Hi
I recently placed an order for a new 383 SBC longblock and but later discovered it's not 100%compatible with my 1991 C4, hopefully these are solvable. One thing is the valve covers are perimeter bolt style so I'll have to find a new pair. Another issue is it doesn't seem to have a hole for the knock sensor from what I was able to see.
Any idea where to drill a hole and does it need to be all the way through to get in contact with the coolant it only needs to be very firmly attached to the engine somewhere in line with a cylinder? Also the oil pan it seems to be missing the oil level threaded hole, but I think the stock should fit.
This is how such block looks like:



Thank you

 

Every sbc has a drain hole on the passenger side, that is where gm put the knock sensor on the 85-91 c4, 84-85, and early 86 c4 used the same style valve cover, but they had perimeter bolts, find a set, they look the same and are functionally identical to the 87-91 valve covers.

The chrome looking plug, remove it and install the knock sensor.

 

https://www.google.com/search?q=1985...86666870117188

They are available as a reproduction, or you can find them used. Seriously, who begins an engine swap without investigating all this, I had piles of the little pieces before my 383 arrived. The engine was cheap, the little things were expensive 😅

 

What about that hole?





This might work:
https://www.summitracing.com/parts/icb-551542

 

Thank you, I’ve seen that chrome looking plug, but doesn’t seem to be exactly in the position of the l98 sensor, anyway I’ll ask the shop for detailes.
I know the ‘85 covers, but there might be problems with rockers clearance. Mine were already prepared, mirror polished, nickel plated and dripping tabs removed, there is magnesium dust all over the place, from grinding and polishing…would take a while to finish a new set. A fit on a center bolt would also not be guaranteed. The reproduction ones seem a better option - cast aluminum vs magnesium that’s hard to maintain, and old ones would need reconditioning.
Adapter plates seems very nice for someone who really needs the stock look, but would bring more complexity, more things that can fail, possibly vibrations and still fitment issues. But it’s better to have options.
I found a pair that looks nice and should fit, c3 style
https://www.summitracing.com/parts/h...-134?rrec=true
Regarding the oil pan, I’ll try to search for something so the guys from the shop can install instead of what they usually fit on these engines. I would actually want something that prevents oil starvation during cornering. They can accept changes to the configuration, even the heads but I think it’s better to stick with what they’ve tested already and works well.
PS those marked by JoBy and Bill are 1/4”NPT, which is the same used by l98 blocks I understand, not sure if the positioning is identical but that wouldn’t be a problem in most cases.

 

I’ve found and oil pan that I think would be more appropriate for my application:
morosso 21811
From what I see, there could be problems when trying to remove the starter because of the additional volumes, what other issues I may have to deal with?
thank you

 

New is always nicer. Are those angle plug heads? Hard to tell from the picture. You might want to check plug access with your manifolds/headers.

 

Does the block have a one piece or a 2 piece rear main seal? Your '91 would have had a one piece RMS from the factory. If the new block is a 2 piece RMS ,then you'll need a different flexplate or flywheel.

 

good observation. I've checked other pictures and they are straight. I guess this would mean they are not going to work with stock manifolds.
main seal is 1 piece, and comes with a billet steel flywheel