[JoeF]

I haven't seen much info here about 670 heads. Is there a lack of interest in them due to compression issues with pump gas? Anyone have any pros/cons, do's/don'ts or opinions on 670's.

[budman]

The early, closed combustion chamber is more efficient in power production than the later open chamber heads. Tests done during the 50's show a 5% increase in power from a closed chamber to a fully open chamber. On the other hand, the airflow is enhanced slightly by getting that part of the chamber out of the way. The additional airflow raises the horsepower and the net result is pretty much a draw. The reason for the change in shape was mostly for pollution considerations. If you look at the aftermarket race heads, you find that they are produced with the minimal combustion chamber philosophy.

[JoeF]

Goatseeker,
Funny you mention HEI. I have an HEI in the car now. What I'm thinking of is switching to a points style distributor with either a Pertronix or small HEI (stock look). Since I don't have a core, I was trying to find a "distributor guy" who might have one that I could buy with the appropriate curve work and rebuild already done. I'd then drop in a Pertronix and be all set.

[goatseeker]

JoeF,
With regard to distributor recurving - have you considered an HEI? I'm going to use a small body HEI distributor conversion from Daves Small Body HEI (www.davessmallbodyhei) on my 462. Check out the pictures and info on his website. For what you would spend on a Mallory or MSD unit you can have yours (or any rebuildable core) converted with custom recurving in a totally stock-appearing, "stealth" distributor.
Just an option to consider.

http://kurtspontiac.homestead.com/TimSimpson66GTO.html

[Skip Fix]

Just open them up to look like a Fast Burn chamber! Should drop the compression down some.

[Skip Fix]

In a Hot Rod build up a few years ago Ken Crocie opened up some 670s kind of like I'm talking about. Dave Bisshop of SD performance said he has some also just partially opened up and they make good hp and take less timing than most other heads. Even most current designed small chamber quench/fast burn heads havc alot more unshrouding around the intake than the 670s do.

[JoeF]

I haven't seen much info here about 670 heads. Is there a lack of interest in them due to compression issues with pump gas? Anyone have any pros/cons, do's/don'ts or opinions on 670's.

[JoeF]

Black 65,
I assume when you say "less ignition lead" you mean less advance. Roughly, what should my curve look like? Most of the info I've seen here says 12 initial 34-36 total all in by 3000.

[Rockcrusher-M22]

Definitely don't get rid of the heads because of the chamber size... Just match up the rest of the engine so the heads can be utilized. I had a set of 670's from my 67 GTO sent to Warrior Racing in Michigan. I spent $1100.00 and had them ported, bronze guides, cut for teflon seals, new valves and assembly. When I got them back they brought a tear to my eye. They were gorgeous and not to mention they KICKED A$$ compared to the #12 RA III I was using. I was able to run these heads with 10.75 CR in a .030 400 zero decked with no pinging on Sunoco 94 octane. As for the chamber, they were pretty much untouched. Only the ports were done. There have been articles written that say the 670 are one of the best overall performance heads Pontiac ever put out.

[Bruce Meyer]

The 670 head came on 67 GTO,s and 400 firebirds and maybe some others. They have big valves and small closed chambers around 72 cc,s. A good head for a 400 if you can stand 10:1 compression. A trick some guys do is open up the chambers to resemble an open chamber head. Drops the compression and improves breathing.

[herdsman]

Joe, I have a set of 1967, 428, 670 heads on a .030 over 400 with TRW forged flat top pistons 9.78cr. I use 93 unleaded gas with no problems. In my 65 GTO it runs 11.73 @ 117. The 400 heads are 72cc the 428 heads are 75cc.

Man, I'm pretty! WHOA MAMA!

[Black 65 GTO]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Lorin Budzinski:
The early, closed combustion chamber is more efficient in power production than the later open chamber heads. Tests done during the 50's show a 5% increase in power from a closed chamber to a fully open chamber. On the other hand, the airflow is enhanced slightly by getting that part of the chamber out of the way. The additional airflow raises the horsepower and the net result is pretty much a draw. The reason for the change in shape was mostly for pollution considerations. If you look at the aftermarket race heads, you find that they are produced with the minimal combustion chamber philosophy.<HR></BLOCKQUOTE>

I agree with Lorin's post!

