trans might like a little more rpm to keep up pressure, and don't forget that Chevy has to move lots of air which is almost the same as driving a heavier car .

    The car will probably work fairly well as is but my experience has been that 350s like about a 22 hundred rpm steady pace for best mpg
     
  7. bobkatrods
    Joined: Sep 22, 2008
    Posts: 625

    bobkatrods
    Member

    I second this advise,,, put a PROPERLY tuned Q Jet back on and run the 3:73.
     
  8. fab32
    Joined: May 14, 2002
    Posts: 13,988

    fab32
    Member Emeritus

    Remember GM uses 3.42 rear gears in just about any their OD trans equipped cars from the factory. I find just about anything from 3.36-4.11 works with an OD. Your engine combination will dictate which ratio in that spectrum will work best.

    Frank
     
  9. buckd
    Joined: Nov 29, 2008
    Posts: 334

    buckd
    Member

    I agree, if your around 2000-2200 RPM you're golden so don't shift into over drive until shifting will bring it into that range. Also I feel that putting the car under load below that range is what brings undo stress on the entire drive line of a stock type engine. BUCKD
     
  10. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,288

    sunbeam
    Member

    You have about a 30% rpm drop in overdrive and a 3.92 to a 2.80 is also about a 30% drop so the rpm and milage should be about the same as driving without overdrive now.
     
  11. Just drive 80 mph, then it will be turning 2000 rpm and the engine will be running very efficiently.

    For your orig question, the 1500 rpm cruising will not really hurt anything, you are not at heavy throttle. It may not be peak efficiency, but if it is running smooth without lugging, I see no reason to change it out. You said that it is just for cruising and not racing. It should get pretty good mpg if you keep the light throttle.

    Yes, the 3.73 ratio would be better, but there is no reason the 2.80 *has* to come out.
     
  12. JeffB2
    Joined: Dec 18, 2006
    Posts: 7,625

    JeffB2
    Member
    from Phoenix,AZ

    You might think "Old Skool" and get this:http://www.ebay.com/itm/283-327-350...t=Vintage_Car_Truck_Parts_Accessories&vxp=mtr Sold a bunch of these back in the 70's during the Jimmy Carter "gas crisis" the small runners increased low speed velocity and were good for 2-3 MPG and improved low end torque, power band is off idle to 4500.I pulled 26 MPG highway with that intake in a '65 El Camino 283 also used the Crower mileage cam which is still available.
     
  13. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    I wanted to use the Q-jet but i don't believe they were on any cars with the 200R/4 overdrive tranys. I was afraid the cable would not pull correct and damage the trany. I bought an add on lever for the Edelbrock and holley carbs to use the cable but never found one listed for the Q-jet.

    I'm assuming the Q-jet is what ever kind chevy put on the 84 4x4 pickups. I ask the guy i bought it from if it was a good one and of course he said " yes" . It's been sitting on the shop shelf for two years so probably needs a kit . I'v rebuilt a lot of carbs but never a Q-jet so that means a trip to a rebuilder. But thanks for the information and help. JIM
     
  14. atomickustom
    Joined: Aug 30, 2005
    Posts: 3,221

    atomickustom
    Member

    Plenty of GM cars with OD came with 3.73 rear axles. I've got one right now in a G-body. (The 3.73 rear end, I mean.)

    First gear will be almost unnecessary. Are you sure you don't want to just drive it without overdrive except on the highway? I know a guy who puts really low-number rear ends (like 2.41, 2.2whatever) in his cars and just keeps the shifter out of overdrive except on the highway and he swears by it. However, he's also running big-block Olds motors that probably have a ton of grunt at low rpms, not a Chevy 350.
     
  15. This ^^^ is rock solid advice - several chapters could be written on each point norms made


    There were plenty of Quadra jets and 200r4 transmissions working together back then.
    The carbs were mostly the electronic versions and I'm sure that the throttle arms have differences but I don't know exactly what they are. ( been a while since I've even seen an Electronicized Qjet) I'm sure the cable bracket bolted to the engine is probably different too. If an eddy carb works the 200r4 cable, a Q jet can too..

    If you had both style carbs in front of you , you could compare.
     
  16. raprap
    Joined: Oct 8, 2009
    Posts: 768

    raprap
    Member
    from Ohio

    I run a 292 CI Inline six, T-5 with 0.72 OD, 3:55 10 bolt and 30" tall tires. I am running 1850 rpm @ 65mph and get from 20-22 mpg!
     
