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Old 01-17-2008, 10:31 PM
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Power gains on 454 with stock heads?

Hello everyone,


I have the little jet boat with a 454 in it. I yanked the heads tonight and found that I have flat top pistons with valve reliefs in them and I have the peanut port style heads.

My question is, stock vs stock, how much more power will a set of oval port or rectangle port heads make over a set of peanut port ones. Would it even be noticible? Just curious because i can get a set of either ovals or rectangular port heads from a friend for about 500 bux.

Also, did 454 heads come stock with the dual coil valve springs? because the ones that are on there now have the outer spring with another coil in the middle. its a gen IV engine by the way.

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Old 01-18-2008, 12:00 AM
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The peanut port heads don't flow much and in a jet boat RPM is a concern. I would go with the oval port heads, you might even would want to deck them a little for a touch much compression since 454's were very low on comp. to start with.
The rectangular port heads would work properly only if you rebuild the engine with hipo parts to match the high flow of those heads. The inside spring is a dampner coil, not really a 2 valve spring head.
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Old 01-18-2008, 12:08 AM
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The pistons are flat tops with 2 reliefs in them. Im not sure if the stock pistons had reliefs, but even so, Ill try and get a nice set of oval port heads. U think i will notice a difference?
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Old 01-18-2008, 12:19 AM
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I really doubt it, you probably have a stock 8:1 comp. 454, they are usually wheezed out by 4500 rpm and really didn't make a lot of hp. You may see a little more rpm but the low compression and weak cam are limiters.

If you have some EXTRA (???) money laying around you could bore it and go with those oval ports, 9.5:1 flat tops and a good Comp Cams marine cam and THEN you would feel a difference. Good luck
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Old 01-18-2008, 12:40 AM
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If I were to go with some iron heads with a 119cc chamber, what would the compression be like with my stock pistons?
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Old 01-18-2008, 12:53 AM
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I think the peanut port heads were 119 cc's also so you wouldn't gain any compression that way. Without tearing it down and rebuilding the only other option is too mill the heads and use a thin head gasket. A COMPETANT machine shop can tell you how much to take off.

But remember, just a point of compression isn't going to do much if any for you, you need the right combination of parts to make an engine perform.
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Old 01-18-2008, 07:36 AM
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If the heads you have are the peanut port (what part # are they?). And if they are open chamber and the pistons are flat tops you could try a closed chamber pass head (the ports are bigger vs peanut port heads) and that will bump your compression up. You can go here to check on chamber size if you have the casting numbers http://www.mortec.com/
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Old 01-18-2008, 08:50 AM
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stock cr is in the mid 7's.

To get 9:1 cr with a 454 and 120cc heads, you will need a dome piston. The dome should be about 0.125" tall. Will need to run higher octane fuel if the cam is short duration.

The power you gain will depend on the cam. Do you know what cam you have?

You could try a set of 402 heads (820's i think). They have 112cc chambers. came on early 70's engines. They should rise cr to 9:1 and they flow well.

I would use a set of 781 or 049 heads before using the peanut heads.
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