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Hi, I have been seeking out used engine options for my 1980 C3. I found a 38,000 mile 400 ci engine. It was new in a 1980 Chevy chassis motorhome. I inspected it, it checked out good.
This 400 engine has quite a bit of smog crap on it. I see air pipes going to each exhaust port. I assume it has an air pump as well. I was hoping I could strip-off all this smog stuff. I haven’t acquired the engine yet, I just went to look at and inspect it. Can anyone confirm if the air pipes are connected to the exhaust manifold at each cylinder? Or are they connected right to the exhaust ports in the heads? In the photo below its looking like the air lines might connect to the heads? Perhaps I can plug these air ports at the heads, when removing the lines?
I am hoping to run the stock heads (with smog crap removed) for year or two. Maybe just replace the intake manifold and install the quadra-jet carb that was on my 1980 when I bought it. Add headers, dual exhaust and get out cruising for this summer.
Here is a photo of the stock 400 engine as it sits, currently in the RV. Thx.
Hi, I have been seeking out used engine options for my 1980 C3. I found a 38,000 mile 400 ci engine. It was new in a 1980 Chevy chassis motorhome. I inspected it, it checked out good.
This 400 engine has quite a bit of smog crap on it. I see air pipes going to each exhaust port. I assume it has an air pump as well. I was hoping I could strip-off all this smog stuff. I haven’t acquired the engine yet, I just went to look at and inspect it. Can anyone confirm if the air pipes are connected to the exhaust manifold at each cylinder? Or are they connected right to the exhaust ports in the heads? In the photo below its looking like the air lines might connect to the heads? Perhaps I can plug these air ports at the heads, when removing the lines?
I am hoping to run the stock heads (with smog crap removed) for year or two. Maybe just replace the intake manifold and install the quadra-jet carb that was on my 1980 when I bought it. Add headers, dual exhaust and get out cruising for this summer.
Here is a photo of the stock 400 engine as it sits, currently in the RV. Thx.
They're great motors BUT I don't need or want another one or this one.
But what is your your purchase price for this ? That will help me guide you ?
AND, what are last Three numbers in block casting Number ? ... should be easy to find along rear ledge either side of dist.
YOUR 1980 vette ex manifolds should easily bolt right up to those OE 400 heads
-add-
I've seen and owned a fair few sbc 400. Never seen one that the air emission pipes screwed into Heads ... Only screwed into ex manifolds. Just swap your 350 ex manifolds onto the 400 heads.
How much it gonna cost ya ?
Last edited by Rebelyell; Apr 13, 2026 at 01:34 AM.
The heads will be replaced eventually with aluminum. This 400 engine is costing me $450 USD.
Seems you're located BC CANADA; where it can get Very cold.
I hope your checks DID include Verifying this motor's coolant is adequate to have prevented freezing (cracks).
If this sbc 400 is running and you're satisfied with your checks; GO Get It Now ! before someone else snags it !
Great score!
Those are very torquey engines.
You must use the front balancer and the rear flexplate from the 400, they are balanced unique to that engine, it is an externally balanced engine.
If you switch it to a manual flywheel, be absolutely sure you get the right external balanced flywheel, or even have it balanced against the oem 400 unit flexplate at a machine shop (safer).
And changing the heads will help a LOT, these only have 8:1 C.R.
But the 400 heads must have steam holes, and use a unique head gasket. Because the cylinders are siamesed.
You can take a standard head and drill the steam holes yourself, with a hand drill even, using the extra holes in the special 400 head gasket as a guide.
Don't know if your car is manual or auto. The 400 flywheel probably won't fit inside your bellhousing. 400 will also use a different starter. Make sure you get the correct flywheel. If 400 auto then the 400 flywheel will probably work but if manual you will probably need a special flywheel. JP
Last edited by peters220; Apr 13, 2026 at 11:41 AM.
Reason: Added info
Don't know if your car is manual or auto. The 400 flywheel probably won't fit inside your bellhousing. 400 will also use a different starter. Make sure you get the correct flywheel. JP
My ‘80 C3 is an automatic. At this time I plan to use the flex plate that is currently on the 400. I do hope to go to a Tremec 5 speed in the future. When I see that through someday, I’ll get the right bell housing.
Did 1980 corvette use the TH350?
Didn't they still use the 168 tooth flywheel/flexplate?
Was the 153 tooth flywheel/flexplate ever used in a late c3?
The last year for the TH-400 was 1977, and only with an L82.
All 80 automatics came with 168-tooth flexplates. Allegedly, some 80 4-speeds came with 153 tooth flywheels, but not the 1980 L82 4-speed, which doesn't exist.
And now I have to crawl under my car and count the teeth on my flywheel...
You can actually tell easier than that.
168T flywheels were about 14" diameter, vs 13" for the 153T.
168T use staggered bolt holes on the starter, the smaller 153T uses the straight across holes.
I wouldn't want you to lose count mid-way and have to start over again...LOL
I gotta believe a 400 flexplate would be the 14" one.
Youtube "expert" didn't mention how typical 350 sbc Main journal OD measures nominal 2.45" while 400's Mains are much larger 2.65" OD.
No direct swap. Yes 350 crank can fit into 400 with either spacers or spacer-bearings. But No 1:1 swap.
I still have a vintage 377" ... +30 over GM 400 block with steel GM 350 crank with spacer bearings. Manley rods & pistons.
Well lucky for you to snag a 400 for that price.....They all looked like that when they were new...pipes, hoses, sensors, vacuum lines, all kinds of crap. The nice thing is you can strip all that stuff off, and have a nice running small block with low miles. You may be fortunate enough to even get the 800CFM Quadrajet with that... If you don't want it, I'd like first dibbs on it
I have a 400 and a 5 speed as well, and love the way it changed the car from a 350 with a 4-speed. The 5 speed is the best change you'll ever make to your car.
1979 400 ci Engine Questions