  17. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,288

    sunbeam
    Member

    I don't know what compression ratio you are running but high loads at 1500 rpm could put you into detonation. New stuff gets by because of sencors.
     
  18. I just did a little experiment for you.
    DD 5.3 with 4l60E , 342 rear gears 28" tall tires.

    In OD @ 1500 rpm speed was 56 mph. Computer said I was getting 21.5 mpg on fresh reset.
    In 3rd with speed at 56mph rpm was up to 1800 rpm fresh reset mpg 22.5 mpg. Increase of 1 mpg.
    In OD @ 1800 rpm speed was 65 . Fresh reset and MPG 24.5 increase of 2 and 3 above base.


    They chose to get in the sweet spot @ 1800 rpm range and used lots of electronics to do it.
    Runs best at 70 but traffic and popo in the way .


    I could hear the thing pinging @ 1500 with the slightest load in OD

    If I were to choose a numerically lower rear gear , I'd need to driving Way Over 65 mph most of the time to get equal MpG. If I were driving mostly at speeds under 50 I would need to choose a numerically higher rear gear to get equal mpg. Alternatively I could build the motor differently and pick my own sweet spot.
     
    Last edited: Feb 20, 2013
  19. norms30a
    Joined: Jul 17, 2008
    Posts: 537

    norms30a
    Member

    I don't want to hijack this thread, just tossing out some info......tciauto...and...bowtieoverdrives... are 2 ministers that can marry the Q jet to the od tranny.
     
  20. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    Yeah I think I will dig out the Q-jet and look it over, maybe get some numbers off of it. I'v had chevys in the 70s era with Q-jets, always liked them. I used the Edelbrock because they are sort of a generic carb and pretty easy to set up and go . Thanks JIM
     
  21. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,428

    Von Rigg Fink
    Member
    from Garage

    just some info from me, for what its worth

    350/700r4-3.55-235p-75r15 rear tire, 2800 # car (estimated)
    running 3 two barrel rochesters ( runs off the center carb until poked than it comes alive)
    i adjusted the OD on the last gear to come in close to 50 MPH..she runs great, and will punch down fast into passing gear if wanted. at first it seemed like it was lugging at 40 to 45 when the OD lock up would come in..so i set it at 50 and if it decideds to lock up sooner and I know im going to be rolling at between 40 and 45 I just keep it out of OD.

    im getting close to between 23-25 MPG as an average across the board driving..both freeway and city, hard to tell what the mileage is, because the car is so fun to drive I just cant keep my foot out of it:D:cool:

    if its lugging, its no good
     
  22. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    Well mine is working about the same as yours , kicks up in to OD at about 50/55 . unless i let up off of the go pedal because of slow traffic , then it's a little sooner. When i get in city traffic 35 or less i pull it down out of OD. I'v only driven it about 600 or less miles with the 350 . So maybe i just need to fill that tank a few times and check things out more before doing anything. Thanks JIM
     
  23. BACAGrizz
    Joined: Aug 27, 2009
    Posts: 201

    BACAGrizz
    Member

    A quick and dirty way to calculate the rpm's would be to divide 1500 by 2.8 then multiply by 3.73 resulting in: 1998. If you know the rpm's at a given ratio then the new ratio is easy to find. Works for trans gears as well as differential gears.
     
  24. Jims35
    Joined: Dec 22, 2009
    Posts: 279

    Jims35
    Member

    That is about what i was looking for,about 2000 at 60 /65 MPH. Well if it ever warms up around here i believe i might try the 3.73 ratio and Q-jet carb. I can always go back if i don't like. Need something to pass the time of day,may as well be working on the old car.Thanks ,good information.
     
  25. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,288

    sunbeam
    Member

    Which lets you drive with less throttle straight or overdrive? Less throttle more mpg.
     
  26. Provided you are in the RPM window.
    Rpm below (or less throttle ) will increase fuel consumption and be hard on parts.
    RPM above ( or more throttle) will increase fuel consumption and have unnecessary rpm .

    Rpm window varies on the components used
    And carb vs fuel injection and engine management is a whole different thing.
     
  27. cshades
    Joined: Sep 2, 2011
    Posts: 442

    cshades
    Member
    from wi

    I actually get better maileage at 80 than i do at 70.I get anywhere from 20-24 mpg depending on roads and fuel.
     
  28. norms30a
    Joined: Jul 17, 2008
    Posts: 537

    norms30a
    Member

    When the weather warms up and you start to play with the Chevy, do the gears. Don't do anything else for a while to see how that one thing changed how it works.

    Always change one thing at a time, then, drive and learn for a while.
     

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