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

Re: deck height:
 

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

Re: deck height:
 

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

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.

Re: deck height:
 

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.

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! :rolleyes:

Re: deck height:
 

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.

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.

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.

Re: deck height:
 

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?

Re: deck height:
 

I believe the ones that were caught earlier this year were stamped but NHRA was aware of this trick for years when one of Warrens 350 Camaros was found to have Crane 1.6 rockers on it and using an undercut cam to make the lift check right. It changed the opening speed of the valves more than anything.

Re: deck height:
 

On the old Challenger we would shim the rocker stands to get the cam to check. It would change the geometry. I would think there are to many variables. If they check the lift at the cam there is no push rod flex ETC. And that can make a diffence especially with todays valve springs.

Re: deck height:
 

One the one hand it seems senseless to hash over this but on the other, my comparison to valve lift makes sense. Well at least to me...
If NHRA has a spec indicated in their books (deck height / rocker ratio) and in the end all they care about is a minimum volume between the top of the piston @ TDC & the chamber and a valve measurement @ maximum valve lift, then why publish the deck height or rocker ratio?
My way of learning NHRA class racing engine blueprinting is if NHRA gives a spec, it is to be adhered too. Not "adjust according to what is convenient". Man, I've spent some money on OEM rods (before after market rod acceptability) adjusting the big end to obtain the exact deck height I desired.
Now I'm wondering why NHRA publishes anything more that the throttle blade diameters on a carb.
And if NHRA specs a positive deck (say a 383 mopar) and I run a negative deck instead, I can save on possible piston to head interference issues and I can probably run a tighter LSA for more power.

Re: deck height:
 

Jeff how confidant would you be with a zero deck height spec? Can you be sure the bearing didn't wear a bit, or the rod didn't stretch a touch? And as far as piston to head problems won't a thicker head gasket achieve the same thing?
If you can't build in a little safety margin you are going to get tossed for stuff that won't help performance one bit.

Re: deck height:
 

Then pull the deck height spec out of the books. Just list a tolerance for gasket and deck height combined.

I'm at a loss to figure out how all those zero deck engines made it through tech for 35+ years before NHRA changed this rule. Guess those old engines did not have bearing wear or rod stretch?
Still trying to figure out why a rocker ratio is so important when using this issue as a comparison.

Re: deck height:
 

It was a stupid no common sense rule if the piston was specified to be .001 down the bore if you were 1 inch down it would be fine. If the specification were .001 out of the bore 1 inch out would be legal. What purpose did the old rule serve?
It wasn't a problem as long as there was more clearance than less. Till I drove my car to Maple Grove, set the record with a motor that had never had a head removed. And had .034 to little deck height. Then curt leshure had a problem, and I had a bigger problem.
As far as tolerance goes my motor had 134,000 miles on it was never out of the car (or had the head off) and it was .034 from the stock (listed) specs.
And on some motors adjusting the rod length is not possible.

Re: deck height:
 

This is the exact quote of the rule about deck height out of the 2006 NHRA Technical Policies & Procedures
I don't think it has changed any since 2006. .

1.2 ENGINE BLOCK
1.2a STOCK AND SUPER STOCK
The deck dimension of the engine block can be either in or out of the block, provided that the
difference in the compression is made up with the cylinder head gasket. Example: if the spec is for
.002-inch deck and .020-inch gasket, and the actual measurement for the engine is .005-inch positive
deck, then a gasket must be at least .027 inches. The opposite is true if the deck is below the block on
an above the block spec, then the gasket may be thinner to the allowable total dimension.