how to tell a 350 from a 400 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blazer Eagle · 01-18-2009, 07:55 PM

so i found a truck that came from the factory with a 400, but i believe it may have a 350 in it, how do i tell if it is a 350 or 400? it has an edelbrock 1409 carb on it if that helps

4everGMtrucks · 01-18-2009, 09:01 PM

i'm pretty sure a 400 has three freeze plugs on each side rather than the standard two that the other small blocks have.

Red_69 · 01-18-2009, 09:02 PM

I don't think that's ALWAYS true. Maybe someone else can chime in.

79Silv4x4 · 01-18-2009, 09:17 PM

What leads you to believe it has a 350 in it???

Blazer Eagle · 01-18-2009, 09:28 PM

the valve covers? say performance 350 on them, but i thought they were interchangeable

bad6772 · 01-18-2009, 09:34 PM

Harmonic Ballancer.....350 or any other small block for that matter OTHER than a 400 is internally balanced, a 400 is externally.. a 400 ballancer is not totally round someone correct me if i am wrong?..........But am pretty sure this is the way to I.D one from the other

chevybuldr · 01-18-2009, 10:02 PM

Not all 400s had 3 plugs on each side. Best way is casting number off the back or the front pad on the front passanger side. Look at the ballancer. All but the 400 has a smooth outer ring, no indents. 400 has an area cut out of it for the external balance.

Blazer Eagle · 01-18-2009, 10:19 PM

i dont really know engines so if anyone has pictures that would help a lot so i could go look

chevybuldr · 01-18-2009, 10:35 PM

look on the front pass side on the block in front of the head.There is a pad there with numbers stamped into the block. Unless somebody machined the motor before. Give those numbers and that will help

Dooley · 01-19-2009, 02:40 AM

This thread should answer your 400 smallblock ID questions.
http://67-72chevytrucks.com/vboard/s...80#post2789780

4everGMtrucks · 01-19-2009, 09:24 AM

according to a book written by david Vizard, in the reference section under casting numbers. the 400 small block with four bolt mains, has a casting number of 3951511, had three freeze plugs and was manufactured from 70-73. the 400's with casting #'s 3951509 or 3030817 had two bolt mains, two freeze plugs and were manufactured between 74-76. you will find the casting number on the block behind the drivers side head.

chevybuldr · 01-19-2009, 11:17 AM

Some 2 bolts have 3 plugs on the side. The one in my 'burb does and its a 4 bolt. Plus I just finished putting 4 bolt caps on a 2 bolt block that also has 3 plugs.

Blazer Eagle · 01-19-2009, 03:15 PM

well i know what to look for but not where

where would i look for the harmonic balancer

where would look for the casting number

and this is in a fully put together complete truck, so if these are hidden behind something bolted on i wont be able to get t o them

Dooley · 01-19-2009, 04:31 PM

Quote:

Originally Posted by Blazer Eagle

well i know what to look for but not where

where would i look for the harmonic balancer

where would look for the casting number

and this is in a fully put together complete truck, so if these are hidden behind something bolted on i wont be able to get t o them

The harmonic balancer is located on the front of the crankshaft between the block and your lower accessory pulleys. Complete casting numbers are usually found on the rear drivers side of the block behind/below the drivers side head. Did you look at the pics in the link that was previously posted?
Here's another pic of the 400 balancer and a 1980 509 engine.

Blazer Eagle · 01-19-2009, 07:58 PM

yeah and im 90% sure its a 350, i guess i did look in the right place there were 4 pullies and they all looked round and normal

arkracing · 01-19-2009, 08:22 PM

Anyway you can post a picture of your balancer? The Pulley's have nothing to do with it.

The best picture would be if you could jack the truck up and take the picture from underneath looking forward at the balancer - if there is a cutout like the one pictured above than it is a 400 (The cutout part of the balancer is facing the rear of the engine)

BigBlocksRule · 01-19-2009, 08:56 PM

If you can crawl under the truck and look at the sides of the block, it'll tell. The 2 or 3 freeze plugs indicator doesn't work - I have a 509 casting block on the stand in my garage and it has only 2 freeze plugs, not even a boss for the third. Look at the sides of the block - if they're perfectly flat, it's a 305 or 350. If it's a 400, there will be small bulges around each cylinder, between 1/8" and 1/4" tall. Chevy only made 3 different casting numbers of 400 blocks - it'll have to end in 817, 509 or 511. The balancer is generally a good way to tell, but I use balancers with the counterweight on the inside, makes 'em look just like a 350 balancer. With this 2-freeze plug block and a balancer like I described, most casual observers will be sure it's a 350. I'm sure as hell not gonna set 'em straight.

01-18-2009, 07:55 PM	#1
Blazer Eagle Registered User Join Date: Oct 2008 Location: PLacerville, CA Posts: 195	how to tell a 350 from a 400 so i found a truck that came from the factory with a 400, but i believe it may have a 350 in it, how do i tell if it is a 350 or 400? it has an edelbrock 1409 carb on it if that helps

01-18-2009, 09:01 PM	#2
4everGMtrucks Registered User Join Date: Sep 2008 Location: grand junction, co Posts: 18	Re: how to tell a 350 from a 400 i'm pretty sure a 400 has three freeze plugs on each side rather than the standard two that the other small blocks have.

