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Old 09-18-2021, 02:22 PM
tom s tom s is offline
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2X Bman,run the right CR and pull into any gas station and not worry about detonation.Tom

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Old 09-18-2021, 03:24 PM
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All great advice from everyone. My vote is go with the 428 and 670s. This will make your 2+2 clone so much better and you won't regret the 428 when done.

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  #23  
Old 09-18-2021, 05:08 PM
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If I was trying to clone a 67 2+2 the first thing I’d be worried about is the front fender/louvers. Do you have those already?

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Old 09-18-2021, 05:17 PM
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Originally Posted by b-man View Post
I’d definitely do the 428 running the correct 670 heads for the right look since you’re trying to replicate a 2+2, nothing worse than having the wrong heads on the engine when you pop the hood if looking for authenticity.

Dished pistons for the right compression ratio so no hassles or additional expenses when filling the tank. Hardened exhaust seats and one piece stainless steel valves for longevity.

As much as I like the 4.00” stock stroke original crank I’d consider slipping in a 4.21” stroke 455 crank. Not really necessary but it would make it a little easier to meet your 450+ HP goal.
No need for me to say anything. As usual, Bart already did! I like the small journal engines for oiling reasons, but if I had any 2+2 of any year, it would have to have a big-journal engine. That's the main magic of those cars.

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Old 09-18-2021, 05:44 PM
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In more than more than 50 years with Pontiacs I have never found a issue with street driving large J cranks.Tom

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Old 09-18-2021, 06:08 PM
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Originally Posted by markpj23 View Post
Looks like I have the 6X heads w/the vertical boss, so 6X-4 heads.
428 with 670s. More torque. No need to buy a stroker kit. All you need is a set of dished pistons and aftermarket rods, and of course bearings, gaskets, cam, lifters, etc. I would also install one-piece valves and hardened seats in the heads. But, you don't need an aftermarket crank or anything special. Cubic inches are king and if you have the budget, go for it. Plus the 428 will look correct.


You said "6X with the vertical boss" - what does that mean? 6x-4 and 6x-8 are identical castings, the only difference is the chamber size and the little number stamped on the machined pad (Secondary Stamping in the attached picture). If you're referring to the presence of the machined pad where the number is, the existence of that pad doesn't mean anything. The number stamped on it is what you need to look at.
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Old 09-18-2021, 07:07 PM
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Originally Posted by bdk1976 View Post
If I was trying to clone a 67 2+2 the first thing I’d be worried about is the front fender/louvers. Do you have those already?
No but am looking. Going to be one of the hardest parts I'm sure....

PM if you have some for sale

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Old 09-18-2021, 07:13 PM
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...You said "6X with the vertical boss" .... If you're referring to the presence of the machined pad where the number is, the existence of that pad doesn't mean anything. The number stamped on it is what you need to look at.
My bad - I misread that page when looking it up. Can't read any secondary stamp on that boss - paint's too thick I believe.

So for now they're 6x mystery heads....

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Old 09-18-2021, 07:15 PM
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Many thanks for all the insight and excellent comments. I was leaning towards the 428 at the start, and have just told the seller I'll take it! Looking forward to the build!

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  #30  
Old 09-18-2021, 07:22 PM
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Something is really amazing with some folks on this site!
They give a big Thumbs up to someone who as dropped a 535 cid motor in there PONTIAC , yet when a guy can’t decide between yanking his 400 out to drop in a 428 he gets all sorts of crap thrown at him from the never over a 400 crowd, lol!

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Old 09-18-2021, 08:14 PM
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all these posts and still no one has given you the correct answer - put the 428 in your current car, keep the 400, buy another Pontiac, and put the 400 in that one.

COME ON PEOPLE!

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Old 09-18-2021, 09:25 PM
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I like the 428 best, had a few 400 and 455, but like the bore/stroke ratio of the 428. Built two 428 and they have been the most responsive engines. Might be the combination of parts too, but really like my 428 matched to my TKX.

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Old 09-18-2021, 09:56 PM
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Quote:
Originally Posted by steve25 View Post
Something is really amazing with some folks on this site!
They give a big Thumbs up to someone who as dropped a 535 cid motor in there PONTIAC , yet when a guy can’t decide between yanking his 400 out to drop in a 428 he gets all sorts of crap thrown at him from the never over a 400 crowd, lol!
I SEE IT THE OTHER WAY AROUND, I see 10 + old timers with lots of Pontiac Experience saying build the 428 engine and drop it in the 2+2.

Building a 428 from pieces is painful at times but he has the majority of parts in a complete engine with needing a compression ratio drop to run today's pump fuel. GOOD pistons are available from Ross, Diamond, JE, among others. I have a set of custom WISECO Forged Pistons with a custom Compression Height. (Also known as a "Dial in your own Compression Ratio") and I have plenty of valve to piston clearance with the camshaft I run.

Good rods, custom pistons and rings for a minimum bore job on the 428 block and 670 heads and you are good to go.

Tom V.

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  #34  
Old 09-19-2021, 12:41 AM
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Originally Posted by darbikrash View Post

If these items are up for replacement, it costs no more to build a 467 stroker from the 400 block and this is a much better solution IMO for a heavy car.
I’d do this. You can always just tell people it’s a 428.

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  #35  
Old 09-19-2021, 11:15 AM
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I’d definitely do the 428 running the correct 670 heads for the right look…
…As much as I like the 4.00” stock stroke original crank I’d consider slipping in a 4.21” stroke 455 crank. Not really necessary but …
I’d do this.

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Old 09-22-2021, 11:28 AM
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I would build the 428 for the added torque/hp but if you’ll use those 670 heads(Rated factory at 10.75 compression)they are no fun for todays pump gas. I would install custom dished pistons and aim for a true 9.1-9.5 compression. You can then use normal pump gas instead of octane additives and race fuel. Either way it will cost you money but less grief at the pumps later on.

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Old 09-22-2021, 04:40 PM
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Wouldn't a 428 with flat pistons and 6X's do better on quench, flow and compression?

  #38  
Old 09-22-2021, 07:03 PM
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Quench, I would say that the 670 heads would have far more of that vs the open chamber 6X heads.

Flow, the 670 heads for several years (with a good valve job) were assumed to be better flowing vs the #16 casting 1968 GTO heads, the "later" Emissions heads, and the non early SD 389/421 heads. Only the 455 SD heads and the RA-IV heads were better.

As posted before, easy to get a piston made that would have a 9.1 to 9.5 compression ratio with the 428 cid engine.

Tom V.

The emissions heads are good for emissions. But do what you want.
10 or 15 cfm difference in port flow is not going to do much on a street engine.

Now a Boosting device!!!!!!!!!!!!!!!!!!!!!!!!!!!

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  #39  
Old 09-22-2021, 07:30 PM
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Originally Posted by Scarebird View Post
Wouldn't a 428 with flat pistons and 6X's do better on quench, flow and compression?
Yes, but the 670's were to make the car look more correct.

The 428 is my favorite for street driving: more torque than a 400, but not so much that street tires have no chance off the line. And it still likes to rev.

I'd make a template of the 670 combustion chamber outline and digitize that to mill a dish exactly that shape into the pistons which will maximize quench, which in turn reduces octane dependency.

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Old 09-22-2021, 07:53 PM
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I think you could make a clay of the combustion chambers and give it to the piston maker to make exactly what you would want?Tom

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