c3 hood mod worth 20hp in increased air flow rates

[grumpyvette]

ShouldntBeHere
posted this really good info on his c3 corvette


The losses to the cars power with the restricted air filter before using the raised hood VS the stock L88 hood

-13 rwhp for having the lid and filter on
-7 rwhp for not having the spacer
-5 to -8 hp for having this hood closed (this was mainly if the air cleaner lid was not on an no filter..

My recent act of desperation to gain 20hp....

STOCK L88 HOOD WON,T CLOSE on FULL SIZE AIR CLEANER ASSEMBLY

A TALLER HOOD SCOOP BARELY CLEARS THE TALLER AIR FILTER BUT IT ALLOWS THE ENGINE TO GAIN 20HP WITH LESS RESTRICTED BREATHING

 

[Rod75]

Re: C3 Hood vs Air Filter Mod

Here’s some comments on my observations.
Prior to correction mod's, he was using a 2" drop L88 A/F base with a 3" filter. This was also placing the top carb bowl vents less than 1" from the solid A/F top. The deeper the 'drop' in the A/F base, the more of a restriction is created. Take a look at the pic's of the base, and notice the 'high wall' design of the base that's just inside the filter ring. I never measured one, but it sure looks to me like some areas of that base have a good 3”+ of inner wall. So this leaves approx 1" of clear filter area to feed his 496 cubes! Of course this isn't gonna cut it. I'm actually surprised that he wasn't loosing more than 20hp!
I used an online air filter calculator for the following: Feeding a 496 cid @ max 6500 rpm
- With a 3” high paper filter would require a 20” diameter for required air filter flow area.
- With a 3” high gauze filter would require a 16.4” diameter.
- With a 4” high paper filter would require a 15” diameter.
- With a 4” high gauze filter would require a 12.3” diameter.
The most common aftermarket air filter diameter is 14", which is what I think he is using.
Now none of these figures is taking into consideration a restrictive drop base.
The owners comment was “After much internet research, it seems the L88 air cleaners still seem to be the top performers, I decided to stick with it”.
Personally, I’d reduce the amt of A/F base drop with the increased hood height.

The L88 hood clearance issue was crowded by the use of a higher aftermkt intake. Then for the strip, he adds a 1" carb spacer too. No wonder he couldn't close the hood in 'race trim'!

I think his hp loss was much more of an air filter restriction issue than hood. But hand in hand one feeds the other. I would have tried other avenues of A/F modification prior to the larger hood.
Hence the old adage: Let it Breathe!