I’ve also been calling this one “Second Helping”, because I had one and I went and got a second helping. A friend at work got this in a package deal of sorts with a truck that he was going to buy to go muddin’ in. He asked if I thought what he was paying for was a good price and I told him “Hell, at that price let me know if you don’t want it, I’ll take it!” Well, he decided to go a different direction and offered it to me and I took it. The whole story can be read here: https://www.jalopyjournal.com/forum/threads/a-tale-of-two-big-blocks.1246022/#post-14250350 The block casting number is 10114182 (’91 and up 454, Gen V 4 bolt) and the heads are casting number 10114156 (91-up, Oval Open chamber, 118cc chamber, intake valve: 2.070, exhaust valve: 1.720, square exhaust ports and screw-in rocker studs. At this point, I’m going to assume that when I take it to be checked it comes back with all the “good” boxes checked. If the crank is good also, not being sure what the value of a Gen V crank is, I may keep it. I’ll probably break even when sell the old crusty heads as is, knowing they aren’t much. But I don’t see a need in them taking up space. The plan is to build an engine around a dual carbureted 6-71 blower circa early to mid 60’s. Think of it as if Duke would have put a blown big block in his yellow ’57 Chevy instead of a small block cruise Tubby’s on Halloween night, 1965. I don’t know what it will eventually go into, but with all that being said, it will be pre ’65!
use the Mark IV block for this. It looks a lot closer to the 60s blocks, although not exact. 4 bolt mains are probably unnecessary. A steel crank would be nice, and you'll want forged pistons. If you plan to keep the rpm below 6500 then you can even use the 3/8" rods, with good bolts. You'll want some old rectangular port open chamber heads. Aluminum ones are getting expensive, see what you can find in iron. You can run a small dome on the piston if you build a 427, or flat top if it's a 454. you probably want forged pistons, too. An old steel 396 crank will work to build a 427, but look at piston weight and crank balancing cost. this one just finished Drag Week, plus the 4000 mile drive to Michigan and back to Az.
NA the oval ports are OK. And modern head designs can get away with smaller ports. But a 60s blower build just has to have the big port GM heads. No question.
I honestly don’t plan on it ever seeing over 6500 rpm. It does seem like everyone agrees, in both threads, that I should swap the direction of the builds. So that’s what I’ll do. @mohr hp , I like the thought of using these heads especially if I can save some money there and put the saved money towards a set of forged pistons.
30 Years ago I built a 6-71/454 very similar to the one Squirrel has in his Nova, except I went with Smog era oval port heads. It made about 640 horsepower and made it all by 6300 rpm. The engine still lives today, and has thousands of street and race miles, using mostly Chevy HP parts.
Call it brain fog from working all day, but this is got me thinking; I've got a line on a forged 396 crank, I could use that in the Mark 4 block, making it a 427 and get a set of forged pistons, good rods (I may have a set of good GM rods, I just don't remember exactly what they are, they were gotten many many moons ago), rebuild these heads to match the correct cam and build that as my blown engine. As for the Gen 5, use the block, crank, rebuild the heads for a .550+ lift cam and build it as a nice little street engine.
396 cranks are lighter than 427 cranks, (the 3rd counterweight back is thicker on a 427 to compensate for heavier pistons-7/8" vs 3/4" on a 396) so you might have a tough time getting it balanced unless you're using light weight forging's similar to the 396 piston weight. Not that it can't be done, it just might cost more to make it all happen. Just something else to consider if cost is a major factor. Personally, I'd rather have a 427 than a 454. JMHO Good call on using the Gen 5 for a nice street engine.
The biggest advantage to the 427 that I've found, is that the art on the car is accurate. It's a magical number.
This one is now going to be the naturally aspirated engine. I've also updated the title to both the big block builds. A little update: I bought a complete factory rotating assembly and a complete set of heads from a local guy, that only wanting the block for his build. My two boys and I have taken the block to the machine shop to be checked and cleaned. If all is good he (Bryan) is going to bore it .030, install new galley plugs, freeze plugs and new cam bearings. Bryan is also going to get a new set of pistons coming this way. When they get here, I'll take the rotating assembly I've bought and have him check the crank and rods, and if they are ok, he can balance the rotating assembly. At that point, I get the short block assembled, call Clay Smith and take the heads to be cleaned and gone through.
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