Switching out a 305 for a 350 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Kenneth · 11-24-2003, 06:16 PM

Now, this has been talked about in bits and pieces as I found in the archive, but for a novice weekend mechanic it's not exactly clear. So let's say I want to switch out a 305 for a 350 with minimal cost, nothing fancy. Can you keep everything from the 305 but the main rebuilt engine parts? Apparently the engine block is the same, but what else? I imagine you have to get a new intake manifold and carb? pulley's, fuel pump, fly wheel, tranny, power steering pump mounts are all going to go back on the same? I'd love to switch to a 350, but if everything ain't going back the way I took it off then I'm going to get in over my head and get some crazy-ass head-aches

thanks for any input,
Kenneth

86SILVERADO · 11-24-2003, 07:52 PM

Everything will bolt on just fine including the manifold and the carb. You may want to go with a bigger carb because of having the 350 but the carb that came with the 305 will work if cost is a consideration. You just need to make sure that if you have a two peice rear main seal that you stick with a similar vintage 350 so that you will not need a new flywheel. As long as you stick with as close to the same year 350 as possible you will have no problems.

Jonboy · 11-24-2003, 08:08 PM

the easiest way to do this in a weekend is to get your 350, then pull the 305. Set them next to each other, and swap parts from the old engine to the new. All sensors, accessories, and brakets will swap over. The main considerations are that the small block family went to oil pan mounted dipsticks in about 78-79, and one piece rear main seal in 86. If you use an older engine in a newer truck, the oil dipstick will hit the stock exhaust manifolds.

Eyegore · 11-24-2003, 09:38 PM

86siverado & kenneth, are the exhaust amnifolds the same 305/350? I always thought the 305's were a little smaller. I may be wrong but I tried buying some old exhaust maniflods and they would not blot up to the 350, I went to a mechanic and he said that they were for a 305 and that is why they wouldn't fit. So now I'm confused.
I'm only asking since my son wants to do this swap in the future.

76HighSierra · 11-24-2003, 10:06 PM

Quote:

Originally posted by tom mathein
86siverado & kenneth, are the exhaust amnifolds the same 305/350? I always thought the 305's were a little smaller. I may be wrong but I tried buying some old exhaust maniflods and they would not blot up to the 350, I went to a mechanic and he said that they were for a 305 and that is why they wouldn't fit. So now I'm confused.
I'm only asking since my son wants to do this swap in the future.

The ony difference in the bolt pattern, where the manifold meets the cylinder heads(on ALL SBC's), is in 1979 (I think) they added an extra bolt hole to the frontmost exhaust port on the driver's/left side, and to the rearmost port on the passenger's/right side. This change occured throughout the entire SBC line, not just 305's. The vintage of the exhaust manifolds you buy, should be similar to the ones they are replacing.

86SILVERADO · 11-24-2003, 11:19 PM

like 76 said, the only way you can get in trouble is if you bought an older 350 with the different bolt pattern in the heads. What happens is you will not be able to put the last manifold bolt through because the flanges do not line up with the hole in the head. As long as you have a newer 350 you will be able to swap exhaust manifolds no problem.

suburbasaurus · 11-25-2003, 12:57 AM

the 350 will bolt directly in place of the 305 with no mods. if you use a 86-prior 350 the difference is the flywheel(has smaller bolt pattern), the fuel pump pushrod hole has a small plug in it that will need to be knocked out(only if it were equipped with TBI).and the 87-95 heads have a center bolt valve cover and the middle intake bolts have a 30 degree angle instead of a 45 degree angle, as far as "7 bolt" heads, 81 was the first year they put them on the trucks. all 81-87 trucks came with 7 bolt heads. if your new engine has heads with 7 bolt holes on the exaust ports it will be no problem. the older 6 bolt manifolds will bolt to the newer heads without any problems. another thing is in 80 the dipstick moved to the passenger side.

PHOENIX · 11-25-2003, 11:18 AM

I believe you will have to change the harmonic balance or remark your current to match the 350.

Verify this first, I am not 100% sure.

Kenneth · 11-25-2003, 05:20 PM

Thanks for the input
I failed to mention the fact that I'm looking to replace a '76 305 (again from the El Camino), with a 350. But the way y'all been talking it sounds like as a long as I stick with a mid 70's 350 I'll have no problems. Thanks for the help.
Kenneth

Eyegore · 11-25-2003, 05:35 PM

OK, so I look for a block newer than 80 from what your saying, but how do you identify a newer block, serial number? I ask because most of the block(s) I look at are already out of the truck and are laying side by side and I want to make sure I chose the right one. Also, is there a differnce in a car (caprice, camaro) block and a truck block? For example is the distributor the same, when we had the engine replaced a few years back they said I needed a new distributor since the one we had (the whole engine) was from a car.
Sorry, this is where you learn - from the people who been there, every time I ask someone behind the parts counter they look at you as if they were in to much of a hurry to even care.

Thank you

RussTburb · 11-25-2003, 05:45 PM

kenneth, It is to bad you are in texas I have a great running 350 that is comming out of a 73 El Camino! sorry to tease you!lol good luck with your project and jsut take your time and make sure you get all the parts off the 305 onto the 350. I have done 3 of these and have very little problems.
Dennis

86SILVERADO · 11-25-2003, 07:57 PM

Tom

Just make sure the dipstick is on the passenger side and you are all set.

