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Cam Choice (Duration vs MPG)

Discussion in 'The Hokey Ass Message Board' started by scoggman, Jan 31, 2013.

  1. scoggman
    Joined: Feb 25, 2009
    Posts: 471

    scoggman
    Member

    I've got a 355 and a set of vortec heads which I plan on cutting down the bosses and putting Z28 springs on for higher lift, 650 edelbrock and an air gap intake. My question is about cam duration.

    It's going in my model a coupe, which I plan to drive just about every day (70 mile round trip to work). What cam duration should I be looking for? I've been reading about the VooDoo 268 or 262, but is this going to be too much? Should I be looking for something in the 230 range? Of coarse we all want 700 hp and 35mpg, which I know isn't going to happen, I just wanted to know from your experience how much duration is a good balance for MPG and performance. Is a 230 going to get 0....3.....5....mpg better than the 268?

    Thanks,
    Jon
     
  2. big duece
    Joined: Jul 28, 2008
    Posts: 5,494

    big duece
    Member
    from kansas

    212-218 would be my choice for mpg, 230 is getting pretty racey
     
  3. Physics tells us that it will take the same amount of power to run down the road at say 65 mph, regardless of the cam. What you want to do is maximize engine efficiency while making that level of power. Efficiency = mileage.

    You should call the cam companies and talk to them about your total combo. Not just engine size, but trans, rearend gear, tire diam, vehicle weight, and so on.

    An OD trans will help mileage, and not really affect power - as long as you have enough rpm the engine is running good. Bigger cam at low rpm is not so efficient. Minimize overlap, so a LSA of 112-116 is better. Duration at .050 lift is really the number you need, something around 220 will be pretty mild and help mileage.
     
  4. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    It's not a small block Chev, but I have been running a Comp Cams Extreme energy 268 grind in my 360 in the Plymouth for about 7 years now and doing exactly what you are talking about. Well, for awhile there my daily drive was more like 180 miles one way per day, but thats a different story! Back to the grind, for an engine in that size class with some decent heads on it, it's about as humpity as I would like to go. I had bigger and badder in that engine, but nothing that was as good an all around cam. Happy at freeway speeds at about 2200 -2500.
     
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  5. pdq67
    Joined: Feb 12, 2007
    Posts: 787

    pdq67
    Member

    Please consider the good old Crane 274H0-6 for a mild hy-cam that will talk to you at idle and just off and will do dam good for an old-school cam, imho..

    Note, nothing fancy at all here but it will do you good.

    Or for a stock early L-48 350 engine that is right at 10 to 1 CR, I would say install the great old 350hp/327, -151 cam because in this engine it will pull like a freight train. Had one so I flat now.

    pdq67
     
  6. scoggman
    Joined: Feb 25, 2009
    Posts: 471

    scoggman
    Member

    I'm running a camaro t5 and 3:73s in the rear if that helps.

    Thanks!
     
  7. FWilliams
    Joined: Apr 24, 2001
    Posts: 1,984

    FWilliams
    Member


    for an off the shelf cam that needs minimal spring this is your best bet for what you are trying to achieve

    Fred
     
  8. scoggman
    Joined: Feb 25, 2009
    Posts: 471

    scoggman
    Member


    What kind of mpg were you getting with that cam? What gears? Overdrive?

    Thanks,
    Jon
     
  9. GTOMUSTANG
    Joined: Oct 5, 2010
    Posts: 115

    GTOMUSTANG
    Member
    from ct

    Look into variable duration lifters.

    with the Mopar, they use a wider diameter lifter, so the lift ramps on the cam lobes can be steeper before they trap the lifter between the cam lobe and walls of the lifter bores in the block. A steeper cam lobe will allow the valve to open later, since it can get to full lift sooner than a cam with a lifter that gets trapped sooner by that same steep lobe ramp. Opening later--yet getting the same lift and duration--of course decreases the overlap.

    since your Vortec head flows better than a fuelie does, and has a nice angle cut on the valves which can help low lift flow, you can get away with a milder cam with less overlap ground into it (an increase in low lift flow does the same as increasing overlap on a head that flows little at low valve lift).

