Re: Shaker Hood, CFM Comparisons, Questions..Sorry Long

From: Jon Steiger (
Date: Sat Aug 28 1999 - 21:08:11 EDT

On Fri, 27 Aug 1999, GS- wrote:
> For those of us seriously considering a shaker hood
> in the future. I thought it might be wise to pull in
> as many FACTS as possible on the shaker hood design.
> Mainly CFM and compare them with say the newer FIPK
> (large cone and tube).

   That shaker looks pretty cool, but I agree with whoever it
was that said it needs to be bigger. Seems kinda small. :-(

> I know there has already been some discussion on looks
> and earlier Cuda shaker design efficiency. Some were
> a little vague. Basically we can't compare the cone
> and the 14x2.5 element because of the different environment
> the shaker offers (Ram Air). I'm not trying to scare everyone
> away. If its to early to get the facts, I'll settle for a
> little theory and or experience. Here are some basics to
> start out with anyway:
> 14" K&N 2 1/2" tall: 109.9 Square inches (662.7 CFM)
> 8" cone 138.16 Square inches (833.1 CFM)
> (Cudos to Charles Smith, I'm borrowing his calculations)
> The question now is "What is the CFM (14x2.5)when RAM AIR is added?"

   Here is my opinion on the matter... Ignore the ram-air effect,
because there is almost none there anyway. The best thing about
a ram air hood is it supplies the engine with fresh, cold air. That
aspect will definitely make a difference, so you should factor in
underhood vs cold air, but any ram-air effect will be so small that
it can be safely ignored. I don't recall the exact numbers, but
in one of the issues of MPN, they did a feature on the "worlds fastest
crate HEMI"; the Bonneville salt flats streamliner that runs over 300mph
using a 528 HEMI. Anyway, its got a scoop on top of the engine
about the size of a pro-stock scoop, and they mentioned that at 300mph,
they were getting about a quarter psi of ram-air.

  Anyway, based on those numbers, I figure maybe you'd get an additional
.5hp at 60mph and around .9 at 100mph, and those numbers are pretty
optomistic, especially when you consider their scoop is bigger than
the scoop in the shaker or ram-air hoods.

  Basically, I assumed that the pressure from ram air would be directly
proportional to the vehicle's speed (I'm not sure if that's correct),
so if we assume 300mph = .25psi, then 100mph would be .083psi, and
60mph would be .05psi. Then, based on the fact that a Vortech supercharger
with the stock pulley generates about 6psi and 70hp, I assumed that 1psi
equals 11.666hp, so ram air at 60mph would be (11.666 * .05) .583hp,
and ram air at 100mph would be (11.666 * .083) .972hp.

   Another aspect you'll want to consider is wether the openings
in the hood or the shaker are capable of flowing the CFM you need.
If they can flow 1000cfm they should be more than adequate.


  .--- ----------------------------------------.
  | Jon Steiger * AOPA, DoD, EAA, MP Race Team, NMA, SPA, USUA * RP-SEL |
  | '96 Dodge Dakota v8 SLT CC (14.55@94.14), '96 Kolb FireFly 447 |
  `--------------------------- ---'

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