400 heads on 350 block - Chevrolet Forum - Chevy Enthusiasts Forums

Go Back   > >
Log In 

General Tech Good at troubleshooting? Have a non-specific issue? Discuss general tech topics here. IF YOUR QUESTION IS SPECIFIC TO A CERTAIN MODEL, IT DOES NOT GO IN THIS SECTION.

LinkBack Thread Tools Search this Thread
Old 06-23-2007, 12:23 AM
Thread Starter
Join Date: Jun 2007
Posts: 2
Default 400 heads on 350 block

What happens if 400 heads are put on a 350 block? What is lost/gained, etc? Anything I should know or prepare for?
Reply With Quote
Old 06-23-2007, 05:49 PM
Join Date: Jun 2007
Posts: 5
Default RE: 400 heads on 350 block

Hey Kablooie, welcome to the forum! I'm glad to be of some help so soon on here.

400 heads on a 350 block is a great way to increase your midrange and top end power. The swap is a direct bolt - on deal, you just need to be sure to use 400 head gaskets when you do the swap. 400 heads have steamholes drilled into them for heat dispertion, and 350gaskets do not have provisions for these steamholes. 400 heads have 2.02" intake/1.6" exhaust valves on nearly all applicationsversus the 1.94"intake/1.5"exhaust valves found on most 4-bbl 350 heads andI believe 1.78"intake/1.35exhaust valves found on most 2-bbl 350 heads. This in part with generally slightly larger port runner size is what gives you the added midrange and top end. The downfall of course will be a slight decrease in fuel mileage.

Also, another word to the wise on 400 heads....they are prone to cracking in the combustion chamber...generally in the center two cylinders between the valves. If you are uncertain as to if your set are cracked or not, a compitent machine shop can tell you if they are or not. And don't let them tell you that the heads are junk if they are in fact cracked. They're not. The machine shopcan repair thembymachining out and replacing thevalve seats in thecracked combustion chamber. They should be able to do a crack repair as well as a complete rebuild of the heads (repace factory valve guides with bronze guides, 3-angle valve cut, re-seat factory valves, new factory valve seals in conjuntion with umbrella style valve seals, andall newlt-1 valve springs and retainers installed) for about $250

Another question...what are the casting numbers on the heads? The number generally can be found in the "floor" of the oil drain galley for the rocker arms. should be a 6 or 8 digit number. the last three numbers are the casting number on your heads. This will tell you alot about what kind of heads you have as far as what they came off of and what performance they are capable of.

If you want more detailed information, I'll be more than happy to help. You can email me any info you have as well as any numbers and their locations as well as any casting marks you find on the heads. My email adress is Cobra454x@aol.com just be sure to make the subject heading "400 heads" so I know what it is and i dont accidentally delete it.

Look forward to hearing from you. What are you building the engine to do? I'll be glad to point you in the right direction....
Reply With Quote
Old 06-24-2007, 09:47 AM
Thread Starter
Join Date: Jun 2007
Posts: 2
Default RE: 400 heads on 350 block

I will probably by buying a 1972 C10 in a few days. It has a 350 block and 350 trans. My dad has a 350 corvette block (unknown year) with only several thousand miles on the lower end (block, pistons, crank, etc) after having been rebuilt a while back. It is missing the heads and intake, however he has some 400 heads laying around somewhere... When I find them, I'll get you an email. I really appreciate your feedback.
Reply With Quote
Old 01-26-2008, 12:42 PM
Join Date: Jan 2008
Posts: 10
Default RE: 400 heads on 350 block

you need the casting number off the heads. most 400 heads have 76 cc chambers and give poor compression ratio. I think there is some mix up in the valve sixe. the smallest 350 head valve is 1.94 intake 1.6? exhaust. The 1.78 intake may be from a 305.
Reply With Quote
Old 05-23-2010, 08:41 PM
CF Beginner
Join Date: May 2010
Posts: 3

was having some problem with the chevy head casting numbers and had to take it to the dealer. had to pay a bit high amount for it.
Reply With Quote
Old 11-30-2014, 07:51 PM
CF Beginner
Join Date: Nov 2014
Posts: 1
Question 400 heads

I Have an old small block 400 i would like to know if i can make a 427 out of it the cast number is 395509 on the block if you can.
Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
95 Z71 TBI 350 motor swap for 96 block....or 95 LT1 block wise1222 General Tech 0 01-04-2014 06:54 PM
Will heads off 88-93 Chev 350 fit on older block? blown57bowtie General Tech 1 07-03-2011 08:37 AM
350 small block or 572 big block? viborero23 Silverado & Fullsize Pick-ups 6 12-05-2009 10:15 PM
68 Corvette Heads On 93 Chevy 350 block shdwtyler Silverado & Fullsize Pick-ups 0 08-16-2009 04:44 PM
Want to build street/strip 350 silverado...what does the 350 need? Heads? Cam? Intake? 5.0stang Silverado & Fullsize Pick-ups 2 06-21-2006 01:16 AM

350, 400, block, casting, chevy, cracked, engine, heads, markings, marks, numbers, put, sale, ur, work

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -5. The time now is 01:44 PM.