    You've got a light car with a relatively oversized engine for it, a milder rear gear won't hurt you either. Or just increase the size of the rear tires for the same effect, and fill in the rear fenders as a bonus. An 80's Mustang is about the same weight, and a T5 and 3.73 rear gear practically makes 1st gear useless except for spinning the tires at every stoplight. You could go "down" to 3.55 or even 3.27, if that's a ford 8.8 inch in the back.
     
  10. Again, It's Mopar with the advantage of the larger lifter diameter, but the best all around cam I used in a 360 inch small block was the '68 340 4 speed cam (Intake 276 degree .444" lift, Exhaust 284 degree .453" lift with 114 degrees lobe separation). This motor had J heads with 2.02 valves and mild bowl porting, about 8.5 to 1 compression. I put the cam in 4 degrees advanced as well. I ran it with 340 exhaust manifolds, a Weiand stealth dual plane intake, 625 comp series AFB, 2400 stall converter and 3.23 rear gear with 26" tall tires in a 3,400 lb Duster. This thing pulled like a train right up to 6000 rpm, sounded bad ass with 2 1/4" turbo mufflers and had tons of torque - went through a lot of tires on that car.

    I upped the compression to about 9.5 to 1 and went to a 284 degree cam with 1 5/8" headers, 2.5" exhaust, 750 AFB, 3000 stall converter and 3.91 gears later, but it lost the low end grunt and cruiseability that the first combo had, but it was much quicker flat out. Mileage went in the dumper too with the extra duration, converter slippage and lower gears.
     
    Last edited: Feb 1, 2013
  11. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,967

    porknbeaner
    Member

    For mileage you want to match your cruise RPM to your power band. Right at the bottom of your torque curve is about where you want to be cruising. If you are shoting for good mileage try and choose a cam and engine combo that produces a broad flat torque curve, that gives you a little wiggle room when you are driving.

    You cam choice is not based on duration it is based on your total build and what you expect you engine to do withing given parameters.
     
  12. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,838

    Truckedup
    Member

    Generally,a SBC with 9.5 compression,Vortec type heads,600 cfm carb ,headers, good ignition and a modern design cam of about 220 degrees duration at .050 will make 350-375 HP at less than 6000 rpm with a good amount of torque above 3000 rpm.This is not a radical build with reasonable fuel mileage for the HP
    Better mileage comes from a little less cam and a heated intake manifold,180 running temperature with leaner jetting for part throttle.I have tuned a few engines with heated intakes , aggressive spark advance and lean jetting to get outstanding mileage.There was a small loss of top end power,well worth it for sharp throttle response and better mileage.Tuning on the edge like this makes detonation a possibility of course.
     
  13. bobkatrods
    Joined: Sep 22, 2008
    Posts: 621

    bobkatrods
    Member

    As others have indicated,i would keep the cam at 220 or less @.050, i also would run a different intake with a reworked quadrajet...You may think negative on the quadrajet,but if you redo it right it will give you the best mpg and performance when needed.
     
  14. Moedog07
    Joined: Apr 11, 2011
    Posts: 186

    Moedog07
    Member

    Ditto, Keep your cam in the RPM range that you will see most 2200-3000 at Highway speeds.


    Hate me if you want but I am a believer in Quadrajets too. Ride around on two tiny barrels then when you need it open the two GIANT rears. When they are right you can't beat them (except with a tire tool :D).


    .
     
    Last edited: Feb 1, 2013
  15. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,967

    porknbeaner
    Member

    I dunno I beat one with a 4 pound hammer once. :eek:

    QJets are fine, they are all the way or all the way off. They are either good or not good there is nver any in between with them. If you get one right hang onto it; it will be a fine carb for a long time.
     
  16. 283john
    Joined: Nov 17, 2008
    Posts: 753

    283john
    Member

    I run a:
    Comp Cams #249-12-234-2

    Xtreme Energy XE256H Hydraulic Flat Tappet Camshaft
    Lift: .447''/.454''
    Duration: 256°/268°

    in a Vortec-headed 355 in a '84 S-10 pickup. 3.42 rearend and 3-speed th350 trans. The whole truck weighs about 3100 lbs with me in it. Gets around 22 mpg on the highway. Cam is not radical enough to have to install the Z-28 springs. Runs 8.7's in the 1/8th mile.
    Edelbrock 600 carb.
     
