small block Chevy or GMC questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

oldsub86 · 11-02-2009, 10:16 PM

Hey all, I hope you can help me with some questions about interchangability of small block GM engines.
I have a 1972 307 engine that needs to be either rebuilt or replaced. It has a deep knock to it and I am afraid it will prove to be pretty bad when dismantled.

So, I am trying to decide if I should just find another engine and rebuild or at least tear it down and have a look and get it ready to drop in in place of the one I have.

It is important that I be able to re-use all of the front accessory drive setup so I don't want anything to change on the front of the engine. It is also important that I be able to re-use the flywheel set up on the back of the engine without changes.

It really does not matter what displacement I end up with, so if a 350 would swap in, that would be fine. A few quick searches indicate that a 350 would be much less expensive to re-build with some pretty good parts than another 307 of that vintage would be.

So, my big question is: How interchangable are the blocks? Can I change in just about any small block GM engine and if not, what do I look for when trying to find something that will exchange? For example, there is someone locally advertising a 4 bolt main Chevy block. How do I know if it could be made to work? Casting numbers??

Will the existing heads and intake work with just about any block and if not, again, what do I look for? I would think that the heads and intake can be salvaged and I may as well keep them if I don't have to replace them.

I recall seeing books that set out the part numbers for interchanging this stuff but I never bought one when I had the chance.

I am prepared to go buy some parts but I would like to avoid surprises and not buy parts that won't work.

Thanks

Randy

PS - I need to change the line below as I sold the 68 last spring

Eddie H. · 11-02-2009, 10:40 PM

you can use just about any chevy small block including the 283,302,305,307,327,350, and small block 400. All your accessories and mounts will work, except the early (pre 1968) engines didn't have accessory bolt holes in the cyl heads. The intake manifolds will interchange until you get into the 1996-up vortec engines. If you get a 350 or 400, the 307 heads will bolt on, but they have smaller more restrictive valves and are not very good for producing power. The later model, one piece rear seal, roller cam 350's are a good choice if you can find one.

hayhauler71 · 11-02-2009, 10:51 PM

Have you thought about a crate engine. Than you would have something new and with a warranty. Some of these crate engines can be found for around $1500.00. Just another option.

oldsub86 · 11-03-2009, 10:32 AM

Thanks for the responses. I thought the same - that I could use just about any small block. My concern is with regard to issues such as the harmonic balancer as much as anything. Do they swap around on most as well? For example, can I take the one on the existing engine and re-use it on most of the small blocks? If memory serves, it may be different on the 400?

I cannot readily compare as the existing engine is still installed and is 175 miles away. I hope to find something and get it ready here and take it out and install it come spring. That is why I would like to not have surprises when I go to finalize the swap.

Randy

Eddie H. · 11-04-2009, 10:56 PM

Yes, the 400 is externally balanced and uses a different harmonic balancer and flywheel than the other engines.

txsilverado · 11-05-2009, 01:32 AM

An early L31 vortec motor would be a nice choice. You would only need to purchase an aftermarket aluminum intake made for the vortec heads, and if you are replacing a 307, you probably will need to upgrade from a 2bl carb to a 4bl carb anyway. This intake is easy to find at Jeggs and Summit. Here is a list of trucks equipped with the L31 Vortec off of Wikipedia. Also, the Vortec would most likely require going with and electric fuel pump due to no machining for a mechanical pump. However, there is no need for one in the tank, just a low pressure in-line pump would work for your carb. These are cheap and plentiful.

L31 applications:

1996-2003 Chevrolet Express/GMC Savana full-size vans
1996-1999 Chevrolet/GMC C/K full-size trucks
1996-1999 Chevrolet Suburban/GMC Suburban full-size long-wheelbase SUVs
1996-1999 Chevrolet Tahoe/GMC Yukon (and 2000 Tahoe Limited) full-size short-wheelbase SUVs
1999-2000 Cadillac Escalade

