I recently purchased a 1977 L42 with all numbers matching and a completely redone exterior and interior. The engine has some issues, but runs pretty well. Is it better for the value of the car to keep the engine matching and just fix the existing engine or replacing the engine with a more powerful crate motor? What are you opinions?

 

You need to be more specific about the "issues." You said it runs pretty well, what is the problem? An L48 powered '77 is not going to be devalued in my opinion by swapping for a crate motor.

 

Issues: a little sluggish, small oil drip, 1 drip per day, slight gas odor from engine

 

FWIW: L-48 is the base engine. When was the last time your engine was tuned? Why not tune it, then drive it for a while and see how you like it?

 

I have a 78 and went through the same thought process but finally said screw it....its not what I want in its current configuration so..... I'm doing an auto to manual swap and building a 383 stroker.....can't wait for the project to begin!

 

Tune it up, add some springs so full advance is in around 2,500 RPM and set total advance with vacuum canister disconnected to 36 degrees BTDC. I did that on my '77 L-48 and that along with true dual exhausts was better. I wouldn't say the car is fast, but does feel much better. I doubt our cars will ever have much value boost from keeping the original engine.

 

I have a 77 L48. Smog equipment is all gone. Vacuum canister gone, EGR blocked. Hooker side headers and side pipes,, Edlebrock open air cleaner replaced the stock one, and its a 4spd. Its a VERY fun car to drive and plenty quick. If you want to race... get another motor. I don't race.
Regarding your issues... oil leak can be as simple as a leaky valve cover gasket or an oil pressure sending switch. Gas smell is most likely a clogged fuel canister. If your state permits it.. just pull the hose off the carb and plug the carb inlet up. Then... pull the hose off the canister which is down behind the windshield washer reservoir near the master cylinder and plug up that inlet too. No more gas leak.
If its sluggish do a complete tune up and set the timing. The throttle on my car is so crisp it feels like its fuel injected.

 

I have a 78 that has a return line from the fuel pump to tank, and I think it has a non vented gas cap. Will it work ok if I block and cap all lines to the vapor canister?

 

One oil drop every day wouldn't concern me at all, but then I'm dealing with a very leaky '77 right now.

If it's from the main seal at back of engine that's a fairly easy fix, from what I hear. Same for oil pan, and valve covers as was already mentioned.

I like having the original engine just for the sense of it being a survivor of 40 years. I realize collectability might not be what I would have hoped it to be (and I wasn't really needing that as a factor), but I figure there's got to be something of value about the final year of this body style because even with the large production numbers if most end up with replaced engines, well, all the better for the remaining original cars... right? Debatable, I'm sure.

Unfortunately for me it has been pointed out that my car doesn't have the '77 differential/rear drive, it's from '80-'82 I guess. Exhaust was changed, too. And many details missing from engine bay such as air cleaner and other things.
So there goes the complete original C3 Corvette idea for me.

Anyway...

If you have the original catalytic converter exhaust that would be another reason for "sluggishness" I suppose (not that I actually know of facts myself).

Maybe check all vacuum connections, and distributor functionality as was also already said.

Not a powerhouse, the mid-70's 350 engine, but still should have some getup and go to it if optimal. Mine will speed up nicely by putting the foot to the floor but admittedly it can be like pulling a trailer behind a V8 truck if I were to imagine I'm not inside the nice C3 'vette. And my car is ugly both inside and out, not restored.