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Rooster Tail

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New Engine Build
« on: February 09, 2021, 08:33:57 am »
Hello new here to jet boats but not to building engines. I've got a 460 that I am redoing trying to keep it dependable but putting some decent parts in it. Block is going .030 over with a .000 deck, heads are Performer RPM 60665,Pistons are JE flat top -3cc, intake is an Air Gap Performer RPM, Holley 850cfm mechanical carb. I've heard about issues with oil pans so I went with a Dooley 9 qt.
OK so here comes the question Id like to use a solid roller cam but not sure about specs. I was looking at the Comp Cam site and thought the 34-803 or 34-850 looked a bit to much.
Anyone have any first hand experience other than to call comp?
Boat is a 20' Sutphen
  • Boat #1: 1977 Sutphen 20'#039 Super Pacer
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dkcerven352

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Re: New Engine Build
« Reply #1 on: March 19, 2021, 11:14:10 pm »
What are u using it for? With that selection of parts with the stock stroke you are looking at almost 15:1 compression.... i  other words thats a grenade
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mash on it

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Re: New Engine Build
« Reply #2 on: March 20, 2021, 09:14:13 am »
I calculated 9.83:1 compression. (Summit racing)
.727" is huge. And 275°@ .050 isn't friendly with any water cooled exhaust. More compression is needed for a cam like that.

What exhaust are you running?
What impeller?
What hull?
Goals for the boat?

Dan'l


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CJ/RR 212...under construction  "Pistol Annie"

dkcerven352

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Re: New Engine Build
« Reply #3 on: March 24, 2021, 09:30:56 pm »
Your right, something was off with that initial calculation not sure what happened there. Either way the dynamic compression results are a bit steep for reliable performance on pump gas... and as you stated high duration numbers and wet exhaust are not good together. Im curiouse what heads are intended to be used, that can make a huge difference.
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Rooster Tail

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Re: New Engine Build
« Reply #4 on: January 09, 2022, 05:40:58 am »
ok so to update an old post.... the engine is now done we made max torque 526@3800 over 510ft.lbs all the way out to 5200rpm
the horsepower came out to 500@5200 rpm. hp was still climbing up to 6500 but did not care about the numbers after 5200rpm.
Berkeley recommended an "A' cut impeller but use an inducer-
the specs for the engine are as follows,
460 .030 over
SRP flat tops 10.3:1
comp solid roller .634/.634 236@.050 110 separation
Performer RPM 60669 out of the box
Performer air gap intake
850 Holley flowed to 930cfm
exhaust is Berkeley Ported center rise manifolds that have been ported.
looking for a good cruiser to make some noise and go fast.

  • Boat #1: 1977 Sutphen 20'#039 Super Pacer
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Knightnight

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Re: New Engine Build
« Reply #5 on: January 14, 2022, 07:50:47 am »
what compression ratio are you at now? Isn't 930cfm a little overkill at 5200rpm. Most carb calcs would be around 600ish cfm (85% efficiency, race carbs assume 110% efficiency eg FI). Add a little more CFM requirement for marine application (50-100cfm) so maybe around 650-700cfm carb. Wouldn't oversized carb decrease low end response.
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dkcerven352

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Re: New Engine Build
« Reply #6 on: February 04, 2022, 10:15:28 pm »
Port matching, proper runner size/shape, good valve job and tuned exhaust can get into the 90-95% efficiency range without too much trouble.  Given its a 466, that calls for an 832cfm. Choosing the right cam for the job plays a huge roll. From what i have heard from buddies jet boats in particular like the bigger carb selection. This all assumes that everything was done properly ie a straight block, proper clearances etc.
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