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454/420 build up

Old 08-24-2005, 06:54 PM
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Default 454/420 build up

Im thinking of freshening my 454/420 mercs over the winter. They are in a 1982 Excalibur Hawk 40. Currently, the boat does about 58mph thru the original 3" log style manifolds. Im looking to get an honest 70 and keep it reliable.

Im thinking of going with a good set of 4 inch manifolds like GIL or Stainless marine, which should get me past 60MPH alone. I wouldnt mind finding a set of weiand blowers to build it to the 525SC specs.

What do you think would be the most reliable and cost effective way to get about 500Hp out of these? Im thinking 1000HP compared to the 840 I have now should help this thing get closer to 70 with the right props and tuning.

Any ideas? The motors dont burn oil, and still hold a minimum of 35lbs at 700rpm HOT after a good run.
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Old 08-25-2005, 09:27 AM
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Default Re: 454/420 build up

I'm a big fan of the 420's. They've got a lot of potential.

Here's a recipe that really works well for the 420.
Swap out the domed pistons for a set of flat tops.
A decent hyd. roller cam (.610 lift or so. @230-240 duration)
Isky lifters are a must. (I've personally experienced $$ failures with Comp/Crane)
671 Blower/ Superchiller, twin 650 Holleys
Good quality valves, Inconel exhaust/stainless intakes.

Spin it to 5600 @ 8 lbs of boost and make some decent hp for relatively short money.

Works for me!!!!!
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Old 08-25-2005, 10:44 AM
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Default Re: 454/420 build up

Originally Posted by Biggus
I'm a big fan of the 420's. They've got a lot of potential.

Here's a recipe that really works well for the 420.
Swap out the domed pistons for a set of flat tops.
A decent hyd. roller cam (.610 lift or so. @230-240 duration)
Isky lifters are a must. (I've personally experienced $$ failures with Comp/Crane)
671 Blower/ Superchiller, twin 650 Holleys
Good quality valves, Inconel exhaust/stainless intakes.

Spin it to 5600 @ 8 lbs of boost and make some decent hp for relatively short money.

Works for me!!!!!
Do any modifications need to be made to the TRS drives to handle the extra power?
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Old 08-25-2005, 11:39 AM
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Default Re: 454/420 build up

I've been putting 600 H.P. to my TRS in a 9500 lbs. boat for 4 years now, NO BREAKAGE....
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Old 08-25-2005, 03:19 PM
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Default Re: 454/420 build up

Yes spk1, Your TRS drives will explode. The good news is the Konrad 540 will bolt on with no modifications and you can be done with drive failure.

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Old 08-25-2005, 06:33 PM
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Default Re: 454/420 build up

My boat has about 1000 hours on the original TRS and Merc trannies. They have been pushing a 40ft Excalibur around for the past 23 years with out any trouble. I hear lots of people say the TRS are tougher than bravoo's. I blew a bravo with 250 hours on a 23ft boat with a 454/365Hp to smithereens.

Biggus, what kind of numbers did your recipe produce? It sounds good!
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Old 08-25-2005, 06:53 PM
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Default Re: 454/420 build up

My 420's were punched to 468, 10:1 compression, and a Comp 292H cam. I don't know what power they make, but they run damn good.
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Old 08-25-2005, 07:20 PM
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Default Re: 454/420 build up

You don't need blowers to get 500HP from your 420s.
There are lots of part combination that will get you there. Most will tell you to raise the compression a bit, port the heads, and go full roller valve train. Good exhaust manifolds or headers are a must.
Also, if you have BW tranys not Merc 1s, your drive system should be good for 500HP without question. If you do decide to go for blowers and 600+HP, then you may want to consider trany and drive upgrades...
Have Fun!
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Old 09-08-2005, 04:27 PM
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Default Re: 454/420 build up

Originally Posted by cuda
My 420's were punched to 468, 10:1 compression, and a Comp 292H cam. I don't know what power they make, but they run damn good.
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Old 09-08-2005, 07:36 PM
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Default Re: 454/420 build up

Originally Posted by Pat McPherson
You don't need blowers to get 500HP from your 420s.
There are lots of part combination that will get you there. Most will tell you to raise the compression a bit, port the heads, and go full roller valve train. Good exhaust manifolds or headers are a must.
Also, if you have BW tranys not Merc 1s, your drive system should be good for 500HP without question. If you do decide to go for blowers and 600+HP, then you may want to consider trany and drive upgrades...
Have Fun!
Yeah to what Pat said!!! Can't over emphasize the suggestion of a good exhaust system vs the stock Merc cast iron junk. Before you do any other mods, you will need the better breathing exhaust system FIRST---- especially with a boat your size, and weight when only using a 454cid size engine. If you keep those 454cid engines naturally aspirated, then they will need all the help they can get! Just beware---I'm NOT an engine expert! Anyway, have fun.
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