Jim85IROC

I'm planning to buy a 400 block out of a 78 (or close to it) blazer. It's a 2 bolt block that's never had an overbore. Since I currently have a good running 350 that I'm not done playing with in my IROC, I'm going to build the 400 slowly as money permits. I have no deadline, and if necessary, I can stretch it out to incorporate a bigger budget. I haven't picked out a specific target horsepower, nor have I decided whether it's going to be N/A or supercharged. Right now I'm just laying the groundwork on all of this decision making.

So anyway... first of all, how much horsepower can the stock crank support? For the sake of speculation, let's say it's in good enough shape that it's only got to have .010 machined off all of the surfaces.

Let's assume that I'm going to have splayed 4 bolt caps installed too. I plan to assemble it with AFR hardware.

What horsepower level can the stock rods handle?

I'm debating on how big to build this because i don't want so much horsepower that I'm afraid to drive the damn thing to work. Right now I'm leaning toward a n/a application with high compression, AFR 210 or 220 heads, and a holley stealth ram. The way I see it, I should be able to get 500 reliable horsepower out of it with the right combo. Stroking it would require an extremely expensive aftermarket crank, and I don't know that I'm going to get enough return on my investment with it.

So anyway, as you can tell from my rambling, I have no idea where I want to take this project yet. I'd just love to hear from some 400 owners about your combo, how much power you make, and how you like it. Thanks.

Nathan Plemons

A very popular combo with the 400 block is to actually destroke it. Essentially a 383 is a 350 with the stroke of a 400 block. You can reverse this on a 400 block, use a 350 crank and make a 377. The benefit is that you still have the larger bore with the short stroke and you have a motor with at least as much torque as your 350 that will absolutely love to rev. I know at least one guy who easily spins his to 8000 rpm's. It's really a nice setup.

Just a thought, you can always stroke it too and have even more torque :)

Chief Muktar

I am also picking up a 400 block in the near future to do a slow buildup, so I am interested in any ideas that pop up. So the question then becomes how many RPM's can a stock 400 crank handle before it goes boom???? I would love to have a motor with a 7000 RPM red line, but I don't wanna spend the kind of money thats needed to got a forged 350 crank. I think ski_dwn_it is inthe processof building up his 406, and Id85 is about to start if I'm not mistaken, maybe they'll chime in :cheers:

Ramanstud

the above post sounds good, though that means a lot more $$$ in the valvetrain? And out of curiosity- why settle for 0.010" over when you could opt for the more common 0.030": the added displacement as well as more available/cheaper pistons? Just a thought, I don't know for sure- but it seems like 0.030" over pistons are more common than 0.010" over, and might thus be somewhate less expensive....

But a 8000RPM 377? Nice.

CFI-EFI

Piston prices generally don't change with different oversize options. But he wasn't refering to the bore. He was talking about turning the crank. As a rule, you don't want to take any more off of the crank, then necessary.

Good luck, and...

RACE ON!!!

CORKVETTE1

keep the stock crank put in a set of quality pistons and quality 5.7 rods and thats it the stock crank can handle 500 hp all day long

Jim85IROC

Like CFI-EFI said, I was referring to the crank, not the bore... but if I find a good enough assortment of .010 pistons, I may only bore the block .010 as long as that's enough to true the bore. Because of the siamesed bores, you're getting into dangerous territory when you go beyond .030 on a 400 block, so if I only go .010, it leaves me room for another rebuild down the road.

500hp on the stock crank hey? I'd love to say that I want to make a supercharged fire-breathing monster out of this motor, but I'm going to kick myself if I make it too powerful to drive safely.

LD85

Well from all of my studies, still ongoing, the general consensus is that 6500 RPM is the max safe limit for stock bottom end. You will hear from some that say they hit 7000 RPM on occasion but I will not chance trashing a motor I just built so, I plan on maxing my RPM at 6000RPM to be safe/cautious, whatever.

