AboveTheLogic

Maybe I could have chosen my title more wisely...

I bought my C3 back in April and the guy I brought it from knew nothing about it other than the guy HE bought it from would take it to the drags.

This weekend I pulled the oil pan so I can replace the rear main seal and oil pan gasket and get a peek at the bottom end.

Here are the photos I took, can anyone tell me what I've got here?





I can tell that it is obviously a 4-bolt, but what's the story on the crank/rods/pistons? I sent the pictures to an engine builder friend of mine who said they are TRW forged pistons, factory cast rods, factory forged crank, and ARP bolts. I'd like some more opinions. Another source says they are indeed forged rods.

For those of you who like pictures, here are some more pictures of the engine.


Crane 1.5 roller rockers and stud girdle:


I haven't ID'd the heads yet. They appear to be cast aftermarket heads with a Z98 stamp as you can see in the picture above. I couldn't find any other stamps. The casting pattern at the end doesn't match any GM casting charts I've seen. I plan to eventually replace the heads and cam with an aftermarket set that will go well with my super vic intake. I have no idea what cam is in there now but it is hydraulic and seems fairly mild.

mr.beachcomber

Can't help you too much. (Eyesight isn't the same as it was in my youth.) You have the Chevy "X" rods as indicated by the "X" on the rod caps. It was my understanding that the "X" rods were GM forged rods developed for heavy duty use. The rod beams have been re-worked and polished. Wasn't sure, but I thought that I saw a bushed small end in the one picture which would indicate the rod was modified for full floating pistons.

As for the heads, the "Z98" is actually a casting tag from the foundry and not a product number. Also, we may be looking at it upside down as it could actually be "892".

Don't know what cam you have now, but it's unusual to see a mild hydraulic cam with a stud girdle install on the head. (Maybe the previous owner swapped out the racing cam before he sold the Vette.)

Hope this helps!

AboveTheLogic

That does help, thanks.

When I bought the car, it had a clutch can but was wired for electric, and had a holley 600 cfm electric choke carb but had an aftermarket choke cable nearby. So I do know that someone pulled the fan and tossed on a cheap carb. I put an electric fan back on with a new 650 double pumper.

I guess it wouldn't surprise me to learn he swapped cams, seems odd though.

The Z98 thing, yeah it hasn't been helpful at all with identifying those heads. Here's a picture of the casting pattern on the side, maybe I'll get lucky and someone here will recognize it:

mr.beachcomber

Those are pretty much standard accessory holes. Just a guess, but your casting numbers related to product number, manufacturer, etc. are probably obscured by the stud girdle. Take one of those off and check for numbers between the valve springs.

AboveTheLogic

I can see under the girdles fairly easily, and looked several times, no luck.

Here is what I'm taking about when I say casting pattern

http://www.fastnuf.com/Headguide.html

My heads don't match any of those which makes me think they are aftermarket, especially since I can't find any casting numbers in the usual places.

bmans vette

Looks like a lot of stock GM parts.
The rods have been reworked as evidenced by the rod bolts having the dimples in the end for using a stretch gauge as opposed to a torque wrench.
What some are confusing the long main bolts for is the bolts to hold a windage tray. Not a stud girdle. Looks like a stock GM unit in early hp small block.
You are not going to get much more info until you pull the valve covers and start doing some measuring. Look at quality of parts, head part numbers, screw-in studs/push rod guide plate mods, etc.

Good luck - could be a good basis for a build or a decent modded build already.
Look for the block number also.

Bman

AboveTheLogic

It's a 3970010 block. I haven't had the timing cover off to look at the casting numbers there, but the date is 1975 so I think it's the higher nickel content block.

From all I've seen/read so far, I should have a good foundation here for building a 450+ hp beast.

bmans vette

Certainly a good foundation for an early model build.
I have several 010 blocks that have been turned into 383 strokers.
Just remember the old adage about the weakest link in the chain.

Good luck
Bman

AboveTheLogic

I used to own a '94 Z28, learned quite a bit about the weakest leak phenomenon on that car!

Thanks

(Seriously though what was GM thinking then they came out with the 7.5" 10-bolt axle and the optispark )

cv67

Your machinist was right. Basic hot rod motor should hold 450hp just fine


All GM rods were forged fwiw. Check bearings screw it back together-
Curious as to the heads if they were what he was running or stuck on there to sell. Have they had port work done?
The 600 was obviously a "to sell" thing hate when guys do that.

AboveTheLogic

I've had the intake manifold off, I didn't look closesly at the ports to see if they may have been ported but I didn't see anything special about them.



The only reason I want to ID the heads is so I can figure out the combustion chamber size. I want to buy some aftermarket aluminum heads and don't want to pull my existing heads to look at the pistons first.

MSGT-R

From what I can see, those ports look pretty square; they may be ported.

You can pull a spark plug and scope the hole (with a bright light) to see what the top of the piston looks like (i.e. flat or domed), that will help you make a chamber size decision.

AboveTheLogic

Good idea. The piston type is all that I'm missing before I make a choice on which head/cam combo I want to run. I'm hoping to pull the trigger on that next spring and start seeing some real horsepower. Gotta focus on getting it to steer and stop properly first.