421 vs 434 sbc

Hey guys! Will a afr 210/76 heads be compatible with a 10-10.5:1 pump gas 434 sbc? or will a 421 sbc be more suitable? These are the race ready version heads, im putting in a 69 caprice!


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Heavy car + $15,000 race 434 small block = you can afford whatever heads you want.

If you're looking for NA streetable pump gas power, the more cubes the better.

Those heads should be fine. If you're going to spin the motor up to high RPMs I'd consider the Brodix X-11s and have them CNC'd by Brodix.

Yeah, but 434 starts with a raised-cam, wide rail motown block, then has a buttload of machine work and custom parts; crank, rods, pistons, wider oil pan, specialty timing chain and valvetrain, and massive heads to feed it.

If he's putting a $15,000 race engine in a behemoth 69 caprice, then he already has enough money to throw at this project and doesn't need our help deciding on a 434 or a 421... and how do you make a 421 SBC anyway?

both can be done with a stock 400 block. 421- 3.875" stroke, 434- 4" stroke.

Ah...ok. My math was off... I thought that made 420.

I'm just skeptical, because in two and a half years, this guy has made three posts. One talked about a 406, this one talking about a huge-budget 434, and one that just said "waz up".

I'm just being a jerk That's all.

Hey, I'm a jerk on most days. And I wouldn't waste all of that money on a stock 400 block, but you can do it with off the shelf parts if you are so inclined to. If I was looking at those power levels I'd just run a Gen IV engine.

By the way... what stock block can be clearanced for 4" stroke without hitting water or cam? I thought that was strictly raised cam, wide pan rail territory.

Most blocks can with the new rods that are out. Look for 4" stroke kits, you'll see them used to turn 350's into 400's. I forget who all manufactures them, I think SCAT may. Like I said though, when you're dumping 2G's into a rotating assembly, and 2 into heads, it kinda makes sense to put another 2 into a good block.

LOL! Thanks curtis73 you are correct!

Thats neat that y ou can fit 4" cranks into stock blocks. I thought I was risking it by putting 3.875 into a stock block, guess we will find out. I know Ill have to do a little rod grinding.

Then why are you asking us? Give your plastic to a reputable builder and sign the tab when its done.

Just asking to be sure! here in miami everybody races on the street i just wanna look good and have some power to pull my lead sled!

If you've got 15 grand to spend, a 502 Big Block would be a much smarter place to start with that heavy of a car.