I have been looking through the Craigslist in the effort to find a I-6 300 to rebuild or as just a replacement to the old tired one in my 86 and have found several motors out of early 90 model trucks. I was wondering what the differences were other than fuel injection that occurred to the 300 from the early 80's into the 90's.
My thoughts are that if I can find a good motor with solid compression, I could just swap everything over from my 86 to the new on prior to dropping it in. I have already performed a Duraspark II conversion and new non-feedback carb. I just didn't know if there were any physical changes I should look out for. I actually found one yesterday that if I pull it, I can have it for $200. I'll check the compression first...
While an EFI engine will probably just drop right in, you have a couple things that might be an issue. First off, the fuel pump boss is there but the slot is blocked off so you'll either have to go to a electric fuel pump, or cut it out to use the mechanical one.
Also if it is a real late EFI block, it may not have the Z bar connection at the back of the block. This is for the mechanical clutch setup, so if you don't have it don't worry about it.
Lastly you have to worry about the fast burn head, which is what all EFI engines had since beginning production. This one isn't so bad to deal with, it just requires adjusting or "curving" the distributor to more precisely control just how fast the timing comes in. You may not even have to do this, but more than likely if you don't the motor will ping and not run correctly because of it.
IMO if it were me, I'd buy the EFI engine anyway just because it's possibly lower mileage, and none of the things I listed are a deal breaker they just need to be dealt with.
Great info! The one I was looking at was a 92 with 140K on it. I'm ok with going to an electric fuel pump, but mine is a 4 speed with the hydraulic clutch so the z-bar might be an issue.
Is it possible to replace an EFI head with mine if I don't want to go to an EFI engine? I could have the head rebuilt so I would have a new top end, but are there differences in the pistons from year to year?
I guess going to EFI would be cool. I would need to get the computer though.
I'm thinking hard about what Desperado said about getting a fuel injected engine. That might be the way to go. If I can find a donor truck where I can get the fuel pump out of the tank, that would be the best route. Time to start looking...