# 670 Heads - keep original and uncut?



## 67Twistytee (Feb 24, 2014)

I'm faced with speeding up a project to lower the compression on my '67 GTO. It's still standard bore with stock pistons. I've received some good advice both here and elsewhere about opening up the 670 heads to lower compression or use dished pistons. If the engine will be pulled either way due to possible bearing wear, would you choose to leave the 670 heads uncut and install dished pistons or would you open the chambers and use a flat top piston? 

My car is not a show car but it's almost entirely original and I'd prefer to keep the 670 heads on the car (I've searched prior posts and know I can save the heads and use another set with an open chamber design). Beyond originality/value, is there a benefit to leaving the heads intact and using dished pistons? I had an engine builder recommend flat top pistons over dished if I am willing to modify the heads (better quench/tighter squish band?). This will be a street build so I prefer torque over max HP and reliability over speed. I'd like to get the compression below 9.5:1 so I can consistently run pump gas. 

Appreciate the opinions and experiences of those who faced similar options.

Andy


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## ALKYGTO (Mar 29, 2010)

Hey Andy, I'm gonna vote pistons on this one. Easier to change and leaves your original heads intact.


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## 67Twistytee (Feb 24, 2014)

Thanks Alky. What about a valve job and installing hardened seats on the heads? Any unusual risk in cracking them or hitting the water jacket?


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## geeteeohguy (Feb 2, 2008)

My 670's are uncut and stored in my shop. When rebuild time comes, I'm putting dished pistons in on my own '67. That may be awhile, though! Dished pistons are the wiser choice.


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## ALKYGTO (Mar 29, 2010)

^What heads are you running GeeTee, and what is the chamber size and effective CR? A different cylinder head might be the better solution here.

I just looked up Edelbrock aluminum D-ports and the cheapest listed price I found was $2300 for assembled heads. Not cheap but they would solve your problem and I don't see them losing value in the future like a dime a dozen aluminum chevy head + still having the stock 670's you aren't affecting the value of the car. And the advantage of better performance, cooling, pump gas and lighter weight. 

Just a thought as I don't know your budget. :wink2:


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## the65gto (Oct 9, 2008)

ALKYGTO said:


> I just looked up Edelbrock aluminum D-ports and the cheapest listed price I found was $2300 for assembled heads.


Looking at Edelbrock 61599/61579 are ~$1150 if these are the ones that would work for you.


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## the65gto (Oct 9, 2008)

geeteeohguy said:


> My 670's are uncut and stored in my shop. When rebuild time comes, I'm putting dished pistons in on my own '67. That may be awhile, though! Dished pistons are the wiser choice.


Just curious....what are your reasons for taking that option. (rather than aluminum heads, or other options) I am in the same quandary now also. I am thinking that if I change piston type (dished), and while I am in there, new rods, new crank (if stroking) and on and on. :Scottwax1: My goal at the minute is a reg gas cruiser.


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## 67Twistytee (Feb 24, 2014)

I originally mulled over porting the heads and keeping the stock flat top pistons to keep this more economical. Given my desire to keep the heads intact (and a few of other issues that have popped up), I'm now dedicating a larger budget to get the motor pulled and put in new pistons. I don't think I want to swing another +2k on aluminum heads on top of the machine work required to do the pistons and put in a new cam, but I want to do this right and do it once so I can be flexible on budget if it saves me headaches later on. 

The builder I spoke to said he could do it with a dished piston, but I got the impression that modifying the heads, doing a modest over bore, and sticking with a flat top piston would yield better results in terms of power and compression/detonation resistance. I'm not looking to build a beast, but this is an a/c car with a 2.93 rear so I need to maintain a useable power band. Seems like dished pistons and the 670 heads will do the job, I'm just a bit unclear as to what if anything I need to do to the original heads.


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## geeteeohguy (Feb 2, 2008)

Guys, 670 heads are a great performance head. The #12 heads I also have are even better. I like the idea of running stock small chamber Pontiac iron heads on a car, and saving the $2500 that aluminum heads cost. Dished pistons accomplish this. For a LOT less money. I have experienced dished piston/stock head Pontiacs, and they run really hard on pump gas with stock parts. Reliable, made in USA parts. Alky, I am running a pair of #15 heads on my '67 off of a '70 455. 87cc chambers, with screw in stud conversion, but I kept the small valves (more low end torque for my salt flat rear gear). The CR is about 9-9.3:1. It will run 89 octane in cool weather, but will ping on 91 on a 110 degree day pulling a grade. 99% of the time, it runs great without pinging on 91.


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## 67Twistytee (Feb 24, 2014)

Geetee

Thanks for the info. If you were to put your 670 heads back on (with the dished pistons), would you upgrade the valves and seats or leave well enough alone? Also, I know there's a lot of opinions and schools of thought around the cam, but would a 112 LSA/summit 2801 be a good choice for this set-up (400/dished pistons/670 heads)?


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## PontiacJim (Dec 29, 2012)

67Twistytee said:


> Geetee
> 
> Thanks for the info. If you were to put your 670 heads back on (with the dished pistons), would you upgrade the valves and seats or leave well enough alone? Also, I know there's a lot of opinions and schools of thought around the cam, but would a 112 LSA/summit 2801 be a good choice for this set-up (400/dished pistons/670 heads)?


My vote is for the piston change. Check out the post from Chris from Austria about his *fresh rebuild-oil pressure*. He has a couple pics of his engine and it looks like he used the dished pistons. They provide a "D" shape that matches your head and there should be no problems losing the quench area benefits by using the dished pistons.

I have never upgraded my valve seats to the hardened seats. I read that you have to have a capable machinist who knows Pontiac heads to do this as too deep, and you can hit the water jacket. I just go with stainless steel valves which seems to work fine on the couple engine I used them in -but this is my opinion on it. 

Cam choice is subject to many variables. Best to know your actual compression and then go from there on specing one out. I have read in other forums that the Summit cam is a good one for the money.:smile2:


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## geeteeohguy (Feb 2, 2008)

I've never used hardened seats on a Pontiac either. My machinist (now retired) many moons ago said that it wasn't needed on a Pontiac due to the hardness of the stock seats. He did say if I was pulling a trailer or cruising at over 3000 rpm for extended periods of time that it couldn't hurt. I don't pull a trailer and my cruising speed is less than 3000 rpm. The Comp Cams XE series cams seem to work very well with the dished piston 8-9:1 engines. Built a '65 389 with dished slugs and an XE268, and it runs like a scalded cat. On regular gas, too.


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## the65gto (Oct 9, 2008)

the65gto said:


> Looking at Edelbrock 61599/61579 are ~$1150 if these are the ones that would work for you.


What head p/n's are you guys looking at that cost $2500.


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## ALKYGTO (Mar 29, 2010)

the65gto said:


> What head p/n's are you guys looking at that cost $2500.


Are you sure the price you quoted isn't for just one cylinder head? They sell them in pairs or individually.


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## the65gto (Oct 9, 2008)

ALKYGTO said:


> Are you sure the price you quoted isn't for just one cylinder head? They sell them in pairs or individually.


Ok after looking at it again, they are using the word "heads" as a part number and such. But I guess I misunderstood that. Yes 1 head. :00/o:


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