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Technical Pontiac Head Question

Discussion in 'Traditional Hot Rods' started by 31hotrodguy, Mar 17, 2020.

  1. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
    Member

    I need some Pontiac help. I’ve had these 6X heads of awhile an I am wondering how to tell which chambers they are. Obviously they look pretty big but I know Pontiac had a couple of different cc’s available for different size engines. Anybody have any ideas on how to tell? [​IMG][​IMG][​IMG][​IMG][​IMG][​IMG][​IMG]


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  2. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
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    from SW Wyoming

  3. flamedabone
    Joined: Aug 3, 2001
    Posts: 4,808

    flamedabone
    ALLIANCE MEMBER

    Here is another good source. Remember that all cc numbers are approximate.

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

    The largest majority of 6X heads are 6x-4 which are 93cc and 6x-8 which are 101cc. In the real world, there is not much difference. Get a decent performance valve job and bolt them on.

    -Abone.
     
  4. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
    Member

    S55mercury66,
    Thanks, that helped. I was able to find an 8 on the one head. The other I need to wire brush when I get a chance. Looks like they are the bigger ones. That would definitely bring my 10:1 compression down on my 389.


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  5. Fordors
    Joined: Sep 22, 2016
    Posts: 2,964

    Fordors
    Member

    I’d run some numbers, just to see where it ends up before you get set on this combination. Shooting from the hip I’m guessing you might be under 8-1.
    You need to figure cylinder volume + deck clearance and volume + gasket thickness and volume + chamber volume. With that total divide chamber + gasket + deck into total volume to get compression ratio.


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  6. flamedabone
    Joined: Aug 3, 2001
    Posts: 4,808

    flamedabone
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    What year is your 389, and have you seen the tops of the pistons?

    -Abone.
     
  7. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
    Member

    I don’t know. I was around when it was rebuilt but I didn’t own it at the time so I didn’t pay too much attention....wish I did.
    From what I understand the vale angle doesn’t come into play until .500 lift...ish. As for the size of the larger valves someone might know if that is an issue.


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  8. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
    Member
    from SW Wyoming

    Yes, the 101cc heads will definitely drop your compression down more than a tad. I have a set of #62 heads here I keep staring at, but here in the wilderness, Pontiac engines are scarce.
     
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  9. Deuces
    Joined: Nov 3, 2009
    Posts: 18,699

    Deuces
    Member
    from Michigan

    Just curious if there are domed pistons out there in parts land for a Pontiac....???...
    I've never seen any....:confused:
     
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  10. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
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    from SW Wyoming

  11. lostone
    Joined: Oct 13, 2013
    Posts: 1,355

    lostone
    Member
    from kansas

    Not a whole lot on the pontiac domed pistons. Pontiac did compression changes with the head cc's. They are out there just not very popular at least around here growing up.

    Did the 93cc 6x heads on a 455 and milled 30 thousand off them. Gasket matched the intake and exhaust ports, a little clean up under the valves and that motor was a beast. Ran 505 in. 520 ex. Lift With 240 in. 246 ex duration at .50 custom ground cam. Wish I had that motor....
     
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  12. I'm running a set of Jahns pop-up pistons with a pair of smaller valve #46 heads. Compression is 145 across the board. I have a pair of 6X heads on the shelf. Maybe milling them is the answer to more compression.
     
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  13. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
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    Butler performance has a section on rebuilding 6x heads and milling them to raise the compression. I’m going to email them and see how far the 6 x heads can to get 9:1 and if that is possible.


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  14. 55chieftain
    Joined: May 29, 2007
    Posts: 2,186

    55chieftain
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    Autotech makes about any piston you want, very reasonable. 6x heads on a 389 will also require the longer head bolts and pushrods standard for those. The 389 stuff is shorter.
     
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  15. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
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    I knew about the push rods but not the head bolts. Good to know. I’m learning Pontiac stuff as I go.
    I’m still a ways away from switching over. The 389 runs an is a fresh build so I’m just planning for the future.


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  16. pmdguy
    Joined: Dec 4, 2011
    Posts: 61

    pmdguy
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    Look on this boss on the side of the head
    4= small chamber
    8= large chamber 20200319_212721.jpg
     
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  17. Deuces
    Joined: Nov 3, 2009
    Posts: 18,699

    Deuces
    Member
    from Michigan

    So, what's the difference between the 6X and the RAM-AIR series heads????.... Pictures would be great!... Thanks guys! :)
     
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  18. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
    Member
    from SW Wyoming

    It kinda depends on your definition of Ram Air heads. When most of us think of Ram Air heads, we think of the round port Ram Air IV and V heads. However, "Ram Air" was also a term used for engine packages that also used the standard D port heads, with a fresh air package tying the hood to the air cleaner housing. As a general rule, all of the round port heads have a 3 digit id, with one exception being the '73-'74 SD 455 heads, which re-use code 16, and the D port heads have a 2 digit id, like 62 or 6X. Beware if looking to buy Ram Air heads, if you are looking for round exhaust port heads, because technically the Ram Air II and III heads are "Ram Air heads", but are D shaped exhaust port heads. Well, not quite, thanks to @lostone, we know that Ram Air I and Ram Air III heads are D port, while Ram Air II are among the round port heads, sorry for the confusion.
     
