[25stevem]

If you go with custom dished Pistons you really want to try and match the deck of the 670 head in terms of squish area and get .035" to .040" of deck clearance when assembled with a head gasket .

This may mean having the squish area of the piston stick out .005" above the deck.

Has your 400 block been decked to true it up?

[racerboy]

Originally Posted by 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

I think so. I just went to their website and it had a “2022 update”. I have the same curiosity about opening up a set of 670s to run on a 428.


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[25stevem]

Let me say this with absolute certainty!

If you can not get the CC increase you need by machining the spark plug side of the 670 chambers out to the the 68 and up open chamber shape, or better yet the 71 or 72 455 round port chamber shape then you need to run a dished piston period!!

You do not want to go for what Pontiac tried out in 1967 with the 061 D port head chamber shape.

There reduction of the quench are only served to extend how far the flame front had to propagate from the plug to try and light off the mixture on that far side of the chamber, and this only served up a more detonation prone chamber.

I think the engineers at that point had found out that the soon to be used 68 and up chamber shape with its lesser surface to volume ratio definitively helped with emissions so they went all out Hog wild and tried out the 061 chamber shape
And it failed miserably!

It was used for that half year period and then purposely and quietly forgotten about!

It’s too bad that they did not try out what we call today a Heart shaped chamber, as then they would have had a winner!

You can machine about a added 6 CCs out of the 670 heads spark plug wall area before things get too thin to hold up.

If your looking for more then 6 CCs then it’s dished piston time.

Here’s a picture of the 061 chamber which is what you don’t want on the shallow side of the chamber.

[geeteeohguy]

Originally Posted by dmac

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.

I've had my '67 GTO for 39 years, it still has the original 400. I rebuilt it to stock specs in 1988 with forged flat top pistons and a .030 overbore. When 94 premium went away, I started having issues. I ran the 670 heads and it pinged even with water injection. I tried a pair of 1970 #12 heads, same issue. Still detonated unless the timing was way backed off. Only fuel available was 91 octane, now it's 91 with ethanol. About 12-15 years ago I gave in and installed a set of 87cc #15 1970 455 heads. That got me a good running engine with out 9.3 CR. Even with 87 CC heads though, it will want to detonate pulling a grade on a 100 degree day. It's hot and arid where I am, so that may be part of it. Plus, it's jetted for real gas, not the alcohol-laced crap we have now. What I'm getting at is that you'll need at least an 87cc chamber, or better yet, 90cc to run it on 91 pump gas. Grinding your 670's to get 80 cc still won't be enough, IMO. If wanting to run the 400 long block as-is, the easiest cure is bigger chamber heads or aluminum 72cc units.
I have the same issue with my '65 GTO which I built 40+ years ago. It's at 11:1 CR with flat top pistons and needs race gas. Milled 77 heads, about 64cc. I don't drive the car much because of the fuel requirements, it does run like a scalded cat. My options are to tear apart a mint rotating assembly and install dished pistons, bolt on a set of bigger chamber or aluminum heads, or keep running race gas. All are $$$$.

[78w72]

Originally Posted by 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

DCI is definitely still around & building some awesome engines with is RA5 heads & bathtub intakes. hes active on FB almost daily....

surprised theres not more mention of his heads/engines on here, he builds some very impressive engines & the RA5 heads look incredible.

[lust4speed]

I have a set of 670 heads worked by Dave and have opened up another four sets myself. Original untouched 670's come in between 75 and 76 cc's and Dave has said that he can take them out to a maximum of 85cc's. The important thing here is he was referring to untouched heads and he was able to obtain about 9cc's additional volume. After a extremely light clean up surface cut his heads measured a true 83cc's. I've found that with tedious work I can duplicate the chambers, and depending on how much surface area had been machined off I end up between 81 and 83cc's with heads not overly milled. If you are starting with heads that have been shaved down to 68cc's then the most you are going to see are 77cc chambers, and that is with a lot of tedious work and hoping there isn't any imperfections or erosion on the coolant passage under your cut. Like Steve said above, being conservative and not risking ruining the head, you are most likely only going to increase chamber size by about 6cc's. Taking into account the costs of having someone do the work, custom dished pistons to lower compression seem a bargain.

[25stevem]

Valves ( intake and exh ) with a slightly dished face which are not Tulip under the head will buy you back 1.5 CCs if the heads have been milled.

[77 TRASHCAN]

I wish Paul would post here. Again. Paul, you are missed!!!

I have put a bare head on a bare block. With the valve loose in the head. To check clearance. Did this with some other head on my 350 currently in my TA

[25stevem]

Is the above post in response to what's being discussed with in this string, or is it misplaced?