With the closed chamber cylinder head, you have a much larger quench area than an open chamber head. When the air/fuel mixture is compressed with a closed chamber head, the air/fuel mixture becomes much more turbulent. The more turbulent the mixture, the quicker and more efficient the air/fuel mixture will burn.

An engine set up properly (Zero Deck) with closed chamber heads and all other parameters equal, will require LESS ignition lead than an open chamber head.

An added bonus! Closed chamber heads, again with a zero deck, are also more knock resistant than an open chamber head.

Lorin is also correct about the open chamber head and emmisions control. You will notice that all American V8's began to use open chamber heads starting in about 1968. The same approximate time that Federal Smog Laws were being put into place.

I also would not modify the factory 670 chamber. It is an efficient combustion chamber. By changing the shape, you also alter the mixture swirl patterns. Without extensive dyno testing, I personally would not touch the chambers.

If you want to lower compression, properly dish the pistons.

[img]http://groups.msn.com/_Secure/0PAAAABsTshS*JL3aL9Lt3DTWpiaZQYuTwADv04vUiCSGPh1UW kUzJcyoBHF!u5vkOCDRCP1bN46o1zkzqk3S2WcjuGbw2xV8/Black-65-2-1.JPG[/img]

[urhere2]

I hope one of the knowledgable people answer this because I have these on my 400 and was wondering what kind of work I should have done to these, or if I should get different ones when my budget allows.

[Black 65 GTO]

Joe,

There are many variables involved when dealing with both the total amount and rate of advance.

These variables are:

Cylinder Head Design
Type of piston
Type of fuel used
Air/Fuel Ratio
Weight of Vehicle
Rear Gear Ratio
Converter Stall Speed

So, you can see that one set of numbers would not work for any combination.

You can either find the total amount of timing that is ideal by running timing loops on either a dyno or at the drag strip. This involves starting at low, say 30 degrees total timing, and increasing advance by two degrees unitil you reach a maximum power (dyno) or MPH at the dragstrip.

Your timing curve involves much more tuning. This will depend on a lot of the examples above as well as if you intend to drive the car mostly on the street. Also include the vacuum advance as part of your distributor tuning. This makes a world of difference in the drivability!

If you are not willing to invest the amount of time required to acheive the best curve (this can take many hours), I would suggest that you send your distributor to a reputable person to have the curve modified to your intended use and car.

As a matter of fact, there are a few guys on this board that specialize in this service.

[img]http://groups.msn.com/_Secure/0PAAAABsTshS*JL3aL9Lt3DTWpiaZQYuTwADv04vUiCSGPh1UW kUzJcyoBHF!u5vkOCDRCP1bN46o1zkzqk3S2WcjuGbw2xV8/Black-65-2-1.JPG[/img]

[JoeF]

Herdsman,
Unfortuately, I don't have too many specifics on my CR since the engine rebuild was done by the prior owner. With 93 pump gas, I haven't had any pinging under load. I had a short spell of run-on which seemed to go away with the next tank of gas. Cam was described to me as a Ram Air III so I assume it's a 068 or 744 (not sure how I can tell without a tear down). Timing is set at 10 initial and I have yet to spec out the rest of the curve. Based on that I'm assuming that the pistons are dished. Factory advertised CR for the motor is 10.75 which makes me believe I'd be having problems if there weren't some sort of dish on the pistons.

[urhere2]

I knew the compression was high because I get a bit of knock under acceleration, even with 93 octane. I tried some octane boost and it still happens. I think I'll have to find a place that sells race gas to take care of it.

BTW, I am looking to change the carb. Would a 750 be enough or should I go with an 800?

[Bruce Meyer]

Yes the 670 have screw in studs. Cant help you on carb choice since I would recomend a Holley. Block off the heat risers to your manifold and try to run cold air to carb. This will help prevent pinging.

[dlw6767]

i hear a lot of good things about these heads. how come nobody wanted this set i have for 200.00?,,its ok though ,i put them in ebay,in less then 24 hrs they are at 267.00 with 6 days to go..

GTOCRAZY67.....ALWAYS LOOKIN FOR A GREEN LIGHT..

[Z Code 400]

The Keith Black KB346 is said to yield 9.6:1 compression with a 71cc head...Robert

http://www.kb-silvolite.com/kbpontiacpg.htm

[Bruce Meyer]

What kind of carb?