250 L-6 to 350 Questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

6 Door King · 06-19-2013, 09:04 PM

Before anyone directs me to a link within the site, I DID search it and only got returns for older model trucks and my questions are more geared toward motor mounts and engine crossmebers.
1st, INFO: I have an 84 SWB that I am working toward comsetically restoring so I can flip it for a quick profit. I plan to swap out the 4.1 for a 350 from a K30 that is supposed to be turning 400 ponies at the wheels in order to help the truck sell.
Question is this, if my motor is coupled to a 3 speed auto, (not sure if TH350 or 400) and the donor engine was also coupled to a TH350, will my flywheel on the new motor need to be changed? I have heard there are several different patterns.
Second, will the crossmember and engine mounts need to be swapped out? Obviously the engine side of the mounts will be different, but are the mounts on the frame the same and just in different locations like the 67-72 models?
Thanks in advance guys, hope you can all make sense out of my plans and questions.

bob_o · 06-20-2013, 04:59 PM

I have a '75 swb that recently had the 250/3-in-the-knee removed in favor of a 350/350.

I believe you can re-use the flywheel. Though personally I would replace it regardless. They are relatively cheap and you might as well do it while the motor is out.

The motor mounts need to be moved slightly, but the crossmember already has holes drilled for 6's, sb's and bb's. Just took some trial and error to make sure we got them in the right spot.

6 Door King · 06-21-2013, 09:25 PM

Thank you very much for the info. Does anyone know if the flywheel would be different for a TH350 versus a TH400 if both are Chevrolet transmissions? Just trying to gather all my parts and pieces before I immoblize two vehicles by removing engines.

Desert1957 · 06-22-2013, 10:05 AM

When you say 3 speed, is it a 3 speed with a granny low gear? (SM465)
If so I did a swap years ago, everything swapped over.

Desert

6 Door King · 06-23-2013, 07:26 PM

My three speed is an automatic, either a TH350 or 400, only reason I specified that it was three speed auto was to rule it out as a 700R4 as far as flywheel differences. Are there different patterns for TH350 flywheels or are they all the same for Chevy versions?

06-19-2013, 09:04 PM	#1
6 Door King Registered User Join Date: Jun 2008 Location: Franklin Virginia Posts: 204	250 L-6 to 350 Questions Before anyone directs me to a link within the site, I DID search it and only got returns for older model trucks and my questions are more geared toward motor mounts and engine crossmebers. 1st, INFO: I have an 84 SWB that I am working toward comsetically restoring so I can flip it for a quick profit. I plan to swap out the 4.1 for a 350 from a K30 that is supposed to be turning 400 ponies at the wheels in order to help the truck sell. Question is this, if my motor is coupled to a 3 speed auto, (not sure if TH350 or 400) and the donor engine was also coupled to a TH350, will my flywheel on the new motor need to be changed? I have heard there are several different patterns. Second, will the crossmember and engine mounts need to be swapped out? Obviously the engine side of the mounts will be different, but are the mounts on the frame the same and just in different locations like the 67-72 models? Thanks in advance guys, hope you can all make sense out of my plans and questions. __________________ 1954 3100 Nova Subframe, Pontiac Posi, roller for now1967 C-10 SWB 350/350/Posi. Soon to be Crew Cab! 1978 Crew Cab Dually roller 1982 C-30 Rollback, 454, 4 speed 2004 K1500 Suburban Z71 5.3 Kid Mover

06-20-2013, 04:59 PM	#2
bob_o Registered User Join Date: Jan 2012 Location: Arizona Bay Posts: 145	Re: 250 L-6 to 350 Questions I have a '75 swb that recently had the 250/3-in-the-knee removed in favor of a 350/350. I believe you can re-use the flywheel. Though personally I would replace it regardless. They are relatively cheap and you might as well do it while the motor is out. The motor mounts need to be moved slightly, but the crossmember already has holes drilled for 6's, sb's and bb's. Just took some trial and error to make sure we got them in the right spot.

06-21-2013, 09:25 PM	#3
6 Door King Registered User Join Date: Jun 2008 Location: Franklin Virginia Posts: 204	Re: 250 L-6 to 350 Questions Thank you very much for the info. Does anyone know if the flywheel would be different for a TH350 versus a TH400 if both are Chevrolet transmissions? Just trying to gather all my parts and pieces before I immoblize two vehicles by removing engines. __________________ 1954 3100 Nova Subframe, Pontiac Posi, roller for now1967 C-10 SWB 350/350/Posi. Soon to be Crew Cab! 1978 Crew Cab Dually roller 1982 C-30 Rollback, 454, 4 speed 2004 K1500 Suburban Z71 5.3 Kid Mover

06-22-2013, 10:05 AM	#4
Desert1957 Registered User Join Date: Apr 2009 Location: New Freedom Pa. Posts: 1,335	Re: 250 L-6 to 350 Questions When you say 3 speed, is it a 3 speed with a granny low gear? (SM465) If so I did a swap years ago, everything swapped over. Desert

06-23-2013, 07:26 PM	#5
6 Door King Registered User Join Date: Jun 2008 Location: Franklin Virginia Posts: 204	Re: 250 L-6 to 350 Questions My three speed is an automatic, either a TH350 or 400, only reason I specified that it was three speed auto was to rule it out as a 700R4 as far as flywheel differences. Are there different patterns for TH350 flywheels or are they all the same for Chevy versions? __________________ 1954 3100 Nova Subframe, Pontiac Posi, roller for now1967 C-10 SWB 350/350/Posi. Soon to be Crew Cab! 1978 Crew Cab Dually roller 1982 C-30 Rollback, 454, 4 speed 2004 K1500 Suburban Z71 5.3 Kid Mover



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