Kind of a silly question but a shop replaced the 305 in my 85 IROC with a 350 (serpantine belt) and I've just had no time to even look at my car because of work and school.
How can I tell which 350 it has???

 

Casting numbers tell all.

 

Suffix codes tell all, casting numbers just narrow it down to a year range.

 

where are the cast/suffix # on the block?

 

Suffix codes are utterly worthless when dealing with a rebuilt motor. All they will tell you, is what the block was originally used in. You could be looking at a 600 HP race motor, and the suffix codes will tell you that it's a 165 HP 2-barrel out of a truck. Pretty useless. I think you'll agree that the parts that somebody sticks in some motor, don't adjust themselves to whatever the "suffix codes" might indicate that it came with.

Casting numbers will tell you what the block proper is. They will tell you what the heads are. They will NOT tell you what pistons are in the motor, what cam is in it, how far it's been bored, whether it's a roller motor or not, whether it has 2-bolt or 4-bolt main caps, or anything else about it. Nor will "suffix codes" for that matter. They will give you clues about how it originally came; that is, if the "suffix codes" say it was a 87-up L98, then you can be fairly sure it came with a roller cam. But they won't tell you what's in it now.

With a rebuilt motor, about all you can do, is tear it down and inspect the parts.

It's a pretty safe bet though, if this is a rebuilt motor installed at a shop under a competitive bidding type situation (like when you call around and find the "best price"), it has cast rebuilder pistons that are an extra .025" down in the hole compared to stock; some sort of generic heads, which usually end up being either 70s smoggers or truck TBI swirlies; and a generic cam, which is more than likely a copy of the 929. Most likely it will have the cheapest and most generic of all the small parts like rings and bearings and so forth, and the quickest cheapest dirtiest possible machine work. You don't get something for nothing. At best, you get what you pay for. You certainly never get any more than that. Pay the least, get the least.

If you don't want to do that (which I can't really blame you for not wanting to do!), there's not much else you can tell about it. If you like the way it runs, leave it alone; if you don't like the way it runs but you don't want to disable it, leave it alone; if you want to upgrade it somehow, you have no choice but to tear it far enough down to at least see what's actually in it.

 

So the casting number essentially tells you the year range. For example 3970010. What all can you glean from that? It was used in any range of vehicle from 1969-1979 (off the top of my head) and thats about it.

Unless you are trying to stay away from a particular block, the casting number too is utterly worthless on a rebuild. Block casting number will not tell you what the heads are, nor will suffix. I know you know this, but it came out that way.

How can you say a suffix code won't tell you whether a motor is a roller or not? It's application specific. If you have the same block from a truck and a car, 1990, you WILL know it's equpped for a roller cam or not based on suffix code. Nothing will tell you whats inside a rebuilt motor.

Two or four bolt main caps is not necessarily true either...most truck blocks were 4 bolt main, but I understand this is not 100%, and we don't need a pi$$ing match on that either, since no one can state with authority what is what at this point.

 

Sure, the codes might tell you that the block originaly probably did or didn't have a roller cam; but it won't tell you what's in it NOW. And what it originally came with, isn't having a great deal of effect on how it runs, or on what it needs to run better.

IMHO, all of that crap about "what did this motor come out of" is mostly monkey-spank. Kind of like the Firebird history people that will look at a smoking wrecked heap with not one single usable part left on it, and debate endlessly on what RPO codes it had in order to get the combination of ground effects on it that it has, when in reality, some kid living in a trailer just stole them off of various ones and put them on his car. All the codes on Earth won't explain it. Same for a rebuilt motor. In a rebuilt motor, none of those codes has any application whatsoever to the actual issue at hand; namely, what's in it NOW.

And as we all know, all of the roller-eligible block castings, have the casting features for roller cams; they're just either drilled & tapped, or not. Which a block that wasn't used in a rollerized application, still sometimes had tapped holes; so you might get a 638 block with a "T" code, and it might still require no further work to accept a roller setup. But they're always there. Again, not much use in that.

Decoding codes in general just strikes me as futile and a waste of time; especially when dealing with 20-year-old cars that have been hot-rodded since the day they were born, by countless owners in many cases. ANYTHING could have been changed (and probably has) and the code won't show it.

 

It's not a rebuild. It's a new GM crate and the only used parts are the TPI and top end stuff from my old stock 305.

 

Look at the p/n on your receipt.

 

Goodwrench Crate 350
Engine Name: 350 LM1
Horsepower: 249 HP @ 5,000 RPM RPM
Torque: 304 Ft/Lbs @ 3,500 RPM
Compression Ratio: 8.50 to 1
Block: 4 – Bolt, 2 Piece Rear Seal, 4.000” Bore
Crankshaft: Cast Nodular 3.480” Stroke
Heads: Cast Iron, 72cc
Valves: 1.940” / 1.600”
Camshaft lift: 0.390” / 0.410” Hydraulic
Duration @ 0.050”: 195° / 202°
Intake: Not Included

Hummmmmmmmm
What to replace first?

 

Everything but the block casting.

Then work your way toward your goal from there.