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Discussion Starter #1
I'm new to the jet boat thing this year (21' Omega Open Bow, jacuzzi jet) and wiped out some lobes on the cam (Hydraulic flat tappet) a few weeks ago. I'm going to use this as a chance to upgrade. I have a BBC (468, mark IV, 2-bolt main) with a set of ported (bought them that way) large oval port closed chamber heads (milled to 96.4cc) with slightly dished pistons on there now. I also have a set of stock 781 casting (extras), a couple extra 2-bolt blocks, and stock forged crank. I have the opportunity to upgrade to Manley rods (+.250"), 30 or 50 cc dome forged pistons, roller cam and lifters, rev kit (the cam included is a new .726"/.720" lift 284/290 @ 50 with a 108 LSA), Weiand Team G intake, and a set of Jegs Aluminum 119cc rect port cylinder heads (2.30" intake, 1.88" exhaust valves) for a very reasonable price. These are used, but I am going to have all of the parts checked out at the machine shop prior to purchase to verify that the are all sound. The questions i have are: -Has anyone ever used these heads? feedback on them? -Max compression ratio for aluminum heads on this setup? -What is the minimum lobe separation angle LSA for logs vs. headers? (I think the one included is too low from what I have read) -Any other info that would be useful would be very much appreciated! Thanks!
 

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Those heads are Canfields.

Wowzer does that cam have a lot of duration. Need more info on what you are planning to build (rpm range, compression, how to be used, etc) but chances are with that small of a motor and even built for drag race only that cam should not be used. Logs way,way out of the equation.
 

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just a ski boat with bark
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If I read this right you have a 21" open bow jet, if so I would think you would need power at or before 6000rpm. Is this a pump gas build or are you planning on running better fuel, because the 50cc dome pistons sound like way too much, the 30cc dome ones would be pushing the compression limit IMHO even with open chamber aluminum heads, probably 10.5-10.75:1 with a 119cc chamber. The cam you mentioned sounds like way too much duration for this build. What do you have for exhaust on this logs or something better?
 

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Are the heads that Jegs sells now still Canfields? Not tryin to jack! WT:)devil
 

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steelcomp was here
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With the 2.300 valve you don't want to use the jegs heads. Your engine will be a dog unless you want to turn 8500rpm. Chances are they're the 350c intake, not the 310. Either way, the 2.300 valve is way too big for what you're doing. The 781's with 2.19/1.88 valves and a good bowl blend will be a much better choice.
 

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Discussion Starter #8
I believe the Jegs heads have 350 cc intake runners. I was shooting for 10.5:1 or so compression. I think the 50 cc dome with .060 head gaskets and .035 deck gives about 11:1 with 119 cc head if I recall the calcs right. The cam doesn't look like the best choice, but I'm especially interested in whether the heads will work for the application. I know they are really for higher rpm use normally, but it is a budget builld and I am trying to use what I have available without too much added work/cost. The feedback is great so far, any more is appreciated!
 

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Quick Jets says the heads can never be too big. But when he said that, I don't think he was thinking about a 21 ft Omega with a jacuzzi.

Like Steel said they are big and will never get anywhere near the flow velocity they were made for at the RPM you'll be turning. Add to that a cam that is way big, and it becomes a double boggie.

and I don't recommend you running the piston .035 in the hole, plus a .060 gasket for a total fo .095 in the hole and then throw pump gas at a 11 to 1 motor. The combo is screaming detonation!



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Discussion Starter #10
I also have a set of Icon IC 779 pistons (18cc dome) with like a half hour of run time, but could not run the +.250" long rods. Of course I can always buy a set of pistons to match the application if the heads will work...
 

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just a ski boat with bark
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if the heads will work...
Will they allow a 468 to start and run......... yes

Will they work well on a 468....... no

You're not getting it that a 468 in front of a jet pump is not going to run in the rpm range where those 350cc runner heads or that 284/[email protected] cam want to run. In fact the combination you're proposing might run slower than what's in there now.
 

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108 LSA is super tight for a cam that is pushing 290 degrees @ .050 That is a huge cam that will run like :)st
 

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I'm new to the jet boat thing this year (21' Omega Open Bow, jacuzzi jet) and wiped out some lobes on the cam (Hydraulic flat tappet) a few weeks ago. I'm going to use this as a chance to upgrade. I have a BBC (468, mark IV, 2-bolt main) with a set of ported (bought them that way) large oval port closed chamber heads (milled to 96.4cc) with slightly dished pistons on there now. I also have a set of stock 781 casting (extras), a couple extra 2-bolt blocks, and stock forged crank. I have the opportunity to upgrade to Manley rods (+.250"), 30 or 50 cc dome forged pistons, roller cam and lifters, rev kit (the cam included is a new .726"/.720" lift 284/290 @ 50 with a 108 LSA), Weiand Team G intake, and a set of Jegs Aluminum 119cc rect port cylinder heads (2.30" intake, 1.88" exhaust valves) for a very reasonable price. These are used, but I am going to have all of the parts checked out at the machine shop prior to purchase to verify that the are all sound. The questions i have are: -Has anyone ever used these heads? feedback on them? -Max compression ratio for aluminum heads on this setup? -What is the minimum lobe separation angle LSA for logs vs. headers? (I think the one included is too low from what I have read) -Any other info that would be useful would be very much appreciated! Thanks!
Ok, since you asked, here's what I'd suggest. Freshen up the 468 as is, put it in the boat and have a blast skiing/tubing/hanging out. The boat you have is perfect for that. The parts you have are too mismatched and the boat you have isn't a good choice for high HP anyway. Best of luck to you....
 

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Listen to David.
That is really good advice he is offering you.
Sometimes your money ahead to just say no.
 

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I agree with everything that's been said so far. If you are looking to upgrade, I would say switch to a nice roller cam that will work with the parts you have now (heads, etc.)
 

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Discussion Starter #17
New questions...

Thanks for all of the great input guys! While I likely won't use them on this motor, think I'm still going to buy the heads as part of a large lot of parts (great price), I am going to put new pistons (none of those mentioned before) on while I'm freshening up the block, forged since I want to be able to put some nitrous on it comfortably. Also switching to a forged crank that I have sitting here anyway. I have a couple other questions given those changes:

-Should I use a flat top piston with the ported 96.4cc Closed Chamber oval port heads (2.19,1.88 valves) or a 18-27cc dome with the 781 Oval port heads (still stock)? (Obviously I will still have the Jegs Rect port heads and intake mentioned above as an option, but I all input so far indicates not using those for this build)

-I think I will just go with one of the recommended Comp Cams marine roller cams in the neighborhood of 550-600lift and [email protected] to [email protected] duration. Would it be better to go with Hydraulic or Solid Roller? What are the benefits/drawbacks to each in this application?

Thanks in advance for the input
 

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Discussion Starter #18
New info, Jegs Heads are 310cc not 350cc

I found out that the heads are 310cc versions, not 350cc. Would like to know if that would change the input I received before. Thanks!
 

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I believe he said they were used heads. Jegs heads are no longer with the exception of any left in stock. The Canfields are coming back. Don't know if they will be supplying Jegs, but the heads are coming back
I talked to the guy who was clearing out all those canfield heads for the foundry and I think they will be CHANFIELD heads when they come back.What i was told was that he had the patterns for the existing heads and for some changes that were a new and improved version.Could be B>S>but this guy seemed real informed.
 
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