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I have had a few people tell me I need to switch from large ovals to rectangular port heads because of the characteristics of my cam. This is what I got from one person.
small peanut port ovals idle-4000rpm's low torque head
large oval port 1500-6000 rpm's bottom end torque/mid range power
Rectangular port heads 3000-7500 rpm's
My cam is 258@.50,.615 lift,108 lobe sep,solid lifter
I need some info before I go out and buy a different set of heads. I know its spring break but someone has to be around for info.
396
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I would call the cam maker and ask them what the cam is setup for.
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how much comp. are you running? with anything less than 10-1 i would think you would be fine with the large oval port heads. (that would be my choice). with those cam specs and about 9.5-1 and some large oval ports you will have a nice useable motor. with more comp. and maybe even a bit more cam timing you can go to the rect. port heads for more top end. how do you intend to use the boat and what boat (size, wieght, drive) are you putting this motor in? by the way, this is just my opinion. a good hi performance marine motor builder would be your best bet to get info from. not to mention calling the cam manufacturer as suggested earlier.
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I am going to be around 11-1 compression.
18ft jet boat with a berk jet.
I will be spinning around 5700-5900 r's
396
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you know I ran oval Merlins on a 502 on my old jet boat and they ran just fine. Cam was about 264'ish @ 50. motor was the same.
I actually took off a set of 990's and it ran better with the ovals. I think it was the different exhaust port configuration.
Sometimes the higher flowing head is not necessarily the best for your application.
I always made sure that the cam is matched to the rpm range of the boat with special attention to torque curve. Power made over 5,700 rpm is a moot point.
Now maybe you can do better with aluminum aftermarket rectangulars. I didn't try that.
At any rate, I am sold on the new aftermarket stuff (oval or rectangular)
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Originally posted by 396_WAYS_TO_SPIT
I am going to be around 11-1 compression.
18ft jet boat with a berk jet.
396
On pump gas????
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Nope AV gas;) :D :D with 36 degrees timing:D
396
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The set-up you're running is commendable but the cam is overkill for the large oval cylinder head. On a flow bench you can see there is no performance gain from going past a .590" gross lift profile.
Sure it may run just fine but it's more valvetrain movement than one needs for this set-up. Sure the compression is nice and it will survive with that duration and LSA, but your leaning towards a head swap real soon here.
Just my opinion for what it's worth.
~Ty
