Steam Holes in a SB 400 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bluec10 · 11-17-2003, 10:43 PM

Longhorn Man mentioned something about steam holes in the Stroker vs. 400 thread. What are they, what do they do, where do they go, and do you really need them?

68c10owner · 11-17-2003, 10:54 PM

they are between the cylinders on the deck surface. yes you need them if your going to use the motor on the street. the 400 blocks have symiese cylinders and if i remeber correctly, coolant doesn`t flow between the cylinders like it does in a 350 block. i can`t remeber if water actually goes through the steam hole but it keeps the cylinders from over heating by letting the steam out of the area. someone else might have a better way to explain it to you but unless your useing the motor for drag strip use only, you need them and the have to be drilled at a certain angle. most machine shops can do this for $50-$75 depending on the shop.

MrShelley · 11-17-2003, 11:03 PM

Nothing to drilling the steam holes. Use a gasket as a template and drill away. There are six holes per head (two between each cylinder). The holes are 1/8". The holes on the intake side are 30 degrees. The three remaining holes are straight.

Hope this helps.

jimfulco · 11-19-2003, 01:37 AM

The Chevy Power Manual (about $15 from GM) has instructions for drilling the holes.

**truckster** · 11-19-2003, 02:51 AM

They're called steam holes because their purpose is to eliminate steam building up in the water jacket. Steam doesn't transfer heat as efficiently as liquid coolant. The steam holes make sure the liquid keeps flowing.

11-17-2003, 10:43 PM	#1
bluec10 Registered User Join Date: Apr 2002 Location: Manitoba, Canada Posts: 663	Steam Holes in a SB 400 Longhorn Man mentioned something about steam holes in the Stroker vs. 400 thread. What are they, what do they do, where do they go, and do you really need them? __________________ Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said.

11-17-2003, 10:54 PM	#2
68c10owner Registered User Join Date: Oct 2003 Location: Carmichael, California Posts: 3,006	they are between the cylinders on the deck surface. yes you need them if your going to use the motor on the street. the 400 blocks have symiese cylinders and if i remeber correctly, coolant doesn`t flow between the cylinders like it does in a 350 block. i can`t remeber if water actually goes through the steam hole but it keeps the cylinders from over heating by letting the steam out of the area. someone else might have a better way to explain it to you but unless your useing the motor for drag strip use only, you need them and the have to be drilled at a certain angle. most machine shops can do this for $50-$75 depending on the shop. __________________ Anthony

11-19-2003, 01:37 AM	#4
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	The Chevy Power Manual (about $15 from GM) has instructions for drilling the holes. Last edited by jimfulco; 11-19-2003 at 01:53 AM.

11-19-2003, 02:51 AM	#5
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,881	They're called steam holes because their purpose is to eliminate steam building up in the water jacket. Steam doesn't transfer heat as efficiently as liquid coolant. The steam holes make sure the liquid keeps flowing. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

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11-17-2003, 11:03 PM	#3
MrShelley Too Many Clubs Club Join Date: Jul 2003 Location: Kilgore, Texas Posts: 443	Nothing to drilling the steam holes. Use a gasket as a template and drill away. There are six holes per head (two between each cylinder). The holes are 1/8". The holes on the intake side are 30 degrees. The three remaining holes are straight. Hope this helps.



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