7.4LX MPI to Carb, what cam to use
04-19-2008, 08:13 PM
#23
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You may want a single plane oval port intake if you are using O- Port heads. Find a 502 mag takeout cam or one that is close to a 224 - 226 on the intake and 112 to 114 centerline with an exh duration of about 234 and lift at about .520. A lot will depend on compression and exhaust.
Last edited by IRONMAN; 04-19-2008 at 08:33 PM. Reason: add
04-20-2008, 09:51 AM
#25
I've got a Crane 731 that will slide right in. You can re-use the stock lifters and dogbone retainers. You may or may not have to change pushrod length. That would depend on what rocker arms you are using. PM me if interested. The cam is perfect and has less than 1oo hrs total. I got new cams because I went from 502 to 540 CI. Cranes part number is 168731. You can get the specs on Cranes website.
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04-20-2008, 10:50 AM
#26
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Are you sticking with the stock pistons and 8:1 CR? What exhaust are you using. Do you plan on using the stock valvesprings? We need this info to really nail down a perfect cam choice. I think the 731 is identical to the old merc hp450 and hp500 carb cam
04-20-2008, 07:44 PM
#27
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I am using the stock pistons, springs and rockers. A new cam is as far as I want to go into the bottom end for now. I am using a stock 496 exhaust with normal risers. Thanks for all your help.
04-20-2008, 08:06 PM
#28
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sounds almost exactly like what i put together in the last couple months , except i didnt change the cam , not yet anyway
to add to the similarities , my boat is a checkmate 24 , very similiar to your Velocity 23 ,
aside from the cam , i went with large oval heads (781 casting) almost identical to the 049's
and i also went with a high rise single plane intake and holley double pumper , same 496 manifolds , they sound and perform waaaayyy better then the cast crap that was on my engine
i went out yesterday with the same prop from last year , and it seems like i'm gonna need to step up from the 23 pitch to around a 25 or 26 , should see a nice jump in speed
i'll be curious to see how the cam change helps yours out , and maybe convince myself to do the same
to add to the similarities , my boat is a checkmate 24 , very similiar to your Velocity 23 ,
aside from the cam , i went with large oval heads (781 casting) almost identical to the 049's
and i also went with a high rise single plane intake and holley double pumper , same 496 manifolds , they sound and perform waaaayyy better then the cast crap that was on my engine
i went out yesterday with the same prop from last year , and it seems like i'm gonna need to step up from the 23 pitch to around a 25 or 26 , should see a nice jump in speed
i'll be curious to see how the cam change helps yours out , and maybe convince myself to do the same
04-20-2008, 08:25 PM
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I went for the bottom first (not unusual), but I don't have the nerve to run anything but the stock lift until I upgrade the rest of the valvetrain - esp. the ex valves.
