# 1970 455



## mjingle (May 11, 2010)

i am ready to refresh a 1970 yh code 455 w/ #15 heads,i also have a set of #6x- 8 dated 1976. which would be the better choice? also i have 1 #670 dated 1967 that i would like to find another for a third choice. can anyone help?


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## geeteeohguy (Feb 2, 2008)

You need to run about 9.5 compression or lower these days with iron heads. The 670's are a no- no at 72cc, and the 15's, at 87cc, marginal. The 15's were original on that engine, and netted about 10.25 compression. Try the compression ratio calculator on Wallace Racing's site, and look at head charts for the cc's you'll need. A 455 with about 9:1 compression and the right cam can be a real tire shredder on the street, and do it on cheap gas, too. Good luck.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> You need to run about 9.5 compression or lower these days with iron heads. The 670's are a no- no at 72cc, and the 15's, at 87cc, marginal. The 15's were original on that engine, and netted about 10.25 compression. Try the compression ratio calculator on Wallace Racing's site, and look at head charts for the cc's you'll need. A 455 with about 9:1 compression and the right cam can be a real tire shredder on the street, and do it on cheap gas, too. Good luck.


:agree What he said....

Here's a link to another compression ratio calculator.

In a 455, the net horsepower difference between 9.5:1 and 10.0:1 is only about 7, the difference in peak torque is only about 12. In my opinion that makes it just not worth it to try to squeeze every last bit of compression. 
Shoot for a static compression ratio of 9.3:1 or less, with 9.5:1 being the absolute upper limit with iron heads. With aftermarket aluminum heads, you can get away with 10.0:1 because they "pull" more heat out of the combustion chamber.
Cam shaft selection plays a big part in this whole thing too, because with longer duration cams, the intake valve closes "later" in the cycle and compression cannot begin until that intake valve is closed. "Dynamic Compression Ratio" and "Cranking Cylinder Pressure" are both affected by the intake valve closing event. Choose a combination of cam and static compression that keeps your dynamic cr at 7.9:1 or less and your cranking pressure at 170-175 psi or less, and remember the amount of power/torque output you're giving up by staying more on the safe side is a mere pittance.

Always measure your combustion chamber volumes yourself. They can and do vary quite a bit from the factory specs and this is one area where you really want to be certain that you know exactly where you are. It's not hard to do and you don't have to buy a bunch of special equipment. I measured mine with a square piece of plexiglas big enough to cover the chamber and a large plastic medical syringe. Drill a small hole in the plexiglas so that it's at the "top" of the chamber, seal the valves (use grease on the seats if the springs aren't on), seal the plexiglas to the head using a thin film of grease, then use the syringe to measure how much fluid it takes to fill the chamber. I used blue windshield washer solvent because the color makes it easier to see.

6x-8's are a little on the big side, chamber wise, for a 455 unless you mill them quite a bit. 6x-4's are a great choice if you have "enough cam". You can use dished pistons to get some more clearance volume, but use pistons that have the D-shaped dishes if at all possible. Otherwise you'll be sacrificing the 'quench area' (more properly called 'squish' area) where the piston approaches the flat part of the head very closely, like .020 - .030 or so, causing turbulence in the chamber that helps to promote good combustion efficiency and cool 'hot spots' that can tend towards detonation. You want to avoid using thick head gaskets for the same reason: they kill the quench area.

87 cc's will put you very close to 9.8:1, assuming flat top pistons (that actually have about 6 cc's of valve relief in them), a standard bore/stroke 455, 0.040 head gaskets (compressed), and "the usual" Pontiac factory deck height of 0.020 (something else you must measure yourself to be sure). That's too much for all but the most aggressive/nasty roller cams. Making one change: using KB/ICON IC-889 forged pistons with a 15 cc dish would put you at 9.09:1 if you leave things alone, 9.3:1 if you "zero deck" the block. 9.3:1 would be safe on 93 octane with enough cam (something with at least 230 degrees @ .050 intake duration), 9.09:1 would be safe with just about any cam.

I recently built a "400 stroker" (actually a 461) for my 69 GTO. It has iron heads, 9.4:1 compression and a 236/242 @ 0.050 solid roller cam. It makes about 12-13" idle vacuum (which is not quite enough for reliable power brakes so I'm converting to a hydraboost) and 



 On the dyno it made 492 horsepower at 5400 rpm, 543 lb ft. of torque at 3100 rpm - all on 93 octane.

