Cam size, higher compression?
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Cam size, higher compression?

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    1 of 3 Stoojz caribbean20's Avatar
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    Default Cam size, higher compression?

    Motor is a 502 with Dart Pro 1 aluminum heads, 119cc chambers and 310cc intake runners. Estimate compression in the low 9:1 range. Cam is Comp Cams extreme marine hydraulic roller with about 580 lift and 240 @ 50 duration. Recently switched to the Dart heads from the stock GM cast irons but did not change the cam. Other details are Vic Jr. single stage alum intake, Holley 850 w/ vacuum secondaries and EMI Thunder exhaust.

    Need to have shop pull engine and jet intake due to broken bolt and water leak on intake. While the motor is out, WTF? Estimate current HP is about 420 (5,200 RPMs w/ Mag./Bronze A/B cut, Berkeley). Boat (20' Caribbean) and motor runs real good now, but I know the motor is not optimized for the new heads. Thinking about new cam (maybe something in the 640 lift range) and bumping the compression (due to the aluminum heads). I know the first general order is to have the heads flowed for data, but these are rather popular heads, so isn't flow data readily available?

    Looking for advice on proper cam selection (lake application, need to idle in no wake zones) and proper compression (mill the heads?). Will this yield about 500 HP, or a bump of about 70 - 80 HP? If not, probably not worth the trouble.

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    Strap on the JATO konajet74's Avatar
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    Quote Originally Posted by caribbean20 View Post
    Motor is a 502 with Dart Pro 1 aluminum heads, 119cc chambers and 310cc intake runners. Estimate compression in the low 9:1 range. Cam is Comp Cams extreme marine hydraulic roller with about 580 lift and 240 @ 50 duration. Recently switched to the Dart heads from the stock GM cast irons but did not change the cam. Other details are Vic Jr. single stage alum intake, Holley 850 w/ vacuum secondaries and EMI Thunder exhaust.

    Need to have shop pull engine and jet intake due to broken bolt and water leak on intake. While the motor is out, WTF? Estimate current HP is about 420 (5,200 RPMs w/ Mag./Bronze A/B cut, Berkeley). Boat (20' Caribbean) and motor runs real good now, but I know the motor is not optimized for the new heads. Thinking about new cam (maybe something in the 640 lift range) and bumping the compression (due to the aluminum heads). I know the first general order is to have the heads flowed for data, but these are rather popular heads, so isn't flow data readily available?

    Looking for advice on proper cam selection (lake application, need to idle in no wake zones) and proper compression (mill the heads?). Will this yield about 500 HP, or a bump of about 70 - 80 HP? If not, probably not worth the trouble.
    Are you playing with us?? I think you're way underestimating or you have another problem! FYI, my 454 w/ 990's, 226/236 hyd roller, 9.5-1 comp turns an A2 to 5200 (approx 500 +/-). You've got something else going on!

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    1 of 3 Stoojz caribbean20's Avatar
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    No Kona, not messin with ya. Differences on the classic Berk HP chart can also be attributed to loose vs. tight pump, nozzel size, loading, etc. My Berk 12-JG is newly-rebuilt with all the good stuff. Furthermore, I described my package to a veteran motor builder last year when I was thinking about bumping the compression, and he "guessed" my HP spot on at about 430 without any other facts. This jibes with the Berk chart. Maybe my A/B cut is actually an A, but I think the HP sounds about right. I do know this modest package motivates a big 'ol 20.5' semi-V daycruiser to 77 on the top end (GPS), not bad.

    Now, how about thoughts on the cam? Guess I'll check next with C. Straub, if he is still grinding.

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    Like konajet said, I think your way low at 420hp. If that really is what your making, my guess is something isn't right. That should be a solid 500hp motor right now.


    Darrell.
    San Diego.

    28ft Sportcat
    With Twins

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    Senior Member earlbrown's Avatar
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    How did you estimate your compression?


    And do you have any pics of your boat. I've got a 19' Caribbean in my driveway and I hardly ever see any of them around the board.

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    cfm
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    What altitude do you run at ?
    FAct, not theory: Under 1000ft, you are way off with the hp guess unless the tune is out to lunch and or your vac secondaries aren't opening much or your cam specs you mentioned are not anywhere close to what you have. 600HP is more realistic at around 5800rpm or so - edit in: 540 or so at 5200. Also, if you are using the standard springs that come on the Dart heads from Dart for a HR, they are usually too low of psi to run 5k+ with stout cam.

