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360Rocket's 1970 Pontiac GTO Judge

2020 August
of the Month

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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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Thanks guys for your response ...But lets review I have the 46 heads ...to answer bears question  im referring to cfm ..4x heads at .500 flow 171 cfm  6x flow 163 cfm also at .500 46 heads flow 181 cfm at 0500  now if any can get me complete set of heads that flow better for 920.00  please let me know. These heads will have 2.11 intakes, screw in studs installed, surfaced port matched springs .guides , hardened seats etc out the door $920.00 bucks. the above fugues were provided by Rons Pontiac page and another unknown author who mirrored Rons findings. Oh buy the way these heads were also used on the 400 and the 428 in 1969...What im after is compression  to go along with flow..all parts will be all  Pontiac except for Rhoads Lifter ...Im committed to this project so any advise will be greatly appreciated with out the I should buy comments. remember Im trying to move a car that is as long and weighs as much as the enterprise. But will see what happens???

Edited by Yahnke

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I am a big fan of run what you got. So if you have the #46 heads, by all means go with it. Thanks for the tip on the Ron's Pontiac page. I had not seen the flow numbers before. All things considered it is not a bad head (not that I thought it would be horrible in the first place). How much compression are you trying to run? The '69 400 and 428 with the #46 heads were 10:1 compression motors stock and produced 290 and 360 HP respectively. If you are planning on strictly street use, then you don't want to go beyond that since that is about the limit with today's pump gas. If you are going racing, different story altogether.

Edited by Frosty

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frosty Im Hoping to get about 9.5-9.75 ...Were going to pull the engine some time this week,hopefully the engine has not been bored more than .060  i want to keep overbore   between 060 and 030 with zero decking the static compression should be between 9.5-10.0 ...this is going to be a long drawn out process..my build will be all Pontiac parts ,stock intake ram air 4 exhaust 744 cam w/rhoads lifters cliff ruggels q-jet. The car has a curb weight of 4400 lbs that why im using rhoads lifters to  tame the 744 cam down to 068 cam since i need as much low end torque as possible , next question will i race it ??? Im probably dumb enough to do it. Ill Keep you up to date. thanks for the reply

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Yahnke, sounds like you have a motor and plans similar to Indyman Joe's. He has a torque-y, tire-shredding motor in his '72 Luxury Lemans that does an occasional run (or two) down the drag strip (just to put down his buddy's high dollar Camaro). I think you have a solid combination on your hands so long as you realize that you have a street motor to occasionally go racing with. Racing gets much more expensive the faster you want to go. Keep it real and you'll be fine. 

Please keep us up-to-date with you progress. Tear down, inspection, and build up. Oh, and we love pictures all along the way too.

BTW - what are the specs on your cam?

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Frosty you out there...More dilemmas,and changes... had arranged with a repair shop  that dealt with our business,became good friends with the owner Ken, we sat down planned the build that was mutually beneficial for both of us..everything  was going great until middle of february when Ken passed away in his sleep. Lost a good mechanic and friend,...To get back to business during these trying and troublesome times, our last conversation you ask about cam timing I'm using RA4 cam 231in  240exh 113 l/s and 470 lift with 1.50 rockers.also engine is done hopefully pick it next week and have it running by end of the month.Keep your fingers crossed.Will stay in touch,and keep ken and his family in your prayers,Thanks

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Dude sorry to hear about the loss of your friend! That sucks, especially these days with no funerals. We will definitely keep him in our prayers.

The RAIV is a good profile, you should do well. Let us know how it goes,

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