deck height:

Bill Bogues · 11-11-2010, 05:01 AM

I'm putting together a sbc stocker motor for my Nova (71 350/270) . When I put the crank and one rod and piston together in the block, I had a positive deck height. Piston is out about .008. Can I put a thicker head gasket to make up the difference or do the tech people frown on this. Ihad this same thing happen about 20 years ago, got tore down at a race and it passed. I don't know now if the tech people are as benevolent as they were then

M&M Motorsports · 11-11-2010, 05:46 AM

Yes, it's covered in the rule book. Good Luck!

Mike Taylor 3601 · 11-11-2010, 10:40 AM

Yes. they total gasket,deck clearance as long as you stay more than that
Mike Taylor 3601

Jeff Lee · 11-11-2010, 12:02 PM

My impression is that if the specs call for a negative deck, then the piston had better be below the deck of the block. At this point the gasket is not part of the equation.
The opposite is true if the specs call for a positive deck; the piston had better be above the deck of the block.
How much above or below the deck is not the issue as long as the blueprinted engine meets or exceeds the specs; more clearance is allowed, not less clearance.
Since your spec is .002" (below deck) then you'll have to machine the big end of the rods to pull the piston down to where it needs to be.

Note: this is the same issue as the rocker ratio rule. The end result is not the answer, getting there using the specs provided by NHRA is the requirement.

art leong · 11-11-2010, 01:07 PM

Quote:

Originally Posted by Jeff Lee

My impression is that if the specs call for a negative deck, then the piston had better be below the deck of the block. At this point the gasket is not part of the equation.
The opposite is true if the specs call for a positive deck; the piston had better be above the deck of the block.
How much above or below the deck is not the issue as long as the blueprinted engine meets or exceeds the specs; more clearance is allowed, not less clearance.
Since your spec is .002" (below deck) then you'll have to machine the big end of the rods to pull the piston down to where it needs to be.

Note: this is the same issue as the rocker ratio rule. The end result is not the answer, getting there using the specs provided by NHRA is the requirement.

Jeff they used to go by that rule but have since changed it.
What would you say to someone that had a zero deck?
Some of the new rods (cracked caps) cannot be resized.
I got tossed once because I had a minus .020 deck and the specs called for a plus .004.
After that they changed the rule.

Jeff Lee · 11-11-2010, 02:39 PM

Then I would definitely get confirmation on it.

The "old way" meant if the specs were zero deck then it was zero deck. But as you say, that may not matter. But make sure you have the right rocker ratio when obtaining the spec'ed cam lift measured at the valve!

art leong · 11-11-2010, 03:11 PM

Quote:

Originally Posted by Jeff Lee

Then I would definitely get confirmation on it.

The "old way" meant if the specs were zero deck then it was zero deck. But as you say, that may not matter. But make sure you have the right rocker ratio when obtaining the spec'ed cam lift measured at the valve!

When I had a problem and asked why having to little deck height (the piston further down the hole) was a problem. They came up with the cockamamy excuse that "it would allow me to run more camshaft (without having piston to valve problems) I quickly replied how about a thicker head gasket? Wouldn't that achieve the same thing? They were dumfounded. And tossed me anyway.
But the rule got changed a couple of months later.

X-TECH MAN · 11-12-2010, 06:37 PM

Like Art said the rule was changed shortly after Art was tossed for this very same reason. For many years it was as Jeff said. If it was negative deck spec. then it had to be in the hole no matter how thick the head gasket was. One of many changes over the years.

Jeff Lee · 11-12-2010, 06:52 PM

Geez...guess that puts me in old timer category! About when did this change?
When compared to the valve lift / rocker ratio issue, it makes no sense at all.

art leong · 11-12-2010, 07:10 PM

Quote:

Originally Posted by Jeff Lee

Geez...guess that puts me in old timer category! About when did this change?
When compared to the valve lift / rocker ratio issue, it makes no sense at all.

I believe it was changed in 98 or 99.
I'm not sure but didn't the questionable rockers have the ratio stamped into them?

11-11-2010, 05:01 AM	#1
Bill Bogues Member Join Date: Apr 2005 Location: Bethany La. Posts: 322 Likes: 95 Liked 169 Times in 53 Posts	deck height: I'm putting together a sbc stocker motor for my Nova (71 350/270) . When I put the crank and one rod and piston together in the block, I had a positive deck height. Piston is out about .008. Can I put a thicker head gasket to make up the difference or do the tech people frown on this. Ihad this same thing happen about 20 years ago, got tore down at a race and it passed. I don't know now if the tech people are as benevolent as they were then __________________ Bill Bogues 4696 STK

11-11-2010, 05:46 AM	#2
M&M Motorsports Member Join Date: Mar 2008 Location: Jerome, Michigan Posts: 119 Likes: 0 Liked 0 Times in 0 Posts	Re: deck height: Yes, it's covered in the rule book. Good Luck!

11-11-2010, 10:40 AM	#3
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,362 Likes: 337 Liked 279 Times in 96 Posts	Re: deck height: Yes. they total gasket,deck clearance as long as you stay more than that Mike Taylor 3601

11-11-2010, 12:02 PM	#4
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: deck height: My impression is that if the specs call for a negative deck, then the piston had better be below the deck of the block. At this point the gasket is not part of the equation. The opposite is true if the specs call for a positive deck; the piston had better be above the deck of the block. How much above or below the deck is not the issue as long as the blueprinted engine meets or exceeds the specs; more clearance is allowed, not less clearance. Since your spec is .002" (below deck) then you'll have to machine the big end of the rods to pull the piston down to where it needs to be. Note: this is the same issue as the rocker ratio rule. The end result is not the answer, getting there using the specs provided by NHRA is the requirement. __________________ Jeff Lee 7494 D/S '70 AMX

11-11-2010, 02:39 PM	#6
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: deck height: Then I would definitely get confirmation on it. The "old way" meant if the specs were zero deck then it was zero deck. But as you say, that may not matter. But make sure you have the right rocker ratio when obtaining the spec'ed cam lift measured at the valve! __________________ Jeff Lee 7494 D/S '70 AMX

11-12-2010, 06:37 PM	#8
X-TECH MAN Banned Join Date: Dec 2007 Location: Lake Placid, Florida Posts: 3,203 Likes: 1,047 Liked 235 Times in 110 Posts	Re: deck height: Like Art said the rule was changed shortly after Art was tossed for this very same reason. For many years it was as Jeff said. If it was negative deck spec. then it had to be in the hole no matter how thick the head gasket was. One of many changes over the years.

11-12-2010, 06:52 PM	#9
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: deck height: Geez...guess that puts me in old timer category! About when did this change? When compared to the valve lift / rocker ratio issue, it makes no sense at all. __________________ Jeff Lee 7494 D/S '70 AMX