[dmac]

I have a pair of ported 670 heads that were milled down to about 68cc. They need to be milled on the intake side to improve the fit. That isn't the problem. My problem is the CR is too high for the 400, close to zero deck, 4 valve relief, .045 over bore. Race gas isn't available anywhere nearby anymore.

I have 2 possibilities:
use them pretty much as is on a 350 I can rebuild- if the big valves will fit the 350 bore. I can get dished pistons if necessary to adjust CR since the 350 would need pistons anyway.

Or machine the chambers and maybe intentionally recess the valves to get to at least 80 cc chambers if that is possible. Then use them on the 400 which has less than 4000 miles since a 2003 rebuild (when I could get gas for the high compression)

Questions- can I get enough material out of the chambers to get the CR to use? What is maximum cc 670s can be expanded to if anyone knows.

how much work to get the big valve 670s on a 69 350 block. Block will be bored.

[Squidward]

I am running #12's (big valve) on a 72 350 right now. Big valves WILL hit the cylinder wall if you go with too much lift. I measured with checking springs, and got to around .510 lift before valve contact. That was with a used Fel Pro head gasket.

I made my cam choice for a max of .489 lift (Voodoo 702) with this in mind. My 72 block also had the cylinder chamfers, as should your 69 block.

IMO, the high compression 400 heads make an excellent option for a 350 as long as somebody doesn't go cam-crazy. My 12's were ported and cc'd at 68. I think a 670 headed 350 would be a sweet build! I'd tune in for that one!

[74Grandville]

you should not have an issue running dished pistons. I would not sink the valves, you'll effect the short turn effecting flow.

[GTOLiam]

search SD Performance on forum

http://www.sdperformance.com/viewPro...?productID=583

[Formulas]

670's do have a different valve angle than the 12's so MAYBE this may affect what lift the exhaust valve will tap the bore plus I think the 670 valves start out further from the deck to start with due to the closed chamber design.. I would say do a mock up and go from there.... The 670 might be the best heads you can put on a 350

[rexs73gto]

The 670's are an open chamber head as this was the 1st year for the open chamber heads. I would use a thick head gasket & if you can take the pistons you have now in the 400 & have the top of them cut deeper in the valve relief & in the top of the piston to give you the relief you need to run them on the 400.

[gtofreek]

Originally Posted by Formulas

670's do have a different valve angle than the 12's so MAYBE this may affect what lift the exhaust valve will tap the bore plus I think the 670 valves start out further from the deck to start with due to the closed chamber design.. I would say do a mock up and go from there.... The 670 might be the best heads you can put on a 350

Actually both heads have the same 14° valve angle. The 670 head was the first head to have the new valve spread, and angle. It was the only closed chamber head with the new valve angle, and spread.

[gtofreek]

Originally Posted by rexs73gto

The 670's are an open chamber head as this was the 1st year for the open chamber heads. I would use a thick head gasket & if you can take the pistons you have now in the 400 & have the top of them cut deeper in the valve relief & in the top of the piston to give you the relief you need to run them on the 400.

The 670 was a closed chamber head. It was the first head with the new valve angle, which is the same as the open chamber heads, but was the only closed chamber head with that valve angle.

[gtofreek]

670's are a really good d-port head. The best actually. Mine flowed 218 CFM in bone stock condition, with stock valves. With new valves[not a Pontiac replacement valve], and a good valve job, they flowed 228 CFM, without any porting. Most all other d-port heads quit flowing in the 204-210 CFM range.

Like mentioned earlier, the 670 has a little bit deeper chamber[IIRC] than the #12 head, so you may be able to get away with a little more valve lift.

[dmac]

Originally Posted by gtofreek

The 670 was a closed chamber head. It was the first head with the new valve angle, which is the same as the open chamber heads, but was the only closed chamber head with that valve angle.

I am hoping to be able to open up the chamber and use the 670s on the 400. It would save me a lot of money compared to a complete rebuild of the 350. Do you know how many cc's I can gain by opening them up?

[steve25]

I belive SD can CNC them to a open chamber 80 cc size with no concern for failure!

