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400sbc-2bolt main beefed up or 4bolt conversion?

5K views 11 replies 7 participants last post by  vinniekq2 
#1 ·
Basically my builds going to be a 406 but I want a soild bottom-end. I've searched here and alot of other places on pros/cons of both and got alot of info. So my decision...

What I feel would be strongest and best for the bottom-end is ofcourse the more expensive route. Keep it 2bolt, fill the water jacket, splay it and girdle it etc. Aftermarket scat more than likely with 6" rods etc etc. Ideally wanting 10:1. 500ish+torque and 425-450hp to the wheels, ideally.

Second option is cheaper, convert it to a 4bolt. I'd do it right to and spend the money if I did this. I'm just worried for the torque/hp I want it'll wear the bottom-end out quick.

It's more than likely going into a s-10 for mostly street/ some strip. But...I want it coming proper, ya know? heh.


I want strength for hard pulls and just to have the bottom-end strong. I know 400's are a bit infamous for cracks so I figure a solid bottom-end along with what my choices are for the top-end to work with the bottom-end. I'd like to be able to hit 6k when needed ;).

Whats everyones feelings? I'm guessing for the first build it'll cost me anywhere between $1600-$2200ish? Second build maybe $1000-$1800ish? Just the bottom-end work.
 
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#2 ·
By the time you machine the 400 block you're almost to the cost of a SHP block. May be somethin to consider. Btw splayed mains are 4 bolt mains, the bolts just aren't parallel.

If you run a stock 400 block is do at least a short fill, those cylinders are notorious for being thin.
 
#3 ·
I've been to 7500 rpm and over 500 hp with just 2 bolt main and ARP studs, partial block fill,, and line honed mains using SCAT crank w/5.7" rods, and stock crank w/5.7" rods. Street/strip engines, not circle track engines, there is a big difference between hitting high rpms for a few seconds at a time, and constant high rpm use. Last one was together over 10 years and a shoebox full of timeslips before it split a cylinder wall.

Even used a stock 4-bolt block, partial filled, with stock bolts and ran it over 7000 rpm street/strip on a nearly every weekend basis at the strip, about 440 hp, before blowing up a hyper piston and cracking the cylinder wall. Since it was .060" over, it wasn't worth fixing with a sleeve, so I trashed it. Lasted 3 years though, probably would have lasted longer if not for the Hyper issue.

Tried the girdle on a 2-bolt 350 block turned into a 383, boy that was a waste of time...didn't come apart, but tore down at 1 year to change out a leaky home made oil pan. Decided to look at bearings just because we were in there anyway...good thing we did, evidence all over bottom of caps that they were dancing, walking around and causing fretting wear between cap and block. Main bearings looked terrible, rod bearings looked ok.

Found out girdle doesn't help because it is holding cap at the wrong end, it is at the parting line with the block that things have to be held stable. Converted to 4-bolt splayed and no problems since.

2-bolt 400 doesn't have the same problem as 2-bolt 350 because 400 2-bolt main caps are just as long as a 4 bolt cap, where 350 cap is just 1/2 as long...it is contact surface with the block that keeps things from moving around, not the # of bolts or a girdle.

2-bolt 400 caps are similar to 2-bolt BBC caps, they are just a big a 4-bolt caps, just don't have the extra bolts in them..

In your case, my advice is if you are using a cast SCAT crank and street/strip use, don't bother with splayed caps, just stud and line hone the 2-bolt caps....leave the splayed caps to the circle track constant rpm guys.

If you are considering a forged crank, then I would just totally reconsider using a stock block at all....why put a really stout crank in a block with known strength problems over 600 hp....if the block blows, there goes your expensive steel crank with it....same with fancy H-beam rods...just use mid-price I beams in a stock block.
 
#7 · (Edited)
Thanks everyone for your input and info. It's much appreciated being I'm not very familiar with bottom-end assemblies and the technical measurements/etc that go with them.

The reason I'm doing a 400 oldschool sb is just that. It's a sweet oldschool ride that if built right and setup right in the right vehicle, can destroy alot ;). I like new and old but haven't done a oldschool type thing in about 22 years. I've built and had everything from tuners to the steel beasts...favorite was my 4x4 86 s-10 with 32 inch mudders, 9 inches of lift and tons of hp. had a crate ho 350 with about $10k into it. got lucky and hit pretty big on a scratch-off ticket lol

I decided to go with 375-400hp to the tires, high torque ofcourse and stick with the 2bolt. Bringing it this weekend to get gutted. I would do it myself but found out it is .060 over when I pulled the heads so I don't want to risk scratching a cylinder on accident. I'll pay the cash to have it done and if something does happen it's the shops responsibility. also having it sonic tested even though it was rebuilt 5k miles ago. And linehoned. A few questions/wonder arose when we were talking on the phone...

So basically for info my setup in a nutshell is gonna be a s10, 150 shot of juice, ideally 375ish to the wheels, hp. Tranny?..not totally sure yet but hear a 700r4 can be setup nicely for a street ripper. Is this true? Figure with the juice added to the 375ish hp, can that tranny with a decent rebuild and setup for street be strong to handle a weekend of ripping? Gearing not totally sure on yet. Something close to 373's more than likely. Gonna be a cruiser to but mostly setup for some ripper vs ripper on those nice dead straight backroads..no kidding ;).

He said for me to hit the 375-400 to the wheels I'd have to have around 575ish-600 to the crank. Seams like a high percentage. I'd of guessed worst case maybe 30% but closer to maybe 27ish. It's a light truck, would have the tranny setup for street, shiftkit,midrange-semi high rear-end gearing etc etc. They build great motors at this place but that just seams high to me. whats everyones opinion on that?

EDIT: He also said not to put hardener in the waterjacket or anything. I know the 2bolt blocks are solid but not sure how I feel about that. Not sure yet either if I'm sticking with the 5.7 or 6" rods. Probably talk about that with him Saturday.

EDIT2: What could a factory bottom-end 4bolt polished and cut handle hpwise? Thinking of keeping it and building a 383 once the 400 is done. Read in a few places they can handle around 500hp but is that to the crank itself? I'm assuming so.
 
#8 ·
Biggest improvement you can make on a 400 is a longer rod. This reduces piston side loads from skirt into cylinder wall and slows the accelerations between 90 degrees BTDC and ATDC. This eases the unbalanced mass accelerations on the crank which lessons the undamped loads on the it thus the mains benefit with reduced loading.

Bogie
 
#9 ·
Biggest improvement you can make on a 400 is a longer rod. This reduces piston side loads from skirt into cylinder wall and slows the accelerations between 90 degrees BTDC and ATDC. This eases the unbalanced mass accelerations on the crank which lessons the undamped loads on the it thus the mains benefit with reduced loading.

Bogie
Ah ok. Is this still applyable with a 150shot? i'm guessing so but want to make sure. I'll bring it up Saturday when I bring my engine in to get checked/cleaned
 
#10 ·
His percentage lost seems awful high to me, 575-600HP crank should come out to 450-475 roughly at the wheels.

I would not build a 400 stock block without a partial block fill. it doesn't impact cooling , and stabilizes the bottom of the block structure.

All the 400's I've done were 5.7" or 5.85" rod combinations, except the very first hyper piston .060" over 4-bolt, it had the stock short 5.565" rods...and still held up 3 years to 7000 rpm blasts.

Hope you are planning to replace that puny 7.5" 10-bolt rear in the S-10, it breaks easily if you hook it up.
 
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