First decide what you want HP or RPM’s or both. IMHO, If you can afford it go with a forged bottom end then you don’t need to worry about maxing out the bottom end. But 500HP can be hit as Corkvette said with stock crank.

Budget, depending one what components you use, by new or used and scavenge from your old motor like the distributor etc, you can look at spending $5000 easily, more like $600-6500 if you go with forged stuff and more like $7000-7500 if you buy all new parts. I have a spread sheet for my motor and have documented all of the know parts and will add the Gottcha parts at the and for a final mind-boggling tally.

BTW am not an expert at this but definitely know much much more than when I started, the forum is really helpful but at times you will get conflicting info so then you just have to go find out for yourself! There will be no short cut to studying this in depth for sure!

:cheers: :cheers: :cheers:

jimtreber

Maybe I was just lucky but here's my experience with the 406. As in an earlier post of mine, I went with a speed-o-motive crank kit. The crankshaft was tricked but still a cast crank. 12 to 1 Speed Pro's. I had a set of angle plug heads around and used those. Victor JR, nitrous and Comp Cams 244@.050 backed by TH400, 3000 stall switch pitch, and 4.11's. I drove it daily for years with a best of 12.14 on radials. The bock was 2 bolt but at the time the 400 users preferred them because of the thicker webbing. I tried winging it to 6500 but my et's were better with a 6200 shift point. I never had anything break on this car and I don't feel I had a huge investment in it. Again, maybe I was just lucky.

Ken Lanham

One more benefit of the '377' is that there are factory forged 350 cranks out there to be found. Probably in the same junkyard that the 400 block comes from. So you can save quite a bit of money on the rotating assembly and still have a forged bottom end with a 377. If you want to spin to 7000+ rpm, it is worth thinking about.

CorvetteZ51Racer

I don't know how much the stock crank can handle, but my first piece of advice would be to find the stock rods, grasp firmly, and throw them as hard as you can into the nearest trash can. The 400's had rod problems, not because the stock rods suck, but when you combine the stock rods (which, while they don't suck, they're not that good either) with the rpms that people are wanting to spin a motor, with the piston speeds the 400 sees, with the heavy stock pistons, you break rods.

What to build depends on how you want to drive the car. Want a street motor that makes insane torque off-idle, roasts the tires right off the car, and scares the VTEC out of the Honda next to you? Build a 427 stroker. Want a track motor that makes high end power, sings like a Ferrari on roids, but has "stock displacement"? Build a seriously destroked 358 using your 400 block and a used Winston Cup crank. Yes, they're expensive at $1000 used, but how can you argue with a Sonny Bryant billet 3.33" stroke 39lb crank that will allow your motor to rev to 9500 rpm (if you have the valvetrain and heads for it) for the cost of a new Eagle (oooo) forged crank.

Now, I'm not suggesting you go out and build a 9500 rpm 358 destroker with a billet crank that won't idle below 1500 rpm but makes obscene top end power (how would you like 820 HP @ 9500 rpm on a N/A 12:1 motor?) I'm just trying to give you an idle of the options that are available with the big-bore SBC block you have.

*disclaimer* - I also don't suggest trying to spin 9500 rpm on a 2-bolt block, because if you do, at some point your engine will likely become lighter as the crank decides to exit the block :D

Zora

Stroke it....if you got the $$$. :D

CarAteMyMoney

I was also told that the stock crank can handle well over 450 horse when properly balanced and prepared. I have two non-bored 400 blocks that I havent decided what to do with yet. If I decide to build 'em up I'll be going with a stock replacement crank, ARP bolts everywhere, 5.7 rods and the matching pistons.

I also remember hearing that 2-bolt 400 blocks are stronger than standard 2-bolt small blocks, has anyone else heard that?

The advice I was given was to use premium parts on a 400, no brand x crap. That, and to use an aluminum water pump and big butt radiator.

I remember hot rod or something did a build up with a 400 a while ago.. they claimed something like 450 horse/510 ft/lb with 200cc dart iron eagle heads, comp cams xe274, and some kind of holley carb. That sounds about right. I think they used SCAT parts...