The whole package that starts in the engine room...

Engines, Exhaust and Fuel Systems

  1. ChryslerCruiser

    ChryslerCruiser Active Member

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    I am purely in the brainstorming phase here, as I suspect a different rear differential would make the most impact on daily driving of my 82 imperial, and that may well happen when the 7.25 gives up. . . Not that I am going to abuse it, but I understand they are not real robust..

    I am wondering what would be the "best" cam for the car.. optimized a bit for performance a strong consideration for realizing that this is a heavy car, an automatic tranny, and highway gears.. AND realizing that any $$$ spent on the 318 may well not be realized if the car is sold, or the engine is swapped for a 360, so there is a strong budge theme here..

    The previous owner has already swapped on a holley 600, and a dual plane intake, so that leaves the low hanging fruit to be:
    1) Dual exhaust which I guess means moving the gas tank which should not cost too much other than the effort involved.
    2)A camshaft re-grind, (because it is cheaper) to some sort of RV grind, or maybe a 'robust' RV grind that brings the intake duration up to something like 210@.050

    The following article while it is pure advertising at its best, I would like to believe the trend is accurate.
    What are your thoughts on this subject?
    https://www.hotrod.com/articles/mopp-0312-318-long-block-bolt-ons/
     
  2. AJ/FormS

    AJ/FormS Well-Known Member

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    Back up the bus

    If your unit has 2.20 gears ; you are screwed. There is nothing , absolutely nothing (short of super-charging), that you can bolt onto that lazyazz 318 to make it significantly quicker, cuz the 2.20s will take her to over 55 mph, with just barely getting up on the stock cam.
    So; the gears are your very first place to go.

    I tell you what; Go out and weigh your car, then do some timed runs from zero to 50. Next; bolt on whatever bunch of stuff you want,including that 220* cam; but no supercharging. Then equalize the weight and with the same rear gears,repeat the zero to 50; see what I mean? Prove me wrong!
    But if you have 2.45s , well.... then you are not quite as screwed.

    So now, knowing that gears are the key to unlocking even the combo you currently have, decide how important hiway useage is to you, cuz gears are gonna seriously mess with that.
    If the gears need to stay, then 318cubes is not gonna cut it for giddy-up.

    Here's the deal; Cams alone are like a sliding operating window about 1500 rpm wide. If you slide the window up the rpm band, yes it will make more power. But it will give up the power at a lower rpm. If you have 2.20 gears; 50 mph is gonna be about 3500rpm in first gear, and that 220* cam is gonna make peak power at about 5000rpm/70mph. So you can have 100hp more at 5000 but you gotta get there to use it! And worse is that, that 220*cam is gonna give away a bunch of power at all rpms lower than about, IDK , say 3500 rpm! So with 2.20 gears your car could end up SLOWER, from zero to 50, in fact I would bet money on it.
    The 2.20 gears have to go

    Ok; with a 2.45 low gear in the trans, and 27" tires, and 5% slip at WOT;
    2.20 gears make 50MPH to be 3500rpm
    2.45s make 3900
    2.76s=4400
    2.94s =4700
    3.23s=5160
    3.55s make 5700
    If you have a 2.74 low (A999), the rpms will climb 11.8%
    So there you go, pick one.

    For that 220* cam, I choose 3.23s and you will be right on the power peak at that 5160 @50 mph
    For the stock cam, I'd pick the 2.76 s

    What? you wanna go quicker? Put more gear in it...... but you'll have to shift sooner, and then your engine will get down on the lazy part of the power curve again. And there's a chance she'll actually ET slower (zero to 50).
    There are only three cures for the lazy part of the curve; 1) don't operate there, and 2) if you have to, then get a higher stall TC, and 3) pump up the compression... Of those,#3 has the bonus advantage of pumping up the power ALL thru the rpm range, and makes throttle-response a pleasure.
    So if yur not gonna pump up the pressure, then you have a delicate balancing act of synchronizing the cam to the existing pressure, then grabbing a suitable hi-stall. These are in addition to syncing the combo to the chosen gears, and to your useage.
    Welcome to the balancing act.
     
    Last edited: Oct 31, 2019
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  3. ChryslerCruiser

    ChryslerCruiser Active Member

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    It is my understanding that, generally speaking cams over 215*@ .050 move the torque 'band' up the RPM range... and I have no interest for just the reasons you suggest..

    BUT an RV type cam with more lift, and a smudge more duration of lets say 206*@ .050 ought to increase the useable torque off idle up to 3500RPM... and it may carry a bit more airflow through 4500 RPM..
     
  4. Oldiron440

    Oldiron440 Well-Known Member

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    And information is good stuff there's only one thing I'm not agreeing with "And worse is that, that 220*cam is gonna give away a bunch of power at all rpms lower than about, IDK , say 3500 rpm! So with 2.20 gears your car could end up SLOWER, from zero to 50" it's this, I've spent enough time with the dyno to say the torque should start coming on before 2000 rpm and peak around 3700 rpm.
    I had put together a stock bore 289 for my Fairlane with a 218 224 cam, you couldn't hear the cam and with a 3.25 gear it pulled 98 mph in the quarter with a stock converter in drive.
    But you need to build a package like AJ was saying. Cam, gears and converter.
     
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  5. XfbodyX

    XfbodyX Well-Known Member

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    Ive enough new parts laying around for a fresh torquish 318 and figure I will use it for a in between/floater motor when im moving cars or working on another motor, one car has 4:56s so it should be fun to see how it does for about 300 ft.