11-02-2009, 10:16 PM	#1
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	small block Chevy or GMC questions Hey all, I hope you can help me with some questions about interchangability of small block GM engines. I have a 1972 307 engine that needs to be either rebuilt or replaced. It has a deep knock to it and I am afraid it will prove to be pretty bad when dismantled. So, I am trying to decide if I should just find another engine and rebuild or at least tear it down and have a look and get it ready to drop in in place of the one I have. It is important that I be able to re-use all of the front accessory drive setup so I don't want anything to change on the front of the engine. It is also important that I be able to re-use the flywheel set up on the back of the engine without changes. It really does not matter what displacement I end up with, so if a 350 would swap in, that would be fine. A few quick searches indicate that a 350 would be much less expensive to re-build with some pretty good parts than another 307 of that vintage would be. So, my big question is: How interchangable are the blocks? Can I change in just about any small block GM engine and if not, what do I look for when trying to find something that will exchange? For example, there is someone locally advertising a 4 bolt main Chevy block. How do I know if it could be made to work? Casting numbers?? Will the existing heads and intake work with just about any block and if not, again, what do I look for? I would think that the heads and intake can be salvaged and I may as well keep them if I don't have to replace them. I recall seeing books that set out the part numbers for interchanging this stuff but I never bought one when I had the chance. I am prepared to go buy some parts but I would like to avoid surprises and not buy parts that won't work. Thanks Randy PS - I need to change the line below as I sold the 68 last spring __________________ 1968 Chevy - 292 with a powerglide

11-02-2009, 10:40 PM	#2
Eddie H. Registered User Join Date: Mar 2001 Location: Paradise TX USA Posts: 1,200	Re: small block Chevy or GMC questions you can use just about any chevy small block including the 283,302,305,307,327,350, and small block 400. All your accessories and mounts will work, except the early (pre 1968) engines didn't have accessory bolt holes in the cyl heads. The intake manifolds will interchange until you get into the 1996-up vortec engines. If you get a 350 or 400, the 307 heads will bolt on, but they have smaller more restrictive valves and are not very good for producing power. The later model, one piece rear seal, roller cam 350's are a good choice if you can find one. __________________ "Negative people always seem to have a problem for every solution"

11-02-2009, 10:51 PM	#3
hayhauler71 Registered User Join Date: Aug 2009 Location: St. Paul MN. Posts: 1,996	Re: small block Chevy or GMC questions Have you thought about a crate engine. Than you would have something new and with a warranty. Some of these crate engines can be found for around $1500.00. Just another option.

11-03-2009, 10:32 AM	#4
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	Re: small block Chevy or GMC questions Thanks for the responses. I thought the same - that I could use just about any small block. My concern is with regard to issues such as the harmonic balancer as much as anything. Do they swap around on most as well? For example, can I take the one on the existing engine and re-use it on most of the small blocks? If memory serves, it may be different on the 400? I cannot readily compare as the existing engine is still installed and is 175 miles away. I hope to find something and get it ready here and take it out and install it come spring. That is why I would like to not have surprises when I go to finalize the swap. Randy __________________ 1968 Chevy - 292 with a powerglide

11-04-2009, 10:56 PM	#5
Eddie H. Registered User Join Date: Mar 2001 Location: Paradise TX USA Posts: 1,200	Re: small block Chevy or GMC questions Yes, the 400 is externally balanced and uses a different harmonic balancer and flywheel than the other engines. __________________ "Negative people always seem to have a problem for every solution"

11-05-2009, 01:32 AM	#6
txsilverado Registered User Join Date: Oct 2009 Location: Arlington, Texas Posts: 37	Re: small block Chevy or GMC questions An early L31 vortec motor would be a nice choice. You would only need to purchase an aftermarket aluminum intake made for the vortec heads, and if you are replacing a 307, you probably will need to upgrade from a 2bl carb to a 4bl carb anyway. This intake is easy to find at Jeggs and Summit. Here is a list of trucks equipped with the L31 Vortec off of Wikipedia. Also, the Vortec would most likely require going with and electric fuel pump due to no machining for a mechanical pump. However, there is no need for one in the tank, just a low pressure in-line pump would work for your carb. These are cheap and plentiful. L31 applications: 1996-2003 Chevrolet Express/GMC Savana full-size vans 1996-1999 Chevrolet/GMC C/K full-size trucks 1996-1999 Chevrolet Suburban/GMC Suburban full-size long-wheelbase SUVs 1996-1999 Chevrolet Tahoe/GMC Yukon (and 2000 Tahoe Limited) full-size short-wheelbase SUVs 1999-2000 Cadillac Escalade



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