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Discussion Starter #1
I currently have 4x heads on 455 bored .30 over, there are some 62 heads in the area I will be later today. How much better are the 62 heads, if any? He is asking $450, I have not inspected them. When I was rebuilding my 455, I notice a rocker arm, rocker stud and push rod guide plate was damaged (about $30 in parts)

Joe
 

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Not good for your application. Compression ratio will be too high for pump gas.... They're around 72cc...... 87cc would be about ideal...
 

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:agree All the "large valve" Pontiac d-port heads (2.11 intake, 1.77 exhaust, screw-in rocker studs) are pretty much the same in terms of the port configuration, size, shape, and stock flow. The main differences are in chamber sizes, shapes, and configurations. At 72 cc's nominal those #62's would turn it into a "leaded race gas only" engine unless you also changed out pistons and other components to get the static compression ratio back down --- and the ports in those 62's are nearly identical to what you already have. All that's possible to do, but unless you have some overriding passion to run those heads and spend the money it would take to do it, my opinion is that it wouldn't be worth it.

Bear
 

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Those #62s with a .030 overbore would put you around 11.8cr, 87cc would be pushing it at 10.2cr, 92cc will get you under 10cr(9.8 which is better for the pump.....), 96cc will be at 9.5cr and will have larger valves than the 92s.
 

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Discussion Starter #5
Recommed use

Well I was hoping to use the 62's because they where only $450, but 93 octane would not work with that compression ratio.

I currently have 4x heads off a 1973 GTO 400 that need a new rocker, rocker stud and guide

Also I have 66 heads off a 1971 GTO 455 that is a bare block that someone started changing to screw-in studs.

What would be my best choice? Or should I just by some edelbrock 87 cc heads for $2200?

I'm trying to do a budget build, but I want a GTO with some HP.
 

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The 87cc Edelbrock heads would be perhaps the least hassle, if they are ready to bolt on. You will have over 10: 1 compression, which is fine for an aluminum headed engine. Not so with iron heads, which are thermally more efficient. It takes 10:1 with aluminum to equal the amount of energy produced by a 9:1 iron head. That said, you can do the research and get a set of cheap heads that cc out at about 96-100. I recently sold a set of 66's (114cc chambers) for peanuts. They are a 1971 455 head, and you could mill them just a bit to bring them down to 100 cc's or so and be set. That's probably what I'd do. $450 for a set of 62's is not a great deal, in my opinion, unless they are totally professionally re-worked and ready to bolt on. Plus, they are NG for a 455 with normal pistons. All cast iron Pontiac heads '68 -up flow about the same. All can be upgraded to screw in studs and bigger valves. The important thing is to find the right chamber size for your combo if you're running regular flat top pistons.
 

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"It depends" :D If youv'e got the budget for them, aftermarket aluminum heads have the most power potential. The best way is to buy them "bare" then have someone who really knows what they're doing to prep them with good valves, springs, some port work, etc. The components on the "ready to run" heads aren't all that great. Going the bare head route will net you the most power if you build the rest of the engine to take advantage of the heads, but it's also the most expensive solution. By the time they're done you'll spend double (or more) the cost of the bare heads. To really wake them up you'll want a roller cam, good headers, etc etc etc... depending on how rowdy you get with the cam choice, 600, 650+ horsepower out of 455+ inches ain't hard at all. You'll be up into forged crank territory easily. You'll also have way yonder on the far side of $10K into the engine. If that's your destination, that's the cost of the ticket to get there :)

Like A.J. Foyt once said, "Speed is just a matter of money. How fast do you want to go?"

Bear
 

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Discussion Starter #8 (Edited)
Heads

I think I will try to rebuild the one of the heads I have. if I'm trying for close to 100 cc, should I use 73 GTO head that has 98 cc? Maybe put larger valve in it? Or have it tricut?

I talked to the machine shop and they said they cannot machine the 66 heads to 100cc.

Would it be better to use the 4X heads or 66 heads, taking into account the above info?


Thanks

Joe
 

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There are quite a few web sites out there with information on the various Pontiac cylinder heads. Google "Pontiac cylinder head codes" to find a bunch of them. Just about any d-port head with an appropriate chamber volume will be a good starting point as all the ports are pretty much the same. If you're on a budget the trick is to find some heads that don't need a bunch of work/machining. In general, aim for a set of heads that already have the "large valves" (2.11 intake, 1.77 exhaust) and screw-in rocker studs (with pushrod guide plates) as opposed to pressed in rocker studs. Heads can be modified to have both those features but why spend money for parts and machining if you don't have to? The one aspect that's not easily modified is the combustion chamber shape and size, so that should figure significantly in your selection criteria.

