428 Block Strength

[CV355]

I want to apologize in advance because this topic seems to be just shy of the "what oil should I use" repeat questions you see on forums.  But, I can't seem to get a definitive answer anywhere...

I worked with a reputable and trusted local shop to get our 428 rebuilt.  After inspection, the only thing we were able to salvage from the old was the block, everything else is new and rated for 800+hp, TF heads, roller setup, moderate cam, Holley EFI.  The machining work done by this shop is excellent- they pride themselves on it.  My end goal with the car is for it to be a gentle cruiser and show car, no heavy use, but I want a blower on it.  I'm looking at a Procharger F1A, maybe 5-6psi max.  ~600hp is the max goal, and the car will never put it down anywhere but the dyno.   But, I am concerned because of horror stories of FE blocks cracking in the ~500hp+ range, though I assume due to heavy use and launches at the drag strip.  Had it not been for some annoying surgery bills, I wanted to nab a BBM block, but they have been out of stock for a while.

Is this a reasonable goal?  Should I be concerned about the block failing, or am I overthinking this?  I get it, there are many, many factors to block strength.  Let's assume best case scenario- this shop wouldn't have let a block defect fly, and their tuning is excellent.

Funny thing, this is the first time in the last 13 years where I didn't have at least one vehicle with either a supercharger or turbo on it...  Kinda getting antsy...

[My427stang]

It's a big "it depends" but likely fine

C scratch - I see the most stable measurements from one to another, have not seen cracked mains, and walls generally are thicker and bores more centered

A scratch - Some cracked mains, oddly at the bolt holes for #2 or #4, but rare, usually decent sonic check

CX scratch (industrial) - no two alike, and roll the dice on what you will see.

I would say, if mag and sonic checks good, and sonic has some margin, then carefully balanced to include the individual components and torque plate honed to have the bores as straight as you can in operation, and then the tune keeps you out of detonation.  600 is doable.  However anything unchecked may bite you

[Joe-JDC]

If the block has been magnafluxed and inspected for cracks in the main journals area, not bored over .040" or so, it should be safe to 700 hp without an issue.  A zero balance would be mandatory in my experience, and SFI damper and flexplate/flywheel.  Bearing clearance and piston clearance on the high sides of normal and use a good 10-30W oil.  Joe-JDC

[jayb]

My personal rule of thumb for blocks, regardless of NA or supercharged, is 600 HP for a 390 block, 650 for a 428 block, and 750 for a 427 block.  This assumes street tires; race tires and dropping the clutch will shorten the life span on any of these blocks.  A half-fill of hard block will increase my rule of thumb numbers somewhat, but be prepared to add an oil cooler if you do so. 

Just my opinions on those numbers, of course, but they haven't let me down...

[Rory428]

I think Jays opinion is pretty accurate. I have split main webbing on A scratch 428 blocks with 520 HP, but that was with slicks,& 6000 RPM clutch drops. I am sure that same engine just used for cruising around on street tires never would have hurt itself, but my thought is whats the sense of having 500 HP if you never plan to use more than 200 of it? I  would think that a set of cross bolted main caps or possibly a good main girdle would help some.

[gdaddy01]

where does the strength come from on modern blocks , mod motors , l s stuff , coyotes ? I have read about the head bolts going down into the crank area .

[cjshaker]

where does the strength come from on modern blocks , mod motors , l s stuff , coyotes ? I have read about the head bolts going down into the crank area .

There's a lot of engineering in those blocks, and all aided by computer simulation. The block webbing (internal and external, and there's lots of both) is where the strength from twisting comes from. Less twisting greatly aides in stopping cracks from appearing, and bearing related failures. The deep head bolts do add some strength when the heads are added, but head bolt depth of penetration is how they get away with lots of boost, by getting into the meat of the block and not relying on the deck surface.

[blykins]

where does the strength come from on modern blocks , mod motors , l s stuff , coyotes ? I have read about the head bolts going down into the crank area .

In addition to what Doug said, Coyotes and LS engines have relatively small rotating assemblies and lighter components.  Slinging a lot of weight around can really stress a block. 

On aftermarket FE blocks, you will see billet caps, doweled caps, bracing in the lifter valley, and material added in critical spots.  They're beefy. 

[Rory428]

Concerning modern block strength, I have no experience with either the Chevy LS or Ford Modular engines, but as a Toyota dealership mechanic, I have seen inside a number of late Toyota engines. Many of the Toyota V6 engines feature SIX bolts bolts per main bearing cap, 4 vertically into the block, plus 2 crossbolts, like a 427 FE. In addition, all the main bearing caps are integrated into a 1 piece "bedplate", which is attached to the deep skirted block, not only with the vertical main bearing caps, but also with a series of bolts around the plates perimiter. I believe this style of built in rigidity is commonplace with many modern engines.

[WConley]

+1 on what Brent said.  On a typical engine the inertia load (from rotating parts) can meet or exceed the combustion load well before valve float.  The inertia load goes up with the square of rpm, so anything you can save there will pay big dividends!

Strength isn't the only reason for the stouter bottom ends on modern engines.  We were working hard at Ford in the early 90's on engine NVH.  I did lots of tests that showed half-order noise (nails on a chalkboard) got killed off if you kept the caps and the crankcase walls from moving around.  The test engine, with stock two-bolt bottom end, would make you want to run away from the dyno cell as it exceeded 6,000 rpm.  Put a bedplate or a really good girdle on, and it sounded like it wanted to go to 10K all day.  Toyota and Honda were really pushing us on sound quality...

[Posi67]

Well..Mr Conley, my 390 is not going to be happy to hear that info. Does have a "fill" though and I suspect it's lifespan is finite.

[My427stang]

Dale yours doesn’t  count, you have some magic in that car that we all wish we had

[CV355]

All good info as always, guys!  Thanks!

I'm still a little nervous about putting a blower on it this coming Spring, but it sounds like 5-6psi should be within the "assumptive limits" of the block. 

We were working hard at Ford in the early 90's on engine NVH.  I did lots of tests that showed half-order noise (nails on a chalkboard) got killed off if you kept the caps and the crankcase walls from moving around. 

You might have worked with one of my colleagues...  I have dipped my feet in NVH analysis systems in my industry, but one of my colleagues was a guru for it in the 90's.  It's amazing what data you can get from a single accelerometer and rotary encoder these days. 

[blykins]

Why not 600 hp naturally aspirated?

[CV355]

Why not 600 hp naturally aspirated?

The next project will be...  On this car, the goal was less about power and more about cruising and show.  My fear with having a monster of an N/A engine for this build is that it'll get pushed into "unstreetable" territory with a blower.  Gotta have a blower