You never want to sink a intake valve with a 30 degree seat, or add a top cut of any kind to the valve job!

The intake will pick up low lift flow with the top cut but the port also picks up on reversion / back flow on any CID Pontiac , but in terms of a motor who's stroke is bigger then the bore size like a 455 it's a big issue.

The bigger the Cam you run the more reversion and that in turn makes the motor come onto to Cam at a higher rpm and can make for idle tuning issues and the need for a bigger Plenum to dampen the reversion pulses!

A 350 with its bore and stroke being so close to the same dimension is a case in point for being concerned about reversion .

I have seen all too many valve jobs done to a Pontiac head ruin it as a pick for being ported up to flow numbers exceeding 270 Intake cfm@28".

As posted, the more a given valve is sunk in the chamber , the more it eats into the short turn height which will at some point limit the high lift flow .

I am currently working on a set of #13s messed up like this where I have had to take a set of BB Chevy 2.19" valves and cut them down to 2.14" and convert them to a 30 degree seat just to get back a .050" wide seat in the head that will live with roller Cam spring pressure!
This is all due to Chevy shops doing porting and valve jobs on a Pontiac head!!

[Skip Fix]

Tom Wilhite, an old Pontiac racer, used to have a Bridgeport cutter to open 670s up to later style chambers also.

[Formulas]

Didn't realize that was the first year for the new angle.. Thanks ... The closed chamber design is the key to more than .480`ish valve lift on a 350.. If I had a set I would use them over my #48`s in a heart beat on my 350..

[gtofreek]

Originally Posted by dmac

I am hoping to be able to open up the chamber and use the 670s on the 400. It would save me a lot of money compared to a complete rebuild of the 350. Do you know how many cc's I can gain by opening them up?

Not sure, but I think you could probably get 4-5 CC's out of them. Might be able to get it below just 10:1, if they are 68 CC's now. With the right cam, that could work, possibly. Just depends on what you're wanting out of the engine.

[dmac]

Originally Posted by gtofreek

Not sure, but I think you could probably get 4-5 CC's out of them. Might be able to get it below just 10:1, if they are 68 CC's now. With the right cam, that could work, possibly. Just depends on what you're wanting out of the engine.

This is going to be a mild daily driver with 91 octane being the highest available. Reliability will be more important than power. 4-5 cc's probably won't be enough. My son and his wife want to use it as their second vehicle to shop, pick up kids from school, etc. Big change from what my son wanted 10 years ago.He doesn't want to worry about being on the edge tuning-wise. Will probably go with EFI.

Sounds like a total rebuild of the 350 may be the way to go and use the 670s. Maybe save the 400 block and put some aluminum heads on it later.

[gtofreek]

Or just buy some dished pistons for the 400.

[dmac]

Originally Posted by gtofreek

Or just buy some dished pistons for the 400.

May just buy a 'new' pair of iron heads for the 400 from SD and a new cam/lifters and be done with it. I'm trying to balance the amount of work, how long it will take, and amount of money. A pair of 84 cc edelbrocks would work if my son wants to spend the money.

[STEELCITYFIREBIRD]

You'll need to put hardened ex seats in the 670 heads, guides/valves/springs.v-j etc, labor to expand chambers.....

2x--Buy a set of done heads, with desired chamber size for the 400.... and run with it.

[dmac]

Originally Posted by STEELCITYFIREBIRD

You'll need to put hardened ex seats in the 670 heads, guides/valves/springs.v-j etc, labor to expand chambers.....

2x--Buy a set of done heads, with desired chamber size for the 400.... and run with it.

The 670 heads are done except for the small chamber. Probably will use them on the 350 in the future. Complete rebuild of the 350 would cost a lot more than just buying heads with the right size chamber so that is the likely direction.

I did send a message to SD to get a definite answer about opening up the chambers on the 670, but I need to go from 68 cc to at least 80, prefer about 84.

[rohrt]

Is DCI still around. They have pics of the 670s they opened up to a more modern chamber. They said in another post about opening up a closed chamber to 80cc.

https://forums.maxperformanceinc.com...6&postcount=27