Also, learn how to cc heads yourself. It's not hard. I used a flat piece of plexiglas, some grease, a large plastic graduated syringe, and colored windsheild washer fluid. I measured every chamber 3 or 4 times and averaged all the results to ensure I was getting accurate measurements. It's important because just a couple of cc's makes a difference in compression ratio, and Pontiac heads are known to vary a lot from the published factory chamber sizes. This is an area where you want to be positive you know where you stand.

If you have Excel available, I have a spreadsheet I can send you that does all the calculations necessary for compression ratio --- there are also web sites out there that can do it too. For a +0.030 455, assuming "standard" head gasket compressed thickness of 0.042 and a "usual" piston deck clearance of 0.020, a total clearance volume of 114 cc's will put you at about 9.3:1 - a good spot for iron heads. Making up that 114 cc's are 4.5 cc's from deck clearance, 9.45 cc's from head gasket, 6 cc's in the flat top piston valve pockets, and 94 cc's in the chambers. Zero-deck the block and you lose 4.5 cc's, upping compression to 9.65:1 - so you'd need to get those 4.5 cc's "back" from somewhere (like dishing the pistons, using a different head with 98.5 cc chambers, or using (much) thicker head gaskets. Using thick gaskets though is going to effectively eliminate the very beneficial cylinder "quench area" so that's not a preferred choice. That's why having a tool to work with compression ratios is nice. It lets you see the effects of various changes and parts combinations easily before you start putting out the cash.

Bear
 

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Discussion Starter #11
Use "4X" or "66" heads or buy "96" heads

Bear,

If I’m understanding this correctly, I can make 1973 400 “4X” heads perform similar to 1971 400 “96” heads by changing the valves. The “4X” heads are 98 cc and the “96” heads are 96cc. I’m assuming the chamber area is different, but hoping port and polishing and tricutting will help improve flow. I have the “66” and “4X” heads on hand, but both heads need total rebuild. The “66” also have pressed in studs that some started making screw studs and quite after one. It has the big valves and 101cc chamber, it would also match the 1971 455 engine I have. I would rather rebuild/work what I have than pay for another head and be in the same spot. Also, what is my ideal and max compression ratio? Thanks for all the info.

Thanks again,

Joe
 

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73 400 4x's should have 2.11 / 1.66 valves and screw-in studs. "Nominal" chamber size is 98 cc's (but be sure and measure them for certain).

The Word "doc" file I'm attaching to this post contains an embedded Excel spreadsheet you can use to play with numbers.

I started with a .030 over 455, everything else factory "standard/nominal", using 98 cc heads and came up with 9.0:1 compression. That's a great place to be. If you zero-deck the block you'll have very good quench in your chambers and still be at 9.35:1 - that's with flat top pistons. It's hard not to like that configuration... :cheers

If you've got the budget, I'd do these things:
1) upgrade to the larger 7/16" rocker studs - they're much stronger
2) upgrade the exhaust valves to 1.77
3) send the heads off to Dave Wilcox at CVMS for the above, plus porting.

General "rule of thumb" on compression is to shoot for whatever matches the octane rating of the fuel you'll be running 9.3:1 for 93 octane, 8.7:1 for 87 octane, etc. That's not a hard and fast rule - you can vary it some, depending on things like cam profile, state of tune, how good your cooling system is, altitude, etc., but considering that the difference in power output between 10:1 and 9:1 is only about 1.5 percent, it's usually not worth it to try to push the envelope.

Bear
 

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Discussion Starter #13
Bear, thanks for the info

I'm still "on the fence" if I rebuild my 455 with the "66" heads, I'm assuming I can get at least the previous rating of 325 HP.

What HP can I expect on with the "96" heads? (I will have to spend $500 to purchase the bare head)

What HP can I expect on with the "4X" heads with bigger valves?

What price range am I looking at to make these heads usable, all three need at least a total rebuild?

Will be able to use just pump gas, even if I go over 9.3 to 1 compression?

Thanks,
 

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Howdy Joe..

Can't really make any reasonable HP predictions without knowing a lot more, like... specific details on cam (specs, lifter type, rocker arm ratio), carb, intake, exhaust.

Also can't make any guarantees on compression, but knowing what I know... I sure wouldn't try running that much compression on pump gas if there was any way I could avoid it. The miniscule power gains aren't worth the big risk. Say you get it all together at 9.5:1+, then find out it's detonating... then what? It's going to have to come apart and some parts changes made: dished pistons ($$$) or fat head gaskets (not a good idea and might not even solve the problem) or cut WAY back on ignition timing (there goes all the power - so you spent all the time and money for nothing).

