Questions about a 383 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1986Silverado · 04-27-2005, 03:09 PM

Going to pick up a '79 Swb step side this weekend. I am going to pull the engine, which I was told was a 383. Anyway to verify this? Also it is mated to a muncie 3 speed and I want to keep my auto TH350, anybody know which flexplate to get? I am sure it is a 2 piece rear seal block as the dipstick is on the driver side. My main concern is the flexplate. I know the 400 and 350 cranks are gonna use different flexplates. Could I take a parts store the flywheel and let them match it to a flexplate?

**Captkaos** · 04-27-2005, 03:32 PM

Just get a flexplate for a 400 SBC if it really is a 383. The Flywheel will be counterweighted along with the harmonic balancer if it really is a 383.

1986Silverado · 04-27-2005, 03:54 PM

So when I lokk at the flywheel or balancer what do I need to look for to distinguish the difference between a 350 or 400 crank? Thanks

piecesparts · 04-27-2005, 05:36 PM

The counterweights for the flexplate and the harmonic dampener may NOT be there. It depends on the quality of the crankshaft that they built the engine with. A SCAT crank, in most cases, will have the external weights for the 400 crankshaft, BUT a forged steel crank may have the internal weights. I just got another block, recently, and had to build another 383 after I chunked a piston in the first one. I went with a higher quality crank and had to change from externally weighted components to the internally weighted parts. If this motor is a 383, you will have to look at the inside of the block---There has to be a lot of metal removal from the area around where the crank moves, to allow for the extra stroke. The crank will just miss the camshaft area when it rotates. The cylinders would have been bored out .030 for the extra cubes. Just to look at it you can be fooled.

Tom · 04-27-2005, 09:14 PM

Quality of parts has nothing to do with internal or external balancing, just an option. Most times you can go either way with the same crank. I chose an externally balanced SCAT crank because I already had the flywheel for external balance

The only true way to tell is to pull the oil pan and check the stroke.

piecesparts · 04-28-2005, 07:52 AM

Can't make everyone happy????

Tom · 04-28-2005, 08:49 PM

Nothing to do with happiness, just giving some facts

1986Silverado · 04-29-2005, 09:32 AM

Just have to pull the oil pan, huh? Also what would be a good rear ratio to get good gas mileage from such a engine, if it is a 383? Will have a TH-350 behind it. Reason I ask is because the same truck I am getting the engine from has a 12 bolt posi that I may swap in.

04-27-2005, 03:09 PM	#1
1986Silverado What I drive Join Date: Apr 2004 Location: Star, MS Posts: 418	Questions about a 383 Going to pick up a '79 Swb step side this weekend. I am going to pull the engine, which I was told was a 383. Anyway to verify this? Also it is mated to a muncie 3 speed and I want to keep my auto TH350, anybody know which flexplate to get? I am sure it is a 2 piece rear seal block as the dipstick is on the driver side. My main concern is the flexplate. I know the 400 and 350 cranks are gonna use different flexplates. Could I take a parts store the flywheel and let them match it to a flexplate? __________________ 1986 Chevy Crew Cab Dually(Choo-Choo Conversion) 2006 Chevy Equinox

04-27-2005, 03:32 PM	#2
Captkaos www.73-87chevytrucks.com Join Date: Dec 1999 Location: Birmingham, AL Posts: 6,935	Just get a flexplate for a 400 SBC if it really is a 383. The Flywheel will be counterweighted along with the harmonic balancer if it really is a 383. __________________ Chris Lucas 1973 Chevy C-10 1978 GMC Jimmy (2WD) - SOLD 1987 R10 twin turbo LS 1991 R3500 SRW CrewCab 1985 K5 diesel swapped project 1989 K5 2WD conversion w/ Vette susp Project Captkaos Customs 73-87chevytrucks.com

04-27-2005, 03:54 PM	#3
1986Silverado What I drive Join Date: Apr 2004 Location: Star, MS Posts: 418	So when I lokk at the flywheel or balancer what do I need to look for to distinguish the difference between a 350 or 400 crank? Thanks __________________ 1986 Chevy Crew Cab Dually(Choo-Choo Conversion) 2006 Chevy Equinox

04-27-2005, 09:14 PM	#5
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,720	Quality of parts has nothing to do with internal or external balancing, just an option. Most times you can go either way with the same crank. I chose an externally balanced SCAT crank because I already had the flywheel for external balance The only true way to tell is to pull the oil pan and check the stroke. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

04-28-2005, 08:49 PM	#7
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,720	Nothing to do with happiness, just giving some facts __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

04-27-2005, 05:36 PM	#4
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	The counterweights for the flexplate and the harmonic dampener may NOT be there. It depends on the quality of the crankshaft that they built the engine with. A SCAT crank, in most cases, will have the external weights for the 400 crankshaft, BUT a forged steel crank may have the internal weights. I just got another block, recently, and had to build another 383 after I chunked a piston in the first one. I went with a higher quality crank and had to change from externally weighted components to the internally weighted parts. If this motor is a 383, you will have to look at the inside of the block---There has to be a lot of metal removal from the area around where the crank moves, to allow for the extra stroke. The crank will just miss the camshaft area when it rotates. The cylinders would have been bored out .030 for the extra cubes. Just to look at it you can be fooled.

04-28-2005, 07:52 AM	#6
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Can't make everyone happy????

04-29-2005, 09:32 AM	#8
1986Silverado What I drive Join Date: Apr 2004 Location: Star, MS Posts: 418	Just have to pull the oil pan, huh? Also what would be a good rear ratio to get good gas mileage from such a engine, if it is a 383? Will have a TH-350 behind it. Reason I ask is because the same truck I am getting the engine from has a 12 bolt posi that I may swap in. __________________ 1986 Chevy Crew Cab Dually(Choo-Choo Conversion) 2006 Chevy Equinox



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