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.


Sent from my iPhone using Tapatalk

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!