deck height:

[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.

[art leong]

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?

[X-TECH MAN]

Originally Posted by art leong

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?

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.

[art leong]

Originally Posted by X-TECH MAN

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.

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.

[Jeff Lee]

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.

[art leong]

Originally Posted by Jeff Lee

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.

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.

[Jeff Lee]

Originally Posted by art leong

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.

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.