Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: Aluminum cylinder head Q's

  1. #1
    396_WAYS_TO_SPIT
    What happens when you run a cylinder head that is too big for your motor? I have a friend that has a stock 502 BBC and his "car" buddies keep telling him to run a set of dart 355cc heads on his stock 502. This motor is low compression with a hyd flat tappet cam in it. He is running it in a jet as well so it will never see any kind of R's. I figured that I would post this and he can read it with his own eyes.......

  2. #2
    BDMar
    Readers Digest version..... it will be a lazy bitch and won't run anywhere near the rpm needed to make those heads work on a 502 in a jet. A 502 jet running in the low 5000 rpm range, a set of 310's would be just fine.

  3. #3
    eliminated1
    Ok what 396 has forgot to state is i am putting a roller cam in this motor and what is a stock 502. the best i can tell is that the motor is 9:6:1. the pistons are not flat but have a slight dome One engine builder said it might even be 10:0:1 on the comperssion the 502 i have comes in many versions especially when it is not a mercruiser version.Now with that bieng said one of my CAR DUDE buddies has a 496 with a compression 8:9:1 with 355 heads and it made 620 hp at 6200 rpm . he is getting me the dyno sheet today and it had supercharger cam in it . And no the dyno was done without the supercharger . im not worried about holeshot i worry about top end .

  4. #4
    Carnivalride
    Now with that bieng said one of my CAR DUDE buddies has a 496 with a compression 8:9:1 with 355 heads and it made 620 hp at 6200 rpm . he is getting me the dyno sheet today and it had supercharger cam in it . And no the dyno was done without the supercharger . im not worried about holeshot i worry about top end .
    620hp with a set of $3000 dollar cnc ported heads on a big block I'd be embarassed to say 620hp is all my engine made.
    Way over headed here 496cid turning 6200rpm. He would me much better off with a smaller head. Throttle response would be night and day difference and smaller heads would probably make more power due to the higher port velocity having better fuel atomization.

  5. #5
    cfm
    Oh boy. All I can say is if your buying new heads don't spend $$$$ on big dollar improper one's.
    If you have them sitting in your garage and have no $$$ for another set then it is what it is. But this should be the only reason to do this. Just don't expect your motor to be a world beater or even run exactly the way you want.
    I could buy a 1050 Dominator to put on my 400hp small block and make it work okay, but it won't live up to my expectations.
    Don't let cfm #'s skew the brain - there is way more to it than that !
    =======================
    BTW: Call Dart and they will tell you 540-572 or more cid , high compression, etc,etc for recommended use of these heads.

  6. #6
    ck7684
    I'm going to be running Edelbrock RPM-O heads (468 ci tho) and hoping for good holeshot over the stock R heads...then again I'm not huffing or hoping for 900hp...620 would make me quite happy indeed!!

  7. #7
    eliminated1
    Hit the nail on the head . I am borowing them just to see what they will do . and yes i have almost 00.00 dollars in them . I plan on raising the compression over the winter,

  8. #8
    widowmaker
    502 head?
    I spent the money and got a set of 305cc AFR heads for my motor, several folks told me to go bigger, but I stuck with the 305's with cnc chamber option. They should run me into about 700hp with a solid roller around 685 valve lift and 9.2 to 1 compression. I had AFR mill the heads properly to get them down to 114cc chambers.

  9. #9
    Senior Member
    Join Date
    Mar 2010
    Posts
    883
    Way to much head for even a 502. Car guys get to enjoy dumping the clutch at 4000 rpm or running a stall converter that is flashes at 5000. Boats whether jet, VD, or I/O don't get to use such "advantageous RPM providers".
    Whether "FREE" or not you going to be out time and some money for parts and when splashed you are not going to be happy. If you were turning the engine 8500 rpm and running a power band of 7000 to 8500 peak then they may work, but with a peak of 6000 to 6500 you way over headed.
    A 310cc intake runner is enough volume for a 502 CID engine to turn 7000 to 7200 without being a restriction.
    One last thing, with boat engines "power under the curve" is more important then anything. From idle to max rpm you want the greatest amount of power you can make so that curve is flat. This gives you hard accelleration at any point. Two equal engines in power, the one that accellerates the quickest will always with the race. We accomplish this with proper cylinder head cross section to provide port volume and port velocity then add a camshaft with the right valve events to create a valve path to feed and relieve the engine.
    When you get the dyno sheet from you buddy the powerband will be very steep, not broad. . . peaky. What takes more energy to do, walking up a hill or on flat ground? Drag cars need peaky power because they have gearing and transmissions to keep them in that narrow powerband. With boats you need that "walk flat" powerband.

  10. #10
    BrendellaJet
    620hp with a set of $3000 dollar cnc ported heads on a big block I'd be embarassed to say 620hp is all my engine made.
    Way over headed here 496cid turning 6200rpm. He would me much better off with a smaller head. Throttle response would be night and day difference and smaller heads would probably make more power due to the higher port velocity having better fuel atomization.
    Yep, that htng could have made a lot more power with the right head on it.

Page 1 of 2 12 LastLast

Similar Threads

  1. Bow Tie Aluminum BBC Cylinder Heads
    By PE 316 in forum Parts 4 Sale
    Replies: 8
    Last Post: 02-19-2007, 07:01 PM
  2. Bow-Tie Aluminum BBC Cylinder Heads
    By PE 316 in forum Gear Heads
    Replies: 0
    Last Post: 02-16-2007, 12:25 PM
  3. Bow-Tie Aluminum BBC Cylinder Heads
    By PE 316 in forum V-Drives
    Replies: 0
    Last Post: 02-16-2007, 12:23 PM
  4. Which Cylinder head?
    By BrendellaJet in forum Gear Heads
    Replies: 4
    Last Post: 12-03-2003, 05:20 PM
  5. Help with Cylinder Head ID
    By FastRat1 in forum Jet Boats
    Replies: 4
    Last Post: 08-01-2003, 02:31 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •