sreZ28

Here's hoping I'm in the right place...
So I just managed to pick up an '83 Z28 for a song. It's got 70,000 miles, a swapped in 4.10 posi rear with disc brakes, a brand spanking new stage 3 clutch, a rebuilt t-5, etc, etc....
Here's the kicker; the first owner swapped in a 355 2 pc rms small block that is built for race gas (forged l2304 .030 over pistons, decked, 305 smog era heads with a 58cc combustion chamber). He then sold it to a 16 year old who "threw a crankshaft bearing". I'm guessing he tried to run it on pump gas.
From my research, it's got some quality parts. 750 4-barrel holley carb, edelbrock performer intake, etc, but it's going to need a serious rebuild.
I would like this thing to be a mild, streetable, and most importantly running engine; This means dumping some serious compression. My friend who is a mechanic for ford suggested buying a nice set of heads with 74cc combustion chambers. Another friend suggested I pick up a forged 302 crankshaft (eagle makes one with medium journals for around $600) and use the forged 6 inch rods I have laying around with the pistons I already have with .060 milled off the lop.
I came to you guys because unlike these two goons, you seem to know what you're doing. Help me out here, what are tho pro's and cons of each of these, or any reasonable alternatives. I like the sound of the 302 (both literally and for history's sake) but Im skeptical about milling that much off of pistons, and I have no idea where that places me for balance. I like the idea of new heads, but they are very pricy.
Thanks

1991sleeper

iTrader: (-3)

Yea do not mill ur pistons ... u want the top of ur pistons as close to the top of the deck block as possible preferably .0000...and use a .040 head gasket to get .040 quench ... if ur quench is .060 or more ur gonna have a dog of a motor ... pinging all the time and not wanting to take a full timing curve ...

1991sleeper

iTrader: (-3)

U could get the pistons milled and shaped on one side like a reverse dome ... but I think the first thing u need to do is tear it down measure ur deck clearance and figure ur compression with different cc heads ... u prolly don't need to do anything except change heads

2005Impalla

Pull the heads. If you have flat top pistons I would just get a different head with a larger chamber.

sreZ28

Thanks for the responses everyone. I'm sorry, maybe i didn't explain perfectly. I do still have to pull the heads, I'll do that this weekend when i can borrow a depth micrometer. If the block is 9" flat, the parts stack up to 7.5" with the crank and the rods. That means that I need pistons with a compression hight of 1.5" on the nose. Standard 5.7" rod pistons usually have a compression height of about 1.560". I dont know the deck height yet, but if the block is at 9" flat, they'll be .060 out of the bore. If i have this difference milled off, and new valve reliefs milled in, will it damage the structural integrity of the piston? How will this effect the top ring? I'd like the pistons to sit flush with the deck for quench height purposes. Am I missing something here? I am not a mechanic...

sofakingdom

iTrader: (1)

A stock block is 9.025" tall, +.015" -.000" or thereabouts.

A stock rotating assembly is 9.000" tall. 1.56" + 5.7" + (3.48"÷2) = 9.00"

Therefore a stock engine has anywhere from .025" upwards of deck clearance.

I'd suggest leaving the pistons alone. If they're not right for what you need, throw em away and start over.

Most "rebuilder" pistons, including TRWs (replacement truck pistons), add an extra .020" of deck clearance. They may be "designed to fit" engines requiring 1.56" for instance, but in that case will measure 1.54". The catalog will still say 1.56" but you can easily enough measure and find out. Not positive about that particular part # and I'm too lazy to go outside and measure one right ATM.

Best thing to do, is MEASURE your motor as it sits, and go from there.

First thing to do is pull the heads and the oil pan, and the crank; don't disturb the piston/rod combo in any way (leave them in the block); and MEASURE the deck clearance. Inspect everything and see if it can be repaired. If you can put a new crank kit in it, no sense in creating extra work and expense for yourself by taking the pistons out of the bore, thereby requiring new rings. If any rods are tore up, then of course it's unavoidable; but don't do it if you don't have to.

Put some different heads on it. Much as I hate to say it, you might be stuck with 70s smoggers. You can make some of em flow pretty good (487 for example) without too much risk of cracks. That'll get your compression down into a workable range with the pistons you have. That's NOT a "good" way to go, and would certainly NOT be the way to design a motor from the start, but might give you a cheeeeep workaround that'll get you something you can run on pump gas.

If you have to tear the pistons out of the block, THEN it's time to consider piston options. A good set of hypers with a D-cup dish instead of the stock round dish, with the 305 heads, will also put your compression into a manageable range.

Night rider327

iTrader: (13)

Do not do the 302 route... You are giving up too much torque with the 3.00" stroke.

