400 vs 428 - Help Me Decide
 

This thread subtitle says "no question too basic here" so go easy on me :D

I have a basic driver quality 67 convertible with a non-original 400 from the early 70s. My goal is to build a 2+2 clone that I can drive & enjoy. Aside from the clone part, I'd like to stay as original looking as possible while getting as much performance out of the project as I can. Would be happy with around 450hp and thrilled to have more.

I have found a date correct (67) complete 428 engine with 670 heads. It has 4 bolt main caps and has never been apart. Came from a car with about 80k miles on it. Would be a 'correct' engine for my 2+2 clone BUT....

Is it worth the extra price of admission to have a 'correct' 428 in the car, or can I get similar performance for less $$ by just massaging the 400 that's already there? This is really 2 questions:
- is the 428 an inherently better engine that is worth the cost for basic reasons, or
- is it really just personal preference?

The 428 would have to be gone through, machined, etc but I guess I could just add bolt-on goodies to the 400 I already have. Problem is I have NO info on the internals and would probably want to open & inspect anyway before I go stressing some inadequate stock parts. I want to stay 'reasonable' with the build so I can run the 91 octane pump gas available here in the west.

I have the budget to go either way (within reason). So what do you guys recommend?

Go for the 428. When I swapped a 400 shortblock under my RAIV heads HO intake same cam same headers for an NMCA class vs the old 455 short block it felt like a dog with the same 3.42 rear gears. Took 4.10s and a looser convertor to feel the same. The 428 would put you in the middle and I think is the perfect street/strip motor.

Since your car is no light weight build the 428 as it will cost the same as the doing such with the 400, then sell the 400 short block to fund the 428 build.

If the heads on the 400 now are not the 4X series and have about a 100 CC chamber then get them fully rebuilt and bowl ported by someone who knows how to do such with Pontiacs .

First and foremost build the short block up strong first by chucking the stock cast rods !

What are the casting numbers on the center exh port of your 400s heads?

Have to agree that the 428 engine especially in 1967 is a great engine for a 2+2.

670 heads might be a bit high in compression ratio but you can get pistons and rods for the engine that will make it more durable and also get the compression ratio down to a true street gas ratio. 428 all the way!!!!!!!!!!!!!!!

Tom V.

Lots have gone with the 3" main engines because there so few good 3.25 main engines in good shape still out there. If you ever sold the car it would sell for a lot more with a "correct" style 428 engine vs the run of the mill 400 engine.

Would a stroker kit in the 400 make it a viable option instead of the 428?

Easy. `67 428. If you`re gonna clone it, clone it. You will get more torque at the same time without buying a stroker kit.

Looks like I have the 6X heads w/the vertical boss, so 6X-4 heads.

Based on the information you provided, I would choose the 428. This might be surprising to some, because I recently traded away a 428 even-up for a 400. But my reason was my car was getting a stroker kit and I wanted the 3" main size to run 7000 RPM occasionally. Your situation is different. You stated you wanted a 67 2+2 clone and a 428 is a natural. Great bore/stroke ratio, plenty of torque, 4 bolt mains and good reliability with stock internal parts to 5500 RPM. Just what you wanted. With nice iron heads and a good valve job will make 475 Ft. Lbs. torque and a tick over 400 HP. Perfect for what you describe. Also will be more correct for that car. 428 was a great engine.

428 all the way. Keep driving it with the 400 til you get the 428 ready for minimal downtime

"There is no replacement for displacement" so go with the 428 and the factory crankshaft.

To me it depends on what’s involved in the rebuild of either engine. If you are replacing rods, crank and pistons, it’s far better to start with the 400 block.

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.

Absolutely go for the 428! An all original standard bore 67' 428 is very difficult to find and would make your car really stand out. But, in my opinion, you also must keep the 670 heads. Yes, using aluminum heads would give more performance, but you would lose the desired effect. A 67' 2+2 conv with a stick is a great car and the crowning touch is the 428.