    Last edited: Mar 21, 2020
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  19. bchctybob
    Joined: Sep 18, 2011
    Posts: 2,475

    bchctybob
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    So by current standards, what would be the pecking order among the regular D port heads? Most desirable to least desirable on down thru the years. Just getting a little Pontiac education here.
     
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  20. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
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    from SW Wyoming

    I can only give you some general info, but the high performance D port heads have screw in studs and pushrod guideplates. Nos 16 and 62 are from 1969 400 engines, manual and automatic, respectively. Almost all of the heads from 1967 on up are fair breathers, much better than the '66 and earlier heads, except perhaps the early Super Duty pieces. Valve sizes on the later heads range from 1.97/1.66, to 1.97/1.77, to 2.11/1.77 intake and exhaust. If going with iron heads, look for the larger valves, chamber cc and compression ratios would need to be looked at in relation to bore and stroke; what may barely work on a 400 will be unacceptable on a 455, as in the case of my #62's, however, the -8's may put compression down in the 8.0 range on a 389. There is a lot of info out there, and a few ways to get where you need to be compression wise.
     
  21. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
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  22. 67drake
    Joined: Aug 8, 2008
    Posts: 93

    67drake
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    from Avoca WI

    I milled the heads on my Pontiac 400 to raise the compression ratio. Wanting to go a little higher yet, I run a set of Cometic head gaskets that are thinner than stock. Cometics are a little pricey, but it’s another option. If you mill too much off of the heads you will run into intake manifold and valley pan fitment, so the intake will have to also be milled.
     
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  23. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
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    Good to know. Thanks. How much did you take off?


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  24. lostone
    Joined: Oct 13, 2013
    Posts: 1,355

    lostone
    Member
    from kansas

    Ram air 2 heads are round port too.

    It goes ram air (1) & ram air iii are D-port. Ram air II & ram air V are round port. Along with 455 S.D. and over the counter ram air V.

    Rumor has it that the r.a. 3 head was late to the party so instead of being r.a.2 and D-port like r.a. 1 heads. So the ram air 3 head became the round port ram air 2 head. Just by their release dates their number sequence was changed for ever.
     
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  25. bill gruendeman
    Joined: Jun 18, 2019
    Posts: 377

    bill gruendeman
    Member

    Ram air 3 heads are #48 same head as 350 horse 400 with m/t
     
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  26. Joe H
    Joined: Feb 10, 2008
    Posts: 945

    Joe H
    Member

    The 6X heads, -4, -6, -8 are all very good heads, the 4x series heads are very similar, with slightly lower compression. As far as air flow goes, the 4x and 6x out flow any of the early standard and four barrel heads. Most all the normal Pontiac heads flowed about 195 - 200 cfm ( except the RAM AIR with round port exhaust), the 6x will come in around 210-215 cfm @ .500" lift. Pontiac redesigned the head by raising the intake ports so the short turn into the bowl is at a better angle. The smaller exhaust valves don't hurt the flow all that much, and most just leave them. You can installer bigger intake valves if you leave the small exhaust. Here is an article on the TA 6.6 engine which the heads came off of. http://pontiacformula.free.fr/schema/W72pack.pdf

    I have ported my share of the 6x heads and its much easier to get 240 - 250 cfm air flow from these then any of the earlier heads. Your engine will have slightly less compression then the 6.6 did due to cubic inch difference, but you could always bore yours out to 400 inches, or mill the heads.

    Here is the chart for milling, http://www.wallaceracing.com/headmill.htm:/
    Here is the compression ratio chart, /www.wallaceracing.com/cratio0001.htm
    Here is the link to Wallis Racing, be sure to check the tech article section,
    http://www.wallaceracing.com

    Your 389 is over rated on compression so any early head with 72cc will net you 9.5 compression. The '71 HO engines with round port exhaust had about 7.9 -1 compression and still made a ton of torque, so shoot for 8.5 to 9.5 compression and the engine will run just fine.

    Joe
     
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  27. 67drake
    Joined: Aug 8, 2008
    Posts: 93

    67drake
    ALLIANCE MEMBER
    from Avoca WI

    .060”. That’s as much as my engine builder will take off of Pontiac heads. Seems to be the suggested max in Pontiac circles. I know a guy who took .120” off, but that’s rare.
     
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  28. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
    Member
    from SW Wyoming

    Yes, you are correct. I'm going back and edit that.
     
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  29. saltflats
    Joined: Aug 14, 2007
    Posts: 10,312

    saltflats
    Member
    from Missouri

    To bad you don't live closer, I have a part of 670s, these should boost your compression.
     
  30. 31hotrodguy
    Joined: Oct 29, 2013
    Posts: 1,966

    31hotrodguy
    Member

    Joe[/QUOTE]
    Thank you for the info! That was a huge help. I hadn’t seen the compression chart yet on the Wallace website.
    Here is a question. It looks like the 6x heads flow about the same cfm as the Edelbrock aluminum heads? Is this accurate?
    Scott




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