If the 16 year old kid "throw a crank bearing" my guess is he spun a rod or main bearings, so you may need new rods, crank, even major block machine work, and if bad enough the block might not even be useable...

Will not know till you get it apart though.

You can make those dome pistons work on the street with pump fuel. Those heads are a big downfall for your power so a swap to brodix IK, AFR, pro filler, etc will gain you 60-80 HP over the heads you have now, plus you can get larger CC to make those domes work, if you wanted to keep them.

76cc heads will drop the compression down to 9.9:1, you can run 10.5:1 on 92/93 octane with alum heads and the right cam.

Now myself, based on your "mild, streetable, and most importantly running engine" comment I would...

replace pistons with hyper speed pro/sealed power H345NP flat tops, used $150-300 96-00 vortec 062/906 heads, summit stage III vortec intake, the correct cam for your needs.

Then sell off your dome pistons, 305 heads, and intake to recoup your money

2005Impalla

What do you mean by threw a crank bearing? You have a picture?

Keoman

iTrader: (3)

You can always call EOD but they take forever
we always just shot the **** out of them until they blew up.

good luck

2005Impalla

Why would some one use an edelbrock performer intake on a high compression race motor? The 305 heads are great for raising compression but don't flow well for top end. I could not see some one using them and replacing the pistons to further raise compression unless they were racing circle track with the motor. If it were me I would locate another used block and transfer what you want from your old motor. If the crank bearing is too shot your going to need a new crank, bearings, you already want new pistons and you will have to have the new crank balanced. I have not used old rings on new pistons cuz if I am that far in why skimp there and if you get now rings you need to hone the cylinders. The cost starts to add up. First though, open the motor up and see what is really inside the motor.

sreZ28

I got the engine apart over the weekend. Terrible things happened in there. Terrible things.... I'm going to have the block sonic tested. If that fails, what is a good solid block to start with? Obviously I'm looking for a 4 bolt main, is there anything else i should look out for? Any general advice in buying a used block?

Night rider327

iTrader: (13)

Don't get caught up in the factory 4 bolt block thing. The stock 4 bolt main is NOT all that strong really. The outer bolts are placed in the main webs and can crack easy.

An ARP studded 2 bolt main block is much stronger than a factory 4 bolt, and a splayed 4 bolt setup using a 2 bolt main block is about the best you can do.

I'm at 10 years on a 2 bolt main block with ARP studs, 500+ HP, 7300-7400 rpm shift points.

Now as to what block to start with.. If you have to go with a diff block, then I really like going with the '96-00 vortec L31 engines. You can find them pretty easy and cheap now and they come with factory roller cam, PM rods, vortec heads, etc.

aliceempire

iTrader: (14)

sreZ28

Thanks again for all your patience guys. I've been a bit busy with school, but I've managed to work on the car a little bit. So, here's an update:

I managed to pick up a l31 880 block for a song ($150). I pulled the valve covers off, and it's got a nice set of Vortec heads. This block also has rod knock, and I wasn't planning on using it, but the other block is shot, and if it seems like it will clean up nice with a .030 overbore, I'm going to hold onto it. It's from a 96 GM truck, that I believe was an automatic. I've been looking through this and other forums, but have gotten mixed results about what I'll need to do the swap once if I rebuild it. So far I've gathered:
- The flywheel will swap, so long as I use a 2pc rms internally balanced crank and a conversion kit
- I can probably use the Vortec oil pan
- All of the accessory belts from the old block should fit fine.
- To use my carb, I need a vortec specific intake manifold.
- I've also read that I may have issues with a specific threaded hole that needs to be there for a manual transmission.
-Other than that, she'll drop right in.
Is all of this correct? I was hoping this would be a relatively easy swap, especially because the previous owner has done all of the work to swap to a carbed 350.

I'm also putting together a rotating assembly for a 355 as I go, thus far I've managed to pick up a set of SCAT forged 6in rods ($175), and a set of forged Wiseco pistons with a 1.260 compression height ($250), all brand new from an old racer. I chose this configuration because I was told that it would make balancing the crankshaft cheaper. Of course, being overzealous and under-informed, I overshot my goals by a bit. The pistons clock in at 369g, and come with 109g wrist pins. The big end on the rods at 430g and the small end at 176g. I haven't grabbed a crank, bearings, rings, or locks yet. I'm going to grab a forged crank, but they run pricy, especially as they get lighter. How many grams is alright to take off of a forged crank as a general rule? I wont know where I'm at for balancing until I grab bearings, locks, and rings, but a rough estimate would be nice. I don't mind spending a few hundred more bucks if it's worth it.

Thanks again for all your help guys, I really do appreciate it.