11-24-2003, 06:16 PM	#1
Kenneth Registered User Join Date: Jul 2003 Location: Austin, Texas Posts: 53	Switching out a 305 for a 350 Now, this has been talked about in bits and pieces as I found in the archive, but for a novice weekend mechanic it's not exactly clear. So let's say I want to switch out a 305 for a 350 with minimal cost, nothing fancy. Can you keep everything from the 305 but the main rebuilt engine parts? Apparently the engine block is the same, but what else? I imagine you have to get a new intake manifold and carb? pulley's, fuel pump, fly wheel, tranny, power steering pump mounts are all going to go back on the same? I'd love to switch to a 350, but if everything ain't going back the way I took it off then I'm going to get in over my head and get some crazy-ass head-aches thanks for any input, Kenneth

11-24-2003, 07:52 PM	#2
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	Everything will bolt on just fine including the manifold and the carb. You may want to go with a bigger carb because of having the 350 but the carb that came with the 305 will work if cost is a consideration. You just need to make sure that if you have a two peice rear main seal that you stick with a similar vintage 350 so that you will not need a new flywheel. As long as you stick with as close to the same year 350 as possible you will have no problems. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!

11-24-2003, 08:08 PM	#3
Jonboy Slots go on anything! Join Date: May 2003 Location: Richardson, TX Posts: 5,957	the easiest way to do this in a weekend is to get your 350, then pull the 305. Set them next to each other, and swap parts from the old engine to the new. All sensors, accessories, and brakets will swap over. The main considerations are that the small block family went to oil pan mounted dipsticks in about 78-79, and one piece rear main seal in 86. If you use an older engine in a newer truck, the oil dipstick will hit the stock exhaust manifolds. __________________ 1974 Jimmy- 5.3/4L80e/NP241

11-24-2003, 09:38 PM	#4
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	86siverado & kenneth, are the exhaust amnifolds the same 305/350? I always thought the 305's were a little smaller. I may be wrong but I tried buying some old exhaust maniflods and they would not blot up to the 350, I went to a mechanic and he said that they were for a 305 and that is why they wouldn't fit. So now I'm confused. I'm only asking since my son wants to do this swap in the future. __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454

11-24-2003, 11:19 PM	#6
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	like 76 said, the only way you can get in trouble is if you bought an older 350 with the different bolt pattern in the heads. What happens is you will not be able to put the last manifold bolt through because the flanges do not line up with the hole in the head. As long as you have a newer 350 you will be able to swap exhaust manifolds no problem. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!

11-25-2003, 12:57 AM	#7
suburbasaurus Registered User Join Date: Nov 2003 Location: Bee Bayou, La Posts: 9	the 350 will bolt directly in place of the 305 with no mods. if you use a 86-prior 350 the difference is the flywheel(has smaller bolt pattern), the fuel pump pushrod hole has a small plug in it that will need to be knocked out(only if it were equipped with TBI).and the 87-95 heads have a center bolt valve cover and the middle intake bolts have a 30 degree angle instead of a 45 degree angle, as far as "7 bolt" heads, 81 was the first year they put them on the trucks. all 81-87 trucks came with 7 bolt heads. if your new engine has heads with 7 bolt holes on the exaust ports it will be no problem. the older 6 bolt manifolds will bolt to the newer heads without any problems. another thing is in 80 the dipstick moved to the passenger side.

11-25-2003, 11:18 AM	#8
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	I believe you will have to change the harmonic balance or remark your current to match the 350. Verify this first, I am not 100% sure. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

11-25-2003, 05:20 PM	#9
Kenneth Registered User Join Date: Jul 2003 Location: Austin, Texas Posts: 53	Thanks for the input I failed to mention the fact that I'm looking to replace a '76 305 (again from the El Camino), with a 350. But the way y'all been talking it sounds like as a long as I stick with a mid 70's 350 I'll have no problems. Thanks for the help. Kenneth

11-25-2003, 05:35 PM	#10
Eyegore What Hump? Join Date: Apr 2003 Location: New River AZ Posts: 2,009	OK, so I look for a block newer than 80 from what your saying, but how do you identify a newer block, serial number? I ask because most of the block(s) I look at are already out of the truck and are laying side by side and I want to make sure I chose the right one. Also, is there a differnce in a car (caprice, camaro) block and a truck block? For example is the distributor the same, when we had the engine replaced a few years back they said I needed a new distributor since the one we had (the whole engine) was from a car. Sorry, this is where you learn - from the people who been there, every time I ask someone behind the parts counter they look at you as if they were in to much of a hurry to even care. Thank you __________________ Lil red 86 c-10 99 Sub 78 Camper Special w/ 454

11-25-2003, 05:45 PM	#11
RussTburb Registered User Join Date: Mar 2002 Location: Blaine,Wa. U.S.A Posts: 261	kenneth, It is to bad you are in texas I have a great running 350 that is comming out of a 73 El Camino! sorry to tease you!lol good luck with your project and jsut take your time and make sure you get all the parts off the 305 onto the 350. I have done 3 of these and have very little problems. Dennis __________________ "Red-heads not war-heads, Blondes, not bombs, Brunettes, not fighter jets!" Fligh of the Choncords 72 burb 3/4 ton 2wd 06 2500 suburban 8.1L 4x4 84 chev 4x4 diesel 96 Geo Metro with the 4cylbb, lol! Almost 300k just won't die! 89 Honda Civic, runs on the smell of an oily rag! 2008 Aerolite 26qs Travel Trailer (aka "THE BARN")

11-25-2003, 07:57 PM	#12
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	Tom Just make sure the dipstick is on the passenger side and you are all set. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!



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