    Are your EMI's dry thru the tail or is water entering in the stock location ?

    I don't see an Extreme Marine HR with 240 at .050" with .580" lift. Can you post the part or grind # ?
    Last edited by cfm; 04-17-2009 at 03:02 AM.

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    Quote Originally Posted by caribbean20 View Post
    Motor is a 502 with Dart Pro 1 aluminum heads, 119cc chambers and 310cc intake runners. Estimate compression in the low 9:1 range. Cam is Comp Cams extreme marine hydraulic roller with about 580 lift and 240 @ 50 duration. Recently switched to the Dart heads from the stock GM cast irons but did not change the cam. Other details are Vic Jr. single stage alum intake, Holley 850 w/ vacuum secondaries and EMI Thunder exhaust.

    Need to have shop pull engine and jet intake due to broken bolt and water leak on intake. While the motor is out, WTF? Estimate current HP is about 420 (5,200 RPMs w/ Mag./Bronze A/B cut, Berkeley). Boat (20' Caribbean) and motor runs real good now, but I know the motor is not optimized for the new heads. Thinking about new cam (maybe something in the 640 lift range) and bumping the compression (due to the aluminum heads). I know the first general order is to have the heads flowed for data, but these are rather popular heads, so isn't flow data readily available?

    Looking for advice on proper cam selection (lake application, need to idle in no wake zones) and proper compression (mill the heads?). Will this yield about 500 HP, or a bump of about 70 - 80 HP? If not, probably not worth the trouble.
    With what you have you can easliy make 600HP in a Jet configuration. Those darts make extremely good power. Do you still have the OEM lifters in the 502, more lobe lift will require aftermarket tie bar lifters.
    Chris Straub
    Straub Technologies

    3HP is an A$$ Whooping!!! JW

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    1 of 3 Stoojz caribbean20's Avatar
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    Default More details

    I used this chart to estimate HP
    http://www.cpperformance.com/TechTip...r-curve-lg.jpg

    The motor is casting # 10237300, Gen 6 w/forged internals. Original engine builder "told" me compression was in low 9s.

    My cam is Com Cams Xtreme Marine 254/260 duration, 575/575 lift.

    Statistics taken at Mead, elevation 1,150'.

    Running stock lifters with Crower roller valvetrain. New pushrods when we installed the Darts.

    Attached are pix. Water dumps from exhaust at end of chrome tips.

    Not real concerned with HP estimate now, but pretty sure motor is running just fine. Do not see many big jets running high 70s in the "real" world, no matter what HP claims made.

    Bottom line, I am just curious to know what additional HP might be gained from a bigger cam and higher compression to take advantage of the Dart aluminum heads. Motor will be out, does it make sense to tear into it? What might be gained without getting too radical?

    Unfortunately, I live in LA and boat is in Boulder City, NV. My mechanic does more work on Bayliners and Wake Board boats than fast jets, so I have to do the leg work.

    Thanks for all of the feedback.

    Regards,

    Doug
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  11. #9
    cfm
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    My cam is Com Cams Xtreme Marine 254/260 duration, 575/575 lift.
    Thanks for the info.

    Well, my O2 is that your engine probably has 50-60 more hp (or more) than you are using, since you are only running it at 5200rpm. Your cam combined with the rest of the components (springs and hr lifters not included! since I don't know what you have their) probably makes peak hp around 6300-6400rpm. Somewhere in there.

    You could shorten up on duration but use more lift. Those heads will only get better with more valve lift. A conventional cam somewhere around 240,246 with .630-640. lift, however that will still put your peak hp at 5800-6000rpm.

    FYI: peak hp at 5200-5400rpm would require around 222-226 at .050", and I don't think youd want to be there with those heads, cubes, and etc.

    Summary - you should do impellar and/or pump set-up changes to get your rpm up where your motor should already be making a bunch more power. Make sure your springs and lifters can take it. Ti retainers may be good investment at same time.

    All my 02.

    Something to think about.

    Edit in: Definately increase compression, especially if you keep the cam you have now.

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