    Vs a 2bbl ive a oem 4bbl and a oem 600 or 650 spread bore, I do have a tiny port 318 sp2p but I dont thik its worth the time to try it.

    Its an Elgin RV TQ cam.

    The simple cam specs are these.
    Make:
    Chrysler
    Engine:
    273-360 "LA" Mopar
    RPM Range:
    1500 to 4000 RPM
    Camshaft Type:
    Hydraulic Flat Tappet
    Intake Valve Lift:
    .421"
    Exhaust Valve Lift:
    .444"
    Advertised Intake Duration:
    278°
    Advertised Exhaust Duration:
    288°
    Intake Duration @ .050":
    204°
    Exhaust Duration @ .050":
    214°
    Lobe Separation:
    112°
    Intake Centerline:
    108°
    Usage:
    Performance
     
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  6. MiradaMegacab

    MiradaMegacab Well-Known Member

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    839A7FA9-6E95-4969-85FB-E053AF3E9F6C.jpeg
    Simple bolt on. Instant torque....
     
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  7. Oldiron440

    Oldiron440 Well-Known Member

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    X, I did that with my shop truck at one point but it was a 360 and I used 4.10s. It sure went through the gears quickly and would light the tires at will from a standing start. I believe I had a Comp RV cam in it.
     
  8. BudW

    BudW Moderator Staff Member

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    I don’t remember seeing any Imperials with 7¼” differentials before – but I shouldn’t say never.

    AJ/FormS is correct with differential gears. You need to find out what you currently have and fix/change accordingly – FIRST. Differential gears should always come first.

    The 2.2 rear diff gear came out in ’81 (I think) and was commonplace around ’83.
    In ’84, the only two gear options were 2.2 and 2.9 (2.9’s came in police/taxi/tow option cars, only).
    Other factory gear ratios available (for earlier years) are 2.4, 2.7, 3.2, 3.5 and 3.9 and aftermarket has other options.
    Jeep even has 3.0 for 8¼” differentials, which is another option.

    The 2.2 and 2.4 gears are WORTHLESS for a performance gear. They do work well for door stops, (small) boat anchors or paperweights, though.
    2.7 is iffy.
    2.9 is on the edge of being OK.
    3.2 are nice.
    3.5 is where the fun starts.

    My ’86 Fifth Ave and ’77 wagons are a good case and point. Both are 318 2-bbls, both run about the same and both cars weight about the same. The ’77 has a A904 and ’86 has a A999 (which has a better first gear in it than the A904). The ’86 has 2.2 gears and ’77 has 2.9’s. From a dead stop, the ’77 feels like it can circle the ’86 twice before both can cross a 4-lane intersection.

    The ONLY good thing I can think of is the 2.2 gears do a much better job with traction on ice. It is hard to get the tires to slip on ice with the 2.2’s, even at full throttle going uphill (yes exaggerated a bit, but not by much).

    Most of my driving is in town and both cars are demanding 3.2 gears – which I’m working on getting changed.


    Now the problem is there is not many gear sets available for the 7¼” differential that is lower (higher the number = the lower gear ratio) than 2.7’s. There are some but not many. Also, the 7¼” is not very strong – so I would recommend upgrading to an 8¼” if possible.
    The 8¼” was still being used in Jeeps until a short time ago – so gear sets in 3.5 and 3.9’s are easy to obtain. 3.2’s are still plentiful, but not as much as 3.5 or 3.9’s.

    I will highly encourage you to change differential gear ratio first, and then see if you want to perform a camshaft change (or whatever) later.


    Somewhat unrelated to the gear ratio change, I do not recommend to any friends or family, to build (or rebuild) any differential without installing a limited slip at same time. Finding a good (new or used) limited slip carrier is not hard, for most Chrysler differentials - except for the 7¼”. Chrysler came out with the 7¼” in 1960 and only a few years was limited slip available (even aftermarket).
    I also recommend installing all new bearings at same time - so there is no extra labor to install a limited slip, just a few extra $ for the carrier.
    BudW
     
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  9. AJ/FormS

    AJ/FormS Well-Known Member

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    I like and agree with Bud, and offer the following in addition;
    2.20x 2.74(1st gear)=6.03, and 3.91x1.54(2nd gear)=6.02. So if you need to limit your tirespin on a slippery surface, you have the option of using second gear and a manual shift valve body, in conjunction with a more performance oriented rear gear, which will allow a much better first gear performance. I think that manual shift is available in a Transgo TFII kit, which I use in semi-auto mode. And as you can see by the math; you can use up to 3.91s lol, for same gutless no-spin take-off.

    The TFII kit, correct me if I'm wrong;
    will allow a manual low start, and a manual second start,and additionally, you will be able to hold each gear as long as you like.
    But in drive it acts normal. except with crisper and higher rpm upshifts.
     
  10. 89.Fifth

    89.Fifth Well-Known Member

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    I just swapped in a 9.6:1 freshed up and worked 318. It has a 206@.050 intake and 210@.050 exhaust with 450/480 lift. This is on a 999 transmission with 2.24 gears. The rated duration is 262/264

    I will tell you that it feels very much like the stock motor, EXCEPT that overall the power is up *some* and it really shines above 75mph. (in other words it's really coming on at around 2500rpm)

    I plan to switch to a 2.76 gear but personally I would use a smaller cam and plan to switch to that next year. With the current setup I could go down to a 240 advertised cam (190@.050) and build a lot more cylinder pressure down low. All the dyno simulations I've run match up with how the car feels before and after, and that same simulator gives me an extra 30lb/ft at 2000rpm vs my current 206/210 cam.