318 chryslers

Discussion in 'Gas Engines' started by whitepointer23, Apr 23, 2011.

  1. whitepointer23

    whitepointer23 Previous Member

    hi everyone. i have another engine question. if i remove the carter 4 barrel off a 318 and replace it with a small 2 barrel, say a carby that came off a 120 hp engine will it just reduce the 318's horsepower with less fuel usage or will it lean the motor off and burn valves. i am thinking that less cfm with less fuel should just reduce the output, please let me know if i am on the right track.
  2. Frosty

    Frosty Previous Member

    You are correct on both points.

    To use less fuel use less throttle no need to mess with the carb.

    American iron is a thirsty animal but they don't make then unnecessarily so.

    It will burn fuel according to what you ask of it.

    Approx 7 galls per hour at 100hp used.

    Deisel= 5, 2 strokes= 10
  3. whitepointer23

    whitepointer23 Previous Member

    thanks for that frosty, the reason i was asking is if you only need 120 hp instead of 225 a smaller carby might make the engine run smoother and respond better in the lower range due to the higher air velocity of the smaller venturi's.
  4. Frosty

    Frosty Previous Member

    There is torque to consider too, You could try it if you had one but I think it could even make it worse.
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you have a 200 - 220 HP 4 barrel equipped 318, putting a 2 barrel on it will reduce output, but you'll also need an intake too. Engines are just big 'ol air pumps, you reduce the input CFM capacity and she can't crush enough air/fuel mixture to generate the power her cam says she can make. So, the bottom line is how much of a reduction in CFM (or liters per minute if you prefer) will you take away from the engine's capacity. A 318 will want in the ball park about 500 CFM (~14,000 L3/m) at WOT considering the usual cam choices used. If you want to swallow less air, the carp and intake is one way, but efficiency will not improve much without also changing the cam.

    In short, you can ween the little LA engine (my assumption) by squeezing it's neck and not letting it have air/fuel, which will reduce power, but now you're carrying an extra 300 pounds of engine around you don't have to as there are much lighter 120 HP mills to choose from, then a stifled 318. As to the carp swap, the bottom line is CFM, how much air it can swallow in a minute. You could install a big 2 barrel and have very little lose in output. On the other hand you could install a 250 CFM carb and she'll not like it much at all without a matching cam. In the end I don't see the logic behind this type of swap. You'll have similar fuel usage, with less output, unless you match the cam with desired power reduction settings. A 120 HP V8 is nuts, unless you want to swing a big *** prop slow and this will surely require a new cam ground for high torque at modest RPM.

    Carter carbs work just fine, if you know how to tune them, just like any carb. They have their pros and cons about them, just like anything else. The problem most have with them, is they try the things that work on Holley and Rochester fuel mixers and they still don't run right.
  6. whitepointer23

    whitepointer23 Previous Member

    thanks par, the idea was to limit existing engines for economy which i can do by reducing throttle anyway but having 4 barrells it is hard not to use them. this is about my boat which i have discussed on here a few times. i had twin ford mercruisers , 1 was siezed. i was going to put twin diesels in but they would not fit under the floor. i now have 2 chrysler 318's which i got for the right price. my boat left the factory with twin 318's . i think they are la's. same size block as car version.
  7. Bglad
    Joined: May 2010
    Posts: 175
    Likes: 5, Points: 18, Legacy Rep: 67
    Location: Jacksonville, Florida

    Bglad Senior Member

    Disconnect the secondarys on the four barrel carburetors and you won't be able to use them;)
  8. Frosty

    Frosty Previous Member

    Thats a point, either mechanical or vacuum secondaries can easily be disabled.

    But I wouldnt, it still wont make much difference --its your wrist what does it

  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Cutting out the secondaries on a Carter, will all but kill it's ability to get the boat to "ramp up". Depending on the model Carter you have, most have 1 7/16" primaries and 1 11/16" secondaries. Removing the secondaries circuit from the mixer will decrease the CFM of the carb from 500 to 200 or if it's a 400 CFM to 160 or if it's a 625 to 250. The boat will probably not even manage to get over the hump folks.

    For this discussion to continue with reasonable wisdom, the year and model carp needs to be identified. The AFB and AVS look alike, but they're not, the same is true of the Thermo Quad and other Carter carbs.
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