  17. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member


    I have pulled as much as 19 mpg at 2350 rpm (For guys outside the desert southwest that's 90 in my car!) The combo is an aluminum headed 360 Chrysler in a light '48 Plymouth (3100 lbs with me in it), Tremec TKO500 with a .68 over drive, 3.23 gears and 26 1/2" tall rear tires. When it was younger and fresher it happily clicked off high twelves and was pretty much untouchable as a daily driver. The short block is now well into the 100,000 mile range so such monkey shines are not as frequent these days!

    I freshened up bearings and such when I had it apart this last summer, but soon it'll get a new short block with a bit lower compression (I'm at just a shade over 10:1) and my old heads plus a giant single turbo...

    In making this combo, I have tried 5 different cams ranging from wild to mild, degreed as many different ways as possible to test different theories, and this particular cam is BY FAR the best I ever had in it.
     
  18. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    Best advice on this thread so far! In retrospect, it's exactly what took me many changes to work my way into. It all has to work as a complete unit instead of indevidual parts.
     
  19. 283John

    What's your cruise RPM and speed for that mileage?
     
  20. 283john
    Joined: Nov 17, 2008
    Posts: 753

    283john
    Member

    Couldn't tell you to be precise. Speedo uncalibrated and no tach. I would guess right around 60 mph and about 27-2800 rpm. I know I filled it until it shut the gas pump off on the edge of my town. Drove it a little over 90 miles on a two-lane double-nickel highway. Pulled into a gas station and it took 4.12 gallons to refill it. Miles by calculated by map, not odometer.
     
  21. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    call a good cam company. Like COMP... To me anything over 210 at .050 forget the mpg persay...its all relative to engine efficiency....and many factors go into that including alltitude.


    I would go with a 210 duration at .050, no more then 430 lift, and 106 centerline. There are so many other ways to get performance as well, but drivability is what your seem to wanting. ALso as far as the valve springs.... I am not sure what z28 seat pressure is, but you wanna be around 110 for the street.
     
  22. halfdawg
    Joined: Jan 26, 2013
    Posts: 6

    halfdawg
    Member

    I like the Comp XE cams. An XE268 or XE262 for what your doing. Quadrajet is great if you tune it right, not the best for a manual transmission. From a performance standpoint its hard to beat a holley style mech secondary. I have a 350 in a Camaro that I have had really good performance, economy, and durability. Its a 9.5 to 1 compression, big aftermarket heads, Comp XE274 cam, RPM AirGap intake, and a Speed Demon 650 carb.

    So much of the tuning is in the ignition, not the carb. I modded the distributor to obtain 26* base timing with only 10* mechanical advance, then run the vacuum advance on manifold vacume to give around 55* advance at part throttle cruise. That is the secret to good economy, and as soon as you open the throttle it goes right to 36*.

    With this, 4.10 gears, and probably the same T5 the original poster is using I seen 18 - 20 mpg @70 mph on several 400 mile road trips.
     
  23. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,967

    porknbeaner
    Member


    I think that unless some old guy tells you and you believe him or yu went to some school to learn how to make it all work it takes all of us several tries for it to sink in. ;)
     
  24. bobkatrods
    Joined: Sep 22, 2008
    Posts: 621

    bobkatrods
    Member

    beaner. The idea is to make one right, 73-76 Quads are the best, big main air bleeds, react well to the right mods... If it aint right make it right,,,, Look at Cliff Ruggles Quadrajet site,,, You can tune these a lot of different ways... Holley will make more H. P , but for a all around carb cant be beat even with the 4 pounder
     
  25. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    Ya, but half the smarts in this game is picking the right old guy to listen to, THEN doing what he tells ya!
     
  26. This is not a chevy - It is a sbf with Edelbrock alum RPM heads. I run and Edelbrock Performer RPM cam 290/300 duration with 496/520 lift. I run 2 - 600 holleys on a factory 2x4 intake and it gets 18 mpg at 70mph at around 2600 rpms. Don't get squat around town tho!!!
     

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