305 or 350?

[Joe-NC]

I know this question probably gets asked all the time, but I've used the search tool and read plenty of posts on other sites and still don't have an answer.  Other than the casting numbers on the rear flange of the block (which are hardly visible with the engine in the truck, and are probably covered with gunk anyway) ...is there another way to tell a 305 from a 350?

[Grim 82]

It's never a sure indicator because you just never know what's been swapped, but typically a 305 has the timing tab up top at the 12 o'clock position, and a 350 is usually off to the side closer to 3 o'clock. If it runs like it's timed right and the mark on the balancer lines up with the timing tab that will give it away.

[screamin86]

Pull a valve cover and check the casting numbers on the heads and look them up and see what they came on. But you also can run into the issue where someone has 305 heads on a 350 like how my truck is right now.

[fitz]

I've run across small blocks where 305 was stamped on the side of the block behind the power steering pump. I've also pulled a sweet running small block from a 79 K20 thinking it was a 350 4 bolt only to find out it was a 305.
Like grim82 mentioned, you never know what has been swapped around in these things.

[1980c10]

Heads can be identified from the design on the front of the head.

[VileZambonie]

It's easily visible in these trucks if you get in the engine compartment with a flashlight. If it's grimey get a can of brake clean, a screwdriver and a brush. In 5 minutes you'll have your casting number.

[jackjeckel757]

I have no clue what my '77 has either, the vin# says it came with a 305, but the previous owner(who really knew nothing about engines) told me the motor was swapped to another 305 before he owned it.  The plate behind the power steering pump has nothing on it and I can't see the rear one.  I only have a few bolt-on goodies on it and it really moves, and feels like a 350.  I guess I'm gonna pull off a valve cover and see what that says...

[Grim 82]

If it's grimey get a can of brake clean, a screwdriver and a brush. In 5 minutes you'll have your casting number.

^this

If you pop the cover to see what heads you have you still won't know for certain if it's a 350 or not.

[jackjeckel757]

Am I gonna have to pull a head off to find out???

[Grim 82]

No, you just need to find the casting number on the back of the block, and then reference it with mortec.com. But like Vile said you might have to get dirty to get to it, and you might need an inspection mirror to see it.

[1980c10]

remove your air filter housing to see better. then look down behind the drivers side head, right in front of where the transmission bolts up, scrape that grease off with a screw driver, wipe it with a rag and spray some brake cleaner and repeat until you can see the number. push whatever wires or vacuum lines may be in your way out of the way. the number is there, I have read them in the truck so it can be done, you'll have to climb under the hood and stand on the frame next to the engine.

[jackjeckel757]

Thanks for the tips! I'm gonna give it a shot this weekend.

[Joe-NC]

...you'll have to climb under the hood and stand on the frame next to the engine.

That's what I thought. I was hoping there was an easier way. Not to mention that my neighbors probably aren't used to seeing people standing in the engine compartment to work on a vehicle.

I just bought this truck and was told it had a 350, but it feels like a 305. Before I decide where to start tweaking, I want to find out what I'm working with.

[screamin86]

How do you feel the difrence between a 305 or 350? a 305 "can" be made to run very strong. Like was said though some brake clean and some cleaning and you will find your answer.

[1980c10]

btw; you'll want to use a flash light to help you see also.