Good!
You have the perfect set of heads for that build to be street happy !
Grind the the 6X off the tops of the center exh ports if that troubles you and then bag and box up the 670 heads should you ever sell the car and want to max out your profit from doing such.

Do the 428 with the 670 heads. You'll be buying pistons either way you go so simply adjust the compression with the piston choice and run with it. A good cam choice and it'll be fine on pump gas.

Just a thought: 6X have all the exhaust manifold bolt holes and hardened seats. Unless replaced a 670 has soft seats.

2X 670s with custom pistons.Tom

I’d run the 428 straight up, heads and all. Run 100LL or mix Lucas boost at 50/1 with 93 and let her scream. How I run my 16s @ 10.66/1.
Authentic and runs great all the way to 6k.


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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.

All things bring Apples to Apples equal in the Head and Cam department, a bigger motor does NOT make it any easier to attain a certain HP level , it just makes it easier to make a given amount of hp that the flow system will support at a lower rpm, but with more torque and less compression!

2X Bman,run the right CR and pull into any gas station and not worry about detonation.Tom

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.

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 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.

In more than more than 50 years with Pontiacs I have never found a issue with street driving large J cranks.Tom

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.

No but am looking. Going to be one of the hardest parts I'm sure....

PM if you have some for sale :cool:

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....

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! :drive:

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!

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!

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.

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.

I’d do this. You can always just tell people it’s a 428.

I’d do this.

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.

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!!!!!!!!!!!!!!!!!!!!!!!!!!!

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.

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

Not disagreeing with you but always willing to learn, explain how you would "maximize quench". I understand the Mirror Image of the combustion chamber part. Seems like you would need a Gas Ring sealing plan vs a off the shelf cometic type gasket.

Tom V.

And of course proclaiming you have a 428 vs a 400 just sounds cooler at the local cruise or car show!

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By "maximize quench" I mean take advantage of the maximum available quench area by starting with a flat-top piston and only dish an area which is the mirror image of the combustion chamber.

From what I've experienced, minimizing and equalizing quench height is also important, which is why "zero decking" and squaring the block is important.

As to the sealing tech, I'd just use a standard Cometic gasket. I didn't mean to imply anything fancy here.

Years ago, long before I even knew the definition of "quench", I had a '68 Firebird 400 with the stock #16 heads. I got it from the original owner with 70k miles on it. With its ~10.25:1 CR, I had to retard the ignition timing a bunch to run it on CA's 92 octane at the time. I later rebuilt the engine with generic dished pistons which had a ~3/8" lip around the perimeter and the rest of the area was dished, which meant very little quench area. I believe those pistons reduced CR to 8.5:1. I used an 068 cam in place of the orig 067, so not much difference. I was quite disappointed when that engine had almost the same octane appetite as it had with the stock pistons, and now made less power as well.

It just depends on how the chamber is designed.

I've done the bowl type dish on a 428 build decades ago when I used #13 heads on the engine. The chamber is so large on the 13 that the 3/8 lip around the parameter of the piston took up nearly all of the quench the cylinder head had to offer. That one came out to 9.7:1 compression and it ran great on 91 octane for years with a very small 218 @ .050 camshaft.

The 670 head with it's much smaller chamber, I agree I'd dish a piston differently, just as described which would more likely end up with more of a "D" shaped dish.

Here At Last
 

Picked up my 428 yesterday at Fastenal (great shipping service BTW).

YH code casting 9786135 turns out to be date-correct for my car L016 Dec 1, 1966. Intake is J216 Oct 21, 1966. Was pulled from a '67 Grand Prix with about 70K miles on it some 30 years ago and sat in a shop waiting for rebirth. Even has the AC brackets, which will come in handy.

Can't wait to start the build, but it looks like we'll be moving soon so it will be a while....

Cool deal.

If I had that 428 I'd keep the 670 heads and run a 4.25" stroker kit to complement the 4-bolt mains and then sell the 4" stroke crank for a high premium to one of those guys that believe there's something magical about it. I'd run big dish forged pistons with enough volume to drop the compression ratio down to no more than 9.3:1.