01-18-2009, 09:02 PM	#3
Red_69 Registered User Join Date: Apr 2008 Location: IL Posts: 160	Re: how to tell a 350 from a 400 I don't think that's ALWAYS true. Maybe someone else can chime in. __________________ 1986 Chevy 3/4 Ton 4X4

01-18-2009, 09:17 PM	#4
79Silv4x4 Workaholic Join Date: Oct 2002 Location: Katy, TX Posts: 1,589	Re: how to tell a 350 from a 400 What leads you to believe it has a 350 in it??? __________________ 1979 K-10 Silverado (work in progress) 1991 V1500 Subruban 1999 Suburban LT 4x4 2006 Suburban LTZ (daily driver)

01-18-2009, 09:28 PM	#5
Blazer Eagle Registered User Join Date: Oct 2008 Location: PLacerville, CA Posts: 195	Re: how to tell a 350 from a 400 the valve covers? say performance 350 on them, but i thought they were interchangeable

01-18-2009, 09:34 PM	#6
bad6772 Official Site Guitar Shredder Join Date: May 2006 Location: Oz Posts: 3,955	Re: how to tell a 350 from a 400 Harmonic Ballancer.....350 or any other small block for that matter OTHER than a 400 is internally balanced, a 400 is externally.. a 400 ballancer is not totally round someone correct me if i am wrong?..........But am pretty sure this is the way to I.D one from the other Last edited by bad6772; 01-18-2009 at 09:39 PM.

01-18-2009, 10:02 PM	#7
chevybuldr Registered User Join Date: Oct 2008 Location: Livermore ca Posts: 699	Re: how to tell a 350 from a 400 Not all 400s had 3 plugs on each side. Best way is casting number off the back or the front pad on the front passanger side. Look at the ballancer. All but the 400 has a smooth outer ring, no indents. 400 has an area cut out of it for the external balance.

01-18-2009, 10:19 PM	#8
Blazer Eagle Registered User Join Date: Oct 2008 Location: PLacerville, CA Posts: 195	Re: how to tell a 350 from a 400 i dont really know engines so if anyone has pictures that would help a lot so i could go look Last edited by Blazer Eagle; 01-18-2009 at 10:21 PM.

01-18-2009, 10:35 PM	#9
chevybuldr Registered User Join Date: Oct 2008 Location: Livermore ca Posts: 699	Re: how to tell a 350 from a 400 look on the front pass side on the block in front of the head.There is a pad there with numbers stamped into the block. Unless somebody machined the motor before. Give those numbers and that will help

01-19-2009, 02:40 AM	#10
Dooley Registered User Join Date: Mar 2005 Location: North Coast Posts: 1,012	Re: how to tell a 350 from a 400 This thread should answer your 400 smallblock ID questions. http://67-72chevytrucks.com/vboard/s...80#post2789780

01-19-2009, 09:24 AM	#11
4everGMtrucks Registered User Join Date: Sep 2008 Location: grand junction, co Posts: 18	Re: how to tell a 350 from a 400 according to a book written by david Vizard, in the reference section under casting numbers. the 400 small block with four bolt mains, has a casting number of 3951511, had three freeze plugs and was manufactured from 70-73. the 400's with casting #'s 3951509 or 3030817 had two bolt mains, two freeze plugs and were manufactured between 74-76. you will find the casting number on the block behind the drivers side head.

01-19-2009, 11:17 AM	#12
chevybuldr Registered User Join Date: Oct 2008 Location: Livermore ca Posts: 699	Re: how to tell a 350 from a 400 Some 2 bolts have 3 plugs on the side. The one in my 'burb does and its a 4 bolt. Plus I just finished putting 4 bolt caps on a 2 bolt block that also has 3 plugs.

01-19-2009, 03:15 PM	#13
Blazer Eagle Registered User Join Date: Oct 2008 Location: PLacerville, CA Posts: 195	Re: how to tell a 350 from a 400 well i know what to look for but not where where would i look for the harmonic balancer where would look for the casting number and this is in a fully put together complete truck, so if these are hidden behind something bolted on i wont be able to get t o them

01-19-2009, 07:58 PM	#15
Blazer Eagle Registered User Join Date: Oct 2008 Location: PLacerville, CA Posts: 195	Re: how to tell a 350 from a 400 yeah and im 90% sure its a 350, i guess i did look in the right place there were 4 pullies and they all looked round and normal

01-19-2009, 08:22 PM	#16
arkracing Weekend Warrior Join Date: Oct 2004 Location: CT Posts: 1,787	Re: how to tell a 350 from a 400 Anyway you can post a picture of your balancer? The Pulley's have nothing to do with it. The best picture would be if you could jack the truck up and take the picture from underneath looking forward at the balancer - if there is a cutout like the one pictured above than it is a 400 (The cutout part of the balancer is facing the rear of the engine) __________________ -'07 GMC Sierra K2500HD -'66 C10 Suburban -'68/'71 K20 Service Bed Project -'69 Chevy C30 Mason Dump -'33Ford P/U 396ChevyPowered Last edited by arkracing; 01-19-2009 at 08:24 PM.



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01-19-2009, 08:56 PM	#17
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: how to tell a 350 from a 400 If you can crawl under the truck and look at the sides of the block, it'll tell. The 2 or 3 freeze plugs indicator doesn't work - I have a 509 casting block on the stand in my garage and it has only 2 freeze plugs, not even a boss for the third. Look at the sides of the block - if they're perfectly flat, it's a 305 or 350. If it's a 400, there will be small bulges around each cylinder, between 1/8" and 1/4" tall. Chevy only made 3 different casting numbers of 400 blocks - it'll have to end in 817, 509 or 511. The balancer is generally a good way to tell, but I use balancers with the counterweight on the inside, makes 'em look just like a 350 balancer. With this 2-freeze plug block and a balancer like I described, most casual observers will be sure it's a 350. I'm sure as hell not gonna set 'em straight.

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