I'm going to look at an 88 GTA trans am tomorrow and the guy says a mechanic told him it has a 350 in it now.

I checked the vin# and it was an LB9 and it's a T5 also.

he says you can't see the casting #'s on the block behind the drivers side head so is there a quick way to tell by looking at something else on the engine?

the old 305's had a hollowed out harmonic balancer on the back side....do the newer ones?

 

Casting numbers are the easiest way. You can't use a 305 casting to make a 350. Some blocks have 5.0L or 5.7L cast into the block either at the back near the casting number or on the side.

On the pad in front of the passenger side head are a bunch of numbers and letters stamped into the pad. These can usually tell you what the engine is and what it originally came out of. If the block has ever been decked, these numbers get machined off.

The last way is to pull a head and measure the bore.

External components on the engine can't tell you the engine displacement.

Unless someone has changed something, you probably have a 305. A T5 didn't come behind a 350. If it's really a LB9/T5 1988 GTA, and has the G92 RPO code it will have a 9 bolt diff with 3.45 gears. You can easily check to see if it's a 9 bolt or not.

 

i picked up a 350 not to long ago that had a 305 balancer and it was completely stock, you are going to have to pull a head, if it wasnt swapped before than its a 305 because 350s didnt come with t5s if i remember right

 

I agree that measuring the bore would be easiest because if its 3 inches than it is a 350 but if it is 2.5 then it is a 305. Even if you cant figure it out from that one of the easiests things to do is to take it to your local dyno. The LB9 would do 220 horse and the L98 would do 230 horse. But from what I have heard and read is that none of the 350s came with manuals they all came with the 700R4. The reason is because the manuals could not handle the power that the 350s were putting out.

 

Back to skool
350 has 4.00" bore
305 has 3.7" bore

 

You can get an large inspection mirror and and use it to see the casting numbers on the back of the engine. On some late model engines the last 3 digits of the casting number is also on the side of the engine between the freeze plugs (either side) And these are large enough to read.
And as a shot in the dark you could pull a valve cover off and check the casting number off of the head, now unless they put 305 heads on a 350 (or the other way around but I doubt that) you can figure that it is either a 305 or a 350.

 

The last three digits of the casting numbers on the sides of the block should be present on at least the 1985-1992 third generation F-body engines. If the engine does not have the casting numbers on the sides, then most likely the engine isn't original. That doesn't tell you if it is a 305 or a 350 if the casting number isn't easily readable, but if the casting number isn't present then it very well could be a 350 engine. If the casting number is present you can verify what it is quite easily.

Most 305 engines in the F-Bodies I've seen have a 627 casting on the sides of the block. At least the TPI engines do.

 

You sir are dead on, thats why I also said that he can pull off a valve cover and use the casting numbers from the head. Most factory engines will use a 350 head with a 350 and a 305 head for a 305, this is a rule of thumb thing.