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31pontiac's 1959 Bonneville

2019 December
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Been checking with all the experts on which heads are best for a 455...6x???why are these so popular ? seem to have better low speed port velocity  but lees velocity than my 4x at maximum lift..talked to my machinist said maybe try a set of 46 heads off a 350. has better high lift velocity than the 4x and the 6x with a 96cc chamber volume.He suggested replacing intake vales with 2.11 and installing  screw in studs which could also improve low speed velocity. has.anyone tried this combination? would appreciate any advise

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This is a new one on me. I am surprised your machinist is recommending the 46 head. It was installed on both the 350 and 400 motors with either a 96cc or 98cc chamber. The part that puzzles me is the 46 head had a 1.96 intake valve and a 1.66 exhaust. So machine work is required to move it out to a 2.11. There are so many other Pontiac cylinder heads out that that are already 2.11/1.66 or 2.11/1.77, so why pay for the machining if you don't have to.

On my '72 Leman's 455, I run a 7K3 set of heads (off a 400). They are already 2.11/1.77 factory head. It has a triple angle value job and some light porting work to improve flow. Nothing radical. ARP studs and bolts are used through the motor.

This list from Wallace Racing might be better suited to your needs / wants. The nice thing is that most of the Pontiac heads are interchangeable.

http://www.wallaceracing.com/head1.htm

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Thanks Frosty for your reply,but you misunderstood my question anyone  tried these?? Now if you want to give me a price on your 7k3 heads i would by willing to buy them. since there is an  abundance of Pontiac heads in your area  . What i want to do is put them on my 73 GP, and  I dont want to go through alot of port work. these heads are the ones I have .  and they have better  velocity with a 181 cfm at .500 lift than any of the heads like 6x, 96 ,66,64,48 do you see my dilemma?? So i pretty much can see no one has tried this, I will keep you posted on the outcome

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Sorry if I misunderstood your question Yahnke. To answer your question, I can honestly say I know of no one who has tried your particular combination. I do see your dilemma. 

Good luck. Please keep us in the loop on your results.

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Question:  when you say "flow velocity" do you mean actual velocity as in the speed of the moving air column or are you referring to CFM numbers on a flow bench?    If it's pure velocity and not CFM, then 46's probably have a higher flow velocity because of smaller port VOLUME, probably due to those flow velocities being measured with the smaller valves.  For making torque/power, you care about getting the cylinders as full as possible in the shortest possible time  - i.e. maximum volume - CFM.  Given a constant pressure (vacuum depression on a flow bench) a smaller port is naturally going to have a higher flow velocity (speed of the moving air), but that doesn't mean it's going to pass more volume per unit time (CFM).    Do a side by side comparison yourself - put  a balloon over the end of a drinking straw and blow it up.  Now do the same thing using a length of 1-inch pipe.   Which one had the highest "flow velocity" and which one filled the balloon up first?

Another thing with those 46's: the 350 bore size is smaller than 400 (and up) which is why it's really difficult to "go the other way" - put 400-455 heads on a 350 because the tops of the cylinder bores have to be clearanced to clear the valves and keep from killing all the flow due to shrouding.  Going with larger valves in 46's is going to probably have a similar effect due to the outside edges of the valves being extremely close to the edges of those smaller diameter chambers, that is if the larger valves will fit at all.   You might be able to work the outsides of chambers to provide some valve relief and unshroud the valves but that's going to also increase chamber volume and lower compression.

Lastly, if this combination was a good idea then there'd be other people doing it, considering that 350 heads are easier to find now than 400-455 heads.  There's probably a reason that no one has heard of this combination.

Cheers,

Bear

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I would find a set of #12, #13, or 48's and call it a day. These heads are awesome! I put a set of 13's on a 77' trans Am i had with a 280H comp cam and it made the engine really come alive.!

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