69 cowl induction rarity

[black69]

I needed someone to check my logic on the fresh air hood. If there were 10K hoods produced on cars in 69, and the pace cars took up around 3700 of them, and the copos took up the remaining 700, would that mean roughly 5600 hoods were left to go towards the remaining SS cars (pace cars are ss cars) and Z28s?
That's my current logic. To me it is fairly rare to have a real cowl induction hood on a 69 if you look at the 5600 vs the total z28s + SS cars totals (around 55K?). Its like a 10% chance you would run across a real one.
Am I missing something?

[JohnZ]

It also missed the first four months of production.

[william]

COPOs may not be included in that total. The ducted hood was not listed on documentation as it was included with 9560 & 9561.

Don't forget Z10s-another 500 or so where ZL2 was a required option.

Otherwise, yes. A factory ducted hood 69 is rare. Most Z/28s were not built with one.

[black69]

thanks. I do wonder how much difference in peformance a fresh air hood provides over the standard hood. I wonder if a L78 with the hood would be any worse off against an L89 without the hood. Would the weight savings get canceled by the heated air coming through the radiator..just a question I had...

I know my 65 L78 425hp vette runs fairly different once it starts seeing more hot air feeding it and becomes sluggish, but with cold air it is just a blast to drive. The L78 camaro with the fresh air hood runs fine all the time and I have let it get pretty hot (210).

[JohnZ]

The standard rule of thumb is that there's a 1% power gain for every 10*F reduction in intake air temperature.

[black69]

was there any pressure added as the air drafted off the base of the windshield with that hood? . And if so, are their horsepower rule of thumb numbers for that?

I am thinking with underhood temps brewing pretty high at a head to head drag, a L89 ss hood car would be closer than you think with a ZL2 L78 when the pedals went to the floor.

[jdv69z]

COPOs may not be included in that total. The ducted hood was not listed on documentation as it was included with 9560 & 9561.

Don't forget Z10s-another 500 or so where ZL2 was a required option.

Otherwise, yes. A factory ducted hood 69 is rare. Most Z/28s were not built with one.

I'm wondering if maybe Chevrolet sold more of these hoods over the counter than as original equipment??

[JohnZ]

was there any pressure added as the air drafted off the base of the windshield with that hood? . And if so, are their horsepower rule of thumb numbers for that?

Probably zero net effect from that; even forward-facing hood scoops didn't really do anything, as they're in stagnant boundary layer airflow. That's why the scoop on a Pro Stocker has the intake 18" above the normal hood surface.

[68Zproject]

I heard from a Chevelle guru, that the ZL2 hood was worth about 10hp.  I thinks it's anyone's guess.

[Rallyegreen69z]

How can we know if we have an original hood or not?

[no69x-44]

How can we know if we have an original hood or not?

The orginal hoods had "notch" on the side edges of the hood up near the hoods meet the windshield.  The Repro hoods do not have that little notched out area and are smooth on the side edges. 

[duntov3030]

How can we know if we have an original hood or not?

The orginal hoods had "notch" on the side edges of the hood up near the hoods meet the windshield.  The Repro hoods do not have that little notched out area and are smooth on the side edges. 

Can someone post a pic of this notch?  Thanks.

[JohnZ]

Photos below - the hood with a straight line in the side flange at the rear is the repro, and the hood where that line is a "notch" is the GM hood.

[Rallyegreen69z]

Thanks

[68Zproject]

Is there any way to date an original hood?