When I was planning my build, I licensed a copy of this program and used it to work out the combination of cam, heads, compression ratio, etc. I found it very helpful. I also recommend getting in touch with a reputable builder who is willing to consult with you and not just try to sell you parts/services. For me, that was Jim Lehart of Central Virginia Machine. I can't say enough good about this guy - he really knows his stuff and he'll share it with you whether you spend any money with him or not.

Most importantly --- HAVE FUN!! arty:

Bear


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## tyler t (Aug 15, 2010)

sounds mean  very useful link bear thank you, will come in handy when i rebuild the stock #'s matching 400 that came out my 69 i got sitting in my shed. dont have the heads anymore. 
would you recomend alumium heads? there 1000 bucks, are they worth it?


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## BearGFR (Aug 25, 2008)

tyler t said:


> sounds mean  very useful link bear thank you, will come in handy when i rebuild the stock #'s matching 400 that came out my 69 i got sitting in my shed. dont have the heads anymore.
> would you recomend alumium heads? there 1000 bucks, are they worth it?


"Worth it" is a relative term that you have to decide, but I can tell you that if you're after big power they're the only game in town. Edelbrocks as cast/out of the box will out flow even my genuine Ram Air IV's, including the port work that's been done on them. When you add to that the facts that the E-heads come with chambers large enough to easily put compression where you need it to be for pump gas, plus they come with hardened valve seats so they'll live on unleaded, the choice is obvious. Then too they're lighter - and any weight you can get off the front end does marvelous things for weight transfer/traction. There are only two reasons that I stubbornly stayed with my Ram Air IV's: 1) I bought them many years ago, long before anything else was available and 2) I wanted to build a motor that I could pass off as "stock" to the casual observer - and I wanted the "cool" factor that comes with being able to say "Ram Air IV".

The hot ticket for the E-heads is to buy bare/rough castings then have them finish ported and assembled with "the good stuff" by someone who really knows his business. Dave Wilcox at CVMS is one of the best there is.

If I were to do nothing else except swap my heads for a set of E-heads like that, I'd pick up a good 50 HP, probably more.

Bear


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## jholodniuk (Nov 29, 2010)

Wow I didn't know the Edel's would add that much more. Definitely going to be in the future for me! BTW, sounds very very mean.


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## BearGFR (Aug 25, 2008)

jholodniuk said:


> Wow I didn't know the Edel's would add that much more. Definitely going to be in the future for me! BTW, sounds very very mean.


Well, I don't have any actual flow numbers to plug into my modeling software so that was just a guess based on what others are doing with those heads.

I use a program called Engine Analyzer Plus that's licensed by Performance Trends. It's a terrific tool for "playing" with different engine combinations to get a ballpark estimate of what effect various changes would have.

Bear


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## BearGFR (Aug 25, 2008)

jholodniuk said:


> BTW, sounds very very mean.


Well thanks for the kind words. If you like what it sounds like through the mufflers, try this one on for size...






Bear


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## tyler t (Aug 15, 2010)

sounds like there "worth it" to me hahaha to be honest id paint the aluminum heads and try to pass it off as stock. 
if you wanna hear meeeean click the link in my signature hahahaha


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## James Gould (Oct 25, 2017)

mjingle said:


> i am ready to refresh a 1970 yh code 455 w/ #15 heads,i also have a set of #6x- 8 dated 1976. which would be the better choice? also i have 1 #670 dated 1967 that i would like to find another for a third choice. can anyone help?


I have a 1970 Pontic 455 4dr har4dtop for sale.


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## Bobby Conner (11 mo ago)

BearGFR said:


> :agree What he said....
> 
> Here's a link to another compression ratio calculator.
> 
> ...


Just read your old post on this I recently purchased a 67 Gto that has been setting up for over 10 years. I knew it did not have original motor but he told me it was a 400 out of a 1970
I thought about ls3 swap because everyone seems to go that rout. Pull numbers off the block and block is 9799140. Xf stamp in the front and #64 heads. Turned out to be 455 ho
Still cost bunch to fix, but might have changed on ls3 swap now. Just looking at good mods
On motor to max performance. Any suggestions.
Thanks,
Bobby.


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