[1950Mercury]

I am in the near future thinking of building a 421 or 428 engine. Since none are falling on my lap at a decent price I have been considering a 389 block or a 400 block. I already have a 68 0071 400 block which is 2 bolt main. So the question being how are these aftermarket cranks with 3" mains working out in 2 bolt main blocks? is it basically get correct pistons for the 4" stroke or is there a bunch of machine work on the crank? in other words are these cranks any good? I was considering a cast crank but what I see from Butler it takes Chevy rods. Is there a 4" stroke 3" main that uses the 6.625 Pontiac rod? I am not after huge cubic inch or super high horse. Probably 425-450 tops. I would like to find a 8789 block bore .030 and be happy with a 428. Otherwise I will take this 0071 block to +.060

[Tim Corcoran]

Why not use the 400 block put in a 4.25 stroke crank a .030 over bore. You can get a stroker kit from Butler that includes crank pistons rings rods bearings and the price is reasonable. It comes all balanced ready to go. You choose select the pistons rods etc.

[performerrpm]

i have a complete 988 .030 studded 2 bolt 0 decked, and a forged 434 stroker kit, eagle h beams, icon forged 10cc pistons and a rpm 3" main 4" stroke crank. id turn lose of all of it. need balanced, bearings n rings to complete. if nothing lands in your lap lol...still in boxes.

[steve25]

Do you currently have a set of Pontiac rods you want to use?

If not a crank set of usage of Chevy rods is the way to go , especially in the cost department.

[mgarblik]

Originally Posted by steve25

Do you currently have a set of Pontiac rods you want to use?

If not a crank set of usage of Chevy rods is the way to go , especially in the cost department.

I agree with this! The Chevy rod size opens you up to all kinds of options in the bearing department. With the Pontiac size you are limited to STD, -010, -.020. That's about all without really digging deep for options. With the Chevy size, STD, -.001, +.001, -.009, -.010,-.011, -.019, -.020, -.021, Aluminum, Bi-metal, Tri-metal, Narrow, coated, all this is readily available.

All the above is important because aftermarket cranks often need tweaking to get the correct oil clearance.

[1950Mercury]

If a 421 don't come my way I will end up using my 0071 block. Will probably need to go to .060 as it had some rust in # 3 hole. It's too bad as this motor looks to have less then 5,000 miles on a rebuild. It was abandon in a storage locker. If I was chasing after big power I would consider Chevy rods and pouring a crap load of $$$ in a motor but at my advanced age and fixed income I am just after a good streetable engine for a 66 GTO.

[Jay S]

For a mild build you could use a cheaper nodular 4.25” crank with BBC 2.2” rod journals for around $500, and Chevy rods are about $400 for cheaper I beams. There may not be a cheaper nodular crank option for a 4” stroke, good chance the only option will be aftermarket forged. The 4” stroke forged cranks will be closer to $1000, but you could use your factory rods. When you figure what the costs are and get down to what is an available it is not really cheaper to do a 4” crank over a 4.25” in a 3” engine. The cheapest way to build a 4” engine is starting with a 421 or 428.

[steve25]

It seems you’re failing to see what folks are telling you here if you go the route of a complete rotating assy.

The BBC rods and matching piston provide greater longevity and power due to mechanical differences in most cases.

[Formulajones]

Do you have Pontiac rods resized with bolts done an ready to go? If not the aftermarket Chevy rod makes more sense from a cost perspective. Like mentioned it's also a more common bearing size.

I agree with Jay, if cost is a factor I'd bet you can do a 4.25 setup cheaper if using the non forged stuff.

If you find a factory 4" crank it'll take some work to fit your 400 block. I built an engine like that 25 years ago because I had the parts laying around. The crank needs the seal area welded up and turned. The rest just needs machined and finished. It wasn't exactly a dirt cheap operation 25 years ago and finding someone now capable and skilled to weld and grind the crank properly is even more difficult today.

This day and age, I wouldn't even bother, I'd just buy a new 4.250 setup and run with it.

[steve25]

Let’s go all the way back to square one here.

If the OP is only looking looking for 425 to 450 hp then why the heck not just build the 400 as a 412 with the ,060” overbore?

He sounds like he just wants a fun reliable ride that can burn some rubber and surly a 400 can do that easy with a out of the box set of Aluminum D port heads and a cam that can be lived with .

Everybody’s obsession with building a stroker motor to me is getting out of hand here especially since the OP is on a fixed income level.

I bet the OP can turn up a 65/ 66 389 Armasteel crank and a set of redone factory rods and save himself at least 300 bucks on his rebuild cost right there.

[Formulajones]

He's the one that asked about doing a 428+ build but doesn't have a 4" crank

That's why you start looking at rotate assemblies and realize a 4.250 setup is sometimes cheaper and makes more sense.

If he decides he's happy with a 400 then by all means rebuild it.

[1950Mercury]

If I was considering a 4.250 stroke why not just start with a 455? The car already has a 389 turned into a 400 and cammed 670 heads. 3x2's. Car runs okay for what it is. But down the line I would like to build my own motor so I know what is in it. I like motors about 427 c.i. Its a good number. Any bigger and they are huge gas guzzlers and all it is is a pissing contest to who has the biggest engine. BFD. 421 or 428 are factory Pontiac engines. And yes a well built 400 can produce good power. I had a very well built 400 = .060 12.5 to 1 850 Holley in the mid 70's That I had to get rid of because I was on the verge of loosing my license and that would have cost me my job. My question in the beginning was how reliable are these 4" stroke aftermarket cranks is a 2 bolt main motor? Buttler sells 4" cranks for about $1200.00. Its getting tough to find a 421 or 428 for that price. I dont have to have a 421 or 428. I would just like to have one.

[performerrpm]

the 4.250 is a proven crank in a 400 2 bolt block...the 4" in a 400 2 bolt is just as good as it was in a 2 bolt 428 plus some with smaller mains.

cant go wrong with either 4" or 4.25...the potential is just gonna be in different spots.

as steve25 said...400s even capeable...im actually doing what he said to the T with the d port edelbrock/ cam...its my bastard child build but honestly it would walk the dog on my hi school 400 i thought was so badass as a teen

[Jay S]

Done correctly there should be no difference in reliability for any of these options. There should not be very much difference in fuel efficiency with any of those stroker options either. Build what ever you like, a lot of people love the 4” stroke engines.

[Dragncar]

428 cranks and 455 blocks are not too hard to find. Everyone seems to luv 440 build when they do it.
Kicking myself for selling the 3.25 x 4" forged crank awhile back. Sold a 3" main Scat too.
I have a nice 74 455 just sitting there.

[performerrpm]

i have a 4 bolt 428 just chillin....and a 20/20 crank i traded a 6.0ls motor for ...seems the popularity of the large main blocks got hampered by the 400 based builds...its just chillin under the shelf too...among other parts.

[PontiacHO]

455 block (.030) and 4 inch stroke. 439 cubic inches. That one seems fun…

[ponchjoe]

Molnar makes a forged 3”main x 4” stroke crank

[Skip Fix]

I still have a P Dude 4" stroke billet with Pontiac journals for a future build!