If you want the cheapest route based on where you are right now, have those 4x's freshened up (valve job, guides if they need them, plus new springs, retainers, locks, and seals) - then cc them to get the exact chamber size so you know where you're at with them. Stay with the 1.66 exhaust valves and the Pontiac bottleneck rocker studs if you need to. Opt for roller tipped rockers and adjustable rocker nuts (poly locks) if you can swing it - factory arrangement if not.

I have a software tool here that models engines. I just put together a sample engine using some gross assumptions (4x heads at 98 cc's, stock valves, Comp Cams XE262H, factory iron intake, 750 cfm Qjet, "good" exhaust manifolds) using a +.030 Pontiac 455. The model predicted 355 HP at 4300 rpm, 451 lb. ft. of torque at 3400. That's probably "ball park" close, but don't take that to the bank. Zero-decking the block was good for about another 5 HP and 5 lb. ft. I got the same sort of change by bumping compression from 9:1 to 9.6:1, but that also generated warnings about detonation. Good 4-tube headers were good for about another 30HP, 30 lb. ft. Leaving everything else the same and running "my" heads made about the same +30/30 difference with iron exhaust manifolds, +60/60 with "my" heads and good headers. If nothing else, that should show you that power production is about air flow, not compression.

Bear
 

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Discussion Starter #15 (Edited)
Thanks,

Would it be worth it to change to bigger valves on the 4X heads or having the valves triple cut?

I will purchase new comp cam springs to match to the cam. I will also check summit racing for Pontiac bottleneck rocker studs, roller tipped rockers and adjustable rocker nuts.

I does have long tube headers, I believe they are hooker.

Again thanks for all the information

Joe
 

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Discussion Starter #16
Rev 1,

Just dropped off both sets of heads at the machine shop. The “66” heads someone starting changing the pressed in rocker studs to screw in. They tapped one hole and quit. Now the 7/16” studs need to be replaced with 1/2” studs which the machine shop cannot do. He will check out the “4X” heads to see if they are usable.
 

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Would it be worth it to change to bigger valves on the 4X heads or having the valves triple cut?
Are there benefits to doing that? Yes... but only you can decide if the cost is "worth it" to you. Changing from 1.66 to 1.77 exhaust valves would be worth somewhere in the neighborhood of 15-20 HP on the engine I modeled.

I will purchase new comp cam springs to match to the cam. I will also check summit racing for Pontiac bottleneck rocker studs, roller tipped rockers and adjustable rocker nuts.
I really like Scorpion rockers. Quality stuff and they're USA made. Tell me again which cam you're using? Only use the bottleneck studs if you already have them. Though it probably won't be a problem unless you go aggressive on the valve springs, they've been known to break at the bottleneck. The larger 'chevy style' studs are stronger and are what you should use if you're having to have the heads modified anyway.

I does have long tube headers, I believe they are hooker.
What's the diameter on the primary tubes? If they're "too big" it's going to cost you bottom end torque. Also I've heard that Hookers are among the most difficult to install, fit, and seal - but they make good power if they're properly sized.

Bear
 

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73 400 4x's should have 2.11 / 1.66 valves and screw-in studs. "Nominal" chamber size is 98 cc's (but be sure and measure them for certain).

Actually, those 4x's may be 114cc? Which would put the c.r. in the mid 8's.

1973 400 230HP 4x screw-in stud 2.11/1.66 98cc
1973 455 215,250HP 4x screw-in stud 2.11/1.66 114cc

Here's another good calculator for figuring out compression. Click on your cubes(455), overbore(.030) and type in the head cc's. You can also change a few other options if needed.

Compression Ratio Calculator - Wallace Racing
 

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Discussion Starter #19
Thanks for the info,

The cam I’m using a COMP Cams Xtreme Energy Cam and Lifter Kits (CL51-223-4). Should I get ARP rocker studs? If so, Pontiac or Chevy style ARP studs? Are the Chevy bolts 7/16 or 1/2?

I’m not sure the diameter of the headers. I will stop by the storage unit and check it out tomorrow after work. It was a pain to remove the headers.

The heads came off a 400, but I will double check. Thanks for the info.
 

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Discussion Starter #20
Haven't been to the garage in a awhile busy work schedule and a broke finger. I decided to buy 96 heads from butler performance and I will start the install this weekend and do the what I can with my hands.
 
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