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Old 05-07-2005, 02:25   #1 (permalink)
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406 Stroker with open or closed chamber

(Also added this thread to '351 stroker kits')

Im building a 406 Stroker, with SRP(Ross) Pistons, Forged Scat Crank and H-Beams, Roller Rockers etc..
My concern is that I have just bought a brand new set of 2V heads, open chamber..and have got many different opinions on running 4V Valves or to keep the 2V valves for airpspeed. Are closed chamber going to be better that open chamber? and is it a myth that 4V valves in 2V heads will give any better performance?

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Old 05-07-2005, 02:47   #2 (permalink)
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Re: 406 Stroker with open or closed chamber

Best of both worlds is to go for a 4V exhuast valve and keep with the 2V inlet. 4V inlet valve will kill air speed..
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Old 05-07-2005, 03:19   #3 (permalink)
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Re: 406 Stroker with open or closed chamber

Quote:
Originally Posted by ViGiLaNtE
(Also added this thread to '351 stroker kits')

Im building a 406 Stroker, with SRP(Ross) Pistons, Forged Scat Crank and H-Beams, Roller Rockers etc..
My concern is that I have just bought a brand new set of 2V heads, open chamber..and have got many different opinions on running 4V Valves or to keep the 2V valves for airpspeed. Are closed chamber going to be better that open chamber? and is it a myth that 4V valves in 2V heads will give any better performance?

Cheers
ViGiLaNtE351
What is it that you are expecting out of your combination?That should be the first question you should ask yourself.Ideally a set of either CHI or AfD haeds will probably fit the bill better than any iron head can do.If one could afford it then this is certainly the way to go.If one can,t justifythe added expense then i would sway the open chamber heads would be better suited in an engine of this size.The reality is that both open and closed chamber heads have their good and bad points.On one hand the closed chamber heads offer significantly reduced chamber size allowing an increase in comp ratio at the cost of having a chamber that shrouds the valves and impedes gas flow.On the other hand the open head flows as well if not better at the cost of low compression,approx 8.9 to 1 in stock form. With significantly more than 351 cubes you may find the standard size open chamber head may put the comp back up to a reasonable standard.I haven,t done the math as yet so it would be interesting to know.
As far as valve sizes are concerned it is generally accepted these days that the 4v valve size was probably too large for the 2v head to work properly. A smaller valve of around 2.1 or slightly larger is about the best size to use since this allows a more gradual turn in to the short side.
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Old 05-07-2005, 03:24   #4 (permalink)
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Re: 406 Stroker with open or closed chamber

The math has been done.Assuming a 4.03 bore 4 inch stroke,zero deck engine with 77 cc chambers you end up with around 10.2 to 1 compression.Absolutley smashing,I say.
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Old 05-07-2005, 07:26   #5 (permalink)
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Re: 406 Stroker with open or closed chamber

You have gone that far with the bottem end, before considering what heads to run ?? I do not believe you!

Start with what heads you have/can afford, then build a bottem end to suit.

Heads make the power, the correct cam will allow you to see the power and the correct bottem end will hold together.

Valve size is critically determined by flow requirements. You need to speak to a head specialist or AFD or CHI.

Tell them what you require and they will tell you what heads you need!
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Old 05-07-2005, 08:03   #6 (permalink)
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Re: 406 Stroker with open or closed chamber

No way i would use those heads on a 406, AFD 4v's or CHI 218's would be the go.
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Old 05-07-2005, 16:53   #7 (permalink)
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Re: 406 Stroker with open or closed chamber

If you cant afford the outrite cost of alloys why not port plated 4V opens! these can be had for resonable money as not many people want them ie was a set a few weeks ago on US ebay went for about $220.

With 406 cubes the comp would be as russxr67 said and they would work out cheaper than trying to get 2Vs working properly!
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Old 05-08-2005, 02:39   #8 (permalink)
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Re: 406 Stroker with open or closed chamber

Sounds like a bit to mull over by the looks. The reason im using cast 2v heads is that I got them for a steal. Cant quite afford the alloy head setup just yet, so I might at least opt for the 2v Inlet,4v Exh setup. Would polishing the ports be a good idea while I have the chance?

By the way, I havent bought any of the engine parts yet (except for the heads), its just been a scribble on paper with different prices on all variations I want to go for.
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Old 05-08-2005, 04:17   #9 (permalink)
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Re: 406 Stroker with open or closed chamber

Quote:
Originally Posted by ViGiLaNtE
Sounds like a bit to mull over by the looks. The reason im using cast 2v heads is that I got them for a steal. Cant quite afford the alloy head setup just yet, so I might at least opt for the 2v Inlet,4v Exh setup. Would polishing the ports be a good idea while I have the chance?

By the way, I havent bought any of the engine parts yet (except for the heads), its just been a scribble on paper with different prices on all variations I want to go for.
Having spent a heap of money on 2V CC heads with 4v valves replacing valve guides and having hardened seats installed it's a waste of time & money.

If I were you I would just use the cast heads as they are and save the money for alloys. Whatever you don't spend (read waste because you are very unlikely to recoup it) on the cast heads means you will have the alloys sooner

UNLESS the cast heads have already been machined and drilled for 7/16th studs you will be running pissy rockers anyway. Save for some RR's while saving for your alloys. Machining work on Clevo heads costs because of the canted (angled) valve arrangement which involves a lot of setup time and many machine shops won't even tackle the job
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Old 05-08-2005, 05:05   #10 (permalink)
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Re: 406 Stroker with open or closed chamber

closed closed closed closed without question CLOSED chameber heads.. these are the reason why the heads make such good power... the QUENCH
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