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Old 02-14-2018, 02:06 AM   #1
70c10guy
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406 Build!

Hi guys, I have a 400 small block that I acquired on a per day ďtrade.Ē

Itís at the machine shop as of now. Having him disassemble the short block and hot tank it.

I am getting the short block built for my boat. Itís a 17í ski boat.

Hereís the story, I couldnít pass up a deal on a set of NEW vortec heads. So I bought them. Unfortunately the chamber size is a bit on the small end for the 400.

Iím wanting to get the short block built to a 406. I found pistons on summit that have a 14cc dish to them. With the block being 0 decked, .040 head gaskets, and the vortec heads, my compression ratio is at around 10.6:1

Wanted to stay around 9.5-10:1 but I canít find pistons that fit my application. I will be using the stock rods and I mostly see piston applications for the 5.7 rods.

So my question to everyone here is will I be safe with a 10.6:1 compression in the boat?

Does anyone have any experience using a bigger dish piston for a 5.565 rod? (More than 14cc dish, if so please Inform me)

Donít really want to get other heads as well.

The boat will see a max rpm of possibly 5000? Not all day long though. Just occasional. Hoping to hear from someone here as this has been bugging me.. I was just going to bite the bullet and keep my timing on the conservative side but I had to ask!!! Thanks everyone in advance.
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Old 02-14-2018, 07:38 AM   #2
b454rat
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Re: 406 Build!

I built a similar motor but for a truck and was an awesome motor, but boats see more loads than a truck....and stick with 5.7 rods
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Old 02-14-2018, 07:50 AM   #3
rsavage
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Re: 406 Build!

I think that you will have trouble finding gas with enough octane on the water. Where I live, 91 octane is what is available at marinas. 93 is marginal on 10.5 with iron heads. Aluminum heads maybe. Make sure that you let the machine shop check the block for cracks before you start buying parts. My engine machinist told me that 1 out of every two that people bring him are cracked.
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Old 02-14-2018, 09:39 AM   #4
70c10guy
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Re: 406 Build!

So you’re saying that this combo might not work for a boat? I am trailering the boat and will not go far on the water. By me there’s a Stewart’s that has 93 non ethanol. All the landscapers go there. In the marinas by me there’s also 93. I can’t run 10.6:1 on 93 then huh? I’m gonna have to talk to my machinist then to see if he can mill the pistons down some more.
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Old 02-14-2018, 01:20 PM   #5
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Re: 406 Build!

I am certainly no expert. Based on my experience with higher compression iron headed motors in my classics, I have to run a mixture of some race gas and 93 pump to prevent detonation. I have the block maching done, rotating assembly balance and installed and then do the rest - but the machine shop has to know what heads and cam I will be using to match pistons. Boats have some relatively high load/high rev use for longer periods of time than does a classic car's normal use. If you have thru hull exhausts you probably won't be able to hear it if it is detonating. I'd suggest going with what your engine builder suggests. Your block is already .030 over, so depending on whether or not it needs to be cleaned up and by how much will determine whether it is usable. Once that is determined, can start having it put together. Heads and cam have to be known to know what pistons can be used to get where you want to be on compression. You don't want to put a bunch of money in an engine that won't work for your application if you can't get the CR down to say 9:1. A 4 bolt 350 block starting with a standard bore might be a better investment?
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Old 02-14-2018, 01:22 PM   #6
70c10guy
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Re: 406 Build!

This is actually a standard bore 400. It’s a virgin block. If I can get the 14cc dish pistons mulled down some more hat would be ideal. I’ll see what he says. Thanks!
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Old 02-14-2018, 03:45 PM   #7
DieselSJ
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Re: 406 Build!

What cam? Cam selection can have a huge impact on what fuel you can run. You can't solely determine fuel quality based on static compression ratio.
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Old 02-14-2018, 05:30 PM   #8
70c10guy
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Re: 406 Build!

Still contemplating on what cam to run. It will be between comp’s xm270 or xe268h. Can anyone with these cams chime in? Maybe to see how manners are of the cam.
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Old 02-14-2018, 07:15 PM   #9
Dead Parrot
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Re: 406 Build!

Since this is a new build, might do some research on using E85. Supposed to have an octane rating of around 100 depending on time of year. You might have to alcohol proof your fuel system if you make the switch.

Since alcohol is a less energy dense fuel, your 'mileage' might suffer but a ski boat really isn't about mileage anyway.
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Old 02-14-2018, 08:49 PM   #10
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Re: 406 Build!

Not a bad idea..
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Old 02-14-2018, 09:48 PM   #11
b454rat
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Re: 406 Build!

The motor I built had the XE268 in it, and sounded absolutely awesome!!!!! It was a torque monster too. If I could build another small block it would be a 400, only thing special if you even wanna call it that, was using 5.7" rods.
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Old 02-15-2018, 12:55 AM   #12
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Re: 406 Build!

You might take a look thru this thread and get some ideas what others have done.

http://www.67-72chevytrucks.com/vboa...d.php?t=612016

You can typically get away with a little more compression with the Vortec heads due to the combustion chamber design. Running a D-dish piston with a good quench will help as well. You need to calculate the dynamic compression to know weather the engine will run on your 93 octane pump gas or not.
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Old 02-15-2018, 01:11 AM   #13
70c10guy
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Re: 406 Build!

Thanks everyone that replied. And captain, I will look through that and try and get some different ideas!
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