Help identifying my engine

[Skutt]

I am driving a 1988 GMC S15 4X4 that I got from my sister. It's a great little truck and I hope to keep it and fix it up a bit as time goes by. About five years ago my sister asked me to put a new engine in the truck for her so of course I said I would. She paid for everything and I did the work. We ordered a replacement crate motor through our local NAPA dealer. The truck had a 2.8L so thats what I ordered and installed.

The original engine had 248,000 miles on it, great little engine. The new engine has 23,000 miles now and runs great. I put all the original equipment back on the new engine except for things that were worn out but replaced with stock replacement parts for the 2.8L. The new engine has quite a bit more power than the old engine ever had so I am suspicious that I didn't get a 2.8L but perhaps I have a 3.4L. It reminds me more of the 65' Malibu I had years ago with the 283 power pack engine. The pickup is very snappy now with this new engine. I just did a road trip two weeks ago, about 600 miles round trip and got as much as 26.4 MPG cruising at 60 to 65 MPH all the way.

The way this engine performs I have doubts that it is a 2.8L but how can I tell for certain what I have? I am just curious to identify my engine only to satisfy my curiosity. It runs great and I love the increased power with good economy.

[Superdave]

there is a 25-30 HP difference between the 2.8 and 3.4, that would be noticeable for sure.

your best bet is to look over the block and post up any casting numbers that you find.

[86FieroSEv6]

Personally, I think you're just noticing the difference between a well worn engine and a fresh tight squeezer. Because the wear takes place over a great deal of time, people are often amazed at the change in performance because it declines so gradually that it is not immediately apparent. Then when the new mill goes in, it's like "I can't believe it!". Some of it is compression loss to be sure, but a great deal of the difference can be attributed to timing chain slack causing the cam to be retarded. Even a few degrees of cam retard can have dramatic effects.

[CrazyCutlass]

I agree with Fiero. Also consider the dirt the engine accumulated over the years in the intakes ports and on the valves, that make restriction to air flow. I once clean the carbon on the valves and intake ports on a 82 Tercel and beleve me, that was quite anoter engine after that. I really felt a difference.