Yes, I figured out that if I want to do something different than stock then I don't want to get it at GMPD.

 

so this is a direct replacement for what it came with? Everything is the same?

 

I've come to the conclusion that they don't know. Maybe a 'standard balance' is what you get when you assemble a list of standard parts together and a heavy external 'standard balance' flywheel will in most cases smooth everything out.

So if you are lucky enough to get a shortblock with similar components to that which your car came with then it would be considered a direct replacement. Factory rpm limits are relatively low and the engine should hold together under normal use.

 

No, 89er. This is not how it works.

On the matter of internally and externally balanced SBC engines, have
a look at what NavyVet and CFI-EFI had to say four years ago.

Whats the deal with a Harmonic balancer/ balancing after a stroker??

.

 

As 89er suggests, I don't know much if anything more
than you do. Let's have a closer look.

The description specifically says it is a replacement
for 1990-1992 Corvette w/ 5.7L (L98-8). Is everything
the same? I do not know but I believe that the OEM rods
were cast, not powdered metal. I feel that PM offers an
improvement over cast.

What is not clear to me is what the compression ratio
will be when this assembly is mated with the OEM D-113
aluminum heads.

Your '90 is rated at 10.25:1, while my '89 is rated at 9.5:1.
The difference lies in the piston shape, in '90 the tops
became flat with four valve reliefs while I understand the
'89 & earlier aluminum-headed engines have dished tops.
See Dr. Evil's post here - 91 L98 What have I got?

The information about the short block describes the pistons
as flat top hypereutectic's. The reason for my uncertainty is
that while researching, I believe I saw long blocks based on
this SB where the compression was listed as 9.6:1.

It is not clear whether the SB ships with a flexplate for an
automatic. As indicated by NavyVet in the link above, the L98
with single rear main seal is externally balanced at the
flexplate/flywheel.

.

 

That's a great thread. Reading NavyVet's note confirms my belief that GMPD does not know if the replacement short block has the correct balance.

 

"What is not clear to me is what the compression ratio
will be when this assembly is mated with the OEM D-113
aluminum heads.

Your '90 is rated at 10.25:1, while my '89 is rated at 9.5:1.
The difference lies in the piston shape, in '90 the tops
became flat with four valve reliefs while I understand the
'89 & earlier aluminum-headed engines have dished tops.
See Dr. Evil's post here - 91 L98 What have I got?

The information about the short block describes the pistons
as flat top hypereutectic's. The reason for my uncertainty is
that while researching, I believe I saw long blocks based on
this SB where the compression was listed as 9.6:1.

It is not clear whether the SB ships with a flexplate for an
automatic. As indicated by NavyVet in the link above, the L98
with single rear main seal is externally balanced at the
flexplate/flywheel."


Hi guys,
I just got off the phone w/ Allen at Pace and he re-assured me that it is internally balance. It does not come w/ a flexplate or damper. I'm guessing that the 9.6:1 qouted on the long blocks was figured w/ the more conventional 64cc heads.

Thanks for the info on the pistons Slalom. I never could figure out the increase in compression for the 90-91 but that makes sense as my '88 has dished +valve reliefs. I will take some pics of my '88 piston tops and the new pistons when it arrives. (It shipped on the 13th.) It looks like I will be the guinny(sp?) pig for this so hopefully it all goes welll!!

 

If this is true, then that would mean that you cannot use your stock flywheel/flexplate?

 

That's how I understand it also and I'm ordering the Ram C4 push type conversion. (Clutch/PP/Al FW).

 

Hmmm, is that so?

Well, from pg 171 of the 2006 GM Performance Parts
catalog (p/n #19157556). The emphasis is their's

I am curious why there is so little info about p/n #12510735.
I looked on www.goodwrench and www.gmperformanceparts
for it without success. Ditto at Superior (SuperChevy.) and
Gilbert (Sallee). A local CDN dealer shows it as discontinued.

The following info is from Pace's details on the p/n #12556121 L31 4-bolt.
(I didn't look further to relocate the reference that presented similar
info on the p/n #12510735 L98)

 

Hmmm, interesting. The compression ratios you found were for a 4 bolt version but I guess I'll have to do a little more research.. Grrr.

This is going to P%&& me off if I have to disassemble and balance everything.

Thanks for the reference and time to make another phone call!!

 

Here's a more complete portion of what NavyVet wrote, I've highlighted
some text you didn't include.

For whatever reason, some '95 & '96 rotating components appear to
have come down the line that were at the limits or perhaps outside
the balance tolerance range - so a fix was devised.

My vote is that components of many externally balanced mass-produced
engines are built to tolerances and then assembled without being
dynamically balanced at the factory. If you need a new flywheel or
flexplate you buy one and it comes balanced to the design tolerance.

.

 

Let me help - the 2-bolt L31 long block is p/n #12530282. Pace
describes this as having 9.4:1 compression with 64cc chambers. The
4-bolt L31 long block is p/n #12530283 - also described as having
9.4:1 w/ 64cc chambers.

Think of it as an opportunity to double-check and optimize your
engine.

.

 

It does seem like we still have conflicting information regarding balancing.

I was seriously looking at a short block but now I am thinking the best way is to machine a 'seasoned' block and balance the rotating mass (new pistons, etc) from the harmonic balancer to the flywheel at the machine shop.

 

"Think of it as an opportunity to double-check and optimize your
engine." You are one of those glass half full guys, aren't you.

I haven't talked to Pace since the last post but the long block link on the website is working now and it shows 9.6 CR w/ 65.3 cc heads. I plugged that info into a CR computer w/ .049 gasket and .025 deck (std) and it comes out to 2cc valve reliefs. Not an exact science but I will find out soon enough.

Not that this confirms anything for this appl. but I also noticed that the ZZ4 short block is listed as internally balanced w/ a 1pc seal.

****Apology to 89er for hijacking the thread but hopefully the info is of interest to you too.

 

No apology needed for me - it's not my thread. The problem of getting a replacement block has been on my todo list for a project I started ten years ago on a 1985 4+3 to ZF conversion. The car had 80K miles when it went up on blocks. In three more years I won't have to emission test it so it is beginning to get interesting.

 

Uhm, it is daniel0213's thread. Maybe he can comment about
whether he feels that info about a sub-$900 L98 shortblock is on-topic
or not.

While I wish I could feel confident enough to just assemble
and install, the experiences of others (even with 'hand-built' LS7's)
guarantees I would be taking it at least partially apart before proceeding.

Not big on p/n's are you. Link, please.

I meant to check on the balance of the ZZ4 - thanks for mentioning
it is listed as internal.

 

If you are buying a 350 engine from Chevy, with a one piece rear main seal, it WILL be neutrally balanced in front and externally balanced in the rear.

 

I have never seen or heard of it any other way.

 

I'm so confused! I have a flywheel and a balancer. Can i order the engine from GM that is listed above and bolt my flywheel and balancer back to it and be good, or do i need to take everything and have it balanced. i just want to replace the motor with a stock version and have eveything be the same!