MyniceSS

iTrader: (4)

Which block era is better..... The pre 80's 454 with a two piece rear seal or the gen VI with the one piece seal? What's the pros and cons of both, and which is a better foundation to build a high hp Boosted foundation on. Thanks in advanced.

midwestT/A

The pre 80's block is way better as long as you have a 4-bolt main block. The new blocks are easier to get but there are a lot of drawbacks:

Very thin castings (safe overbore is .030 and beyond that is questionable)
Use different oil pans and timing covers (expensive compared to Gen IV)

I wouldn't take either block beyond 1000hp, then you have a potential (but many do, do it ok) bomb on you hands.

Spend the money and buy a dart block for a high horsepower boosted application.

Just my opinion, not hard set rules.

Hope this helps.

MyniceSS

iTrader: (4)

Thanks, that actually helped quite a bit. But what's the safe power limit of the pre 80's block?

midwestT/A

The one that is in my car is a 289 casting 4-bolt main block from the 70's. In my car and two others before it, it has been pushing between 1000-1100hp on Nitrous for about 4 years now with no major problems to the block. The block is not filled either, it is as stock as can be with main and head studs. We burned one piston due to the nitrous but that's it. You might also consider o-ringing the cylinder so it will handle more compression or boost safer.

MyniceSS

iTrader: (4)

Nice, can you explain what o-ringing the heads mean?

midwestT/A

I have never had this done, but I have had a couple of friends who have so I will give it my best shot, a machine shop could maybe explain it better? I know it helps to better seal the head and gasket to the block:

It is a small groove cut in the top of the block around the cylinder bore that is filled with a copper o-ring to help better seal the chamber.

If I am wrong about anything please let me know, but this how I understand it.

Hope this helps.

NEokcTERROR

iTrader: (10)

Here is my 20+ years of big block chevy block integrity experience.

'91 is the first year for one piece rear main seals. The early '80's saw reductions in mass in the block i.e. thinner castings.

The '91 and newer blocks seem to have poorer materials in the main caps. We have fixed / had fixed many blocks that have experienced spun main bearings. On numerous occassions the cap didn't fit the registers in the block any more. To remedy this we put the cap in a press and bend it by supporting it on the outer edges and pressing in the middle of the cap to effectively spread the register area. Then mill the bottom where the cap meets the block back flat and align bore the mains. When we have tried to spread the caps on the '91 and newer block we have broken the main cap in 2 pieces which has never happened on the pre '91 blocks in our experience.

The later block '80 - '90 don't really seem to have any weaknesses to support high horsepower levels. I have a '88, 4-bolt, 468, stock caps, and ARP main studs that has 65 passes on it not counting street races and driving around that makes 1380 on both systems.

I have a friend that has a '67 camaro like mine with a 2 bolt studded block in it. I don't know any HP figures but it runs 8.60's on one system, and it has never had any block problems even with the .125 over bore to make it a 482.

I would say if you plan to make a thousand or more just to stay earlier than '91, and find a four bolt if you can. I personally don't have a problem with early 2-bolt blocks as long as they have main studs, and aren't ran on a bad tune-up. Of course if you rattle it on the bottle there's no telling what may break.

Usually the O-ring is stainless piano wire exposed .018 above the deck and used with a copper gasket. FelPro makes a head gasket with an O-ring in it for high HP that you cut a groove in the cylinder head to mate with it. I haven't tried it yet. However my sons truck has them with 468 inches, twin 70mm turbos and a N2O system, but we haven't fired it up yet. We'll see what happens. I do know of people making over 1,200 on them without problems.

Hope I have been of some help.

Bo Woody