[pjdutton]

Have read about the 1975 and newer blocks being weaker than earlier ones.I have 2 blocks that need rebores,one is a 75 400 and the other is a 71 350.The 400 block is a 500557 casting and I am not sure which one to have the money spent on.I`m only looking to make around 350 flywheel horsepower,nothing special.Any advice would be helpful.

[Half-Inch Stud]

naw, no special bolt-ons.

Lighter slugs, Forged-rods, balance-to-remove excess crank weight.

[PONTIAC DUDE]

The 350's & 455's aren't a problem.

It's the late 75 to 79 400 blocks that have the issue. Do a search on here and you will see pics of the difference between the early and later 400 block.

But 350 hp won't be a problem with the 557 block. I would make sure it has solid dowels in the mains and bottom fill it. Deburr any flashing or casting lines to remove stress risers. Keep the bore to .030 or .040 max.

[harry k]

had a 76 T/A 400 557 block , stroked to 461 ,sonic tested ok , produces 355 RWHP for a hard driver and knock on wood

official http://pontiacdragdays.com/Sponsors.htm dyno sponsor

[Skip Fix]

I have one under some RAIV heads pushing around 400 hp and spinning 7000 before, so that level you will probably be OK. 12 teens @ 111 weighing 3900lbs.

[Region Warrior]

Agree with the others, would'nt worry about it under 500hp.

[pjdutton]

Thanks for replies.I think I may have been overly cautious.

[GRX]

#481988 = early '75 = thicker

#500557 = late '75 = thinner

And I agree with the others. That #557 block will be fine in the stated HP range. As always, spend a little extra to have the block magnafluxed. If nothing else, for piece of mind.

[flamedabone]

Do you mean like THIS???


This was my old 500557 '75 400 block. It lived a good while in my daily driver 12.90 car. Then...one day it didn't...

Be nice to your thin 400 and it will most likely live a long time.

-Abone.

[Motor Daddy]

Here's the twin.

[Z Code 400]

Hey Motor Daddy!!!! Click on this link for some fun and look at the CID on the .060" oversize 400!!!!!.....Robert



Bwwwwwwaaaaahahahahahahahahahahaha!!!!

[GRX]

Ouch ...... double ouch!

Those blocks are definitely thinner than the '75 cast #481988 block I have here.

Pulled the block out of the bag (looking a little rusty) and snapped off a few images. Notice this particular block was cast late '74 but has the '75 casting mark.

Most importantly, look at the same main web (#3) as shown above. Much thicker in the early '75 block. Straight up from main saddle to cam tunnel essentially.

[Steve Hoog]

Everything cast at some point just after 70 is softer also, I don't know where the exact line in the sand is but it is there.

[GRX]

Yes, popular thinking is that the '70 and earlier blocks were higher nickel content.

One thing is for certain, the older molds were put together differently. Results in stronger castings.
For more info please see the last 3 posts in this thread.
http://forums.maxperformanceinc.com/...d.php?t=490695

[Half-Inch Stud]

flamedabone, motor-daddy: those are important photos becasue they both show a 2-Bolt block with #3Bust-out....on right...across from the Motor-Mount that Is PULLING for it to bust.

As if you both had STEEL Caps....what kind of Main Caps&Fastners?

[Motor Daddy]

Mine was bored +.030", but otherwise completely stock. The motor produced roughly 450 HP NA, and I also hit it with a 150 shot for almost 4 years, and went through probably 100+ bottle refills.

One day I went out to check the oil. I pulled the dipstick out, and heard the lower dipstick tube fall into the pan. Of course the dipstick couldn't be used after that because it would hit the crank. I pulled the motor and found my windage tray broke out three of the four mounting holes completely. The lower dipstick tube was broken off the bracket, and the bracket was broken at the main cap where it mounts. When I went to clean the pan, I found a dowel pin. I looked at the mains, and sure enough, #3 dowel was missing. I wondered at the time why the dowel pin would fall into the pan. I inspected it closely and found a crack about 1" starting at the dowel pin hole. I reinserted the dowel, slapped the motor together, and reinstalled it in the car.

That was almost 2 years before that pic was taken when I finally removed the engine due to lower end noises (bad bearings). For those two years, I continued to beat the crap out of the motor with the cracked block, nitrous and all (600 HP) and it never completely died before I pulled it.

I definitely wouldn't recommend a 500557 block for anything over 400 HP.





Z Code, Two wrongs don't make a right. I already did the math for you. A 400 +.060" is not even a 412, although you can call it that if you round off. What it definitily is NOT is a 413! Just go ahead and finish that 417, 409, or 314! Which one do you prefer? That seems to be how you decide what to call it, personal preference. LOL

[Half-Inch Stud]

Just KNEW splittin straight-up to the Cam bearing was not as-big-a-deal.

A telling summary of that block crack history...tink I heard it before.
Do you suppose a Mid-Plate would have kept that block from cracking-out the #3??
--------------------------------------------------------------------------
motor-daddy: curious to your opinion of the PMD 350 CID nameplate?

[Motor Daddy]

HIS, I really don't know squat about metal, but if I had to guess, I would say the dowel hole causes a weak spot in an area that is already weak. I don't think that crack would have ever resulted if there was no dowel hole there. Look how thin the metal is on each side of the dowel hole. It's a crack waiting to happen!

HIS, You don't want to get me started on my thoughts on CID! LOL

[Z Code 400]

Hey Motor-Daddy......Just giving you a bad time....Actually, I am planning on putting a roller in my .060" over 400 and putting the .466"/.466" - 220°/226° - 111.5° LSA hydraulic flat tappet in my 354......I mean 350....:-)

[Motor Daddy]

My 400 +.060" (411.68) runs [email protected] in a 3860 lb car on street tires with a Crower 60310, and a Torker II, and idles with 12" of vacuum at 900 RPM. Let me know what that roller runs when you get it done.