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getrdunn 03-24-2021 11:02 AM


Originally Posted by thisislivin (Post 4782893)
what are the valve sizes?

2.300/1.88.

KAAMA 08-07-2023 12:14 AM

Here's something to consider guys------

Snap, I think you're right about the cam duration, my friend, because after seeing the dyno results on this thread of a 548"engine destined for marine use, In my opinion for what it's worth, it's tipping a little too much/too late on the high end of the RPM band/scale/curve with the Torque peaking a little too late @5100rpm...and peak HP @6300rpm. It tells me the cam is a little on the large size of duration and I think the head size (340cc) is a bit too large for a 548" engine for your application as well unless maybe you have a small, light weight boat (?)----or maybe destined for Offshore Racing?.

It may look great on a dyno sheet paper if all you are going after is a HP number (700hp)---so you got your HP goal of 700hp, but probably at the expense of sluggish soggy mid-range torque loss. I don't know how heavy the boat is or what kind of hull design these engines are now sitting in (???)----are these engines in a cat/tunnel hull boat or something small/light? What RRM do you doing find yourself cruising your boat at with these engines now?----are you usually running/cruising into the 5000+rpm range?

I think the engines would be better suited with the same original cam profile duration numbers of 242*/252* (or even a hair smaller) that were removed when your new cams were being ground. But perhaps your boat runs well and you are very happy with the performance attitude and results.

Anyway, to anyone reading this, this is a friendly/civil argument and I am not slamming anyone, or trying to start a poopoo storm, but if you want to counter my claims with your own, then I would enjoy hearing your feedback/your thoughts. Just remember, I am not an expert just have some limited experience with stuff of my own and it's just my .02 Thanks everyone, Mark

snapmorgan 08-07-2023 07:18 AM

These engines were for a 30' Eliminator cat. Didn't need much low end torque to get this boat moving. The owner was only interested in going fast, which it is.

adk61 08-07-2023 07:21 AM

Combination
 

Originally Posted by KAAMA (Post 4875822)
Here's something to consider guys------

Snap, I think you're right about the cam duration, my friend, because after seeing the dyno results on this thread of a 548"engine destined for marine use, In my opinion for what it's worth, it's tipping a little too much/too late on the high end of the RPM band/scale/curve with the Torque peaking a little too late @5100rpm...and peak HP @6300rpm. It tells me the cam is a little on the large size of duration and I think the head size (340cc) is a bit too large for a 548" engine for your application as well unless maybe you have a small, light weight boat (?)----or maybe destined for Offshore Racing?.

It may look great on a dyno sheet paper if all you are going after is a HP number (700hp)---so you got your HP goal of 700hp, but probably at the expense of sluggish soggy mid-range torque loss. I don't know how heavy the boat is or what kind of hull design these engines are now sitting in (???)----are these engines in a cat/tunnel hull boat or something small/light? What RRM do you doing find yourself cruising your boat at with these engines now?----are you usually running/cruising into the 5000+rpm range?

I think the engines would be better suited with the same original cam profile duration numbers of 242*/252* (or even a hair smaller) that were removed when your new cams were being ground. But perhaps your boat runs well and you are very happy with the performance attitude and results.

Anyway, to anyone reading this, this is a friendly/civil argument and I am not slamming anyone, or trying to start a poopoo storm, but if you want to counter my claims with your own, then I would enjoy hearing your feedback/your thoughts. Just remember, I am not an expert just have some limited experience with stuff of my own and it's just my .02 Thanks everyone, Mark

It is a cat, that said, the power band is on the high side, however depending on size, weight and intended usage I think Snap hit his target as he desired..
your comments would be correct if the application were a bigger heavier V bottom with different power curve requirements , but a cat is a different animal altogether..

KAAMA 08-07-2023 08:24 AM

I kinda thought it might be a small Cat---thanks for the feedback guys,

adk61 08-07-2023 08:27 AM

If you think that's a big cam then you will totally disagree with what my blower cams are 🤪

KAAMA 08-07-2023 09:11 AM


Originally Posted by adk61 (Post 4875839)
If you think that's a big cam then you will totally disagree with what my blower cams are 🤪

I hear you and you can certainly do what you feel and believe is right, but for me, if I am going to "err" on a cam profile/size selection, then I usually try to err on the smaller size---but that's just me and I am not an engine builder---but the freedom to choose is always nice.

Also, I tend to think there is a little more slack for blower applications when it comes to cam/head profiles as a blower just comes in like gangbusters with power everywhere---- blowers are a little more forgiving and have a little more of a "window" compared to naturally aspirated engines that can be a little more sensitive to head and cam sizes, etc.. .

Tartilla 08-08-2023 02:31 AM


Originally Posted by KAAMA (Post 4875846)
I hear you and you can certainly do what you feel and believe is right, but for me, if I am going to "err" on a cam profile/size selection, then I usually try to err on the smaller size---but that's just me and I am not an engine builder---but the freedom to choose is always nice.

Also, I tend to think there is a little more slack for blower applications when it comes to cam/head profiles as a blower just comes in like gangbusters with power everywhere---- blowers are a little more forgiving and have a little more of a "window" compared to naturally aspirated engines that can be a little more sensitive to head and cam sizes, etc.. .

I like to plan for peak rpm on the right side of the peak HP curve. Tha way I achieve the HP goals, and have a cam that is a bit smaller, so part throttle manners and performance are enhanced.

Best scenario is an engine combo that holds within 10hp of peak for 500 rpm or more. This creates the ultimate prop selection opportunity.


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