Team Chevelle banner

400 heads on a 350 block

453 Views 20 Replies 10 Participants Last post by  71350SS
Hello,

If I wanted to put some heads that were on a 400 small block on a 350 block would this be ok? The heads have steam holes, the 350 does not.

Also, any issues if I ran a head gasket that had provisions for steam holes but the the block did not?

Thanks,
Rick
1 - 20 of 21 Posts

· Registered
Joined
·
12,621 Posts
It would probably be fine for sealing, but water impinging on the deck surface not going anywhere will eventually cause a pit to form. The steam holes were for the 400 block. There will still be water flowing in the head.
 

· Registered
Joined
·
84 Posts
Discussion Starter · #6 ·
The 400 gasket will work but it has a larger bore size and is not really correct for the 350 block. Not sure if any of the other holes are different.
Thanks. Apologies for being vague, here is more color. i have some old heads off my motor that I want my dad to have for his 350. That is where the 350 engine/400 heads question comes into play.

When pulling my heads I see that my 400 block (world motown block) doesn't have steam holes, but my new heads are drilled for steam holes. Further, I had bought gaskets for steam holes and just installed them. Before I get much further I wanted to ask those more intelligent than me on the situation how bad an idea this may be on the dumb scale.
 

· Super Moderator
Joined
·
14,251 Posts
Thanks. Apologies for being vague, here is more color. i have some old heads off my motor that I want my dad to have for his 350. That is where the 350 engine/400 heads question comes into play.

When pulling my heads I see that my 400 block (world motown block) doesn't have steam holes, but my new heads are drilled for steam holes. Further, I had bought gaskets for steam holes and just installed them. Before I get much further I wanted to ask those more intelligent than me on the situation how bad an idea this may be on the dumb scale.
Ok, did not realize what block you had. No need for the steam holes with the Motown block because it is a saimese bore and you will be fine with the 400 gaskets with the steam holes. The holes will not hurt a thing.

Your Dad can put the old heads with the steam holes on the 350 block, Also no problem and no need to worry about the steam holes. Just use the 350 gasket.

You are fine with both :)
 

· Registered
Joined
·
84 Posts
Discussion Starter · #9 ·
Ok, did not realize what block you had. No need for the steam holes with the Motown block because it is a saimese bore and you will be fine with the 400 gaskets with the steam holes. The holes will not hurt a thing.

Your Dad can put the old heads with the steam holes on the 350 block, Also no problem and no need to worry about the steam holes. Just use the 350 gasket.

You are fine with both :)
Hi Bill,

I really appreciate you taking the time to answer my questions thoroughly. It's guys like you that help give this site a good reputation. I wish a good day to you, sir.

Rick
 

· Registered
Joined
·
14,161 Posts
As Bill mentioned, you will be fine with either a 350 or 400 gasket.
Personally, if I had 350 gaskets, that would be my first choice. BUT, if I had 400 gaskets, I would not hesitate to use them. MOST 400 heads gaskets, such as Felpro, are a superior gasket because they have to positively seal a smaller surface area.
 
  • Like
Reactions: RickSBC400

· Registered
Joined
·
84 Posts
Discussion Starter · #11 ·
As Bill mentioned, you will be fine with either a 350 or 400 gasket.
Personally, if I had 350 gaskets, that would be my first choice. BUT, if I had 400 gaskets, I would not hesitate to use them. MOST 400 heads gaskets, such as Felpro, are a superior gasket because they have to positively seal a smaller surface area.
Thanks for the feedback, Tom.
 

· Registered
Joined
·
14,161 Posts
The 400 heads to stay away form are the 487-X heads as the X means they are 80cc's so the 350 will have super low compression.
You are right,BUT, all SB400 heads had the large chambers (76-80 cc). When using factory Chev heads on big cube small blocks (383-400+), I have had good results with the early style 327-350 heads which have about 64cc chambers and 2.02/1.6 valves and flat top pistons on 91 octane NON-ethanol gas.

Also, I have never done it, but the next SB400 that I build with 400 heads (76-80cc), I plan to use domed style pistons. I'm thinking this will result in the range of 10.5:1 compression.
 
  • Like
Reactions: 68Chevele

· Registered
Joined
·
5,036 Posts
You are right,BUT, all SB400 heads had the large chambers (76-80 cc). When using factory Chev heads on big cube small blocks (383-400+), I have had good results with the early style 327-350 heads which have about 64cc chambers and 2.02/1.6 valves and flat top pistons on 91 octane NON-ethanol gas.

Also, I have never done it, but the next SB400 that I build with 400 heads (76-80cc), I plan to use domed style pistons. I'm thinking this will result in the range of 10.5:1 compression.
I ran my junk 400 with those 80cc heads with a puppy cam and ran 12.80's with it. Two weeks later with a stock set of Vortec heads all else the same, the car ran 12.26 quite a pickup with heads only. Funny thing was those old 400 heads had 1.6 exhaust valve stock from the factory. I had like 6 circle track guys waiting in line to buy them, 1st guy gave me $225 for those junk heads, I was happy with that.
 

· Registered
Joined
·
22 Posts
I would not use the 400 head gaskets with steam holes on a 350 block, the 400 head gasket are made to fit 4.125 cyl or larger for bore jobs. the 350 head gaskets are made for a 4.00 cyl hole or larger for bore job. it would be like putting a 350 head gasket on a 305, I would not do it, just my opinion.
 
1 - 20 of 21 Posts
Top