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RonW 01-19-17 01:04AM

Modifying 670 head chambers
1 Attachment(s)
New guy here. Looking for info on opening the combustion chambers on a set of 670 heads.

I read on-line SD Performance has a program to port 670's and create a heart shaped chamber. Anybody know what the chamber size is?

I'm still in the planning stage with my 67 Le Mans. It has a 67 GTO drive train, interior and front clip.

I'd like to build an old school Saturday night special. I'm thinking a 433ci with a solid lifter cam.

Trouble is I plan to run it on California 91 octane, so I'll need to keep the compression down below 9.5:1 and that would take a 91cc combustion chamber in my 670's?

Trying to avoid dished piston's if possible.

Thanks for any info. Here's a pic of my car.

rexs73gto 01-19-17 03:11AM

1st off you need to start with a different set of heads as the 670's are already 10.5 to 1 compression already. You need a set of 4x or 6x to start then work your magic on them. There 8.2 or 8 5 or so .

tjs44 01-19-17 12:40PM

The #64 1970 455 HO heads work great with your 433 with our 91 gas.Tom

Gach 01-19-17 03:07PM

The 670 heads I believe have a 65 cc chamber, that's a tall order trying to modify them yourself. I'm guessing SD has a CNC program that gets all the chambers the same size when opening up the chambers.

The 670 heads were the high performance head and the most sort after head because of the compression they created, it was the 400 ci high performance head. Back in 1967. Do yourself a big favor and either have SD do them or get another set that will drop the compression.

No way you can hand open the those chambers and get them all the same. Nothing worse then having uneven compression in every cylinder.

RonW 01-19-17 11:42PM

Thanks for everyone's input.

I guess I didn't ask my question clearly. Does anyone know if SD Performance can open up the 670 chambers to 91cc?

I do have a pair of 4X-7H heads (should originally be 98cc). I liked the idea that the 670's have a larger quench area.

Although, I should be able to mill the 4X's down to 92cc that would work out to 9.42:1. Guess I have my answer.

I also have Jim Hands book on "Building High Performance Pontiac's". He shows how to port 6X's, should work for 4x's too.

rexs73gto 01-20-17 04:06AM

Theres no way to get your 670's to 91 CC as you would be cutting into the bottom of the rocker floor . Theres not that much material to cut that much out with out breaking through. You would have to use a dish piston & you said you didn't want that. Some of the 4X & 6X heads are very good flowing & can be made to be even better with some work,,,, but IMO you should go to an Alum. head as you'll have almost as much money in those iron heads as the Alum heads & the Alum. heads will flow better out of the box then the worked iron heads & then you put a little bit of work in the Alum heads & they will out flow any of the iron heads then & you can have higher compression that will live better on our junk gas of today.

Mb125 01-20-17 01:51PM


Originally Posted by rexs73gto (Post 441996)
but IMO you should go to an Alum. head as you'll have almost as much money in those iron heads as the Alum heads & the Alum.

Says who?
I don't have that much in mine that even equals price of 1 aluminum head
Flow numbers are just a tool for selling heads.

tjs44 01-20-17 03:54PM

Ron W,are you coming to the pontiac car show at the fullerton airport tomorrow?Would be good for you to come out.I will have a couple cars there including my 69 RA V bird.Tom

92GTA 01-20-17 10:31PM

670 heads are around 72cc, not 65cc.

I ended up going with a dished piston because as mentioned, getting them opened up enough to be less than 9.5:1 without a dished piston isn't really feasible.

My CR is between 9.4 and 9.6:1. She will run ok on 87 with the timing down but does great on 91 will all the timing she wants, no issues.

I'll be going with e heads from SD when I upgrade next, then I'll sell my mint 670 heads to someone restoring a 67 GTO to help cover the costs since I haven't modified them aside from a complete rebuild and hardened seats.

turbo louie 01-21-17 07:20PM

Just tune it for e85 an use the 670's. It a good head!

92GTA 01-21-17 07:30PM

IF they are ported correctly I'd agree, in that case they may be the best Pontiac iron head you can get (for a closed chamber).

Gach 01-21-17 08:24PM

They are closed chamber heads that have a chamber volume between 68 and 74 CCs. The ones I had measured 65 cc. You can't take it for granted they all Measure 72 cc. Just saying.

rexs73gto 01-22-17 03:38AM

Mb125 were did you get your heads ported & cc'ed & all new valves & guides & springs & the 3 angle valve job for less then the cost of 1 head?? Because thats what you get with new Alum. heads & I don'y know any shop that will do that at a price of around 1k for each head. Because thats what you would have to do to match the new Alum. heads. Because if they can do all that for under that price I want to send a set to them to.

Mb125 01-22-17 11:29AM

I do most of my own work
Paul carter did the valve job and guides

rexs73gto 01-23-17 12:21AM

I received a PM from someone who goes nameless so no ego's get hurt but as for the use of E-heads or any Alum. heads seems to be the part to pick on now days., against the iron heads. We as a Pontiac community waited a long time to have these heads & now that we do it seems that everyone or some seem to think that it better to use the iron heads because some of the heads have come from the Mgf's needing a bit of work. If they do you send them back to where you got them & Eldo will make them correct for you at no charge. But some seem to think that because some come in needing that all of them are bad & cost SO much more to but then to spend as much money on OLD heads rather then buy the NEW Alum. heads that will flow much better then almost any of the iron heads. Not to include the RA IV & SD heads but even those won't flow as much as the round port Alum. heads with equal work in them. $ for $ the Alum. heads are far ahead of the iron heads IMO & a lot of others unless you have someone doing the work for free. I use to like the iron heads to until I got a set of Alum. heads & realized that they are far superior . If I would have got a bad set of heads I would have taken them back as would most , but again $ for $ it's almost impossible to beat the Alum. heads for use flow & price against the old iron heads.

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